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Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot. Do not operate combat robots without proper safeguards.

Q: I have a 12v 700mah battery and a charger with the same output can it charge it safely?

A: Way too little information.

A battery charger must be correctly matched to the battery. A charger designed for NiCad batteries cannot, for example, be safely used to charge lithium batteries. Assuming that your charger is the correct type for your specific battery, most batteries can be charged at a rate that will fully charge them in one hour. Your 700 mAH battery can likely be charged at a 700 mA rate with an appropriate charger, but check with the battery manufacturer for a battery spec sheet to find the maximum charge rate.

A: I don't know where that 'wikifact' came from. Early Battlebots rules said:

Later BattleBots rules were modified to explicitly restrict lasers to "Class IIIa or below".

Current RFL rules forbid any lights that impair the view of entrants, judges, or the audience. Lasers above Class I - which are very low power - are specifically forbidden.

So, yes you can use very low power, eye-safe lasers as long as they don't interfere with anyone viewing the robots.

Q: I want to make an RC Helicopter so i want all relevant details apart from it i want to know about servo motors , 4 channel transistor and reciever. What all things would be requires and i also want some knowledge about transistor and reciever ?

A: Mark J. here: we give short answers to questions about combat robots. Maybe you could find a website called 'Ask Some Guy: R/C Helicopters Q&A' and hope that he has time to write a few dozen pages to answer your very general questions. If I ever write a book about R/C helicopters I'll be sure to send you a copy.

A: The Futaba 6EX is a 6-channel 2.4 GHz radio system, but only the throttle channel will failsafe on loss of signal. Under US combat rules a combat robot with active weaponry must failsafe all drivetrain and weapon channels on signal loss. The Futaba 6EX does not meet that requirement.

Check the rules governing your competition to see what failsafe functions are required.

A: What speed controller are you using? A simple pistol grip radio like the Traxxas requires an ESC with on-board mixing to control a differential steering robot, and this sounds like an ESC set-up problem. Check your ESC documentation.

Q: I was using old servo ESC's, does this mean I'll have to get a new ESC?

A: It might be a good idea, but you can use an inexpensive plug-in channel mixer (or a fancier version) between the receiver and the ESCs.

Your transmitter throttle trigger sends out commands to only one channel of the receiver, and your steering knob sends commands to the other channel. If you have an ESC plugged into each receiver channel, only one will respond to throttle commands -- the other will respond only to steering input. A channel mixer will take the throttle and steering information from the receiver and send appropriate signals to the two ESCs so that both motors will respond to throttle and steering commands correctly.

1. Plug the two leads from the mixer into the output ports on your receiver.

2. Plug the ESCs into the output ports on the mixer.

3. Power up and adjust the throttle and steering trims to get the motors to stop. You may need to re-adjust the trims as the set-up process goes on. Servo ESCs are very sensitive to transmitter input -- just a little input will push them to full throttle. Your transmitter has no sensitivity adjustment, so it may be a little touchy to drive.

4. Throttle test: pull the trigger back (forward command):
   • If the robot turns either left or right, swap the positions of the two mixer leads plugged into the receiver.
   • If the robot moves backward, flip the throttle reverse switch on the transmitter.
   • If the robot moves forward, move on to the turning test.

5. Turning test: rotate the steering knob to the right (right turn command):
   • If the robot turns left, flip the steering reverse switch on the transmitter.
   • If the robot turns right, you're done. Go kick butt.

Q: I was looking at the diagram on #19, and I was wondering, my receiver has a battery port, in the diagram it appeared as if there was no battery port. Could you explain this?

A: Some receivers have a separate battery port and some do not.

• Most robot Electronic Speed Controllers (ESC) have a Battery Eliminator Circuit (BEC) that will feed 5 volts to the receiver thru the receiver cable(s), eliminating the need for a separate receiver battery.

• If there is no BEC and your receiver has no battery port, a receiver battery connector may be plugged into any unused port since the (+) and (-) lead pins for each port access a common power bus.

Q: My battery port has 3 leads, how do I run a battery through it then? Could you just give me a diagram of a BEC-less circuit?

A: There is a wiring diagram on page 2 of the Traxxas manual. Battery + is red wire, battery - is black wire, the white 'signal' wire is not used in the battery hook-up. Exceed 6 volts at your own risk!

Q: So just to make sure I'm right; the BEC-less circuit is just like the BEC circuit except that it has a small battery running through the receiver?

A: Since you're using hacked servo ESCs that draw power for their motors from the receiver cable, this 'small battery' will be the only battery in your 'bot -- so maybe it isn't so small. Your circuit will look like the Traxxas manual diagram, but with the V-tail mixer in between the receiver and the servos.

Do not exceed the max voltage rating of the receiver.

Q: I'm switching to sturdier ESC. Does this mean I'll be using two batteries now?

A: Good plan. If you're switching to a real ESC it will probably have a battery eliminator circuit. If so, you need only a single battery and you will wire like the diagram in #19. Many ESCs also have a built-in mixer, eliminating the need for the stand-alone V-tail mixer.

Q: Can you give me a diagram of how you wired Rat Amok? A: The wireing for our infamous rat trap antweight 'Rat Amok' is very simple -- no diagram required. The drive motors are hacked servos; they simply plug into receiver outputs 1 and 2 for Elevon mixing. The rat trap release is controlled by a very small servo plugged into receiver output 5 and controlled by the landing gear switch of the Futaba transmitter. A small 6 volt NiMHd battery pack plugs into the battery port of the receiver and powers everything. Q: How do directly wire the battery to the receiver? A: First, check the voltage tollerance range for the receiver and servos. Exceeding their maximum voltage can very quickly fry the receiver. Solder a servo cable to the battery terminals: red wire to the '+' terminal, black wire (sometimes brown) to the '-' terminal. The third wire is not used. Plug the cable into any unused port in the receiver and you've got power for the receiver and servos. You can splice a switch in the '+' wire, or just unplug the battery to turn off the power. This method does NOT work for more conventional robots with a discrete Electronic Speed Controller. Most ESCs have a 'Battery Eliminator Circuit' (BEC) that feeds a steady 5 volts to the receiver thru the receiver connections. See #19 for a wireing diagram that includes drive and weapon ESCs.

A: Thank you for providing full information on your radio and stick preference -- it helps a lot. The wireing is easy, but the transmitter setup takes a little work. For right stick throttle and right stick steering on a Mode 2 transmitter:

1. Select WINGTAILMIX from the SETUP LIST on your DX6i transmitter and activate the ELEVON option. Check the DX6i manual for detailed instructions.

2. Plug your left ESC into the channel 1 (AILE) receiver port.

3. Plug your right ESC into the channel 2 (ELEV) receiver port.

• If the robot moves forward, good! Go directly to the Turning Test.
• If the robot moves backward, select REVERSE from the transmitter SETUP LIST and reverse both the ELEV and AILE channels.
• If the robot spins to the right, reverse only the ELEV channel.
• If the robot spins to the left, reverse only the AILE channel.

• If the robot spins right, your basic setup is done.
• If the robot spins left, swap the ports your ESCs are plugged into (left into ELEV, right into AILE) and repeat the Throttle and Turning tests.

Q: After i tested it, because both of the single channel speed controllers have a BEC, I've cut the red wire that leads from the ESC to the receiver, however, the motors that is connected to the ESC that has the cutted red wire won't move even after i moved the forward throttle(only the motor that is connected to the ESC that still have the uncutted red wire moves). What should i do?

A: You haven't told me what speed controllers you're using. You mentioned that they were 'like' Victors, but Victors have no battery eliminator circuit (BEC). It might help if I knew.

Cutting the red (power +) wire from the ESC to the receiver should not cause a problem with the speed controller. The receiver uses only the ground and signal wires to communicate with the ESC. My guess is that you damaged one of the other wires while cutting the red power wire in the center of the flat receiver cable. Examine and test the remaining wires. If all else fails, patch the red wire to confirm that the ESC still does work with all three wires in place.

A: No, two different things.

• Frequency crystals are parts of R/C transmitter and receiver circuitry that control the frequency with which the radio communication takes place. FM radio systems typically have crystals that can be replaced to change the frequency to avoid interference with other robots.

• Frequency clips are a set of labels maintained by the robot combat event organizer. If you want to turn on your transmitter for testing or to enter combat, you must first obtain the frequency clip that matches the frequency of your radio from the EO, attach ('clip') it to your transmitter antenna, and return it when you are done. This system helps prevent inadvertant interference from multiple transmitter operating at the same time. At some events there was additional frequency security -- transmitters themselves were impounded and had to be checked out.

A: To control one drive motor forward/backward you need:

• a single-channel bi-directional (reverseable) speed controller connected to one output channel on your receiver.

• two single-channel bi-directional speed controllers connected to two output channels on your receiver, or
• one two-channel bi-directional speed controller connected to two output channels on your receiver.

Which receiver output channels you will plug your speed controller leads into depends on which transmitter sticks you want to use for control and whether you want simple 'tank steer' or the more convenient and adjustable 'channel mixing'. Search this archive for 'create proportional drive mixing'. There is also useful information in our transmitter programming guide. The guide is written for Futaba transmitters, but a lot of the information applies to all radio systems.

Mark J. here: for the record, the Spektrum AR6210 is not intended for use in a combat robot. If the transmitter signal is lost, channel 3 (throttle) will failsafe to a set position, but all other channels will lock in the position they last received from the transmitter. Whether or not your event organizer cares about your safety, I can't recommend that you use this receiver.

A: Combat robots are dangerous. Combat tournament rules require that robot propulsion and weapon systems shut down if the radio control signal is lost; the robot control systems must safely respond to a radio 'fail' condition. The specific requirements of the failsafe response depend on the weight class and weapon type -- see #18 for specific requirements.

From the RFL ruleset:

Q: What's a master kill switch?

A: A master kill switch is another safety device. In case of short circuit, fire, or a runaway condition caused by equipment failure, tournament rules require a single manually operated master power switch that will safely cut power to the major electrical systems of the robot.

From the RFL ruleset:

A: Instructions for crimping and soldering PowerPole connectors are at the Anderson Power Products website.

A: How many wires you can crimp into an Anderson PowerPole connector depends on which model of the connector you use and how big the wires are. The 45 amp PowerPoles will crimp a single 10 guage wire -- three 14 guage wires should just about cram in there. I solder the connection after crimping just to make sure everything stays put.

Q: Hi Aaron, in the wiring diagram [ #19], there are some links which connected the battery power from the battery to the motors. what can i use for the links? can i use gator clips?

A: The electrical connectors must handle high amps and survive severe mechanical shock loading -- so no alligator clips, please. We like Deans Ultra plugs for small robots and Anderson PowerPole connectors for larger applications.

Would that be the best way to program this, or do you have any suggestions for possible solutions?

A: Mark J. here: as the radio specialist for Team Run Amok I'm going to intercept this question.

You haven't mentioned if this weapon is a spinner, a lifter, or something else entirely. Without knowing what the weapon is I can't offer a 'best' control option. For example: that 'Throttle Cut' push button on the DX6i is not a 'toggle', it's a momentary contact switch that is active only so long as you continue to hold it down. That could become inconvenient and tiresome for some types of weaponry. You also wouldn't want to abruptly reverse a spinner from full-speed; you'd want a gradual 'spin down' to avoid killing the motor and ESC.

The simple generic solution is to assign the weapon to the ratcheted throttle channel (or rudder channel if a spring-center is more convenient) for full proportional forward/reverse weapon control from the left stick, and use Delta-Wing (Elevon) mixing to control the robot drive system from the right stick.

If you really want to use the transmitter switches for on/off and forward/reverse control the weapon, send me more information about the weapon itself and I'll see what I can recommend.

A: You didn't tell me what size packs you're looking for. A quick web search ('A123 battery packs') turns up several sources (Electricwingman, Esprit Model...) and a selection of small packs ARE available thru Robot Marketplace. Take another look around.

A: I don't think you understand what a Battery Eliminator Circuit (BEC) does.

An R/C receiver typically requires a lower voltage power supply than the main battery for the vehicle. A BEC is a voltage regulator that connects to the main system battery and provides a stable 5 volts to power the receiver via a standard receiver cable. This eliminates the need for a separate small battery to power the receiver. Search for 'how do battery eliminator circuits work' in this archive for more info.

Receivers do not have BECs -- but Electronic Speed Controllers (ESCs) often have a built-in BEC to power the receiver. This makes sense as the ESC will be attached to the main battery and already has a cable going to the receiver that can carry the power. Check the documentaion for the ESC you plan to use to see if it has a BEC.

If main battery power is available to the BEC and the BEC is connected to your receiver, the receiver will be active and can be bound.

Note: the Spektrum AR6255 receiver has a relatively broad input voltage tolerance: 3.5 to 9.6 volts. If your main battery is within this range you can power this receiver directly from the main battery without a BEC via a standard receiver cable.

I was think I would like to use two high amp Mosfets. Is this possible? If so, what would the wiring look like? Simular like battery isolator, but totally disconnect the primary battery.

A: If the two battery sources are identical, just wire them in parallel to double the capacity. No need to complicate things with MosFETs and switching. Keep it simple.

A: Mark J. here: most of the switches on your DX6i aren't 'channels'. Your radio is a six channel transmitter designed primarilly for aircraft, so some of the functions don't do anything at all useful for a combat robot.

• The first four channels (THRO) (AILE) (ELEV) and (RUDO) are proportionally controlled by left/right and up/down for the two control sticks.

• Channel 5 (GEAR) is by default controlled by the 'Gear' switch and can provide two position instruction to a device plugged into the [GER] port of the receiver with the flip of that switch. Useful for activating a flipper, gyro, or weapon ESC.

• Channel 6 (FLAP) is by default controlled by the 'Flap' switch -- but it effects multiple receiver output ports. Activation of this channel mixes in a set amount of response to both the [AILE] and [AUX] receiver outputs, plus optional response from the [ELEV] output. This makes perfect sense for an airplane, and no sense at all for a robot.

  If you really need to use the [AUX] output and control it with the Flap switch, you can either move the robot steering off the [AILE] output channel or set a 'programmable mix' to offset the effect of the (FLAP) input on the [AILE] output. Both are fairly advanced tweeks -- leave it alone unless you really need that sixth channel.

Tip: aileron dual rates are VERY useful in combat robot control. See if you can figure out why and how.

A: Sorry, we don't work with BASIC Stamp programming. There are a couple autonomous robot builders on the Western Allied Robotics forum that may be able to help -- try a post there.

A: Futaba is a major R/C manufacturer that builds quality equipment. However, the 4YF FHSS is a really basic 'entry level' radio with very limited features. Most importantly the 4YF FHSS system does not failsafe, which makes it generally unacceptable for combat robot use.

We have posts covering our recommendations for combat robot R/C gear in this archive. I suggest you start there rather than asking our opinion on every inexpensive radio you find.

A: Mark J. here: no, the electrical components of a typical combat robot are wired as a parallel circuit. Each of the components will be able to access the full voltage of the battery. The voltage needs of the components are NOT additive.

Example: a battery pack in a combat robot provides 7.4 volts. If wired as shown in #19, both drive motors, the weapon motor, both ESCs and the power light can each access the full battery voltage of 7.4 volts. The receiver is typically powered by a voltage regulator built into the drive ESC and will have its voltage limited to about 5 volts.

The voltage requirements of the components are not additive, but the amperage requirements of the components ARE additive. If the two drive motors have a maximum current draw of 4 amps each and the weapon motor has a maximum current draw of 8 amps, the battery may have to deliver 16 amps in a 'worst case' situation. The current draw of the ESCs, receiver, and power light are trivial.

Q: Hi Aaron, how do i connect the channels in the R/Cs to the ESCs so that they control the robot and the weapon? and how do you do a "channel mixing"? A: See #19 for help in connecting up the ESCs and the receiver. Channel mixing is a function commonly built into R/C transmitters and speed controllers. Consult your radio or ESC manual for specific instructions on use of the function. For additional info search this archive for "proportional drive mixing". Q: After I saw the FAQ, i noticed that there's a "link" between the cables from the ESCs and the batteries. What is the use of those links? what's the consequences if I dont use it? where can i get it? A: That's your power switch. Many competitions require the switch to be in the form of a removeable link. Search this archive for "removeable link" for an explanation and sources. Q: 1 more question, FAQ #19 showed the wiring for 2 [motor] robots. How do you connect [four] motors to their ESCs? A: Robots with two motors per side typically connect those motors in parallel to the output of a single ESC. Search the archive for "run 4 motors" for a diagram and design considerations. You can save both of us time and effort if you check the archives before asking a question.

P.S. I have ordered Grant Imahara's book and already got another one based on your recommendation. Thank you very much!

A: Ten years ago a 'good' R/C system in common useage by combat builders cost twice what a 'good' radio does now, so I don't feel comfortable setting a fixed price line. Also, the demands of combat robotics are different than for other R/C applications -- one $200 radio model might be great for robot combat, while another $200 radio might be a real headache.

As with many combat robot components, I recommend that you see what radio systems are popular with successful builders. Until you have enough experience to go your own way, following the lead of other teams is a good plan. If winning teams aren't using that $40 'Super Bamboo 3000' radio you found on-line there's most likely a really good reason.

Q: The [Popular R/C transmitter] with [Super Bamboo receiver] combo has been used successfully by both [team #1] and [team #2] over the past year or so. Total cost for the [popular transmitter]/[Bamboo receiver] combo is around $[very little]. (West Chester)

A: I know that [team #1] has looked into [Super Bamboo] radio gear, but I can't verify use of that specific R/C system in combat by either of the teams you mention. If they are using it they're in the minority and taking chances I can't recommend. Don't push your luck -- you'll feel really dumb if your $[very little] radio glitches and boots you out of a tournament.

A: The failsafe behavior of the DX5e depends on the receiver used with it.

