Link to Ask Aaron

Tentacle Drivetrain Calculator

Excel Spinner Spreadsheet spacer

Optimum Robot Drivetrain Gearing spacer

Radio Guides spacer

The Hamburger is Bad spacer

Solenoid and Relay Guide spacer

Ask Aaron 10th Anniversary spacer

Aaron's Greatest Hits spacer


4954 Questions and Answers about Combat Robotics
from Team Run Amok
Ten Years of Ask Aaron

Team Run Amok receives a lot of email asking about the design and operation of combat robots. In 2003 my son and team member Aaron Joerger (then 12 years old) requested a question and answer page to document our responses.

Got a question? We welcome combat robot questions. Check the Ask Aaron Archives first to see if your question has already been answered, then click the blue button.

The Ask Aaron Archives Click to browse thousands of previously answered questions by category, or search for specific topics. Includes FAQ

Caution   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.
In Memorium: Aaron Joerger, 1991 - 2013
The 'Ask Aaron' project was important to Aaron, and I continue the site in his memory. Thank you for the many kind messages of sympathy and support that have found their way to me. Aaron's obituary
- Mark Joerger   

Welcome to my website Recent Questions
Not all the questions we receive at Ask Aaron are serious. Some are odd, some misdirected, and a few are incomprehensible. Aaron enjoyed dealing with these questions, and I've collected some of his best responses in a in a special page:
Aaron's Greatest Hits
Aaron's Greatest Hits

Q: can you please give the specifications of the dc motor we need to use to rotate a 3kg cicular disc at 1000 rpm ? [India]

A: [Mark J.] The power needed to spin a 3 KG disc to 1000 RPM depends on:

  • How quickly you want the disc to reach 1000 RPM; and
  • The diameter of the disc.
The power to sustain the disc at 1000 RPM is negligable, so it all comes down to how quickly you want your disc to reach the required speed. A larger diameter disc will take longer to spin up to speed than a smaller disc of the same mass, but it will store more energy for a greater impact.


  • An aluminum disc 300 mm in diameter and 15 mm thick weighs 3 kg. It will store about 170 joules of energy at 1000 RPM. A 'Small Johnson' motor with 0.56 N-m stall torque and a no-load 24,000 RPM speed geared down 24:1 will spin this disc up to 1000 RPM in about 0.8 second -- very quick, but very little stored energy.

  • An aluminum disc 600 mm in diameter and 4 mm thick weighs 3 kg. It will store about 730 joules of energy at 1000 RPM. The same 'Small Johnson' motor with 0.56 N-m stall torque and a no-load 24,000 RPM speed geared down 24:1 will spin this disc up to 1000 RPM in about 3.5 seconds -- much slower, but much better energy storage.

  • An aluminum disc 600 mm in diameter and 4 mm thick weighs 3 kg. It will store about 730 joules of energy at 1000 RPM. An Ampflow E30-150 motor with 5.0 N-m stall torque and a no-load 5700 RPM speed geared down 5.7:1 will spin this disc up to 1000 RPM in about 1.7 seconds -- a good balance of speed and energy storage.
I will mention that most builders choose to spin their weapons faster than 1000 RPM. Doubling the speed to 2000 RPM will give four times the energy storage, but will require four times as long to spin up to full speed. You didn't mention the weight class of your robot, but a useful spinning weapon will require at least 40 joules of energy storage per kilo of robot weight. Plan accordingly.

Q: was the vdd kit the first combat robot kit, or was it just the first notable one? [Nate F. in Pennsylvania]

A: [Mark J.] Exactly which combat robot 'kit' was first depends a lot on exactly how incomplete a package you're willing to accept as a kit, Nate.

Inspired by the successful antweight competitor of the same name from Team Think Tank, the V.D.D. (Vertical Disk of Destruction) antweight kits first appeared at the Robot Marketplace in late 2003. They were far from complete kits, and the instructions were more of a set of suggestions than a complete guide. For $100 you got:

  • 2 Tamiya drive gearboxes;
  • 10 carbon rods;
  • 1 bottle of rubber CA glue;
  • 8 yards of Kevlar thread;
  • 2 wheel adapters;
  • 2 foam wheels;
  • 2 brushed drive motors with capacitors;
  • 1 brushed weapon motor with gearbox;
  • 1 weapon blade hub;
  • 1 hex wench and hardware.
'VDD Kit

To complete the kit you needed: speed controllers, radio gear, servo leads, armor of your own design, a weapon blade, a 9.6 volt battery, and a battery charger.

The chassis was constructed by strapping the carbon rods to the gearboxes and to each other with the Kevlar thread and soaking the junctions with cyanoacrylate glue. This was not a task for an inexperienced builder, and I suspect that many of the purchased kits were never completed.

