Q: Could you use a robot from The Machine Lab as a sublight combat robot, like the MMP-5?

A: The Machine Lab robots are not designed for combat. The chassis is thin aluminum, the wheels are unprotected, and they are slow (less than 3 MPH). Without radio the 4.5 pound MMP-5 lists at $545, the 8 pound MMP-8 is $795, and the 30 pound MMP-30 is $4045.

You'd do much, much better with the BattleKits Featherweight. It is designed for combat, fully armored, and plenty quick. For $499 you get an armored chassis and drivetrain with two E-150 Magmotors. Add battery, ESC and radio and you have a competitive featherweight.

A: Read this archive for lots of info on converting R/C toys to combat robots.

A two pound robot would fight in the beetleweight class which has a maximum weight of three pounds. Full information on weight classes, radio requirements, and other design issues can be found in the current Robot Fighting League rules.

A: No. First, it would have very poor maneuverability. As a bot's overall wheelbase increases compared to width, the bot becomes more stable in a straight line and more difficult to turn. You'd have a very long robot that would be easy pickings for a more maneuverable opponent.

Second, pushing power is limited by the weight on the drive wheels. Power beyond what you need to spin the wheels will not significantly add to pushing power. Correctly geared, additional power can provide better acceleration and/or top speed -- but speed has very limited use in a tight insect-class arena and the 4-motor Inertia Labs chassis is plenty quick to start with.

A: Not that I have seen. The pro series 'Biohazard' with 6-wheel drive and a lifter was more appealing for conversion.

A: Mark J. here: the Inertia Labs antweight kit provides a quick and durable platform that is easy to assemble. It does have a few problems that prevent me from recommending it to beginners:

• There is very little room in the enclosed radio/battery compartment. Any additional equipment has to be hung off the outside.
• The one-piece machined aluminum chassis is difficult to repair if it is badly damaged.
• The price for a complete kit is quite high and some of the components of the kit (charger, transmitter) would need to be upgraded to move to a higher weight class.

Q: Isn't the Inertia Labs chassis $45 cheaper at the Inertia Labs website than at the Robot Marketplace?

A: The price for the bare chassis at Robot Marketplace is $25 -- same as from Inertia Labs. I don't think that Robot Marketplace has updated the prices for the individual components in their complete kit.

Q: I have all the parts to build an Inertia Labs antweight flipper. Would it be a good first robot?

A: I recommend that first-time builders keep their robots very simple. You'll have enough new things to worry about with battery maintenance, R/C system set-up, traction issues, ESC mixing, driving, radio interference, wireing, tournament procedures, and repair problems. You really don't need to add to that with pneumatic valving systems, pressure tanks, weapons channels, digital switches, complex attack maneuvers, and additional pit checklist items.

I'd suggest that you build the basic Inertia Labs platform, bolt a sturdy wedge onto it, and go out and get some experience before tackling a pneumatic flipper.

Q: Would it be a good idea to make a full body spinner using the Inertia Labs chassis as the platform?

A: An effective FBS uses as much of the available weight allowance as possible for the weapon system. You would be wasting weight to use a four motor, bulletproof chassis as the basis for an FBS.

Q: This is more of a comment than a question, but the Inertia Labs antweight kit can be bought for less than half the Robot Marketplace price directly from Inertia Labs.

A: Mark J. here: the kits from Robot Marketplace and Inertia Labs are different. The Robot Marketplace 'complete kit' has all of the components of the Inertia Labs kit plus:

• an upgrade to the Scorpion HX ESC with weapon channel (from Ant 100)
• an upgrade to 730 mAh Lipoly battery (from 480 mAh)
• a Laser 4 radio system with crystals
• an EFlight LiPoly battery charger, and
• an Astroflight DC power supply.

A: The Pro Series toys have a much different internal layout than the smaller Custom Series, but the hack is similar. You need to disable the 'battle damage' sensor and lock the slip clutch on the weapon gearbox. If you're going to use the active weapon in competition you'll need to replace the 3-channel AM radio and motor / weapon controllers -- an FM radio with drivetrain and weapon failsafe is the minimum required for an active weapon beetleweight. The rest of the chassis and drive train are useable as-is. The Pro Series use a 6 volt NiCad pack, but I run mine on 7.2 volts.

A: You can be patient and hope one shows up on EBay.

A: Mark J. here: how about a kit that comes with a vertical spinning disk already? The Team Thinktank VDD kit is out of production, but you might be able to scrounge enough parts to put one together. Ask around on the Delphi robot forums.

Big spinning disk weapons typically do kinda stick out all over. Based on the theory that "the best defense is a strong offense", most big spinners concentrate all available weight into the weapon system itself rather than into armor or a 4-motor drive system like the Inertia Labs design. From that perspective, the Robot Marketplace Advanced Antweight Starter Package better fits the bill. As I have pointed out here before, the Robot Marketplace packages are not as much 'kits' as just a box full of parts. If this is your first combat robot, you're gonna be looking at that box of parts and doing a lot of head scratching.