• The Spektrum AR6255 receiver will failsafe to setable positions on all channels and meets all current failsafe requirements.

• The AR6115 and AR600 receivers kinda-sorta failsafe by sending out a 'null' signal that relies on the behavior of the device plugged into it to respond properly.

Q: Does the [Spektrum] DX6i [R/C transmitter] Failsafe?

A: Same deal as the DX5e.

Q: is the ar600 receiver legal for combat robotics? This question is related to the question on the dx5e

A: Mark J. here: the failsafe requirements for combat robotics address the behavior of the entire robot when the transmitter signal is lost.

• The Spektrum AR600 itself is neither legal nor illegal -- proper failsafe response with this receiver depends upon correct interpretation by your ESC/controllers of the 'null' signal this receiver sends on loss of transmitter signal.

• The Spectrum AR6255 receiver is entirely legal. It sends specific shut-down instructions to the ESC/controllers on loss of transmitter signal which guarantees correct failsafe bahavior.

Q: The Hobby King "orange" receiver will failsafe on all channels when bound to a DX5e or a DX6i.

A: I cannot confirm that, and I DO NOT recommend Hobby King products for use in combat robots. Like Aaron said above, don't go cheap on your radio.

Update: an article in the January, 2012 issue of Servo Magazine says that the Hobby King R410 and R610 receivers will bind to the Spektrum DSM2 transmitters and implies (but never actually states) that they do failsafe on all channels. You can roll the dice if you like, but I'm not going into combat with a $5.95 receiver.

Q: IS the [Tactic] TTX404 transmitter with the [Tactic] TR-624 receiver legal for combat robotics? Is it good?

A: Pay close attention because I'm getting tired of saying this:

I'm not going to go thru all the chinese knock-off radio systems individually to point out their flaws and list the things that would make you wish you'd spent a few more bucks. Legal or not, I recommend that you stay away from cheap, off-brand radio gear!

Most robot builders choose Spektrum radios, and for good reasons. Here are a few:

• Good resale value.
• Readable documentation.
• Established record in combat robotics.
• An army of robot builders to ask for set-up help.

A: An Electronic Speed Controller (ESC) takes the signal from the R/C receiver and translates it into controlled power levels for weapon or drive motors. There is a great deal of discussion about the selection and use of ESCs in the archive.

A: Holy cripes man -- read the event rules!! No respectable event would allow uncontrolled weapon motors. you will also (I hope) be required to have an R/C system that shuts down all weapon and drive power if the R/C signal fails. Safety first! See #18.

A: There is no difference in the operation of an R/C peizo gyro on robots with 2, 4 or more wheels. The turn signal from the receiver is sent to the gyro where it is compared to the actual turning motion of the robot. The gyro modifies the turn signal and sends it on to the signal mixer. The mixer sends the modified signal to the left and right side ESCs to keep the robot on the desired course despite minor mechanical or environmental influences.

• Two-wheeled robots are difficult to keep pointed straight under power -- they tend to turn even when the R/C signal calls for a straight course. A gyro will hold the course steady.

• Four-wheeled robots have no difficulty tracking straight, but do have trouble maintaining a smooth turn. A gyro will juggle the turn signal to keep the turn rate smooth and constant.

Q: It's me gyro guy again. Would i need a gyro if i used 2 motors to run 4 wheels like BioHazard?

A: First, 'BioHazard' runs six wheels - not four. Six wheel robots tend to be both stable and very maneuverable.

I'm not sure any robot 'needs' a gyro. Build it and see how it handles. Handling depends on factors like weight distribution, wheel track, wheelbase, and tire width. If you have trouble holding a straight line or carving a smooth turn you can add a gyro to assist.

A: Mark J. here: yes, the Airtronics SD-5G is suitable for robot combat. It meets the minimum requirements for all weight classes and weapon types, it has the usual features to adjust the radio response to your preferences, and the manual is complete and written in understandable english.

A: Mark J. here: think about what you're asking. If you're in the middle of a robot fight do you really want circuitry that shuts down your robot to 'protect' your battery?

In combat, robots do not run fuses, circuit breakers, or any device that could decide to protect the robot by shutting it down in the middle of a fight. Size your battery to provide ample power for a 'worst case' match. If you're worried, you can use an audible warning module to let you know when your battery is getting low and give you the option of shutting down, but don't use a cutoff!

A: Mark J. here: some Futaba transmitters (3PK, 7U, 8U, 9C, T10C, 12FG, 12Z, 14MZ) do allow for replacement of the frequency module with a 2.4 GHz conversion package that includes a new receiver and antenna. The resulting transmitter/receiver package is entirely ground legal, just like a standard 2.4 GHz system.

A: Mark J. here: I don't recommend going cheap on electronics, and the Turnigy 9x (AKA SkyFly 9x) is a really cheap knock-off radio system. It doesn't even come with a manual. If you have never owned a 2.4 gHz radio, I certainly wouldn't recommend starting with this one. Features are limited, programming is awkward, and quality control is poor.

You're getting what you pay for, which in this case is very little. In fact, you get too little for a combat robot -- there are no failsafes. That makes it useless for robots with active weapons. Save your money and buy a quality radio.

A: I don't know what level of information you're looking for, and this is not a topic where you're going to pick up useable skills from reading a couple of websites. Try a web search for "RF circuits" and browse the results to see what's available. I can recommend a good school for an EE degree if you like.

A: Yes, it can and has been done with either wired or wireless PS2 controllers. You need a microcontroller interface, which is not particularly simple. Lynxmotion has the parts and tutorials to help guide you thru the process.

A: Stay away from these, Antony. There are no specs given for either the battery or the charger. Buy a quality li-poly battery and charger -- this is not a place to scrimp.

A: Mark J. here: yes, Sealed Lead Acid (SLA) batteries are the most forgiving of the battery technologies available for combat robots. Our charging technique for the 'Hawker' brand SLAs used in 'Run Amok' and 'The Gap' was really simple: plug into constant-voltage power supply and walk away. It simply wasn't possible to over or under-charge them, and there was no possibility of damaging the batteries.

The next step down on the 'idiot proof' scale are the Nickel Cadmium (NiCad) and Nickel Metal Hydride (NiMHd) cells. A good quality constant amperage 'peak detector' smart charger will pretty much automate the charging process, although you do have to look out for 'false peaks' that can prematurely stop the charging. Buy a quality charger and you should have no trouble, even in a busy combat pit.

Another step down brings you to the newer Lithium Iron Phosphate (LiFePO4) cells, also known as 'A123' or 'M1'. Although less 'dangerous' than other lithium battery types, the A123 cells do require considerable care to perform well. Special 'cell balancing' equipment is needed to keep the battery packs competition ready, but relatively simple 'voltage cutoff' charging can be done between matches.

A: There are two widely used ways to encode information on a radio wave: 'amplitude modulation' (AM) is the simpler method that requires less complex and expensive equipment, but is more vulnerable to interference. R/C toys use AM radio systems. Hobby grade radios generally use the more complex 'frequency modulation' system to assure better control. Only very light combat robots without active weaponry are allowed to use AM radios.

A: Mark J. here: you can't directly judge the amperage capacity of a switch by the size of the wire attached to it -- but 20 gauge wire itself is rated for only 11 amps max. It is likely that any switch using such small wire would be rated for no more than 5 amps. Trying to push 35 amps thru such a switch will cause catastrophic failure very quickly.

Q: My mistake: it is more likely 19/18 awg. The switch is roughly the same size as this switch. It would just need to handle 35 amps for a half second in case the weapon motor stalls. It is a big weapon motor. What do other beetleweights use for a switch for similar levels of current?

A: Consider how bad you would feel when this switch failed and took you out of a tournament after all the work you put into building your robot and getting there. The switch in the picture is an R/C receiver switch, designed to handle less than an amp. DO NOT USE THIS SWITCH FOR YOUR WEAPON MOTOR!!

The preferred method for high current control in a small and light package is to make a 'removable link' from a suitable wire connector. See the diagram at right for proper use. We use Deans connectors for this purpose.

Reply: That idea never occurred to me. Thanks!

A: No transmitter can 'shut off' a gyro unless the gyro has a dedicated second channel for sensitivity control. Pick a gyro with a remote sensitivity control and any radio system with a spare channel can turn off the gyro.

A 'death spin' happens when a gyro enhanced robot gets itself inverted. The 'left-right' controls don't change when the robot is inverted, but the gyro corrections are reversed! The robot will spin uncontrollably as the gyro keeps adding more and more 'correction' in the wrong direction. Unless you can shut down the gyro your only option is to turn off the transmitter and let the 'fail-safe' shut the whole robot down -- you're hosed!

A: Heat is the big enemy of LiPo batteries. A tiny spark with no heating or signs of swelling likely did no damage. Inspect after every use, as you should do with any LiPo battery, and you should be fine.

Q: How paranoid should I be about charging a Lipo? Keep in mind that my definition of paranoid is much more extreme than those of other people. For quick reference, what other people call "extremely careful" is what I would call "moderately concerned." Example: When I first heard that you should never charge a Lipo unattended, I thought they meant you had to sit and stare at it the whole time or else you risked Armageddon.

A: LiPo cells give ample warning of trouble. Use a quality charger intended for LiPo batteries, keep the battery within its discharge amperage rating, and inspect after use for signs of swelling. If you want to be extra careful, there are flameproof 'charging bags' available from hobby suppliers. Maybe you should keep your friend in one?

A: Mark J. here: ideally you shouldn't rely on the ESC to decide on what to do on signal loss -- it should be handled by the receiver. If your receiver takes no decisive action and simply defaults to 'no signal' then the ESC should correctly shut down. To be certain, I would recommend that you select an ESC that specifies its action on signal loss.

A: A solid-state peizo gyro will greatly improve both straight-line and turning control on a two-wheeled robot. All of your questions about gyros have been previously answered in posts found in this archive - start reading! You will also be interested in the Team Run Amok gyro guide. Write back if you have specific questions not already answered.

Q: Hi Aaron, follow up on the gyro issue. I manage to find GWS GW/PG-02 Dual-Rate Piezo Gyro. and this stuff is just within my budget. The problem is i'm not really sure whether it will work with my system & honestly i'm not really sure about the wiring/connection. What i can tell you is that the ESC (Sabertooth) that i use allows channel mixing, and i use the left analog stick on my Futaba transmitter to control both Forward/Reverse & TurnLeft/TurnRight motions. I have browse through your gyro guide but didn't understand it quite well. Please help me further. Thanks!

A: OK, here are the high points...

• All hobby radio systems output the same signal from the receiver, so all hobby gyros are compatible with all hobby receivers.

• No gyros are compatible with transmitter-based radio mixing -- transmitter channel mixing must be turned off. You must use the mixing function of your speed controller or an on-board stand-alone mixer downstream from the gyro.

• There is a gyro wiring diagram in this archive: search for "I want to build a two-wheeled robot with a gyro".

• For steering and throttle on left stick, the gyro will plug into channel 4 output on your receiver and the Sabertooth 'channel 1' lead will plug into the gyro. The 'channel 2' Sabertooth lead will plug into the channel 3 output on the receiver.

• Gyros are NOT INVERTIBLE. If your robot is invertible you must use a gyro that can be turned off via a spare R/C channel or the robot will spin uncontrollably when inverted. the GWS GW/PG-02 gyro does have a remote sensitivity adjustment, but the description of that adjustment in the manual does not describe it well enough for me to tell if it will work for inverted robotic operation.

A: The 'Arduino Nano Carrier' board was a prototyping board developed for a class at MIT. It is not, AFAIK, commercially available. The 'Arduino Nano 3.0' board itself is available thru a link on the page you reference.

Additional questions about the Arduino microcontroller should be directed to the Arduino Forum -- it is not a component commonly used in combat robots.

Q: Do you have any diagram or info for the circuit board?

A: No. Please direct Arduino questions to the Arduino Forum.

A: Mark J. here: in the BattleBots era many teams had a 'weapons officer' who operated the weapon via a small switchbox on a long, hard-wired 'tether' plugged into the transmitter. This freed the driver from worrying about the weapon status and kept his attention focused on maneuvering the robot.

Now that reliable radio systems are much less expensive, it's simpler and more convenient to give the weapons officer their own transmitter with a dedicated weapon receiver in the robot.

A: Lots of potential trouble points here. My first guess is that you haven't 'bound' the receiver to the transmitter. Follow the instructions in the AR500 user guide or on page 9 of the DX5e manual. Read the rest of the manual while you're at it.

Q: Hi, I cant bind the reciever to the transmitter because the light on the RECIEVER (there's supposed to be an amber one) won't light up. The Esc's light works. I think the ESC is giving it power. The amber light on the Reciever should be flashing but it's just staying off.

A: Check to make sure the receiver is being powered by the ESC -- it sounds as if there is no power to the receiver. If the receiver is getting power and you're getting no response from it, I think the receiver is fried.

Q: To check the power to the reciever can I use a voltmeter? If sowhere do I check. (which wires?)

A: Power the electrics up and unplug one of the ESC connectors from the receiver. Check the power at the connector plug with a voltmeter. The red(+) and brown(-) wires carry 5 volt power. Be extra careful to avoid shorting the power connections with the voltmeter probes.

Note that it is possible to insert the ESC plugs into the receiver upside down. This will do no damage, but the receiver will have no power. The correct insertion has the brown wire closest to the bottom edge of the AR500.

More information can be provided if needed.

A: I don't think that more information is going to help. You don't mention what specific radio system you're using, but I'm going to guess that it's at fault. You can't afford to rely on a radio that won't hold settings and goes glitchy at a competition. Replace it, and make sure it's a quality radio.

Q: It is a spectrum 5, with an AR500 receiver.

A: Mark J. here: electronic trouble (especially intermittent radio trouble) is very tough to diagnose remotely. I think Aaron's suspicion is reasonable; your radio receiver and/or transmitter has gone glitchy and should be replaced.

A: RFL regulations do not require radio failsafes for one-pound robots without an active weapon. Antweights with an active weapon require a failsafe only on the weapon channel.

The Spektum AR6200 receiver has a suitable failsafe response only on channel 3. The other channels do something undesirable for a combat robot: they lock in the position they last had before signal loss. This behavior is not allowable for classes heavier than antweights, but does meet minimum RFL specs if the weapon is controlled by channel 3.

The event organizer has the final say on what is and is not allowed at the event, so best to check with them before you commit to this receiver.

A: Replaceable 'crystals' are used by some hobby grade transmitters and receivers to control the precise frequency upon which the radio commands are sent and received. You may remove the crystals and plug in crystals of a different frequency to switch the radio system to another 'channel' within the same 'band' to avoid interference from another radio on the same channel. Instructions for swapping out crystals will be in the user manual.

Newer 'spread spectrum' radios operating on 900 MHz or 2.4 GHz do not use replaceable crystals and will adjust their signal to avoid interference without any operator involvement.

Toy R/C systems do not have replaceable crystals. Toy radios in the US operate on either 27 MHz or 49 MHz and generally do not allow for channel change. The use of toy radio systems for antweights is limited to robots without active weapons and should be cleared with the event organizer prior to the event.

A: I haven't personally used the Spektrum Microlight receiver, but the comments at Robot Marketplace are all quite positive, and Spektrum in general makes quality products.

Note that the receiver has non-standard failsafe response on all but the throttle channel -- make sure the weapon ESC you select will respond correctly to a 'no signal' input from the receiver and shut down the weapon motor.

A: The Robot Fighting League (RFL) regulations require radio systems that 'failsafe' by bringing the robot drivetrain and weapon to a stop on loss of radio signal for all robots weighing more than 12 pounds and for robots of any weight with active weapons. The regulations do allow for 'homebrew' radio failsafe systems that meet specific criteria:

• Amplitude modulation (AM) radios are not allowed for control of robots that require a failsafe system, even if equipped with a failsafe device.

• Any homebuilt or modified radio system must be approved in advance of the tournament by the event organizer.

A: Mark J. here: you have a mode 2 DX6i transmitter and you want throttle on the right stick and steering on the left? No problem. Instead of using Elevon (Delta-Wing) mixing, use V-Tail. Your motor outputs will be channels 3 and 4 on the receiver. Consult your manual for specific instructions on setting up a wing-tail mix.

Here is the setup matrix for modes and mixes to put the controls on the sticks you want to use:

It is possible to change a DX6i transmitter from Mode 2 to Mode 1 thru a hidden menu. You can also swap the spring centering mechanism from the right stick to the left. Here's a tutorial.

A: Mark J. here: diagram this and you'll see the problem. It works only if the voltages of the two systems are identical. If there is a voltage difference there will be a reverse current flow thru the lower voltage circuit when the switch is 'off', likely destroying the electronics and the battery. Power diodes in the ground circuit could prevent this, but it isn't worth the trouble. Use a DPST switch or energize a relay with one circuit to switch the second circuit.

A: Mark J. here: there should be no compatibility issues between any hobby receiver and any hobby Electronic Speed Controller (ESC). In this case, I'm suspicious of a problem with the Battery Eliminator Circuit (BEC) in the Hobbywing ESC.

1. You should have only one source feeding power to your receiver. If your main drive ESC also has a BEC you need to cut the power lead (the red wire in the three wire receiver lead) on any other components that may be feeding power to your receiver.

2. The BEC output from the Hobbywing is programmable - it may be set incorrectly. If you're going to use the BEC on the Hobbywing, check the voltage output to make sure it's in range and stable. It's entirely possible that your 'bargain' ESC has a erratic voltage regulator that fried your two 'bargain' receivers.

A: If you're building an ant I recommend going one of two ways:

• Go really cheap and pull the electronics and drive motors out of an R/C toy - see the archive for more info; or

• Buy quality electronics that won't have to be replaced immeditely when you upgrade your robot and will retain good value if you decide to get out of the sport - search thru this archive for recommendations on this option.