The Robot Marketplace had been offering 'Robot Starter Packages' in assorted weight classes for some time prior to the appearance of the VDD kit. These packages were complete sets of components -- motors, gearboxes, wheels, speed controllers, battery, and charger -- but they left the chassis design entirely to the builder.

Q: i got a helical gear of 11.5 cm outer diameter with face width of 2.1 cm , internal diameter of 10 cm,number of teeth as 22. in which automobile it is used, how much load can it transmit,its speed in rpm . [India]

A: [Mark J.] So, you pulled a random transmission gear out of a wrecking yard and based on a general description of dimensions and tooth count you'd like me to track it back to the vehicle it came from and produce unpublished performance specifications?

I don't know whether to laugh or cry. Robot questions, please.

Q: Did "Original Sin" the first time inside mechanical failure disabled(lost all tires are not included) in CC2012 by "Electric Boogaloo"?
By the way,happy Chinese New Year! in chinese,it called "Chunjie" (Spring Festival) [China]

A: [Mark J.] 'Original Sin' has proven itself to be a very durable competitor. I don't have a record of reason for loss in each individual match, but I've written to Original Sin's builder Gary Gin to ask him if the Combots Cup loss to 'Electric Boogaloo' was the first due to internal failure. I'll post his answer -- when available.

Update -- Builder Gary Gin replies: "The loss to EB was a tap out due to excessive external damage. At RG 2011 I had a loss due to receiver failure."

Q: Hi Mark, what do you think of abrasive disks as cutting weapons? [India]

A: [Mark J.] NO CERAMIC CUTTING DISKS!!! It doesn't take much of an impact to shatter the disk, sending sharp shards at high speed in all directions. Given the average combat arena in India, that's a disaster. No sane event organizer would allow you to use such a weapon, plus they simply aren't effective at doing significant damage to your opponent.

If you are intent on using a cutting blade, an arrangement like that used by 'Gloomy' is your best option: an all-metal circular cutting saw attached to a movable arm that keeps the blade out of harm's way until the opponent is pinned and the blade can be put to good use. See: Gloomy vs. Hyperactive.

Q: ...and also about how much pressure would be needed to make a decent lifter in midweight class.

A: The power of a pneumatic ram is calculated by multiplying the gas pressure by the area of the piston. A lower pressure simply requires a larger diameter cylinder to compensate. I suggest that you read the Team Da Vinci Robotics Understanding Pneumatics page to get a good overview of combat pneumatic weapons and how to calculate the force of your lifter design.

A typical 'low pressure' pneumatic lifter will operate at 150 psi. Commercial pneumatic regulators, cylinders, and other components certified for this pressure are widely available and are relatively safe to work with.

Our own heavyweight lifter 'The Gap' uses a 150 psi pneumatic system to power a 3" diameter actuator. The actuator provides 1000 pounds of force, which translates to more than 400 pounds of lifting force out at the tip of the lifter arm.

'The Gap' launches a trash can at the 'Da Vinci Days' robot festival.
Team Run Amok's
'The Gap'

Q: Hi Mark, I am in the process of designing my first robot (lightweight) and was wondering whether it is possible to use a thyristor as an esc, wikipedia seems to be ambiguous on this topic. [India]

A: [Mark J.] Silicon controlled rectifiers (SCRs, also known as thyristors) are commonly used to control AC motors and can be used to control DC electric motors(examples). However, they are far from ideal for the type of control circuits desired in combat robots. Combat ESCs are based on highly efficient MOS-FET devices.

More to the point: I can't recommend trying to 'home brew' an electronic speed controller. A full-featured ESC is a terribly complex design challenge (example). I've seen many attempts by builders to wire up their own controllers. The best of them were disappointing, and the great majority were entirely disastrous. You can't afford to have poor, unreliable motor controllers in your combat robot -- use a reliable and proven ESC or take up a different hobby.

Q: Hey mark,
I have a basic wedge shaped bot with 4 48 VDC motors comnected directly to the tyres. I am planning to make a wired combat bot and have 4 push buttons in my remote, can you tell me how to connect the motors so that the front two buttons move the bot forward and rare buttons move it backwards? (I have taught of shorting the right motors and the left motors) please tell me how could i do the connections?
Waiting for your reply.
Thankyou [India]

A: [Mark J.] You'll need four double pole double throw (DPDT) momentary contact push-button switches. The switches must be rated for the voltage and amperage that the motors will use. You didn't mention the stall amperage of your motors, but I think you're going to have trouble finding push-button switches that are capable of handling that great a load.

Assuming that you can locate adequate switches, the diagram at right shows the circuit for one side of the robot. Duplicate the circuit for the other side.