As to just going forwards and backwards, you'll still need an interface to interpret the output from the receiver and send power to the motors. The R/C relay interfaces needed to do that are both heavier and more expensive than small speed controllers. There are small, light, inexpensive R/C switches, but they only provide on/off control - no reversing. You'll be much better off to go with full function speed controllers.

I suppose you could modify a pair of R/C servos for continuous rotation. Servos have a very small speed controller built into their internal controller board. It's an inexpensive approach that gives proportional forward and reverse control and simply plugs directly into your receiver - but servos are very slow compared to current antweights or hacked toys. I haven't seen a servo powered ant in many years.

Q: hey what would be a good toy to hack for an antweight?

A: There are several hackable toys discussed in the archive. The Johnny Lightning 'Battle Wheels' R/C toy is widely available and could be a good bet.

When I looked it up, the gyro did not mention it was compatible with Spektrum. Is this true? What would happen if I filed off the groove on the plug and put it into the receiver? If it wouldn't work, where can I find a spektrum compatible gyro?

A: The output signal from all modern R/C receivers is the same, but there are differences in the plugs and wire colors. Some PG-03s came with Hitec 'S' connectors with orang/red/brown wires, and some came with the Futaba 'J' style plug with white/red/black wires.

Your PG-03 has the 'J' plug with the little tab that keeps it from being inserted upside-down into a receiver socket that has a groove for the tab to fit into. See the Servo City Connector Types page for a full explanation. Just shave off that tab and you'll be fine. If it doesn't work, you've plugged it in upside down.

I don't want to use the 1 amp Picoswitch from the RobotMarketPlace because it requires an antiparallel [flyback] diode, while the 10 amp Battleswitch is too heavy and overkill since the valve probably uses around 1 amp at most. The Pololu switches are a possibility but I am not experienced enough in electronics to understand the description well. I have realized that I could use a Fingertech tiny esc to control my valve as it is both compact and lighweight, using the switches on my DX6 instead of the control sticks for the on/reverse effect. What is your suggestion? Thank you.

A: Mark J. here: hold on... the auxiliary channel on your Ant 150 had no reverse, so why do you now need on / off / reverse for your solenoid?

• Adding a flyback diode to the output of the Picoswitch is trivial, so if it will otherwise meet your needs you can certainly use it. The Picoswitch is a simple on/off switch - no reversing capability.

• Team Run Amok has used the RCE200 R/C switch to control pneumatic solenoids with excellent results. It is larger than the Picoswitch, but requires no external diode and has a few extra bells and whistles. It is also an on/off switch with no reversing.

• The Pololu R/C switch with MOSFET is inexpensive, very compact, and has the capacity to control a solenoid. It does require a bit of knowledge, soldering, and puzzling out to hook up correctly. Very possible to goof up. Again, a simple on/off switch.

A: It sounds like you aren't controlling these servos with standard hobby radio gear - true?

A standard hobby servo responds to 'pulses' sent along its signal wire to it from the radio receiver (or a device emulating a receiver). The position of the servo depends on the length of the pulse. With a hobby grade radio system it is possible to rotate the servo fast or slow as many degrees as you like. The servo will then attempt to hold its assigned position against external forces. You can find an explanation of the pulse code system at the Seattle Robotics Society servo page.

A servo should not be stalled. The motor draws large current when stalled and the heat build-up from this current will damage the motor rather quickly.

A: Mark J. here: general note - the new LiFePO4 and A123 cells require a different charge cycle with a lower cutoff voltage than other lithium cell types. Do not attempt to charge these cells with a charger designed for Li-Poly or Li-Ion chemistry.

The AstroFlight 109d charger requires the 555 Software upgrade chip in order to be useable with the A123 cells. The upgrade chip will convert a 109 or 110 Deluxe charger to charge only A123 cells -- you will lose the capacity to charge other cell types. The Robot Marketplace sells a 109 with the upgrade chip installed, but there are less expensive A123 chargers that can switch between different cell types (example) including some that do not require an external power supply (example). I'd suggest looking into alternative chargers to see if they meet your needs before buying an upgraded 109.

Back to your question: the AstroFlight 109 requires the full specified DC power input in order to provide the full specified voltage and amperage output. If you will not be pushing the charger to these limits, a DC power supply with less capacity may be used. You didn't tell me how large a battery pack you plan to charge so I can't comment directly on the suitability of your 8.3 amp power supply.

Q: Thanks for the A123 help! and about my power supply, I will mostly be charging 2 and 4 cell A123s so I belive it should work. I called Battlepacks and they were quite helpfull. On their website they sell an Astroflight 109, and they probably already installed the chip as well. As far as balancers, they have an A123 balancer as well. And seeing so many builders use the Astroflight I figure it might be a good investment. Thanks You for all your help!
Daniel

A: You're welcome, Daniel.

I suspect that a lot of builders use the AstroFlight 109 for their A123 batteries because they had a 109 to charge their LiPolys and they were able to convert for the small price of the upgrade chip. I like AstroFlight chargers for their reliability and simplicity of use, but if you don't already have a 109 it's expensive for the limited functionality you get. A lot of the R/C aircraft guys seem to be using a Thunder Power charger that is very flexible and includes a cell balancer.

1) When buying a transmitter and receiver, do they have to be from the same company? the same # of channels? Or does simply having matching frequency crystals make them work together?

A: Mark J here: the currently favored 2.4 GHz radio systems do not have crystals. The transmitter and receiver 'talk' back and forth and 'agree' on a frequency that is free and uncluttered. This DSM system is still evolving and has some significant differences between manufacturers and even between current and earlier radios from the same manufacturer. The number of channels does not have to match, but check the documentation carefully for compatability with your chosen receiver. Stick with the same manufacturer.

If you are considering an 'old school' FM radio system, be advised that some combat robot tournaments no longer allow their use. There are two 'flavors' of FM signal used by different manufacturers: positive shift and negative shift. A receiver designed for one shift type will not recognize the other signal regardless of crystal frequency compatability. HiTec and Futaba use negative shift, while Airtronics and JR use positive shift. Some third-party receivers will work with either type of shift -- check their documentation for compatability. Again, the number of channels does not have to be an exact match, although there are some differences in the signal from two or three channel 'pistol grip' transmitters that may cause incompatability in receivers with four or more channels.

Check #18 for minimum radio requirements for specific weight classes and weapon type. Again, some events may have higher requirements. Check the rule set of specific events you plan to enter. I advise picking out a nice 2.4 GHz system that will be accepted anywhere in any class.

2) Once I get my servos spinning, how do I translate that into larger motors driving the robot? Thanks again, -Russell

A: Inside your servo is a very small electronic speed controller (ESC) that translates the signal from the radio receiver into variable power and polarity to control the servo motor. To control a larger motor you need a larger ESC. See #21 for help in selecting drive motors and matching ESCs. #19 shows how everything gets wired up.

A: Sure. Your computerized transmitter's 'Adjustable Throttle Volume' (ATV) function can set the amount of servo travel on any channel, and even do it differently on each side of the 'neutral' position. See our Futaba transmitter programming guide for more info.

Q: Can you also do the ATV thing with the 5 Channel Spektrum DSM2 2.4ghz?

A: Spektrum calls it 'Travel Adjust'. I believe it's available on every radio they currently make - except the budget 5-channel DX5e: you only get the basics for $60.

Q: Thanks. In addition... damn. That was the one I wanted to buy.

A: I know it's tempting to go for the 'bargain' radio package, but the additional functions on a 'full featured' radio can tame an unruly robot and turn a sitting duck into a tiger. You'd outgrow that DX5e quickly, so spend the extra dollars now and save the expense of a future upgrade.

A: Obtaining warranty service is covered in the manual. The charger has a 5 year guarantee "against workmanship and manufacturing defects" thru the manufacturer. You can call their tech number and ask, but I wouldn't think that a crushed connector would be covered.

Either way, a new Tamiya connector is about $2 at your local hobby shop. That's cheaper than shipping the unit in under warranty -- replace it yourself.

A: Mark J here: pure technical fluffery. The condition you describe only occurs at partial throttle where the controller output voltage is well below the battery level and the current flow is a fraction of the full-power maximum. The peak amperage for which you must design is never higher than the motor draw at the maximum load it will see in operation. The controller cannot stuff more amps thru the circuit than the motor can draw, nor can it supply more total wattage than it draws from the battery.

Consult the Team Tentacle Torque & Amp-Hour Calculator to calculate the expected maximum operating amperage draw for your drive motors.

A: Hey, how come I didn't get hired for that job?

Faulty radios are uncommon. What is common is to hook everything up and test it without first fully charging the battery pack. A low battery charge will cause symptoms exactly as you describe. With a low battery, the red 'error' LED on the Sabertooth will flash as the motors sputter and draw the voltage below required levels for operation of the electronics. Give the battery a full charge before proceeding.

The next likely culprit is that your Sabertooth ESC is not set-up correctly for R/C control. You say you know it's working properly, but take a minute to step thru the Sabertooth DIP switch wizard and correct any errors in the switch settings. You most likely want:

• 'Other' battery
• Radio control
• Radio and receiver
• Independent mode (for tank steering)
• Exponential response

With the DIP switches set correctly, block the wheels up off the ground and power up the robot - leave the transmitter off. The Sabertooth should display a single dimly glowing blue LED labeled 'status1'. Turn on the transmitter. The 'status1' light should glow brighter to indicate that a control signal is being received. Exercise the transmitter controls and watch the motor response and Sabertooth indicator LEDs. The single blue 'status 1' light should remain brightly lit and no other lights should come on while the motors respond to forward/reverse commands.

If still no joy write back. Report your findings and give me your email address - we can step thru isolating individual components to find the trouble.

A: There are different grades of each battery chemistry type and the maximum charge rate varies with both the chemistry type and the manufacturer. Wherever possible, find and follow the manufacturer's specs for charge rate. This is particularly vital for batteries using lithium based chemistry -- don't fool around with them, they can catch fire if improperly charged!

That said, as a very general rule NiMHd cells should be charged at a rate no greater than '1C' - the rate needed to recharge the fully discharged cell in one hour. For example, a battery made from 4000 mAh NiMHd cells should be charged at no more than 4 amps (4000 mA). Small cells (like AA or AAA size) typically require lower charge rates (try 1/2 C). Monitor the temperature of the battery during the first few charges. Too high a charge rate will make the cells very hot, especially near the end of the charge. Lower the charge rate if the cells get hot.

Q: I can't find a battery charger for Nimh's that is low enough to charge my beetleweight's 400 milliamp 7.2 volt nimh battery pack. what should I do?

A: You should look harder. There are multiple NiCad/NiMh chargers at the Robot Marketplace that have adjustable outputs suitable for your small pack.

Q: Oh ya. Battery guy here again. I ordered my battery using the robot marketplace's custom antweight pack section. Who exactly would I contact for charging information?

A: My 'manufacturer' I mean the company that builds the cells, not the guys who put them together into a pack. In your case, that would be GP batteries: see their Data Sheet for GP40AAAM cells. They recommend 200 to 400 mA for a fast charge.

My guess is that I didn't install the gyro correctly. What is the proper way of aligning and installing a gyro?

A: Mark J here: I'd agree that you have installed the gyro incorrectly. The manual that comes with your gyro should refer to a 'corrective axis' or 'gyro axis of rotation' and diagram how the gyro should be installed relative to that axis. In a combat robot the corrective axis is a line running from the center of the chassis vertically straight up to the sky -- same as in a helicopter, which is likely diagramed. This often means mounting the gyro case 'standing on end' rather than flat on the chassis. It sounds like you currently have the gyro axis of rotation oriented along an axis running thru the robot from left to right.

When properly aligned, an outside force pushing the nose of the robot to one side will result in the robot self-activating the drive system and returning the nose to the original orientation. As noted in the Run Amok gyro guide, a solid-state gyro cannot be used with receiver mixing. You must go 'tank style' control or use an on-board mixer.

Write back if this doesn't clear up you problem.

In theory, this should be enough to dramatically increase the motor's power for a short period, yet be short enough to not fry the motor. (I know from experience that 3 volt motors can survive 150v discharges) That could decrease a spinner's spinup time, make an electric hammer more destructive, give some electric lifters more speed, etc.

A: Mark J here: if you directly charge a capacitor from a 12 volt battery you'll get a capacitor charged to 12 volts - no more. The voltage marked on the side of a capacitor is its maximum operating voltage, not a voltage to which the capacitor will magically charge. The charged capacitor could deliver additional amperage on weapon motor start-up, but no additional voltage. If your battery is adequate for the task you'd see no appreciable performance difference. If your battery in inadequate you'd do better to use the weight of the capacitor toward a larger battery.

It is possible to use a voltage multiplier circuit to charge the capacitor to a voltage higher than the battery supply. You would need to isolate the capacitor from the main weapon circuit, charge it, then switch it in just as the weapon is fired. This is difficult, dangerous, may require advance approval under RFL rules (section 6.2), and runs the risk of frying not just the motor but the battery and any electronics in the circuit. Even if you did all that I believe the results would be negligible as the additional true power (watts) delivered to the motor would be small.

Don't get fancy. If you want more power use a larger motor and/or boost the battery voltage and cross your fingers.

A: The short answer is 'no' -- not with a two-channel radio.

You can have an active weapon that fires autonomously, but the weapon system must de-activate and become inert on radio signal loss. Section 4.4.1 of the RFL ruleset says:

I can't think of a way to accomplish that without a dedicated, failsafe weapon radio channel.

A: A lighweight with a spinner requires a coded FM or digital 900 MHz/2.4 GHz radio with failsafes on weapon and drive channels. The most popular radio for your needs is the Spektrum DX6i for its full set of features and low price. You'll probably want to select the Spektrum AR500 receiver to go with it.

Note: there is no R/C 'killswitch' on a modern combat robot. The current rules require the radio system itself to 'failsafe' to zero throttle and weapon power on loss of radio signal. The Spektrum DX6i conforms to this requirement.

A: Combat robots have the same need to combine R/C control signals so that the input from two sticks control two output devices in different ways. It is called 'mixing'.

Computerized R/C transmitters generally come with mixing options built in. You're looking for 'elevon mixing' (although technically you have a 'taileron'). Check your R/C manual to see if you have this option and how to set it up. If your radio does not have built in mixing, you can add an inexpensive stand-alone mixer between the receiver and the servos.

Flying a plane with this type of two servo set-up is not particularly easy; you only have elevator and aileron control, no rudder. To turn you have to roll the plane to one side with the ailerions, then apply elevator to 'climb' the plane into the turn. Best luck.

Thank you very much!

A: Mark J here: I'd suggest a Team Delta RCE220 Dual-Ended Switch in each robot. Hook each into channel 3 (throttle) on their respective receivers.

• Wire ESC power for robot 'A' thru the 'normally open' terminals on relay X
• Wire ESC power for robot 'B' in series thru the 'normally closed' terminals on both relays X and Y
• Wire ESC power for robot 'C' thru the 'normally open' terminals on relay Y

• With channel 3 pulled 'down' - relay X will be active and only robot 'A' will have power.
• With channel 3 'centered' - both relays will be inactive and only robot 'B' will have power.
• With channel 3 pushed 'up' - relay Y will be active and only robot 'C' will have power'

NOTE: if you're willing to take a couple of seconds to switch between model memories to switch robot control I think this can all be done with transmitter programming. No 'kill switches' needed and all ESCs would remain powered at all times. It's pretty sticky programming and I'll need to test it before I pass it on. Let me know if you're interested (and tell me which Futaba transmitter you have).

A: How many more channels do you need? You aren't going to get more simultaneous independent proportional control channels by post-processing the receiver signal. It is possible to 'piggyback' additional on/off control signals onto the existing channels (see VANTEC Hitchiker KeyKoder) but this requires extensive modification to the transmitter as well as the receiver.

It is also possible to split a single proportional control channel to provide simple on-off control two (or more) devices (see: Team Delta R/C Dual-Ended Switch) but control of the two devices will not be simultaneous. Something similar to this could be done with microcontroller receiver post-processing.

A: I think I understand. You want to be able to plug two 7.4 volt batteries into your 'bot to produce 14.8 volts, right? I'm guessing you want to keep the batteries separate because your charger won't handle a 4-cell battery. Diagram at right.

Q: If you have two 7.4 volt 800 mAh batteries hooked up to make 14.8 volts, would that battery series hold 1600 mAh?

A: No. Two 7.4 volt 800 mAh batteries in series will give 14.8 volts with an 800 mAh capacity. Two 7.4 volt 800 mAh batteries in parallel will give 7.4 volts with a 1600 mAh capacity. You can get either double the voltage or double the capacity, not both.

Now I'm entirely clueless on how 'Continuous Discharge' relates to 'Max Continuous Current'. I thought the E-Flite 1500mAh 7.4V Double Cell 2S LiPoly Pack, 13g would cover my beetles needs but it's only a guess. Do you have any ideas on which battery would efficiently handle the robots power needs, and more importantly how you calculated which one was effective?

A: Mark J. here: you've done a great job using the appropriate tools -- the Team Tentacle Torque & Amp-Hour Calculator and the Team Run Amok Spinner Excel spreadsheet -- and you've come to a spot where you're unsure about how to proceed. That's what we're here for!

First, let's clear up the 'Continuous Discharge' and 'Max Continuous Current' confusion using that 1500 mAh E-Flite LiPoly pack you mentioned. Continuous discharge for that pack is '20C'. The 'C' relates back to the capacity of the pack -- 1500 mAh. That pack can discharge at a maximum continuous rate of twenty times 1500 milliamps = 30 amps = maximum continuous current.

There are two main considerations in selecting a LiPoly battery pack: capacity and discharge rate. Capacity measured in milliamp hours (mAh) is needed to provide enough power to get thru a match. The discharge rate measured in amps must exceed the current used by the robot in order to protect the battery from damage caused by discharge heat. LiPoly batteries are very sensitive to heat damage.

• Capacity: if your calculations are correct you only need 426 mAh to power your 'bot for a 5 minute match. I like to have a comfortable buffer of battery capacity above the calculated requirement, so anything over about 600 mAh would cover this requirement with ample spare capacity.

• Discharge rate: this is a little tougher to estimate. A few seconds of current averaging 1.5 times maximum continuous current won't do harm to the battery, so you do have a little room for error.
  • For the drive, the Tentacle calculator says the peak amp requirement is no greater than 4.56 amps at maximum 'push'.

  • For the weapon, I use the maximum amperage rating of the weapon motor divided by 1.5 as an estimate of the needed continuous current. The Axi 2808/24 has a max amperage rating of 22 amps. The Axi can draw much more than that - over 60 amps at stall - but a properly designed weapon drive will not allow the weapon motor to stall.

The 1250 mAh E-Flight pack should cover your power needs with a good margin to spare. It has almost three times the power capacity you need, and the 25 amp continuous current rating exceeds the estimated requirement of 20 amps. Just don't bog down the weapon motor!

A: Mark J here: the main problem with overvolting a servo is the small ESC that controls the servo motor. When you raise the voltage you also raise the amperage the servo motor will draw, and that can fry the ESC when the servo is heavily loaded. I don't know how heavily you load the servo, but I do know that if I tell you to go ahead at 7.2 volts and the servo smokes you're gonna be ticked off with me -- so no, I can't say it's safe to overvolt it.

If you're running the receiver from a battery eliminator circuit (BEC) in your electronic speed controller, it's already regulated to 5 volts -- but a high-torque servo draws a fair amount of current and may overload the BEC. If the receiver is running direct from the battery, dropping the voltage correctly requires knowledge of the amps the servos draw under load, and I don't know what that number is for your application.

I guess my recommendation is to either find another way to get more speed or just roll the dice with the servo.

Q: Hi Mark, about the servo, could I coil up a bunch of the red wire leading to the electrical servo lead to lose some voltage? How long would I need it to get around 6 volts, when my initial battery charge is 8.4 volts? Thanks.

A: This is going to take a little explaining, but I would be lax to deprive you of a complete answer. Pull up a chair...

Adding impedance does not directly control voltage, it controls current. You will get a voltage drop from extra wire length, but the amount of drop will fluctuate with the relative values of your added 'constant' impedance and the highly variable impedance of the servo as its load changes -- see Wikipedia article on 'voltage divider' for the math. If you have enough impedance to reduce the voltage to 6 volts at low servo loading, you're going to get so large a voltage drop when the servo motor is heavily loaded that the electronics will stop functioning! No, adding impedance in an attempt to hold voltage constant is a poor approach.

There are ways to directly reduce voltage but, as pointed out previously, dropping the voltage correctly requires knowledge of the amps the servo draws under load. The venerable 7805 voltage regulator chip can provide a stable 5 volts at up to 1 amp from a DC power source as high as 35 volts. The problem: your high torque servo will most certainly pull more than 1 amp if asked to supply full torque. You could verify this with an amp meter.

Another possible solution: a forward-biased silicon diode will drop the voltage flowing thru it by about 0.65 volts. Place several of these in series and you can get the voltage drop you need -- but the diodes must be capable of flowing the current you require for the servo. Again, we don't know what that amperage load is, only that it is fairly large. All this brings us to one simple solution that does not require knowledge of the amperage draw: place a 'tap wire' into your battery pack, a couple cells short of the last cell in the pack. This tap wire will draw 6 volts from the first 5 cells in the pack to power the receiver and servo, while the full pack powers your drive motors. No calculations, no semiconductors to overload, just a clean 6 volts. Don't worry about the actual 'peak' battery voltage. When a servo says it has a max voltage of 6 volts they are allowing for a little higher voltage from a freshly charged 5-cell NiCad/NiMHd pack.

A: Combat robots typically use solenoid-operated air control valves that open and close electricaly, with an R/C switch interface to allow remote operation. The Team Da Vinci Understanding Pneumatics page gives a good overview of combat robot pneumatics.

I’m planning on 2 drive motors that put out about 5-6mph on maybe 6" wheels, maybe the [BaneBots] 28mm Planetary Gearmotor, RS-385 Motor (not sure the right ratio but I’m sure the calculator you provided will. Which is fantastically helpful btw!) Maybe around 20 Amp stall amperage?

A: Mark J. here: I'm a fan of the educational and recreational aspects of building your own electronics, but I have to point out that there is precious little advantage to doing so when building a combat robot. I've seen many homebrew radio systems and speed contollers, and there wasn't one of them that I liked as much (or that performed as well) as standard off-the-shelf products. A combat arena is a hostile and expensive place to find the weaknesses of your electronics design.

First, check with the event organizers of tournaments in which you expect to compete to see if they are even willing to consider allowing a homebrew system. There will be concerns about interference and failsafe requirements so be prepaired for a lot of questions, skeptical frowns, and extra scrutiny from the tech inspector. Note that failsafe requirements are different if you plan on an 'active' weapon - see #18. Be aware that event organizers may overrule the RFL radio recommendations.

Let's sort out the difference between an H-bridge and an ESC:

• An H-bridge allows three control states: full forward, full reverse, and off. Attempting to control a quick robot in a small arena with a H-bridge is not recommended!

• An Electronic Speed Controller (ESC) allows full range control over speed from full forward thru full reverse. Note that model aircraft ESCs don't have reverse 'cause airplanes don't back up.

• Some ESCs have failsafe mechanisms and some don't. Failsafe electronics are usually built into the radio system - as are useful features like variable exponential response, adjustable travel volume, custom rate channel mixing, dual rates, and position trims. Best luck in emulating those features on a Xbox controller.

A pair of BaneBots 36mm 20:1 RS-385 gearmotors at 7.2 volts in a beetle spinning 3" wheels will give a top speed near 7 MPH in a small arena and will break the wheels free in a dead push at less than 3 amps each. If you're tight on weight, the BaneBots 24mm 20:1 RS-370 gearmotors weigh 35% less (3.3 oz. vs. 5.1 oz. each) and will provide comparable performance. A five amp dual-channel ESC should do fine for such an application and can weigh well less than one ounce.

My team travels with a steel pot with lid, welding gloves (to the elbow style) & a small (3 lb) ABC fire extinguisher. Assuming safe handling/ charging practices (OK some would say LiPo & combat is inherently unsafe, but that to one side for the moment), are we correctly equipped in case of a fire?

A: Mark J. here: thanks for the kind words! As chief battery officer for the team, I'll take this one.

You're much better equipped to handle a LiPoly battery fire than most teams. Manufacturers recommend charging LiPoly batteries in a fireproof container with an ABC dry chemical fire extinguisher handy. You have that covered, and the welding gloves could certainly be useful. I'd be just a little worried about the lid blowing off your steel pot -- LiPo ignition can be fairly violent.

You are right to treat LiPoly batteries with respect. An improperly charged, damaged, or too-rapidly discharged (shorted) LiPoly can burst into flame. YouTube has plenty of videos of this happening. Typically there is a ball or jet of smoke and flame from the ruptured pack which may propel the battery some distance, so just placing the battery on a fireproof surface won't do -- it needs to be contained.

If you do get a fire, use a dry chemical extinguisher or just back away if it can burn safely. There may be multiple flame-ups as individual cells ignite, so it's best to stay back and deal with it from a distance. Do not use water on a LiPoly fire! Sand will smother the fire effectively if a dry extinguisher isn't available.

If you're tired of hauling around that steel pot, there are specially designed bags for charging and storage of LiPoly batteries. They're easy to pack, are less likely to short out your charger if something goes 'poof', and the lid won't blow off.

Always charge your Lithium battery with a correct lithium battery charger, never use a 'puffy' battery (indicates damage and gas release), and do observe safety protocols. Read thru the Great Planes LiPoly manual for safe handling practices.

A: Read thru this archive for suggestions on suitable combat robot radio systems.

The Electronic Speed Controller (ESC) determines the current your electrical system can handle, and the ESC is a separate item from the R/C radio. Any hobby radio system can be used to control any ESC that has a standard R/C interface. The capacity of available ESCs ranges from 2 amps to well over 300 amps. Information on ESC selection is also in this archive.

A: No. The reciever receives the radio signal and translates it into a coded series of low power pulses. The ESC interprets these pulses into speed and direction information and supplies high current to the motor. You need both pieces!

A: We've said before that no matter what type of robot you're building it makes very little sense to purchase a 'cheap' radio system. If you continue to build robots you will soon want to upgrade your radio and will find that the resale value of that cheap radio is small. Buy a good radio system and your robot will benefit from the improved performance and your wallet will benefit from better resale if you do need to sell.

I'd recommend a full-featured DSM 2.4 Ghz system with a display screen and full failsafes. Such a radio meets all performance requirements for all weight classes. The popular Spektrum DX6i transmitter with BR6000 receiver is an example.

A: That's exactly how the failsafes on the BR6000 receiver function - all channels are driven to a pre-programmed position on loss of transmitter signal. You can set the failsafe position wherever you like: see Spektrum's BR6000 failsafe position instructions.

The AR500 receiver would only failsafe channel 3 to its programmed position and would send no position information to the other channels. Other manufacturers have different options on failsafe positioning, but your Spektrum is working as designed.

A: Mark J. here: first, check to make sure your receiver needs to be fed no more that 6 volts. Some receivers - Spektrum, for example - can handle 12 volts or more.

Second, many ESCs have a built-in voltage regulator that will supply a nice safe 5 volts to the receiver thru the servo lead with no direct battery connection needed. If your ESC has such a Battery Eliminator Circuit (BEC) you will neither need or want to supply power from an additional source.

You can use a zener diode as a voltage regulator by placing the zener diode in parallel with the power terminals of your receiver with a current limiting resistor upstream. You may have to fiddle with the resistor value to get proper regulation. A better and more stable solution would be to use an inexpensive 7805 voltage regulator chip.

A: It's best to have all the cells at a similar state of charge when the pack is assembled, but a long and slow (~50 mA) 'trickle charge' of the pack will bring all cells up to full if there is an imbalance.

A: Sure. The Speed 100 Electronic Speed Controller has a built-in Battery Eliminator Circuit (BEC) that regulates the voltage fed to the receiver down to a safe 5 volts regardless of the battery voltage. Your lifter servo is plugged into the receiver and is operating off this same 5 volt feed. To get full battery voltage to the servo you'll need to disconnect the positive power wire from the servo plug (the red wire on most servos) and patch it into the positive lead from the battery. The signal and ground wires remain plugged into the receiver. This will bypass the BEC for the servo and leave the receiver at 5 volts.

Q: So it would be fine to take off the servo pin, cut the individual pin off the red wire, strip the end, and put it in the screw terminal [on the Ant 100] with the other red battery connector? It wouldn't cause any shorts or anything? Thanks.

A: Mark J. here: yes, you've read the diagram correctly. The receiver uses the 'signal' and 'ground' wires to communicate with the servo controller - which is actually a very small ESC. The red 'power' wire supplies positive 'juice' to the servo controller and motor, which also use the ground wire as a return path to the battery. The ground is continuous and unregulated thru the receiver and back thru the ESC to the battery -- no shorts, no conflicts. Assuming that your servo can handle 7.2 volts, you're home free.

P.S. - Aaron is sulking because you didn't believe him, but we both understand that it's better to ask than to watch your electronics go up in smoke.

A: Mark J. here: in early 2009 Spektrum discovered that a few specific production runs of their DX6i transmitter had bad stick potentiometers. The affected date codes and instructions for returning those transmitters for service are listed at the Spektrum website. Anything you buy now should be fine, but check the date code on older transmitters.

A: See Zpatula's page - at the bottom. See also a diagram in #19.

A: We used the Team Delta RCE220 Dual Ended Switch to control the lifter on Zpatula. It's overkill for a beetleweight, but there was room in the chassis and we had one in our parts bin.

The lifter is built to operate with the motor running in a single direction, but it is much better to use a bi-directional (forward/reverse) motor controller for quicker and more predictable response. The RCE220 can be connected as a bi-directional 'H-bridge' and has special input connections that allow the use of 'limit switches' to stop the motor when the lifter reaches maximum and minimum height. This makes control of the lifter much simpler.

The lifter is also built with a 'slip clutch' that limits torque and prevents the motor from stalling. You will want to lock-out this clutch to allow full lifting power, but this may cause the motor to stall under heavy lifting. The stock motor consumes about 2 amps when stalled @ 6 volts. If you use an ESC to control the lifter you'll want one with at least that much peak capacity. Something like the FingerTech tiny ESC could be marginally adequate to control this lifter motor up/down. The RCE220 we use is rated at 12 amps.

A: Mark J. here: that's not a simple question and I cannot answer it in a short paragraph. I'd suggest you start by reading the article describing the Spektrum DSM technology at the Spektrum website.

A: Mark J. here: This is the Exceed 2.4GHz radio offered under another name. I have reviewed this radio previously -- search for 'Exceed' in this archive. Fingertech claims that their 'tinyESC' will correctly failsafe with this radio, but I'm not sure which other ESCs will failsafe properly.

A: Building your own speed controllers? The output of an R/C receiver is a pulse width modulation providing a 4 to 6 volt 'high' signal for a length of 1.0 to 2.0 milliseconds on a 20 millisecond cycle. A detailed description of the signal and an example of interfacing can be found at Chuck McManis' website.

A: Sure - the Spektrum DX6 is a full-function transmitter with all the bells and whistles. Spektrum calls it 'Travel Adjustment' but it's the same as ATV.

A: A puffy LiPo is a bad LiPo. Heat is a LiPo's worst enemy. It's toast. Do not try to charge it - charging a damaged LiPo can cause a fire or small explosion. Dispose of it properly (see instructions in the archive) and go buy a new one.

A: This info is widely available on the 'net, so I'm not going to repeat it here.

• For coding PWM on the ATMega: http://mil.ufl.edu/~achamber/servoPWMfaq.html

• For using PWM with the L293 motor driver: http://www.me.umn.edu/courses/me2011/robot/technotes/L293/L293.html

A: Mark J. here: we've warned people off of the Exceed 2.4Ghz radio in earlier posts. The last place you want to 'go cheap' is on your electronics. How functional a radio system do you think you're going to get for $45? The radio is manufactured in China by a company called 'Fly Sky' and is marketed under several names. It is (IMHO) entirely unsuitable for use with combat robots.

• The manual is an unintelligable translation from chinese. Example: "When you buy the CT6 series remote systems, with a programming line you can set up the program by your own, this will bring you happiness."

• No on-board function adjustments except mechanical trims. All other functions must be adjusted via a computer connection, so plan to bring a laptop with you to the tournament.

• If you do sort out the software and computer connection, the functions available are limited: endpoint, reverse, subtrim, dual-rates (Ch 1, 2, and 4), stick mode assignment, and some sort of exponential rate adjustment for Ch 3 and another channel I can't identify.

• No standard channel mixing (elevon, v-tail). Either figure out how to adapt a helicopter swashplate mix to your robot or program your own user mix.

• No batteries - buy your own.

• No failsafes - relies on a correct response from the ESC to be legal for active weapons or classes above hobbyweight.

I will repeat my opinion - this system is unsuitable for robot combat. Check question #16 in the and then go look around for your wallet some more.

A: I suspect that your robot is moving 'forward' because your test area isn't level and it's actually moving 'downhill'. There are several posts in the archive about 'meltybrain' systems to get controlled movement from thwackbots. You'll spend a WHOLE lot more money trying to get meltybrain to work than you would on a top-flight FM radio.

A: Yes - I'm not a fan of the Exceed radio system, but the receiver has standard outputs that any R/C component can plug right into.

A: The Lithium Nano batteries have a very high discharge and recharge rate, as well has high energy density. Drawbacks are the need for a specialized charging system and a bulky cylindrical shape -- too bulky for use in most insect-class designs where the high energy density might best be used.

A: I'd suggest that you pay the extra $5 for that LiPoly pack you found at BatterySpace and stop wasting your time (and mine).

A: Mark J. here: if the lifter servo is digital, yes. If the lifter servo is analog, maybe/maybe not. There is a certain amount of 'interpretation' here.

The Sabertooth ESC with the failsafe DIP switch turned on will take care of the drive motors, but the AR500 receiver sends no signal at all (except on channel 3 - see below) when it looses contact with the receiver. A digital servo will freeze in place when this happens, but an analog servo may creep. Technically it wouldn't be in compliance and a picky tech inspector may call you on this.

The AR500 will failsafe channel 3 to a pre-set position on signal loss. A servo lifter controlled by channel 3 would snap to the pre-set position. The rules say that all motion is supposed to stop with signal loss but interpretation of this rule can vary from event to event. I would suggest contacting the organizer of the event you plan to enter for their opinion.

Q: Could you recommend a digital servo under $50 with 100 oz/in at 5 volts?

A: I can come close: the Hitec HS-5645MG Digital High Torque servo produces 143 oz/in of torque at 4.8 volts. Metal gears, 2.1 ounces, $54.99. There are some no-name chinese digital servos well under $50, but I woudn't use them. You'll forget about spending the extra money a lot quicker than you'd forget about a cheap servo failing and taking you out of a tournament.

A: The INDI 16X705 charger is an all-in-one charger with a built-in power supply -- no external power supply needed. I've seen mixed reviews for Integy chargers, but the list of features and price are tough to beat. The charger comes with a standard Kyosho connector, but you can take it off and put on anything you like.

A: I'll assume that you have a charged battery in there someplace that delivers between 6 and 18 volts. Take a look at the wiring diagram in the (#19) to make sure you've got everything hooked up correctly, and double check battery polarity. If you're certain that the wiring is correct it's time to suspect a faulty ESC.

A: See the wiring diagram in the (#19).

A: Largely useless for robots. It has a very low power output and does not meet robot failsafe requirements.