Forward/off/reverse control of two motors with DPDT switches

Q: what is the best possible weapon against 'Tauro Maximus'?? [India]

A: [Mark J.] Let's look at the fight record. In US competition from 2009 thru 2014, heavyweight drum robot 'Tauro Maximus' lost 11 of its 32 fights:

  • One loss to 'DXTER' - a hinged wedge
  • One loss to 'Polar Vortex' - a lifting wedge
  • One loss to 'Last Rights' - a horizontal bar spinner
  • Two losses to 'Original Sin' - a pivoting wedge
  • Three losses to 'Great Pumpkin' - a simple wedge
  • Three losses to 'Sewer Snake' - a forked wedge/lifter
Ten of those eleven losses were to some form of wedge. A smooth low wedge or scoop surface gives no edge for a drum impactor to strike against, neutralizing the drum weapon.

Q: In a PopSci article titled "A Brief History of the Demise of BattleBots", author Kelsey Atherton claims that BattleBots was killed by boring, invincible wedges. Is that true? [Colorado]

A: [Mark J.] From the inagural competition in Long Beach (1999) thru the final televised 'Season 5.0' (2002), fourteen different robots won class titles at BattleBots events. By weapon type, there were:

  • 1 horizontal blade spinner;
  • 1 clampbot with hammers;
  • 1 vertical disk spinner;
  • 2 full-body spinners;
  • 1 overhead axe;
  • 1 thwackbot;
  • 2 sawbots;
  • 2 flippers;
  • 3 lifters;
  • and ZERO passive wedges.
I believe that adequately refutes Mr. Atherton's premise.

Q: Hi Mark, Sage here. I hope everything's well.
I was almost gonna buy the Sabertooth 2x60 ESC but just then some builders said that it's impact sensitive. They said that whenever they got hit, the ESC reset which made them lose the stick centre position. That's really bugging me because being a spinner killer, my bot would definitely need to tolerate a lot of abuse and losing the stick centre in the middle of a match isn't acceptable.
Now I'm considering a pair of the Talon SRX single channel ESCs, sold at the VEX robotics site. What bugs me again is that they were specially designed for FIRST use. I'm a bit doubtful about their effectiveness in combat. Are they good, or should I stick with the Sabertooth?
And yeah I decided to go for pair of E30-400 gearmotors instead of the hydraulic power pack ones, they were just too slow.

A: [Mark J.] As I recall, you're building a lightweight (~60 pound) robot with AmpFlow motors geared 8:1 and 6" wheels. Your calculations indicate a maximum amp consumption of less than 30 amps per motor before wheel spin limits greater current use.

I keep hearing about Sabertooth controllers giving trouble in combat, but the claim seems to come from reports of a very few US builders that have been picked up and broadly repeated 'second hand'. I've not heard of any such problems reported directly by Indian builders. I'm really not sure how big a problem this is.

The Talon SRX controllers are fairly new, but have been tested in lightweight combat robots using AmpFlow motors with good results. You should not dismiss these controllers just because they were built for FIRST competition. Note that the Talon ESC is not plug-in ready for R/C control -- it needs to have a standard connector added and may require a firmware update. See the User's Guide for details.

The choice betwen the two controllers is not simple:

  • The Talon SRX has many features that will not be used in robot combat, and lacks a few features that could be very useful -- like current limiting.
  • The Sabertooth 2x60 does have some known callibration quirks and limited reports of resetting after impact, but it is rich in combat features.
I'm a bit worried about using an ESC without current limiting with motors that can pull more than twice the peak current rating of the controller if the drive train jams or is otherwise restricted. If you do pick the Talons, I would suggest using them with a battery pack with a low 'burst current' rating that may help limit amperage spikes.

Q: Hey Mark, Sage again.
Actually the number of Indian builders facing the issue of resetting after impact in the Sabertooth 2x60 is substantial. I've even seen videos of matches which were lost due to this problem.
So, if not the Talons, how about a pair of the Holmes Hobbies BR-XL ESCs? The site says they're rated for 80A continuous but I'll take it with a pinch of salt. Nevertheless, they have been used in the 30lb class with good results so I guess they'll just work out for me. What do u think?
Another ESC I'm considering is the Ragebridge (I'll install a fan myself) which has some great combat features. I hope it doesn't have issues like the Sabertooth. What do you say? Ragebridge, Sabertooth or Holmes?

A: Forgive my scientific skepticism, but I believe that what you've seen are videos where it was claimed that the match was lost because the ESC glitched. If a specific controller gains a reputation - deserved or not - for transient impact failure, it becomes very tempting for a builder to blame a 'bot failure on the easy explanation. How many of these claimed failures are actual ESC glitches, I can't say.

I hesitate to recommend a specific ESC because there are elements in your design that I just don't know about that could greatly influence that choice. The best I can do is to share some comments that may help you in your decision:

  • If you believe the Sabertooths are flawed then you don't need to ask me about them -- they're out.