A: Servos are 'neutral timed' for equal speed and torque in either direction.

A: Twisting pairs of wires together is a well known technique to reduce transmission or reception of radio frequency signals. See the Wikipedia article on twisted pairs. Robot motor leads are often loosely twisted to prevent them from radiating radio interference that can cause trouble for receivers.

The Spektrum BR6000 receiver is really two receivers in a single package, each operating on a different frequency. The two antenna wires on the BR6000 receiver lead to a separate receivers inside the housing. Twisting the antenna leads around each other forms a 'twisted pair' that may interfere with reception. Keep the antennas away from each other and away from other electronics.

A: Mark J. here: I strongly recommend against going cheap on your electronics -- particularly on your R/C gear. It would be false economy to save a few bucks on the radio only to get washed out of a tournament when it glitches. I don't see any mention of failsafe capability for this system and it's anyone's guess if it is compatible with Spektrum receivers. Don't do it.

A: Mark J. here: three possibilities:

1. the pack isn't being fully charged;
2. the pack is old, damaged, or has a dead cell;
3. the robot really is drawing that much juice.

Q: The racing battery pack is a Duratrax DTXC2146 7.2V 42000mAh HiMH Battery. It is about 6 months old,and I have a Duratrax IntelliPeak Pulse Charger. My robot isn't really a robot, its an old Tamiya King Tiger tank with clutch mechanism. I'm not sure what motor it has, but the motor is about 2 inches long and 1 1/4 inches wide. I am peak charging the battery at about 2 amps. THANKS!

A: It's unlikely that your motor could be sucking down enough amps to drain a 4200 mAh pack in 20 minutes. Make sure there is no binding in the drive mechanism, but I suspect a battery problem.

NiMH packs can be damaged by recharging while still 'hot' from a recent rapid discharge. 'Old' refers to the number of charge/discharge cycles the pack has been thru, not just it's physical age. The Duratrax charger does not display the amp-hours put into the pack during the charge, so it is of no direct diagnostic help. Still, a 2-amp charge rate should take better than two hours to fully charge your drained pack -- is that about how long it's taking?

Try charging the pack at 1 amp and letting it drop into automatic trickle charge mode overnight. If that doesn't give better results I think it's time to buy a new pack.

No trouble soldering PCBs, but the wire is giving me fits. At best, I get a shoddy coating of solder on the wire, and it doesn't seem to soak up the solder like I think it should. I have 18, 16, and 12 gauge wire yet to solder, and I'm afraid to even try it. Any advice? Is my equipment too wimpy for the job? [Dave B.]

A: Mark J. here: your equipment is more than up to the job, Dave. What you need is some paste flux. Dip the end of the wire into the flux to coat it. Apply a tinned iron and the solder will soak into the wire like water into a damp sponge.

The battery was only shorted for a moment (maybe one second). It did get pretty warm, but not hot. What are the chances that I damaged my battery? Do you think it would still be combat worthy? The robot is yet to be completed, so I won't be able to test the battery for awhile. [Dave B.]

A: Mark J. here: everybody gets a case of the dumbs now and again, Dave.

LiPolys do not appreciate being shorted. Examine the battery casing: it should be taught and flat. If there is any bulging or 'inflation' the battery has been damaged and is unsafe to use. If it looks OK I'd put it on a heat-resistant surface away from flammables and run it thru a couple of charge/discharge cycles. If it behaves normally, run it.

A: Most computerized transmitters have a menu page to swap modes. The DX6i has one, but it's undocumented and really well hidden:

Press the selection roller and hold down while turning on the transmitter. Release the roller when 'SETUP LIST' appears. Rotate the roller to highlight 'COPY/RESET' and press the roller. Rotate the roller to highlight 'RESET' and press the roller. When prompted with 'SURE NO/YES', rotate the roller to highlight 'List'. Toggle the 'AIL D/R' switch (top right of the transmitter) from position 1 to position 0 a few times. Secret hidden menu! Select your desired mode with the roller and press to accept.

I don't have a DX6i here to try this on -- let me know how it works.

A: Mark J. here: I suggest you read the Run Amok Guide to Combat Robot Gyros for details on mixing and gyro inversion. Briefly:

• Gyros are not compatible with transmitter mixing. You will need to use the on-board mixer function on your Sabertooth to run a gyro.

• If you use the Sabertooth mixer you can assign the throttle and steering to any stick and axis you like: for left stick throttle with right stick steering plug throttle into channel 3 and steering into channel 1.

• An inverted robot with a gyro will go into an uncontrolable 'death spin' unless the gyro can be shut off with a spare radio channel. The 'invert' function on the Sabertooth will not solve this problem - you must have a gyro with a remote shut down feature.

Q: Thanks Mark. Could I have two gyros and use the spare chanel to switch between the one for right side up and the one for inverted with two transistors spliced into the logic cable? As an alternative, could I use the "Remote Gain Dual Mode Heading Lock Gyro MS-044"?

A: Are you all that sure that your 'bot will need a gyro at all? I'd suggest trying it before going to a gyro.

I don't like the 'two gyros' idea. If you want to try something unusual, how about mounting the gyro on a tiny servo and rotating it back upright when you invert?

The MS-44 manual does talk briefly about 'gyro sense reversal', but this will not correct the 'death spin' problem. Helicopter gyros simply never face the same problem as a skid-steer robot - when inverted, helicopter direction controls reverse and the gyros are designed for that.

A: Hi again, Anthony. I'll be glad to help, but I need to know more about your robot and where you are in setting up the electronics. I also neen to know how you'd like to have the controls set up: do you want to have forward/back and left/right on one stick or have throttle and steering on different sticks? Would you rather have independent throttle for the two sides of the robot on two sticks (tank steer)?

You can get information on some of the set-up options in the Run Amok Transmitter Programming Guide. It was written for a Futaba radio, but you have most of the same options on your Spektrum. For a little help in wiring up the receiver and your ESC, see the wiring diagram in the (#19).

Write back and let me know what specific help you need. Oh, and tell me if your Spektrum is Mode 1 or Mode 2.

Q: My robot uses three channels -- 2 for drive and one for weapon. It is an antweight with a vertical saw and two hacked Hitec servos for drive. I want tank steer and my transmitter is Mode 2. My electronics are already set up. What ports do I plug these parts into? Thanks for your help!!!!!

A: OK, Anthony - tank steer is the simplest control system to set-up, but your left control stick does not spring-center like the right stick. You will need to modify the spring centering system by opening up the case and transferring the spring assembly from the left-right axis to the up/down axis. Tricky, but some help with this can be found at www.max3design.com.

• Your left drive motor plugs into channel 3 and will be controlled by the left stick on your transmitter.
• Your right drive motor plugs into channel 2 and will be controlled by the right stick on your transmitter.
• The weapon ESC plugs into channel 5 and will be controlled by the landing gear switch on the upper left corner of your transmitter.

Once the receiver is 'bound', you can check the control response. Each drive motor should spin 'forward' when it's stick is moved forward and 'backward' when the stick is pulled back. They should not move at all when the sticks are centered. You can adjust the 'no movement' point with the channel 2 (elevator) and 3 (throttle) 'trim' adjustments (see your manual). If direction response is reversed, it can be corrected by the 'servo reversing' function (see your manual). Likewise, if the weapon motor is 'on' with the switch in the 'off' position, use servo reversing on channel 5 (gear). If the weapon motor spins backward, reverse the power leads from the ESC.

That should get you rolling, Anthony. Take it off the block and drive it around. Leave the weapon disconnected outside safe containment - PLEASE!

A: I'm not sure I understand the question. If you are trying to use the Battle Switch like an ESC to control a weapon motor, the switch and motor system should be connected to the battery in parallel to the drive ESC. Connecting the weapon switch and motor to the drive ESC battery connections would be OK. Wiring would be similar to the wiring diagram in the #19.

Team Delta also makes R/C switch interfaces. Theirs have built-in radio fault failsafes.

A: The device labled 'Removeable Power Link' in the diagram is the master switch. In large robots this switch is usually a 'removeable link' for safety purposes. A removeable link is just a connector with one side shorted by a loop of wire -- pull the connector apart and the circuit is broken. See Team Delta switches/links and Robot Maketplace power switches.

Smaller class robots can use a simple single pole single throw (SPST) switch of suitable capacity, or you can make a removeable link out of a small connector. Some form of master power disconnect switch is required by all current rulesets.

See also the wiring diagram in the #19.

A: A Futaba connector is not suitable for high amperage connections -- it's only good for about 3 amps. Replace the Futaba connector with a Deans Micro Plug and run wires from the plug to the Sabertooth screw terminals. Connect the weapon ESC power leads to those same screw terminals and you're in business.

Can't solder? Now would be a great time to learn.

A: Probably not, but you haven't given me enough info to say for sure. Several different problems can trigger a shutdown and give you the red error light.

The first thing I'd check would be the battery. If it's lithium the #3 dip switch should be down, if not the switch should be up. If the battery does not have enough output capacity to deliver full amperage to your motors the supply voltage will drop and the Sabertooth may shut down. Fully charge the battery and try again. If no joy, test the setup with a larger battery (or smaller motors).

Make sure the other dip switch setting are right, and double-check all the connections to make sure they are correct and tight.

Q: I have the dip switches set right. The only thing I connected wrong was the pigtail servo lead off the 5v side of the ESC - I hooked the ground wire to the S2. Plenty of bats.

A: Mark J. here: you didn't think it was worth mentioning that the receiver was incorrectly wired when the ESC failed? More info needed:

• What are your dip switch settings?
• What battery are you running -- type, voltage, capacity?
• What drill motors?
• What receiver?
• When the pigtail ground was incorrectly connected to S2, what was the pigtail signal lead connected to?
• If you power up the ESC now, are any of the indicator lights lit? Which ones?
• If the receiver has a power light, does it light up when the ESC is powered?

- Dip switches 1 and 4.

Assuming that you mean that 1 and 4 are 'off' (down toward the numbers) and the others are 'on', that puts you in R/C mode with no mixing. That's fine...

- Battery is 12v lead acid, 7.2 AH

A single 12 volt battery -- OK.

- Craftsman 19.2 drill motors.

Whoa! Even at 12 volts those motors will pull more amps than the 'peak' output rating of the ESC if loaded down near stall. At 24 volts they'd pull a whole lot more. I wouldn't try to run those motors on a Sabertooth 2X25 -- it's gonna overload and shut down anytime the motors are pushed.

- Futaba R606FS 6 channel 2.4.

Should be fine...

- Pig tail was connected to receiver.

OK, but you told me that the ground wire was connected to 'S2' on the ESC. To what were the other two wires (signal and power) connected?

- [Update] Signal to 'S1' and power was connected to the 5V.

From the dip switch settings I'm assuming that you're doing mixing in the transmitter. Grounding the 'S2' input to the ESC should have done no harm, but you would have had no steering.

- All the lights on receiver work.

Good...

- No lights on ESC work.

Not good...

- It has exactly 5v on ESC.

OK, no lights on the ESC has convinced me that there has been a failure in the Sabertooth. I think it's a poor choice to control those motors -- it's going to shut down everytime the motors are put under any real load. Still, the claimed overload protection should have kept the ESC from frying during your very short test. Get in touch with Dimension Engineering and give them all of the information you've given me. They may replace it under warranty or offer repair service, but I wouldn't use that ESC for those motors.

Q: The drill motors have the factory planetary gearing then geared down 4:1 gearing on top of that. Will that make any difference in the amount of amps it would be? Does that effect it at all? Trying to not spend $500 on a Vantec. BTW Thanks for all the help.

A:This project sounds like something other than a combat robot.

The amperage draw of the motors will depend on the voltage, gearing, wheel diameter, vehicle weight, and the resistance the vehicle is encountering. You can use the Team Tentacle Torque & Amp-Hour Calculator to approximate the amperage draw when the vehicle is pushing full force against an immoveable object. This is a common condition with a combat robot, but maybe not for whatever you're building.

The Craftsman 19.2 volt motor/gearbox is not one of the motor choices available on the Tentacle Calculator, but you can use the 'DeWalt 18v Low' motor selection as a reasonable stand-in. Enter your 'Operating Voltage' (12), Robot Weight (fully loaded - ??), Wheel Diameter (??), and Gear Ratio (4:1). Leave the other values at default. The 'Amps (per motor) to spin wheels' output will give you the maximum expected amperage draw.

Robot builders generally make sure their ESC can deliver their maximum expected amp demand for a good long time. Buying a $500 ESC that meets your requirement is a lot cheaper than buying a succession of marginal ESCs that keep failing and knocking you out of tournaments. Happy robot builders do not go cheap on their ESCs.

Q: You are correct sir, I'm actually building a 1/10 scale D9 dozer. I know you don't deal with these models, however it's very similar to a robot and you are the only one that I've found that knows what I need to do. So here is what I have:

• Weight - 78 lbs
• Track on the ground is 17" long and 2.75" wide
• Blade is 17" wide and 8" high

A: OK, now that I know what we're working with I can be of more help.

Track and blade size are not factors. I'll guess that the diameter of the tread drive sprocket is about 4": that gets entered into the calculator in place of wheel diameter. Plugging all that in, I get a peak amp draw of only around 6 amps when pushing hard with the treads spinning for traction. You might pull more amps working in thick mud or another surface where the treads could really dig in -- I don't know exactly what dozer modelers do with their toys. Top speed is about 1 MPH.

If this were a robot, I'd convert that excess torque into speed, but the slow speed will be realistic for a model dozer. The added advantage is that the projected amperage draw is well within the capacity of the Sabertooth 2X25 ESC.

We still don't know what blew out your ESC during the test, but let's chalk that up to some hidden defect. Get the Sabertooth repaired and you should be fine.

Q: Mark J, YOU ARE THE MAN!!!!! I appreciate all the help. And I know that in the future, I can count on you. Is there anyway that I could send you a pic of what I'm building?

A: Happy to help. I've advised all sorts of non-robot projects here -- small trains, camera booms, electric bicycles, automotive interiors -- but this is my first mini bulldozer. I'd like to see a picture: send me your email address (I won't publish it) and I'll contact you.

A: First, it's hard to argue with the record Team WhoopAss has put together. If something is on their robot, it's there for a reason.

Hexy Jr. was built during the BattleBots era when IFI Robotics controller systems were the rage. Most of the odd electronic bits, including the custom controller board, were for the IFI radio system. You wouldn't need all that with the current radio systems.

The other things I see on their parts list are standard items for a well designed pneumatic weaponed 'bot. They did it right.

A: The Spektrum FAQ says that their AR6000 receiver draws about 40 mA -- the BR6000 should be the same. If you need to peg the consumption more precisely just supply the BR6000 with 5 volts and monitor power consumption with an amp meter.

Note: a receiver passes power to servos and gyros (but not ESCs). If you have such devices plugged in to the receiver you'll need to measure power consumption with everything installed and under simulated load.

A: We've always used Deans connectors on our sub-light robots and we've never had a problem with them. The new Deans Micro Plugs should be fine for a beetle.

A: It's good to be cautious with voltages applied to radio systems. Some receivers are more sensitive than others, so always consult the manual when going outside the normal range. Spektrum says that all of their Digital Spectrum Modulation (DSM) receivers have an operational range of 3.5 to 9 volts, so you should be fine at 7.2 volts.

The BR6000 receiver can and should be used with either the DX5e or DX6i transmitters. It has full fail-safe features that are required in most weight classes and weapon options.

A: Not recommended. If you connect the batteries in series, the weaker battery will drain down before the other and current flow will try to reverse-charge it. At best this could damage the discharged battery and at worst it could burst into flame. Connecting them in parallel would be safer, but I think I'd avoid the whole thing.

A: What does this have to do with combat robots?

A: I'm not sure that I understand your question. NiMH cells in series can deliver as much voltage as you like, so I'm guessing you mean the voltage where the cell is effectively drained? The chart shows a typical voltage vs. discharge state for a NiMH cell. When fully charged the cell can provide a little better than 1.3 volts under load. By the time it gets down to 1.1 volts it's pretty much drained. The discharge rate and cell temperature will impact the discharge curve.

A: Lithium batteries are picky about storage conditions, but Nickel Metal Hydride cells aren't. Store them at room temperature and give them a charge once a year. They'll loose charge during storage, but a couple of charge/discharge cycles and they'll pop right back to full capacity.

A: Mark J. here: that's the joystick set-up I like to use. It's possible to set-up the Sabertooth to give you left/right and forward/back control on any sticks you like. For left stick throttle, right stick steering with a mode 2 Spektrum:

• Leave transmitter mixing off (default).
• Flip the #1 option switch on the Sabertooth 'ON' to enable on-board mixing.
• Plug the Fwd/CH1 connector from the Sabertooth into the throttle output on the receiver (channel 3).
• Plug the Turn/CH2 connector from the Sabertooth into the aileron output on the receiver (channel 1).

A: Mark J. here: Li-ion batteries do irreversably lose capacity as they age, whether they are used or not. The loss is greatest when the cells are fully charged and at high temperatures. For best results drain them to about half capacity, seal in plastic bags, and store in your refrigerator. This will cut your loss by about 90% compared to fully charged batteries at room temperature..

Alternate solution: sell them to somebody who can use them now.

A: Mark J. here: DeWalt drill motors spin faster counterclockwise than clockwise because the brush timing has been advanced to improve efficiency when spinning counter-clockwise. Used in a robot, the left-side motor will run a little faster than the right-side motor and the 'bot will curve to the right rather than go straight under full power.

A peizo gyro is used in an R/C system to detect turning movement that has not been initiated by the R/C transmitter. When such turning is detected the gyro modifies the output of the receiver to correct for that movement. Peizo gyros were developed for R/C helicopters to monitor the action of the tail rotor and keep the chopper pointed in the right direction, but they can be very handy in specific robot applications as well.

Back to your question: yes -- since the turning of the robot happens without R/C turning input a heading-hold type peizo gyro would sense this as 'drift' and would correct the turning motion by reducing power to the left-side motor.

A: No clue.

A: Receivers do not 'supply' voltage -- they pass on the voltage from the source that powers them. The Battery Eliminator Circuit (BEC) of a typical Electronic Speed Controller (ESC) provides 5 volts. The Spektrum receivers can operate directly from a power source as high as 9 volts and would pass that voltage directly thru to the receiver power output line.

A: Take a look at the removable crystal for the transmitter and/or receiver. They should both be labeled with a frequency channel number. If that channel number is between 61 and 90 (75.410 to 75.990 MHz) then the radio is 75 MHz ground frequency. If the Transmitter is not 75 MHz, a 75 MHz receiver will not work with it -- they have to match.

A certified technician can retune a Futaba radio from 72 MHz to 75 MHz, but it would be less expensive to buy a radio on the correct frequency band to start with.

A: The Spektrum DX5e is brand new and I have received no feedback from robot builders, so I cannot make a recommendation. I can tell you that it is a very basic 5-channel transmitter that lacks many useful features that make a robot much easier to set up and more comfortable to drive.

Q: What features does it lack compared to the DX6?

A: The DX5e has few features compared to the fully computerized DX6. Some examples:

• no LCD display;
• no batteries or charger;
• no multi-model memory;
• no adjustable travel volume;
• no user programmable mixes;
• no exponential response settings;
• fixed dual-rates - not selectable by channel;
• only one non-adjustable mixing mode (elevon).

Q: Could you use the DX5e with the BR6000?

A: Yes, and you should use the BR6000 receiver for the full failsafe features. The AR500 receiver does not correctly failsafe for robot applications.

Q: You can buy the DX5e on 'Mode 1' or 'Mode 2'. What does that mean?

A: There are two 'standard' ways that input channels are assigned to the two control sticks. Mode 2 is the U.S. standard with the elevator channel assigned to the vertical stick axis on the right side of the transmitter. Mode 1 is the European standard and has the elevator channel on the left stick. Computerized transmitters generally allow you to switch between modes, but the DX5e doesn't so you have to pick.

If you're going to use the included 'elevon' mixing and want 'single stick' control of throttle and steering on the right stick, pick Mode 2. Elevon mixing in Mode 1 will give you throttle on the left stick and steering on the right. More information on modes and mixing can be found in our transmitter programming guide

Q: Does the DX5e have a low battery light or something?

A: Yes, that's covered in the DX5e manual. See page six, and read the rest of it while you're there.

A: Yes, but I'm not sure why you'd need to. If you're short on space, it would be easier to take the connector plugs apart and plug in the individual wires.

A: Sure -- just keep the total length as close to the original as possible. Search this archive for 'original length' for a full discussion.

A: Lithium batteries are very sensitive to abuse, and an abused lithium battery can burst into flame.

• never charge lithium batteries with a charger not specifically designed for them;
• never discharge lithium batteries at a higher amp draw than they are rated.

A: The whole difference between digital and analog servos is in the electronic controller board inside the servo. Digital servos have a microprocessor on that board that can process the signal from the receiver and send more precise, quicker control information to the servo motor. If you're flying a helicopter this is important. If you're powering an ant lifter or hacking a servo for a drivetrain, you'll never notice a difference.

A: Spektrum DX3R.

Q: What inexpensive 3 channel 75 MHz transmitter would you suggest?

A: The 75 MHz band is on the way out. If you buy an inexpensive 75 MHz radio you're going to need to upgrade soon and nobody is going to want to buy your outdated R/C system. Buying the Spektrum radio will save you money and trouble in the long run. I've said before, I don't recommend scrimping on electronics.

Q: What do you do if you are using the Inertia Labs chassis, but the Spectrum BR6000 receiver is to big to fit inside?

A: I'd make a new cover for the chassis to fit the BR6000, but I have a feeling you aren't going to be happy 'til I give you the name of a 3 channel 75 MHz pistol grip system. We don't use pistol grip transmitters, but if I wanted an inexpensive 75 MHz pistol system exclusively for antweight use I'd go with the Futaba 3PM.

Q: Are there any 2.4 GHz receivers that are the size of the GWS micro receivers? It is supposed to fit in the Inertia Labs chassis.

A: Although not as small as the GWS pico receiver, the Futaba R603FF receiver that comes with the 2.4 GHz version of the Futaba 3PM pistol grip system is 1.5" by 1" x 0.55" and will fit in the Inertia Labs chassis next to the Barello ESC. I recommended the Spektrum system over this Futaba because I don't know any robot builders who have used the Futaba 2.4 GHz systems, but the specifications look great and it is less expensive than the Spektrum.

Q: Would you suggest the 3 channel 75 MHz Hitech Aggressor SRX-3 for a inexpensive antweight transmitter?

A: There are two different 75 MHz Hitech Aggressors: AM and FM. The AM Aggressor is very cheap, but combat robots create a lot of electrical 'noise' that interferes with AM radio. AM radios are not allowed for robots with active weapons, and not at all in some competitions. I cannot recommend that you purchase an AM radio. The FM Aggressor is more expensive than the Futaba 3PM and has no useful additional features. I like Futaba.

Q: Can the Futaba 3PM 3 Channel transmitter use a GWS micro receiver as the receiver?

A: No. The GWS receivers work well with 4 channel and higher transmitters, but there have been many problems reported by builders trying to use them with 2 and 3 channel transmitters. Something's different about the signal coding in transmitters with less than 4 channels.

Q: I'm thinking about using a Futaba 14MZ 2.4GHz Radio System for my antweight. I only have $80, and I can't find the price of the 14MZ. Can you tell me how much it costs and if its a good radio for me?

A: You can't find the price of the 14MZ??? I put "Futaba 14MZ" into Google and it spit prices all over me. Very nice radio, but a little out of your price range. Street price is about $2300.

We could have saved a lot of time if you'd mentioned your budget at the start.

A: Mark J. here: once again, Robogames has screwed up their ruleset with conflicting statements. We had the same problem last year. Section 4 of the Robogames ruleset says ants can use any approved ground frequency, even AM radio. It says ants require no drive failsafe. It says ants do not require coded radio as long as their weapons will failsafe. It also says:

This effectively restricts all weight classes to 2.4 GHz spread spectrum systems.

Last year, under the same confused ruleset, Robogames did let antweights compete with 75 MHz systems. It is unclear if that was a one-year exemption. I can only recommend that you write to Dave Calkins (dcalkins@robolympics.net) and ask for clarification. Let me know what you find out.

A: GWS offers both 4 and 6 channel systems. The Inertia Labs desciption of the GWS transmitter is messed up -- the title and picture are of the 4-channel GWT-4A but the text describes the 6-channel GWT-6A. The price matches up to the 6-channel unit, but the receiver offered is 4-channel.

I'd suggest refering to Robot Marketplace and their GWS systems. Their descriptions are correct and their price for the equivalent transmitter and receiver package is the same.

The GWS radios are low-end, no frills systems. They do not have any computerized functions, mixing, or failsafes. Their only advantage is low price. I'm not a fan of skimping on electronics.

A: A big puff of smoke is always a bad sign. I'll assume you've tried hooking the receiver up correctly and seeing if it works? I wouldn't get my hopes up, but depending on which two pins you happened to overvolt it's possible that you just blew out one channel output. Try it. Even if it's fried, it probably won't be the worst mistake you'll make in robot combat. We've made some really big ones!

A: Mark J. here: the DX6i is compatible with the AR6000 receiver, although some people have reported problems getting the receiver to bind. Keep the transmitter at least 6 feet away from the receiver during the binding. It may take a few tries.

1. With the power off, plug the bind plug into the BAT port of the AR6000.
2. Power on the receiver by connecting the battery to any unused port. The blue LED should be blinking.
3. Position the throttle stick in the desired fail-safe position.
4. Pull and hold the trainer switch on the top of the transmitter and turn on the power switch. It may take several seconds for the system to connect. The LED on the receiver should go solid green, indicating the system has connected.
5. Remove the bind plug from the receiver.

Repeat for each receiver. Your prior receiver programming should be intact.

A: An antweight with an active weapon requires an FM radio, and the weapon must shut down on loss of radio signal. The MicroBotParts and GWS pico receivers are both FM-PPM single conversion receivers, but FM-PPM radio systems do not themselves provide a failsafe. Check this: explanation of FM-PPM and FM-PCM radio systems.

Some weapon motor controllers, like the Team Delta Solid State D-Switch, have failsafe circuitry built in that is independent of the radio system. Alternately, several manufacturers make tiny failsafe modules that plug in betwwen the receiver and the controller. Either of these options would meet the weapon failsafe requirement.

If your old JR receiver provided correct failsafe, I'd suggest soldering a new antenna wire onto it.

A: A 'channel' has the ability to independently control one item on your robot, like speed and direction instructions for motor(s) on one side of the robot. Two channels could control motors on each side of the robot, and a third channel could control activation of a weapon. A single channel can control mutiple motors, as long as they are all doing the same thing at the same time.

Note that there are also two two basic designs for R/C transmitters: 'pistol grip' and 'twin stick'.

• Most hobby grade 2 or 3 channel transmitters are the pistol grip design with a throttle trigger, a large self-centering steering knob, and a smaller knob or switch for the third channel. These are designed for controlling R/C cars. It is possible to find 4 channel pistol grip transmitters, but they are uncommon.

• Most hobby grade transmitters with 4 or more channels are twin stick design, intended for use with model aircraft. These transmitters have two joysticks side-by-side, with each joystick controlling two channels: one channel in the up/down direction and another in the left/right direction. Additional channels may be controlled by knobs or switches. Some 2 or 3 channel stick transmitters exist, but again they are uncommon.

A: Mark J. here: good morning, and how are things in Mumbai? If I understand your request, you're looking for a circuit design to convert 12 volts to 24 volts to power a relay. I'd rewind the relay for 12 volts, but if you want to do it the hard way take a look at Harry Lythall's Practical Voltage Converter (archived).

A: Mark J. here: I hope you don't think that you can run your 'bot without a battery!

A battery eliminator circuit (BEC) is a voltage regulator or converter that takes the voltage from your main battery pack and reduces it to 5 volts to power the radio receiver. This allows you to 'eliminate' the separate battery pack for radio gear.

Most small electronic speed controllers (ESC) have a BEC built in. High quality stand-alone BECs are available for larger applications from Team Delta.

There is no set-up required for the built-in BECs; just plug your receiver into the ESC and connect the ESC to your battery pack. The ESC will feed power back to the receiver thru the 3-wire connector. The Team Delta units come with full instructions and require four solder connections.

Q: If a voltage regulator can take a larger voltage and bring it down to 5 volts, could it also take 24 volts and bring it down to 12 volts? That way I could run my 12 volt drive from my 24 volt weapon battery pack.

A: The bad news is that voltage regulators and converters are limited in the amperage they can provide. A radio receiver takes far less current than your drive system. A regulator with enough capacity for your drive would be very expensive, bulky, and heavy.

The good news is that you don't need a voltage regulator to run your 12 volt drive from your 24 volt battery. If your transmitter has 'ATV' (Adjustable Throttle Volume) you can set the transmitter to send a maximum 1/2 throttle signal to your drive ESC -- your drive motors will only 'see' 12 volts from the speed controller. As long as your ESC can handle 24 volts, you're home free.

A: See the gyro post in the (#20).

Q: Do you have to put a gryo in a `bot?

A: Absolutely not. Very few combat robots use gyros, but many that are difficult to control would be better off if they did.

A: The only electronics from a Vex Robotics Kit that can be used with combat robot components is the R/C transmitter. Nothing else will interface with standard hobby electronics. Search for 'Vex' on this archive page for more info.

A: Mark J. here: I haven't had my hands on a new DX6i yet, but the DX6i manual (13.3 megabyte PDF) goes over the new features:

• The transmitter case has been redesigned. It looks more modern and has a larger LCD display.

• The clunky programming interface has been improved with a 'roller' design to move thru menu selections.

• The new DX6i may have more range than the old DX6, which was recommended only for moderate-range applications. The DX6 had plenty of range for robot combat applications.

• The DX6i has additional programming functions for airplanes and helicopters, but no added features that will be useful for most robot applications.

Q: I just wanted to let you know, the Robot Marketplace removes the AR6000 if you purchase the BR6000 receiver with the DX6. I'm not sure if this is the case with the DX6i, but it's likely.

A: It's a different deal. Robot Marketplace was able to substitute the BR6000 for the AR6000 receiver at no cost with the Spektrum DX6 system. The new DX6i system comes with the AR6200 receiver for $180, and for an additional $50 you buy the BR6000 robot receiver. For $230 you get both receivers.

A: The simple way is to bind the receiver to a new transmitter. That will unbind it from the old transmitter.

If you want to unbind without a new bind:

1. Turn on the receiver without the bind plug.
2. Turn on the transmitter while holding down the bind button.
3. Wait 30 seconds.
4. Turn off the receiver.
5. Turn off the transmitter.

A: Mark J. here: the mixing instructions for the 9CAP at Mad Overlord assume that your speed controller has no mixing capability. You can set up either your 9CAP or your RDFR23 to mix, but not both!

• Simplest solution: follow the instructions in your Vantec manual to turn off the onboard mixing on your RDFR23.

• Alternate solution: reset your 9CAP to a clean configuration -- no mixing! Plug the Vantec steering cable into receiver channel 1 and the throttle cable into channel 2.

A: Yes, but I don't know why you'd want to.

A: Mark J. here: electrical noise reduction is more of an art than a science. The optimum capacitance value varies with the RPM and load on the motor, so there is no single 'best' value for a combat robot application. Try 0.1uF as a starting point. See also the Team Delta Application Note #1 on reducing motor electrical noise.

A: Sure. The problem comes if you try to use different battery types wired in series or parallel for a common current draw. Don't do that!

A: Mark J. here: all battery types have reduced amp-hour output under heavy current draw. How much reduction depends on the internal resistence of the battery and the discharge rate. Thunder Power claims very low internal resistence and very little reduction in amp/hour capacity at high current draw for their latest series of extreme performance LiPoly batteries (chart). The R/C helicopter guys say the chart is about right. Under combat robot loads, you can expect very close to the full rated power from a fresh Thunder Power battery pack.

A: There's no such thing as a free lunch. An AstroFlight 110D charger can pull up to 16 amps at full output. If your power supply can't pump out 32 amps then you can't run two 110Ds at full output, but you might get away with two at less than maximum charge rate.

A: Mark J. here: LiPoly batteries don't come in exactly 12 volts -- but then your lead acid battery wasn't exactly 12 volts either. The closest you can get in LiPoly would be 11.1 volts for a 3-cell battery. Two problems:

1. LiPoly batteries can be destroyed and even burst into flame if the amperage draw is too great. You need to determine the maximum amperage draw of your bike and obtain a LiPoly capable of handling that large a draw.
2. LiPoly batteries require a different charger than lead acid batteries. Do NOT attempt to charge LiPolys with a lead acid charger!

As for your second question, I don't know what you mean by a '500 watt rc'. If you are talking about R/C speed controllers, they are rated by maximum amperage draw and voltage. Again, you would need to determine the maximum amperage draw under operating conditions of the 500 watt motor you reference and match that to a specific speed controller.

A: Mark J. here: do not mix dissimilar batteries! Way too many things could go wrong and result in a battery explosion. I can't figure out why you'd want to mix SLAs and NiMHs.

A: You don't want a trickle charger for combat robot applications. Trickle charging simply supplies a very limited current at an appropriate voltage. Is is designed to charge a battery over a long time period or maintain the charge on a battery between infrequent uses. If your SLA is an automotive/motorcycle/marine type, an appropriate charger can be purchased at an auto supply store.

Note that some specialty SLA batteries do not respond well to trickle charging. Hawker batteries for example must be charged at a high initial amperage rate or they loose capacity. Check with the manufacturer of your battery for their charging recommendations if in doubt.

A: The Spektrum BR6000 receiver can be programmed to failsafe to any input position on any channel. Instructions for programming the BR6000 receiver are at the Spektrum website. If you program your weapon channel to failsafe to "off" position it will shut off the R/C switch controlling your weapon solenoid when signal is lost.

The Spektrum AR6000 receiver does not have full failsafe capacity and is not legal for robots that require failsafes on weapon and drive systems.

A: Do not switch the polarity of the servo - instant fried electronics. Almost all hobby R/C transmitters have a 'servo reverse' switch or function that will invert the servo direction. Use that! You can also buy a tiny electronic servo reverser that plugs in between the receiver and servo.

You can wire two servos in parallel and plug them into a single receiver output. Your local hobby shop can provide a 'Y-connector' for that purpose, or you can splice the wires yourself

A: Mark J. here: Some readers may wonder why you want to do this. Servos can be 'hacked' to provide continuous rotation and used as drive motors. 'Overvolting' the servo will provide more speed and power at the cost of reduced lifespan. Many receivers and other R/C electronics, however, are very sensitive to increased voltage and can fail or malfunction if pushed to higher voltages. The trick is to run the receiver at a correct voltage while providing higher voltage to the servo.

A servo lead has three wires:

Note: although extensively used in the past, servos are inferior to other insect class drivetrains. I don't recommend them.

A: Gyros don't prevent the death spin, they CAUSE the death spin if they invert. See the gyro guide for info. I don't know of any event which has either required or disallowed the use of gyros.

A: Mark J. here: the inexpensive Gardner crimper is best used with the 30 amp Anderson Powerpole connectors. The contacts for the 15, 30, and 45 amp connectors are the same, so actual power capacity of the connectors are also the same -- about 100 amps. The difference is in the size of wire the connectors will accept. The 30 amp powerpoles will accept up to 10 gauge wire (really). You may want to solder the 45 amp connectors rather than trying to crimp them. See: this archived article for instructions on crimping with the Gardner tool.