  • In your last post you were concerned that the Talon SRX wasn't a real combat ESC, but now you're considering the Holmes BR-XL -- a hobby R/C controller? Their specs are good and their feature list is OK, but they have far less robot heritage than the Talons. I'd be willing to use either the Talon or the Holmes, but they are both vulnerable to unexpected current surges from a big motor like the AmpFlow E30-400 if anything goes wrong. A little risky.

  • Ragebridge? Designed specifically for combat with true current limiting. Simple to use, no frills, correct fail-safe response, and excellent motor control feel. Downsides: big footprint, no protective case, requires special mounting care. If you have room to properly mount it, this ESC could be a very good option.
I can't tell you much more than that, Sage. As in many engineering choices, there may not be a clear 'best'. Pick your poison -- best luck.

Feedback: Thanks a lot Mark! Your reply was bang-on. It was all I needed! I'm going for the Ragebridge...
Your help has been invaluable to me!

Q: I have an e30-150 ampflo motor. I am wondering what the radial load rating is. The website does not say. I do not want to use a gear box. [Texas]

A: [Mark J.] No gearbox? Doesn't sound like a robot application. Suggest you contact AmpFlow for guidance on shaft radial loading limits.

Q: hi mark...i am having drum bot when i give a big hit to opponent my shaft bends inside. first i tried 20mm shaft in MS it bends. and then i used 25mm shaft at EN24 It also bends , what can i do at which mm and which material i have to use? [India]

A: [Mark J.] You've told me almost nothing about your robot, but you want me to tell you how much larger/stronger a specific part must be to keep it from failing again? See Frequently Asked Questions #17.

Ask Aaron isn't an engineering service, but if I were spec'ing a weapon shaft I'd need a lot more information:

  • Shaft length?
  • Drum weight?
  • Weight class?
  • Peak drum speed?
  • Live shaft or dead shaft?
  • Dimensions of the drum?
  • Where exactly did the others bend?
  • What is the design of the shaft support?
I suspect that the problem isn't the size of the shaft or the material from which it is made. You didn't mention if the shaft was hardened, but a 25 mm EN24 shaft is difficult to bend. If I had to guess I'd say the problem is a flawed design in the support and bearing placement for the shaft, but I can't confirm that because you haven't told me anything about your design. The hamburger is bad.

Q: hi mark ... i am making a 10 kg war bot .. with a vertical disc ( very thick , like a fat drum ) of 4 kg . I was planning to use two small johnson motor ( the one on robotmarketplace ) , for the weapon geared down to 3000 rpm . will this much speed and torque be good enough? also is 4 kg god , or shall i increase the weight ? Each motor gives 0.36 HP . [India]

A: [Mark J.] Spinning weapons of a given mass can have very different performance characteristics depending on how that mass is distributed. Example - here are calculated energy storage values for three different hollow steel drum weapons with the same mass and length, but different diameters:

  • 15 cm long - 15 cm diameter - 14 mm wall thickness: mass is 7 kg and it stores 2900 joules of energy at 4000 RPM

  • 15 cm long - 20 cm diameter - 10 mm wall thickness: mass is 7 kg and it stores 5600 joules of energy at 4000 RPM

  • 15 cm long - 25 cm diameter -  8 mm wall thickness: mass is 7 kg and it stores 9200 joules of energy at 4000 RPM

For me to calculate the performance of your 'fat drum' weapon you'll need to give me more detail: material, length, diameter, and wall thickness if hollow. Tell me those things and I'll tell you if your weapon has enough energy and how long it will take to spin up.

Four kilos of weapon in a ten kilo 'bot is plenty -- if it's the right shape.

Q: I would like to add details ... the drum is 7.5cm dia , and 15 cm long solid mild steel . this is non- machined piece so not sure of weight. the pulley will be machined in the same piece and used with a dead shaft of 1.6 cm dia. I don't want to make it hollow , just enough required for the dead shaft to go in ... used with bearings . so will this setup be enough for 10 kg , and how much will be the energy stored?

A: A useful spinning weapon will require about 40 joules of energy storage per kilo of robot weight -- at a minimum. Using two 'Small Johnson' motors geared down to 3000 RPM, the Run Amok Excel Spinner Spreadsheet calculates:

  • A steel cylinder 7.5 cm in diameter and 15 cm in length with a 2 cm hole running thru the center will have a mass of 4.84 kilos (not counting impactor teeth). It will store 180 joules of energy at 3000 RPM and will spin up to speed in about 0.5 second. That's 18 joules per kilo of 'bot weight -- not nearly enough to be effective.
The problem isn't the mass of the drum. The problem is that the mass is concentrated very close to the rotational axis. Rotating mass stores more energy as it is placed farther away from the rotational axis. Let's run the numbers on some 4 kg weapons with different dimensions:
  • A steel disc 15 cm in diameter and 3 cm thick with a 2 cm hole in the center will have a mass of 4.06 kg. It will store 580 joules of energy at 3000 RPM and will spin up to speed in about 1.7 seconds. That's 58 joules per kilo of 'bot weight -- enough to be very effective.