A: Sure. Most teams have only a single transmitter that they use for all of their 'bots. One word of caution: at some large tournaments the insect classes run in a small arena at the same time that the larger 'bots are fighting in the big arena. In that case you may need a backup driver and a spare transmitter. Same deal if you have more than one 'bot entered in a single weight class -- you may end up fighting yourself!

Q: If you end up fighting yourself, can't you forfeit one of ur bots and still win?

A: Mark J. here: --- WEAK! ---

If you enter a robot in a tournament you should be prepared to fight it under any and all circumstances; if not for your pride then for the benefit of the spectators. Allowing such a forfeit would be at the discretion of the event organizer. I'd throw both your 'bots out.

A: If a radio system has failsafe capability, it will say so somewhere in the descriptive text -- it's a feature they want you to know about! AM and regular FM (PMM) systems generally do not failsafe. Coded FM (PCM or IPD), 900 MHz, and 2.4 GHz systems may failsafe.

Part of the problem you're having is that Robot Marketplace currently sells only one radio system under $200 that is full failsafe: the Spektrum DX6 2.4 GHz with BR6000 receiver.

Note: All Spektrum 2.4 GHz systems failsafe, but systems with the AR6000 receiver fail to the last speed setting received from the transmitter. This is not legal for robot combat which requires drive and weapon systems to stop on signal loss. The Spektrum BR6000 receiver corrected this problem.

A: Mark J. here: lots of variables! Rule of thumb: a typical spinner adds about 40% to the capacity needed for the drive motors.

If you're determined to go thru some rough calculations, you can use the Team Run Amok Spinning Weapon Excel Spreadsheet to calculate the energy capacity of your weapon in joules. Each time the weapon is depleted and must spin up it will consume approximately:

A: The current RFL rules require all robots with active weapons to have fail-safe electronics which will stop all robot motion if the radio signal is lost. Robots weighing 12 pounds or above must use FM radio with PCM or IPD coding, or digital 900 MHz or 2.4 GHz systems.

The GWS GWT-4A does not meet any of these requirements. It may be used for passive weapon robots up to 12 pounds, or for active weapon robots up to 6 pounds if add-on fail-safes are included.

Note that a few tournaments now require digital 900 MHz or 2.4 GHz systems for all robots. Check with the specific event organizer to be sure.

A: The Spektrum DX6 is a full-featured R/C system. It has multiple pre-set and custom programmable mixes and couplings built in. A full description is in the owners manual.

So, would I be able to use a normal FM system with my Antweight?

A: Mark J. here: From the discussion on the on-line forums, I think the intent is to require ALL combat robots at Robogames to run 'spread spectrum' radio systems -- sections 4.4.4 thru 4.4.6 should have been removed. However, I've always had trouble with Dave Calkins' logic. Write to him for clarification: dcalkins@robotics-society.org. Dave sometimes ignores his email, so 'cc' a copy of your question to Simone Davalos: simone@robotics-society.org.

Q: I talked to Dave Calkins. He told me:

A: Six words? I guess that helps a little, but it still leaves beetles, sublights, and AM radio uncertain. Robogames was once a popular and well-run event. I'm sorry to see it fall into confusion.

A: The AstroFlight 110D can charge up to 24 NiCad or NiMHd cells in series. That's a nominal 28.8 volts. A single 12 volt pack can be charged at up to 8 amps, but the maximum charge rate starts to drop above 14.4 volts. A single 24 volt pack (or two 12 volt packs in series) can be charged at a maximum 5 amps.

It's possible to charge multiple packs in parallel, but the charge amperage gets split between the packs. Two 24 volt packs charging in parallel would each charge at only 2.5 amps maximum. That won't save any time compared to charging each pack by itself.

If you need to charge higher voltage packs or multiple packs in series, pay a few extra dollars for the AstroFlight 112D. It can charge up to 40 cells in series (48 volts nominal), can pump 8 amps into a single 12 or 24 volt pack, and can charge two 24 volt packs in series at 4 amps.

You might also consider the ElectriFly Triton2 charger.

A: Each time the transmitter is turned on it 'listens' to radio activity on the 2.4 GHz band, selects an unused channel, and transmits a code to the receiver to tell it what channel to use. Your 900 MHz or 2.4 GHz wireless phone works pretty much the same way.

More information at Spektrum R/C.

Q: So from what you're saying, the 2.4Ghz radio only works with the receiver it comes with? If not, do you have to sync it with a receiver?

A: When a 2.4 GHz receiver is used for the first time with a transmitter it has to be 'taught' the receiver's code in a process called 'binding'. You only need to do that once, and you can bind multiple receivers to the same transmitter.

A: For a start, browse:

• Pololu Robotics
• Dr. Robot
• Robot Shop.

Q: After seeing Team Tentacle's 'Thinkling' I've decided to go with the Baby Orangutan MCU and two Devantech SRF08 ultrasonic rangefinders. How do I wire all of this? Is there anything else I need for the electronics? Thanks.

A: Mark J. here: hold on there, Cowboy... I'd say you were more than a little ahead of yourself. Nobody who's ready to build an autonomous combat robot is going to write to me and ask how it all gets wired up. Even if you can get your sensors, MCU, motors, weapon (you're missing a weapon controller), and remote activation R/C (you're missing that, too) wired correctly, the robot is just going to sit there without software. How are your programming skills?

Sit down with a good book on autonomous robots, like Robot Programming: A Practical Guide to Behavior-Based Robotics by Joe Jones. Technical information on how to communicate with the SRF08 is at the Devantech website, and the Pololu website has links to documentation for the Baby Orangutang.

Once you're confident that you can 'wire up' and program the robot controller and peripherals, write back and we can discuss design issues and combat theory.

A: Mark J. here: it isn't quite that simple. AM systems are incompatible with FM systems. 'Negative shift' coding (Futaba, Hitec) is not compatible with 'positive shift' (Airtronics and JR). Some 'third party' receivers can use either shift pattern. If the transmitter and receiver have the same coding, operate on the same frequency band (27/49/50/53/75/900/2400 MHz), and use the same modulation (AM or FM) then yes, matched frequency crystals (75 MHz and lower) will probably make them compatible. The 900 and 2400 MHz radios do not use crystals.

Stick with a single manufacturer for transmitters and receivers and you should be OK.

A: For your first R/C system, you can:

• Start with something simple and upgrade when you need to,
• Start with a system that will handle your future needs and save the trouble (and expense) of a later upgrade.

The GWS GWT-4A has no fail safe capability, no channel mixing, no dual rates, no exponential response, no receiver battery pack, and it will require at least one extra set of frequency crystals for competition use. Just plain vanilla R/C. It's cheap to purchase (a little over $100, with listed options), but it's also gonna return little of the purchase price when you go to sell it -- and you're gonna need a better system as soon as you move up past the hobbyweight class or go to an active weapon.

For less than $200 you can purchase a system like the Spektrum DX6 with the BR6000 receiver. You'll get all the features you're gonna need for any practical combat robot in any weight class. It requires no extra crystals, has full fail-safes, three channel mixes, dual rates, exponential response, a receiver battery pack, and four micro servos that you don't need and can sell on EBay to further reduce the price. If you should decide that combat robots aren't your thing, you can sell the Spektrum for a good price to someone who made the $100 mistake of buying a cheap system for their first robot.

A: Sure -- the 2007 RFL Standard Extensible Rule Set allows use of any ground-legal frequency (27/49/50/53/75/900/2400 MHz in the United States) in any weight class. See the (#18) for specific fail-safe requirements.

A. The usual solution is to use one transmitter and two receivers all on the same frequency. Put one receiver in each articulated section, plug the local ESC or weapon controller into the appropriate output slot and you're set. It's more reliable than running long extension leads from one side to the other and risking failure from flexed and twisted wires.

Some non-articulated 'bots also use two receivers for redundant back-up. JuggerBot / Tricerabot used twin receivers for separate dual-channel front and rear speed controllers. If either receiver or ESC failed, they could continue the match with at least partial power.

A: The Vex Robotics System radio control gear has a different data format than hobby R/C systems. It is not compatible with standard combat robot components. Use the HiTec!

Comment: I have some information to add to your answer to the question about the Vex radio system. The Vex transmitter uses pretty much standard Futaba data encoding, it's the receiver that's the problem. If you replace the receiver the system works just fine with standard R/C equipment.

I've tested the Vex transmitter with Microbotparts and Futaba AS receivers. They work well and can even use the Vex crystals. Microbotparts have a 6 channel receiver available for $29.95, though it is not on the webite -- just ask. I've also used the Vex transmitter with the Sombra Shadow 3 and Polk Hobbies' Seeker 6 synthesized receivers.

Great site, keep up the good work. [Wreno - North Texas Battle Group - BattleBots on the water with a WW2 theme]

Reply: Thanks, Wreno. I knew the data outputs of the Vex system weren't compatible with standard R/C, but didn't know the source of the problem. A 6-channel transmitter with crystals for that price is a bargain, but robot guys should be aware that the Vex transmitter has only primitive channel mixing and no ATV, fail safes, exponential response, or dual rates.

A: A pistol grip radio will work, but we use standard twin-stick transmitters: left stick forward and back for the speed controller, right stick 'side to side' controls the steering servo. No mixing required. You could put both throttle and steering on one stick, but we like them separate.

We set up our differential steering 'bots the same way, throttle on left stick and steering on the right, using elevon mixing. See our transmitter programming guide for more info on channel mixing.

A: Mark J. here: when an invertible robot is flipped upside down, left / right steering response remains correct but the throttle response is reversed; a forward transmitter command will back the robot up and vice versa. An 'inverted' switch reverses the response of your throttle to compensate for this, but you don't usually add-on an inverted switch -- it's already there:

1. Many twin-stick transmitters will have a toggle switch that controls channel 5, or channel 3 on pistol style radios. Some speed controllers (like the Scorpion HX) and some on-board mixers (like the IMX-1) have an extra input lead that will reverse throttle response. Plug that lead into appropriate channel on your receiver and the toggle on your transmitter becomes an inverted switch. The Scorpion HX ESC can also reverse throttle automatically in response to a 'gravity switch' on the robot itself, but there is too much vibration on a combat robot for me to recommend that.

2. If you have a computerized transmitter with user-defined functions, you may be able to assign a custom function to one of the available switches on the transmitter to reverse the throttle response. See my tutorial on Programming the Futaba 6XAPs for Combat Robotics for more information on computerized transmitters.

3. Non-computerized transmitters usually have a mechanical 'servo reversing' slide switch for each channel. You can simply flick the reversing switch for your throttle channel when inverted. You may want to fasten an extension onto the small reversing switch to make it easier to find in combat. I suppose you could replace the small slide switch with a larger toggle switch if you really want to do a mod.

A: Mark J. here: the Robot Fighting League accepts use of 27/49/50/53/75/900/2400 MHz radio systems for combat robot control in the USA, as long as the radio system has the required failsafe protocol for your weight class and weapon type. However, you must have an amateur radio operator license to legally operate a radio transmitter on either 50 or 53 MHz.

Be sure to check with the event organizer to make certain they don't require some specific radio type. Some events are talking about going to only 2400 MHz 'spread spectrum' radios.

Q: How come a 72 MHz radio is not legal to use on ground-based vehicles?

A: Model aircraft are particularly sensitive to interference because their altitude gives them increased 'line of sight' reception. The Federal Communications Commission (FCC) made 72 MHz 'airborne only' to assure R/C pilots of clear channels without interference from somebody playing with an R/C dune buggy in a backyard miles away. To even things out, 75 MHz is restricted to 'surface only' uses. All other approved R/C frequencies may be used for either surface or air.

A: You have to pretty much fully enclose an antenna in a box of metal or other conductive material to block the radio signal by forming a Faraday cage. You'll want to keep your antenna spaced away from the metal surfaces and any source of electrical 'noise', but the signal will be able to penetrate thru the plastic sidewalls. Check the Ask Aaron Radio Reception Problems page for more info.

A: The 2007 RFL Ruleset says:

So, digital 2.4 GHz and 900 MHz radio systems are cleared to control any weight class 'bot with either active or inactive weaponry -- equivalent to coded FM.

A: Non-conductive materials like wood, glass fiber composites, and plastics are transparent to commonly used R/C radio frequencies.

A: The Vex Robotics System radio control gear has a non-standard data output format from the receiver. It is not compatible with standard combat robot components. Use the HiTec!

A: Both metal and carbon fiber block radio signals. If the metal or carbon armor completely encloses the 'bot, the radio antenna must stick out thru the armor, or be mounted under a radio-transparent 'window'. See the Ask Aaron Radio Reception Problems page for more info.

A: The 'C' relates to the capacity of the battery pack: a pack with a capacity of 3000 mAh has a 'C' of 3000 mA, or 3 amps. If the maximum discharge rate for that pack is given as '20C', it would be 20 times 3 amps = 60 amps. If you exceed the maximum discharge rate you will risk overheating and damaging the pack, and even setting the pack on fire!

A: Robotlogic.com makes a three-wheel omni mixer called the OMX-3. They also make a Mecanum mixer for four-wheeled Mecanum omnibots.

With the mixer installed, you may assign any stick axis you like for forward / reverse, left / right, and rotate. Search the Ask Aaron archive for more information on omnibots.

A: All freshly charged rechargeable battery packs will read a higher resting voltage than their rating. When placed under load, the voltage will drop down toward the rated voltage. Hitec says the servo will run on a 7.4 volt LiPoly, so don't worry about the extra volt in the resting state -- run it!

A: Mark J. here: a three-cell lithium polymer battery can be safely drained down to 8.4 volts, so running into the 9 volt cutoff is fine. The usual cause of damage to Lipoly batteries is overheating caused by too high a discharge rate. Temperatures over 140 degrees can damage or destroy the pack. Leave some space around the battery for cooling air circulation and keep the discharge rate within the manufacturer's spec. A well cared for Lipoly battery can exceed 1000 charge/discharge cycles. Check the Electrifly Lipoly Manual for more tips on care and disposal.

A: You can mix channels with a computerized transmitter, a plug-in electronic mixer, or a twin-channel controller with built-in mixing. All of them produce the same control style: one control channel (stick axis or throttle trigger) moves the 'bot forward and back, while a second channel (stick axis or wheel) controls turning. If you activate only the turning channel, the 'bot will spin in place without moving forward or back -- just like throwing the control sticks in opposite directions when working tank-style.

A: Mark J. here: even small combat robots don't use alkaline batteries! Alkalines are designed to operate in devices with a low current requirement. They cannot provide anywhere near the peak current that NiCad or NiMHd rechargeable batteries can, and in a permanent magnet DC motor current equals torque.

A typical alkaline 9-volt battery can provide just over 1 amp of current, and will last a VERY short time at that current draw. Your screwdriver motors will need at least 5 amps each to develop their full pushing torque potential. A sumo robot that can't push is pretty useless.

A modern AA size NiCad or NiMHd cell can pump out 8 to 10 amps of torque-grinding current and keep it up long enough for a full sumo match. An 8-cell pack will give you a nominal 8.4 volts and would be a far better choice for your 'bot than 9-volt alkalines. Simple chargers for NiCad / NiMHd packs are inexpensive and the charging process is uncomplicated.

Your other choice is a lithium polymer battery. LiPolys are very light and compact for their power capacity, but are more expensive and have lower peak current capacity than NiCads or NiMHd packs of equivalent amp/hour rating. LiPolys also require a different type of charger than other rechargeable packs -- never try to charge a LiPoly battery with a charger not specifically designed for the purpose. A good article on LiPoly care can be found at electrifly.com

A: Twist three wires together, solder, and insulate with heat-shrink tubing. Do not use 'bullet crimp' or 'twist' connectors on a combat robot -- they can fail under impact and vibration. Use stranded wire instead of solid-core for the same reason.

Q: Could I make a 'Y' shape in my wire with 3 ring terminal conectors held together with a nut and bolt?

Don't do that! You'd have three 'crimp' connections each subject to failure, plus a nut and bolt that could vibrate loose. It would also be heavy and bulky. Even though I don't like them, you'd be better off using a 'wire nut' twist connector to hold your three wires together. Best solution: learn to solder.

Q: Hi Aaron. I want to build a two-wheeled robot with a gyro, but I'm having a bit of trouble understanding how that all fits together. Is there a specific type of ESC that I'll have to use to get this to work properly?

Will I be able to use just one control stick (forward, backward, left, right) to control the movement of my robot, or will I have to use two sticks, one for each motor? Thanks!

A: Take a look at my dad's Beginners guide to combat robot gyros page.

R/C gyros are NOT COMPATIBLE with either two-stick (tank style) steering or transmitter mixed single-stick steering. If you're using a gyro, you'll need to use either a stand-alone plug-in electronic channel mixer between your gyro and the ESC, or use an ESC with built-in mixing. Either of these will give you single-stick control.

Many dual-channel ESCs offer built-in mixing: Barello ANT, SOZBots M, Scorpion XL, Vantec RDFR, etc. Check before you buy.

A: Most combat robots turn by 'skid steering' where the wheels on one side of the 'bot turn at a different speed and/or in a different direction than the wheels on the other side. This requires independent control of drive motors on each side of the 'bot. You can operate this type of 'bot by controlling the two sides of the 'bot with vertical motion of the two control sticks on a 'stick' style R/C transmitter (called 'tank steering') but most drivers prefer forward/reverse speed control with vertical motion of one stick and steering with horizontal motion of either the same or the second stick.

By electronically 'mixing' the output of two R/C channels, you can have the vertical motion of one stick (or the throttle trigger on a 'pistol' style transmitter) instruct both drive motors to move the 'bot forward or backward, and the horizontal motion of a stick (or the 'pistol' steering knob) tell the motors to spin at different speeds. This is called 'differential steering'.