  • A hollow steel tube 15 cm in diameter and 7.5 cm in length with a wall thickness of 16 mm will weigh 3.94 kg (not counting end plates -- just an example). It will store 890 joules of energy at 3000 RPM and will spin up to speed in about 2.7 seconds. That's 89 joules per kilo of 'bot weight -- a VERY dangerous weapon.
That's why drum weapons are usually hollow. Reconsider your 'solid drum' design, or at least increase the weapon diameter to make it a disc.

Q: Hey Mark, I've got an... odd design for a fairy weight I've been thinking of.
The idea is to have one wheel to push the bot forward and backwards, and using a spinning disc/bar at the front to turn it, saving weight to put into a bigger weapon while still being able to move around(kinda). My two issues with this is:
A: Can the bot move around reasonably well(I know the design won't be able to move in a straight line with the spinner going, I can live with that)?
B: How do I attach the blade in a way that I can slam it in the other direction to steer with out it coming off AND make it the primary steering device? [Aurora, Oregon]

A: [Mark J.] Hold on... you want to propel the 'bot with a single drive wheel and turn it using only the torque reaction from spinning up a horizontal disc/blade? Wow! That's easily the craziest design concept ever submitted to 'Ask Aaron' -- but if I understand your design, it's not gonna work for a damn.

  • The 'bot will be able to move in a fairly straight line with the weapon spinning. When the disc/bar is fully up to speed there will be very little weapon motor torque attempting to turn the 'bot.

  • Maximum turning action will come from reversing the weapon from full speed. This will be VERY hard on the motor/ESC/battery and may require reprogramming the ESC to allow an instantaneous reversal.

  • With the weapon spinning at full speed the 'bot will only be able to turn in one direction -- the direction it will turn when the weapon motor is reversed.

  • Turning will require slowing the weapon to a stop and spinning it up in the other direction, leaving the 'bot vulnerable during the turning process.

  • Once the 'bot is pointing in the right direction, any changes to the weapon speed will turn it away from the correct line. Very frustrating if the weapon is stopped or spinning slowly.
You get points for imaginative design, but don't bother building the 'bot. It would be a nightmare to drive, and if you can't reliably move toward your opponent you'll get very poor 'aggression points' in judging.

Q: Who was the music composer for Robot Wars? [United States]

A: [Mark J.] See FAQ #37.

Q: [Two days later, same IP address...] Who was the music composer for Robot Wars? [United States]

A: It's apparently too much to ask that you click on the link supplied above and scroll down to #37. Allow me to reprint that FAQ entry here to save you the trouble.

Q: Why are you no longer accepting questions about UK Robot Wars events or competitors?

A: Mark J. here: for many years Aaron and I did our best to answer any and all questions on the broad topic of robot combat. A few years ago we were flooded with a large volume of trivial UK Robot Wars questions that were well outside the mission and focus of this website. 'Ask Aaron' is not a 'fanboy' site and we are not interested in investing our time in this area. We regret having to cut off all UK Robot Wars questions, but the fanboys proved themselves to be both persistent and quite rude.

I hope that's clear.

Q: Dear mark j I need help on a six pound crushing robot. I am currently using a robozone servo gear box with a hitec metal gear servo part number is HS-5685MH the servo output with the 7:1ratio equals 1,411oz of torque then the gear box is connected to a acme screw drive using a acme screw thread and actobotics parts also from servo city. Am I using the right servo for the job or should I buy a more powerful unit like a hitec titanium servo. For drive I am using a actobotics planitary gear box geared 50:1 with a 550 size motor for wheels I am making 3 inch titanium 1mm thick spiked wheels due to the wood constructed on the pen bots arena floor for traction. The armor is mild steel 1mm thick base plate for electronics I am using a sabortooth 12x12 hooked up to 22 guage flexible wet noodle wire. For the radio system I am using a futaba 4YS. With a 4 channel receiver 2.4g for battery I am using a thunder power lipoly rated at 850 mah @11.10 volts. Is this an exceptible set up? Please help from anthony .aka team warpz NYC.

A: [Mark J.] Hi, Anthony.. I've got a number of concerns about your design:

  • A pair of 550 motors geared down 50:1 are wild overkill for a 6 pound robot. You'd be using less than 2% of the available torque from the motors to break traction and spin the wheels. Think about MUCH smaller drive motors.

  • I have serious doubts that the Actobotics components can handle the crushing force you're trying to create. You haven't given me the geometry details of your crushing jaw design, but just because the torque numbers add up to high force levels doesn't mean that the gears won't strip and the jaws won't buckle under those forces.

  • The crushing jaws are going to move VERY slowly. They will require a long time to close down on your opponent before they can even start to 'crush'. Your opponent isn't going to just sit there and wait for the jaws to close. I don't see this as a good attack strategy.

  • If spiked wheels provided good traction on wood surfaces, other builders would be using them. I also doubt that the event organizer is going to be pleased to have spiked wheels tearing up the arena surface. Double check with the event before you commit to the spiked wheel design, and consider more conventional tires.

  • I don't have a manual handy for the Futaba 4Y radio, but I'm worried about the radio's failsafe capability. Check the event's radio failsafe requirements to make sure the entry-level Futaba meets them.

  • Your math is wrong on the torque of the servo gearbox output. Re-check your numbers.
I really doubt that a successful insect class crusher can be built with 'off the shelf' components. Consider a different design?

Antweight combat robots Lame-O and 'Same-O Inferno Q:who is credited as being the first person to hack the RC battlebots toy? [Havertown, Pennsylvania]

A: [Mark J.] I'm not sure he was 'first', but I think we can credit Infernolab's Jason Dante Bardis for proving the worth of BattleBots toy hacks in competition and popularizing their use. Jason's twin hacks 'Lame-O Inferno' and 'Same-O Inferno' were built in June, 2002 and had great success in the early days of antweight combat.

Q: Hey I have a White Rodgers type 124-105111 solenoid I am using as a master switch on a truck [ROBOT]. Need diagram on how to wire so I can kill main positive power to truck [ROBOT]. Any help would be great Thanks. [Charlottesville, Virginia]

A: [Mark J.] We only answer robot questions at 'Ask Aaron', so I had to re-write your query just a bit...

The big terminals on your solenoid are the main power connectors, and the smaller connectors are for the coil. The diagram at the right shows how to wire the solenoid to activate it with a small toggle switch and control the main power output. You will likely want to wire the coil power line into a circuit controlled by the ignition switch, because if you leave the coil energized it will drain the battery. That's what you get for asking a truck question at a robot Q&A site.

Note: disconnecting the main battery power in a vehicle with the engine running may cause a voltage spike that can damage the alternator. A more complex switch is needed if you want to safely shut down the electrical system in a running vehicle.

Basic solenoid power control diagram

Q: Hey Aaron I just wanted to make a featherweight drum bot and i don't know what equipment to use like motors,etc can you help me?? I'm almost a dummy... [India]

A: [Mark J.] Don't be a dummy -- read the FAQ! Start with #4 and #21.

Q: Hey I am using a horizontal spinner I am confused which one is most important speed or bite .since I failed to a wedge bot even though I had enough speed and energy [India]

A: [Mark J.] Which is more important -- the front wheel on a bicycle or the rear wheel? You need both!

  • If you have no bite you have to rely on your opponent to make a mistake and leave a sharp edge exposed for your weapon to grab;
  • If you have no speed your stored energy suffers and even a good hit on your opponent does no damage.
The solution is to design a weapon that has high energy storage at a rotational speed slow enough to deliver great bite. See the Weapon Archive for more discussion on this topic.

The Hamburger is Bad Q: which bearing gives maximum efficiency? [India]

A: [Mark J.] Cost efficient? Wear efficient? Weight efficient? Energy efficient? Drag efficient? Some exotic bearings have effectively zero friction, but have requirements that severely limit their uses. Bearing choice depends on the details of your application. The hamburger is bad.

In a combat robot durability is a much greater concern than efficiency. A bearing that fails is useless, regardless of other favorable attributes.

Q: I've heard that you can anodize metal to change to change it into cool colors. How do I avoid making it weaker when I do so? [Massachusetts]

A: [Mark J.] Anodizing is a process that thickens the natural layer of oxidation on the surface of certain metals. The thickened layer of oxide can reduce surface wear and improve corrosion resistance, but it does not effect the physical properties of the metal beneath the surface. You don't weaken the material by anodizing it.

The effects of anodizing vary with the metal:

  • Anodizing titanium can produce color effects on the surface of the metal;

  • Anodizing aluminum does not directly produce 'cool colors', but the oxide layer can absorb dyes that create bright colors.
Ferrous metals (iron, steel...) cannot be effectively anodized because the iron oxides created do not have properties that improve surface wear resistance or corrosion protection.
Anodized Aluminum - Color Dyed

Q: How long is a piece of string? [Internet Node TCA]

A: [Mark J.] Just long enough - if you're lucky.

Q: What would be better as armor in 30 kg and 60 kg category: 202 stainless steel or 304 stainless steel? Any other suggestions? [India]

A: [Mark J.] Stainless steels are not commonly used for robot armor. Stainless alloys are fomulated for corrosion resistance and high heat performance -- attributes not valued in robot armor. Both of your suggested alloys are relatively 'soft' and deform easily (low yield strength), and neither can be heat treated for improved hardness. Of the two alloys, 202 would be my choice for armor due to its slightly greater hardness and yield strength.