More expensive R/C equipment and some dual-channel motor controllers have channel mixing capability built-in. See our transmitter programming guide for more info on computerized radio transmitters, and our electronic gyro guide for help integrating mixers with gyros. If your equipment does not have mixing built in, you can buy a small electronic channel mixer that plugs into your system between the receiver and the speed controllers that will provide the same functions.

Thank You.

A: Thanks for your compliment about the site!

The short answer to your question is yes -- you can connect multiple Electronic Speed Controllers to a single battery if you connect them as parallel circuits. See the diagram and description of basic robot wiring in the Frequently Asked Questions section.

The longer answer involves the capacity of your battery to provide the current needed by your motors. Your battery must be able to supply enough current (not voltage) to meet the demands of all the motors at once. NiCad batteries can provide a lot of current to meet heavy load conditions, but if the load becomes too great the voltage output will drop. The Ant 100 ESC also supplies power to your radio receiver and if the voltage drops your receiver can start to 'glitch'. Other types of batteries are less able to meet high amperage drains. Lithium batteries can dangerously overheat if the current demand gets too high, resulting in damage to the battery and even fire!

Adding extra cells to your battery pack to raise the voltage is not a good solution. Higher voltage will create a demand by your motors for even more current and your voltage fluctuation will increase. Add up the maximum current consumption for all four of your motors and use a battery with enough capacity to meet that demand.

One last thing: I mentioned above that the Ant 100 supplies power to your radio receiver. Since you'll be using two Ant 100s, you might run into trouble with both of them trying to power the receiver. You'll want to remove both of the red wire connections from the receiver cables coming from one of the ESCs -- either one. You can clip the red wires, desolder them from the circuit board, or remove the connectors from the receiver plugs.

A: Mark J. here: a battery charging jack is a very useful addition to your 'bot. It will minimize charging mistakes in the pits and save critical time between matches.

Select a power plug and wires rated for at least the maximum output of your charger. Find a mounting spot protected from damage but with easy access. The jack will be 'live' to the main battery power, so protect it from accidental shorting!

The jack is wired into the main power cables, between the battery disconnect plug (optional, but handy) and the master power switch. See the diagram at right for details. Check the event rules to determine what type of master power switch is required for your weight class -- a 'removable link' disconnect may be required.

With this set-up, the battery may be charged with the master power switch 'off' for safety, and the battery may be quickly removed or replaced while the charging jack remains with the 'bot.

Q: What type of power plug do you recommend for a heavyweight 'bot charging jack?

A: I use Anderson PowerPole connectors for charger plugs on our larger 'bots. They are available in 15/30/45 amp ratings, have no exposed metal, may be crimped or soldered in place, and require no 'heat shrink' insulation. The PowerPole connectors are available at many hobby shops. Pre-assembled wire sets with PowerPole connectors are available thru Team Delta.

A: Take a look at the diagram and description of basic robot wiring, Alan. Wire in your power switch where the removable power link is in the diagram -- combat robot tournaments often require a removable link instead of a switch. Your multiple lights will replace the single power indicator light in the diagram.

Q: Thanks for your advice. Just to clarify, do I attach three wires to each battery lead and run one + and one - to each ESC and the lights? Thank you very much for your reply.

A: That's right, Alan -- the ESCs and lights are connected in parallel to the battery. Don't forget to insert your switch between one battery lead and the device connections.

Q: I forgot to ask you this question last time. The different parts for my robot have wires of different gauges. Do I have to replace all the wires in one gauge? Will the robot function with wires in various gauges connecting together? Thanks for your reply.

A: Don't worry about the different wire gauges, Alan. The important thing is that the smallest wire in a given circuit is capable of carrying the largest expected current for that circuit. Bigger wire is OK, but smaller wire can overheat under the load, melt thru the insulation, and short out. As long as your robot components are operating within their rated voltage, you should be able to trust that the manufacturer has provided wire of adequate size. Hook 'em up and run 'em!

A: No -- American Wire Gauge (AWG) sizes measure the conductor only, not counting any insulation. The conductor diameter of 18 gauge wire is about 0.04 inch (1.02 mm).

A: Shortening the antenna that much will certainly reduce reception, but you may still have plenty of range. Give it a test run and see how it does.

If you decide to repair the antenna, you can just solder on a length of similar gauge insulated wire to restore the length. Cover the solder joint with heat shrink tubing or a flap of vinyl tape to prevent accidental grounding of the antenna. If you are comfortable soldering PC boards you can open the receiver case, remove the damaged antenna entirely, and solder on a new wire of the correct length.

Q: What is impedance? I hear that even if I solder on a length of similar gauge insulated wire to restore the length, I need the correct impedance as well.

A: Mark J. here: Impedance is a measure of the opposition of an electrical component (like an antenna) to an alternating current (like a radio signal). A proper antenna must have its impedance match the other elements of the system to maximize signal strength.

The main factor determining the impedance of your simple wire antenna is length. Restoring the antenna length by soldering on a length of similar wire will restore the impedance to that of the original antenna.

A: Mark J. here: How quickly you throw the stick forward shouldn't matter to the radio system, so I don't think your problem is entirely with the transmitter set-up.

First, check the set-up procedure in the manual for your Electronic Speed Control (ESC) to make certain that the unit is correctly adjusted to work with your radio. An ESC requires careful adjustment to assure that the motors will respond correctly throughout the entire range of transmitter stick motion. Make certain that your transmitter trim settings are centered during ESC set-up.

Once the ESC is correctly set, the transmitter trim should be adjusted so that both wheels start turning at the same time when the stick is gently pushed forward or back. If you're still veering to one side, reduce the Adjustable Travel Volume (ATV) transmitter setting for the side of the 'bot that is running too fast.

If rapid acceleration is still a problem, check for equal weight on the drive wheels on both sides of the 'bot. If one side of the 'bot has more weight it will get better traction and can cause a spin under hard acceleration. You may need to move some components on the chassis to equalize weight. Backing up may mask the problem by reducing traction to both drive wheels.

For a 4-wheel 'bot, make sure all four wheels are in good contact when the 'bot is on a level surface. Adjust the chassis or motor mounts to correct if required.

For additional help on transmitter set-up, I suggest reading thru my guide to programming radio systems for combat robots. I wrote it with specific reference to Futaba systems, but the general tips are useful for any computer radio.

A: You probably saw the IFI Isaac Control System that is commonly used at the BattleBots IQ competitions. Some builders use this system at other competitions as well.

The IFI system accepts a variety of analog PC joysticks as external controllers. These are the same joysticks you can buy at your computer store. PC joysticks are not compatible with standard R/C transmitters.

A: Check the diagram at the right to see what gets connected to what. Solder the connections with rosin core solder and a non-acid flux. Watch out for sharp points on your connections that could poke thru insulation -- file smooth any rough edges. Large diameter 'heat shrink' plastic tubes are available at R/C hobby shops that will insulate the pack and hold it all together. Smaller diameter heat shrink does a great job of insulating the connector terminals.

A: NiCad or NiMHd cells come with or without metal tabs welded to either end. You can solder your wires to the tabs or directly to the cells. If you're soldering directly to the cell, you'll need a soldering iron with enough power to do the job quickly without heating up the whole cell -- maybe 25 watts. Use rosin core solder and a little non-acid flux.

A: Mark J. here: the operating frequency of your radio does not effect the ability of the system to accommodate a lifting servo. However, the 27 MHz band is used by both 'toy' radios and 'hobby-grade' radio systems. Toy radios are not compatible with hobby grade components like servos.

Toy radios in the USA are on either the 27 MHz or 49 MHz bands. Hobby grade radio systems are commonly available in the USA for the 27 MHz, 72 MHz (aircraft only), and 75 MHz (non-aircraft) frequency bands.

A: Mark J. here: We need to be careful not to mix apples and oranges:

AM (amplitude modulation)and FM (frequency modulation) are two methods of adding information onto a radio wave. All hobby radios are either AM or FM. Of those two methods, FM is less susceptible to electrical 'noise' interference.

PPM (pulse position modulation) and PCM (pulse code modulation) are two methods of encoding the information for radio control before it is added to the radio wave.

• PPM is an analog coding system with servo position represented by a time interval between two pulses. It is the standard system used on hobby radios.

• PCM is a digital coding system with servo position represented by a binary number. A computer in the receiver decodes the number and instructs the servo or speed controller. If no signal reaches the receiver, the computer can send a predetermined 'fail safe' position signal to the servo that can stop the robot and turn off weapons.

A: Mark J. here: Is that the middleweight flamethrower from Minnesota? I don't know about their radio, but the homebrew radio systems I've seen from the few other teams to try it were unreliable and had no advantages over off-the-shelf systems. If you just happen to have a degree in electrical engineering and a lot of time to spend designing, building, and de-bugging a radio system -- go for it. If you want something that works, stick with a professionally built system.

A: Critter Crunch has been fighting robots for a long time. Their first tournament was years before the first Robot Wars, but their rules are, ummmm... different. They do allow both 2 pound and 20 pound robots to operate with a wire cable instead of radio control. The circuit for each motor and weapon runs from the battery thru a long cable to a control box then back thru the cable to the motor/weapon. The control box has switches and maybe rheostats to control the motors. The cable wires have to be heavy enough to carry the motor current, and the robot has to drag the long, heavy cable behind it.

Critter Crunch also allows R/C robots, so why not build a 'bot that can enter other contests?

A: No functional difference. The only reason Robot Marketplace carries the discontinued Thor 883 is so builders who have a pair and smoke one can get an exact replacement.

A: Sure - as an expensive smoke bomb.

A: It would save time if people would check Robot Marketplace before asking me any question that starts with "Where can I buy a...".

Pretty much any place that sells R/C equipment will offer systems with computerized mixing. For a 'bot, you'll want a system on the 75MHz band. Guess what? Robot Marketplace sells a very nice Hitec Laser 6 FM System for less than $135. Check with your local hobby shop as well.

You can also find Electronic Speed Controllers with built-in mixing at (wait for it...) Robot Marketplace.

A: Mark J. here: the IFI Isaac Control System has long been the mandatory R/C system for the BattleBots IQ competition. However, the system has been discontinued by IFI, and used systems are in short supply. BBIQ now strongly encourages the use of the Isaac system, but approves alternate systems on a case-by-case basis.

The Isaac controller is a 'smart' system that prevents radio interference and the need for frequency control and transmitter impound at tournaments. This makes things run much more smoothly for the tournament director. The Isaac also interfaces to the tournament computer and allows the director to remotely shut down power to all 'bots instantly - a big safety plus!

A: An ESC designed to interface with a hobby R/C receiver should have a plug already installed that will fit directly into the channel output socket of your choice on the receiver. See the 'bot wiring diagram. Ask the manufacturer of your ESC for additional info, if needed.

A: Mark J. here: radio systems are assigned to operate on specific frequency 'bands'. Both of the frequency bands you mention are available for use by R/C toys. MHz refers to how many million times per second the radio 'cycles' -- 27 million cycles per second for the 27 MHz radio.

Within each band are several specific frequencies to which a radio system may be tuned. A radio tuned to a specific frequency will not interfere with a radio operating on another frequency.

See also this earlier post.

A: You can scavenge the speed controller out of a toy or servos if you're really cheap, but remember: 'cheap' and 'combat robot' don't mix. If you're going to invest your time and effort, don't allow cheap components to let you down!

A: Two-wheeled robots can be difficult to drive in a straight line without veering to one side and they don't turn in a smooth arc. A piezo gyro senses turning motion, compares it the signal coming from the R/C receiver, and adjusts the signal to the electronic speed controller to keep the robot on the course the driver wants.

My dad has a whole webpage about gyros and combat robots that should answer any additional questions.

A: Mark J. here. The message doesn't seem to be getting thru: cheap and robot combat don't mix. You're going to spend a lot of time and effort building your 'bot and going to the tournament. When some component fails in combat and puts you out of the match, you're gonna wish you hadn't gone cheap.

That said, Tower Hobbies has a Hitec 3-channel pistol grip FM system for $69.99. You'll need either an ESC with built-in mixing or a separate elevon mixer to use it with a 'bot. Inertia Labs will sell you a GWS 4-channel twin-stick FM system for $89.90 (transmitter with crystal $59, micro receiver $21.95, receiver crystal $8.95) that does not require a mixer. Best luck.

A: Mark J. here: a piezoelectric crystal can be made to vary its electrical properties at a very precise frequency. When incorporated into a radio oscillator circuit, the crystal controls the frequency 'channel' on which the set operates. Hobby R/C systems have removable crystals in both the transmitter and receiver that can be replaced with crystals of a slightly different frequency to tune the system to a different channel and avoid interference from other radios.

R/C systems normally come with one set of crystals. Robot tournaments usually require that you have crystals for at least two different channels, so plan to buy a second set. There are different types of crystals for AM, FM single conversion, and FM double conversion -- make sure you get a set that matches your radio.

A: It doesn't take a whole hand to control a R/C channel -- you can easily control two with one finger. R/C airplane guys have to balance throttle, rudder, elevator, aileron, flaps, and landing gear controls. We've got it easy!

For a 'bot, throttle and steering take two sticks if you use simple tank-steer, but you can electronically 'mix' two channels and put both throttle and steering on a single stick operated by one thumb. The on/off control for the weapon can be assigned to a toggle switch that you can flip with an index finger. That leaves seven fingers and a thumb that aren't doing anything except holding the transmitter.

Different manufacturers have slightly different control layouts, but you can see a diagram of a typical Futaba transmitter and get more radio tips at my dad's page: Programming the Futaba 6XAPs for Combat Robotics. I usually run the weapon from the channel 5 toggle switch.

A: Mark J. here: LiPoly batteries have excellent charge retention and capacity recovery after storage. A LiPoly battery stored for six months at room temperature will recover about 95% of its capacity on the first charge cycle. It's still a good idea to discharge/charge cycle your rechargeable battery (LiPoly, NiCad, NiMHd) a couple of times before a competition to assure full capacity. Always follow the manufacturer's procedure for cycling.

A: Make sure the batteries in the car and the transmitter are fresh. If this doesn't help, as a last resort you might want to open up the car to expose the electronics board. There will be a couple of screw adjustments on the board, sealed with a thick, waxy material. Pick one adjuster, scrape away the wax, mark the starting position of the adjuster, and try turning the adjustment screw a little one way and the other to see if the range improves. If not, return it to the starting position and tweak another adjuster. Do NOT try this with the transmitter!

A: Mark J. here: In the USA the "AM Band" refers to commercial radio broadcast frequencies between 520 kHz and 1720 kHz -- a kilohertz is 1000 cycles per second. 49 MHz (49 million cycles per second) band is a 'public service' frequency range a little below VHF television broadcast. It's shared by older wireless phones, baby monitors, and five toy R/C channels. Other toy R/C systems operate on 27 MHz on six frequencies squeezed in between CB radio channels.

Toy R/C systems on 27 or 49 MHz use interference-prone Amplitude Modulation (AM) signals, but 'hobby grade' R/C gear on 27, 72, and 75 MHz use either AM or FM (Frequency Modulation) signals.

A: The Robot Marketplace and Tower Hobbies are both good on-line sources of 75 MHz 'ground frequency' radio systems, but don't forget to check with your local hobby shop!

It's also possible to have a 72 MHz radio converted to 75 MHz. Tower hobbies offers this service on new systems, and a web search will turn up other specialty shops that will do this.

A: Mark J. here: Micro receivers are 'single conversion' designs that are more sensitive to interference than the 'double conversion' design usually found in standard receivers, but if you're only getting 5 feet of reception distance you have problems other than your receiver. Electric motors create a lot of electrical 'noise' that can be a problem -- try adding anti R.F. capacitors across the motor leads. Position the receiver as far away from the motors and ESC as possible. Stretch out the receiver antenna and get it out in the open air, away from metal or carbon armor.

Check the Ask Radio Reception Problems page for more info on the topic.

A: Tech question, Mark J. here: You'll get a nice puff of smoke followed by a quick trip to the trash bin. Solid state switching controls are rated for a maximum amperage flow. Doubling the voltage to a motor also doubles the maximum amperage, so you've already taken the unit to twice it's design limit. I suspect that if you got into a pushing match you'd fry the controller as is. Bigger motor = more amperage = thermal meltdown. Note that not many R/C receivers can handle 12 volts -- try that at your own peril.

A: A remote control transmitter sends variable control signals for several `channels' based on stick, switch, and knob positions on the transmitter. The receiver deciphers the signal and sends separate signals to the channel ports. You can plug various devices into channel ports that read the signals and turn them into mechanical action (servos), variable current flow (electronic speed controllers), or on/off switches (R/C switches). Connect drive motors to the speed controllers, a lifter to the servo, and a weapon to the R/C switch and you've got control of your robot. For more on robot control systems, see: 4QD Robot Control website.

A: Some combat robot ESCs have a short set-up process, but it isn't programming. Some brushless motor controllers have more elaborate programming capability, but most work fine with the default settings. More sophisticated radio systems can be programmed by selecting options from menus for things like channel mixing, but it isn't required to provide basic radio functions. See my dad's page on programming transmitters for details.

A: Tech question, Mark J. here: AWG wire sizes run opposite from the way you'd think, with larger numbers indicating smaller diameter wire. For small wire, amperage capacity approximately doubles with each decrease of three number sizes (thicker wire). A 22 gauge copper wire is conservatively rated to carry 7 amps in conditions found in a combat robot. You might get away with it, but I'd suggest 18 gauge for at least the battery to ESC hookup -- or you could use double strands of 22 gauge if that's what you have.

Always use 'multi-strand' wire in your robot, not solid-core. Solid core can break from repeated flexing and shock.

A: Technical question - Mark J. here: Yes, there are a few:

A: Check with the event organizer before attempting to use any 'cheap' radio system in a 'bot with a spinning weapon. Many combat rules sets require specific safety measures for weapon safety that are not available in inexpensive radios. For robot combat it isn't smart to try to save money on your radio system.