I don't know the full list of materials available to you, but other Indian builders are using EN24 'chromoly' steel. EN24 is much better suited to use as robot armor and should be considerably cheaper than the stainless alloys.

Q: hi .... I would like to add to the 202 armour question . can u plz suggest some good options for armour. So i can see if the material is available to me . I have used 202 and it worked good . Titanium is out of budget . any other Bite proof (lol) good material ? [India]

A: See FAQ #17. Although I'm pleased to comment on specific materials, I don't think it's reasonable to ask me to list and evaluate all possible metal alloys, polymers, and composites so that you can pick thru them. It's better if you do your own homework on this.

I suggest that you read Chapter 3 of the Riobotz Combat Tutorial for an extensive listing of robot structural materials and for guidance on evaluating the specific materials that are available to you. Read the rest of the tutorial while you're at it.

Tip: don't rely purely on the properties of the material. Great armor depends as much on design and mounting as it does on the material itself. I built two champion robots armored with wood.

Q: Hi Aaron,i have a starter motor,and i use it to power my vertical spinner weighing around 6 kg .I am a bit confused about it's i need your help to know whether i should switch over to E30-400 or continue with the starter [India]

A: [Mark J.] There are LOTS of different automotive starter motors with a very wide range of performance, and none of them come with the type of specs a robot builder needs to calculate their suitability for a spinning weapon. Also, starter motors are designed to operate intermittently for a few seconds at a time, not continuously for several minutes. I can't think of any champion robots that use starter motors to power their weapons -- can you?

I really can't give you any advice on the unspecified motor you plan to use. It might work well, it might be completely unsuitable. Personally, I recommend using components that have full specifications and a proven record in combat robots. Let other builders research new motors and risk failure in combat conditions.

Q: can a hollow pipe be used as a dead shaft for drum? [India]

A: [Mark J.] Can a wooden boat carry an elephant? Depends on the boat -- depends on the elephant. The hamburger is bad.

Q: How do I wire BotBitz 85A ESC to wheelchair motor? [Canton, Georgia]

A: [Mark J.] They didn't send you the user manual? Download it: BotBitz 85A User Manual -- wiring instructions are on page 3.

Q: i have made chassis for my robot which is around 15-20kg.which motor would suitable for it? [Maharashtra, India]

A: [Mark J.] You made a chassis before you decided on motors??? All the components of a combat robot must work together, and stuffing motors into a chassis not designed to match their requirements and capabilities is a poor start.

See Frequently Asked Questions #21 for general motor guidance and a link to a tool that is very useful in evaluating possible motors.

I don't know what motors are available to you, and and you haven't given me enough information about your robot for me to be able to make a recommendation. If you would like to send the specifications of a motor you are considering I might be able to evaluate its performance in a 20 KG robot -- but I can't blindly recommend a motor.

Q: will aluminum pulleys work for transmitting power from motor to drum? i mean will the keyway expand wid the jerk created [Maharashtra, India]

A: [Mark J.] The hamburger is bad. There are various grades of aluminum, various designs for hubs, and assorted sizes of pulleys. A properly sized aluminum pulley with a well designed hub made from a good quality aluminum alloy should be fine.

Q: hey my ampflow A series motor shaft is bent, could you offer any suggestion to deal with it.It was damaged during a match. [Tamil Nadu, India]

A: [Mark J.] You bent a 1/2" hardened steel motor shaft? I'd carefully evaluate the weapon/drive design to better isolate the motor shaft from such high loading. AmpFlow motors have a nice long shaft, but you should mount the pully/sprocket/gear as close to the motor bearing as possible to keep excessive loading off the shaft.

Straightening a large diameter shaft is unlikely to yield useable results, and it isn't practical to attempt a shaft replacement in an AmpFlow. I think you mark it 'bad' and save it for parts. Combat robots are an expensive hobby.

Q: I m making a drum bot having ID 120mm,so i will fit bearing housing to end caps as i cannot get 120mm OD bearing having smaller bore. my question is, will the bearing housing sustain impacts caused by drum? [India]

A: [Mark J.] Short answer - yes. The force of the impact will be borne by the impactor, the drum, the endplates, the bearings, the drum shaft, and the shaft supports. Each of these elements must be strong enough to withstand the full force of the weapon backlash. Don't skimp on the bearings!

Q: Hi I have been kicking some robot ideas around for a while, and I am interested in the DeWalt motors. However, the gearbox seems to be the weak point, and it has a nonstandard output. Do you know of any examples of the motors being used without the gearbox? The Robot Marketplace says the output pinion gear is unique, and it appears to be permanently mounted.

Thank you from San Diego.

p.s. I just rediscovered your site after a few years, and I am sorry about Aaron's passing.

A: [Mark J.] Thank you for your mention of Aaron. He is always on my mind, and I miss him terribly.

Dale Hetherington has used DeWalt motors mated to his own gearboxes in several of his projects. He offers advice on removing the nonstandard pinion using a custom gear puller. I suspect you could also carefully grind away one side of the pinion with a Dremel tool and more easilly pop the gear off. The motor shaft is 5mm and can be adapted to a variety of power transfer options.

You also may be interested in the DeWut?! 3 Speed Gearmotor Kit which adapts the 'new-style' DeWalt motor and gearbox to a strong package with a standard output shaft.

Q: Hi, we are using a Hitec Giant Scale HS805-BB Servo motor in a mechanical engineering senior design project. We hoped to have a shaft coming directly out of the spline, but all the Servo Shaft Couplings I can find online are for a C1 size spline, and ours is D1. Do you know of any vendors with D1 size, or at least any vendors that might have a D1 to C1 adapter? Thank you! [New Jersey]

A: [Mark J.] You've just learned a valuable engineering lesson:

In any mechanical design project there is one vital part that should be available off-the-shelf but isn't.

Suggestion: tear apart an old servo and extract the final drive gear that has the C1 splined output shaft. If you don't have an old servo send me your address and I'll send you the output gear. Center the C1 output gear on the output horn of your Giant Scale servo and sink a couple screws thru the gear and into the horn. Presto, you've built your own adapter.

Q: I would appreciate that part! We are on a very limited budget, and do not have a servo to spare. Could you send the part to [address redacted]. Thank you!

A: I'll have it in the mail tomorrow. All my junk servos are Futaba, so if you order accessories make them for the 1/4" Futaba 3F Standard Spline (25 tooth).

Q: hi mark lucky here thanks for ur precious guidance in yr 2014 because of which my team won 3rd prize at ITT B robowars,
again I have one question that upto which hrc I should heat treat the EN24 material? [India]

A: [Mark J.] Glad to hear of your success at Robowars, Lucky.

Check this previous post that addresses hardening EN24 (chromoly 4130) steel. The full answer on hardening depends on the use you will have for the material. If you plan to use it for a weapon impactor you should consider other options.

Q: hi aaron,from india
i need to know the rating of motors which used in cordless drilling machine,whether those motors are good when compared to bane motors ?? [Tamil Nadu, India]

A: [Mark J.] A very wide range of motors are used in cordless drills. Many drills use motors that resemble the BaneBots RS-550 motors (225 watt output), but they are made by differing manufacturers to differing voltage and power specifications. Performance varies greatly: power output runs anywhere from sub-100 watts to more than 900 watts.

The cordless drill gearboxes also vary a great deal:

  • Nearly all have plastic housings;
  • Some have plastic gears in one or more of the reduction stages;
  • Many are held to the motor by the drill case and come apart when removed;
  • All come in odd shapes that are difficult to properly mount to a chassis; and
  • A few have strange output shafts that are a challenge to adapt to a wheel hub.
If you do decide to use cordless drill motors, make sure they are a brand that can be easily adapted to robot use. Check what brands other builders are using successfully. Tips for adapting drill motors for robot use can be found by a websearch for "drill motor hack".

In contrast to drill motors, the BaneBots gearboxes:

  • Are all metal inside and out;
  • Adapt to a variety of small motors;
  • Attach directly to the motor with machine screws;
  • Come in a wide selection of gear reduction ratios;
  • Have a strong standard size output shaft with a keyway; and
  • Are designed for simple and secure mounting to a robot chassis.
Note: motors and gearboxes in more expensive contractor-grade drills are often custom-made to the specifications of the manufacturer and offer superior performance compared to consumer-grade drills. In particular, the powerful and reliable DeWalt 18 volt drill motors have powered a great many combat robots, but they too require extensive modification to be converted to robot use. See Equals Zero Designs - DeWut?! 3 Speed Gearmotor Kit.
Harbor Freight 18 volt drillmotor.

BaneBots P60 gearbox and motor.

Remembering Aaron... 

Q: how can robots help us deal better with hurricanes and why? [Ontario, California]

A: [Aaron] Few people in Nebraska are threatened by hurricanes, so send a swarm of killer robots into low Atlantic and gulf coastal areas to drive the puny human inhabitants toward Nebraska. Problem solved.

Robot haiku:
That's obviously
A question from your homework.
Do your own research.

Aaron's Greatest Hits!
More of Aaron's Poems
Aaron's Minecraft High Dive Video
Aaron's World of Warcraft New Player Guide

Killer Robot drawing by Garrett Shikuma

Got a question?

We welcome combat robot questions. Please search the Ask Aaron Archives first to see if we've already answered your question. Recent Q&A are posted above.

Type your question in the box, then:
Powered by Allforms


Thousands more robot combat questions and answers in the searchable Ask Aaron archives.

Run Amok Combat Robotics homepage
Copyright 2009, 2014 by Mark Joerger
All rights reserved.
Dummy Defense Blueprint Design Exchange