A: The RFL rules say that if you run an 'active weapon' (drum, spinner, flipper, etc.) on an antweight you must run a hobby-grade FM radio and provide an electronic failsafe on the weapon channel to shut the weapon down if the radio fails. That pretty much squashes low-budget toy hacks with active weapons. Stick with a passive wedge or brick design for your toy hack and you'll be legal with the AM radio that came with the toy.

A: Mark J. here: welcome to 'Ask Aaron: questions and answers about bricks on wheels'.

Cheap parts don't get you very far when building a combat robot, and you haven't told me anything about your expectations for this 'brick'. I'll have to make some assumptions:

• you have very little money;
• you want to build a simple robotic platform a couple feet across;
• you want the platform to move forward, backward, and turn; and
• speed and pushing power are not important.

If you're just looking for inexpensive combat robot parts, you can find builders selling used and surplus parts on the Delphi RFL Forum, but you're going to spend hundreds of dollars there to build your brick on wheels. Let's see how little we can spend to get your brick moving. My usual suggestion for building a robot on a limited budget is to start with an R/C toy, but it sounds like you have something quite a bit larger in mind. No problem! We can still start with an R/C toy and patch in a relay driven power amplifier to control the larger motors. Here's a bargain-basement electronics package and drive:

• Grab a 'Fly Wheels' R/C toy. My local toy store is closing them out for $10. We'll use the R/C electronics from the toy for your brick.

• Get rid of those scooter motors. We'd need to build a drive train for them that would be both expensive and difficult. Google 'surplus gearmotor' and look for DC units that spin at some reasonable speed. Drive motors from a child's riding toy would be perfect. Get two for about $15 each.

• While you're shopping surplus, find some double-pole power relays rated about 5 amps with a 5 or 6 volt coil. Get four at about $4 each. We'll use the low power R/C motor controller output to control the relays, and the relays will control the higher-power gearmotors forward / off / reverse.

• Run down to your local Radio Shack and get four 1 amp diodes: about $2 total. The diodes will direct the forward or reverse output from the R/C motor controller to the correct relay.

Here's the wiring diagram for the relay power amplifier for one side:

Open up the Fly Wheels toy. Remove the power wires from the motor on each side. Patch the power wires into the relay coil connections of the two amplifiers as shown. Note the position and orientation of the diodes.

When the amplifiers are installed on both sides load some batteries into the toy transmitter and receiver. Push the right control stick forward. One (and only one) relay on the right side of the robot should click closed. Pull the stick back and the first relay should pop back open and the other relay should click closed. Return the stick to center and all relays should be popped open. Repeat with the left control stick.

If everything is good, hook up the amplifiers to your gearmotors and the main battery. We don't run fuses in combat robots, but a suitably sized inline fuse between each amplifier and the battery would be an excellent idea in your brick.

Prop the drive wheels up off the ground and push the transmitter sticks forward.

• If both wheels spin 'forward', great!
• If both wheels spin 'backward', reverse the power terminals on both motors.
• If one wheel spins 'forward' and one wheel spins 'backward', reverse the power terminals on the backward spinning motor.

I'll leave it to you to find suitable wheels, battery, charger, and hardware. You could do worse than to start with a whole kiddy riding toy and just concentrate on adding the radio and motor controllers. Best luck!

Q: I sent the brick on wheels question, you were a great help -- thanks. I live in San Diego and the nearest robot events are several hundred miles away in San Francisco, so I might want to start my own event. I'm 12 years old and might be able to get help from my dad, uncle and friends.

A: Yes, robot combat events are a little scarce right now. There should be greater interest following the return of BattleBots to TV toward the end of this year (2008). Search the archives for tips on hosting your own event.

A: All sorts of problem with that:

• Airplanes don't back up, so the speed controller doesn't have a reverse. How are you gonna back the 'bot out of a corner?

• The speed controller will quickly fry if the motor is bogged down pushing. Spinning a propeller in the air uses a lot fewer amps than pushing an opponent across an arena.

• The battery is too small. Flying uses much less power than robot combat.

• The motors will need about 30:1 gear reduction with even small wheels. You can't get that much reduction from a single-stage belt drive.

A: You can build a competitive antweight for very little money, but adding a spinning drum weapon creates problems. If the competition uses the standard RFL rules, an antweight with an active weapon requires a minimum FM radio system with an electronic failsafe on the weapon channel. Such a radio system, even purchased used, will eat up your whole budget.

An antweight without an active weapon can run an inexpensive toy AM radio system. Many competitive antweights have been based on R/C toys. Read thru the section of the archive for tips on this inexpensive approach.

Q: OK, I have a Vex transmitter that runs on legal ground frequencies, but the receiver uses a phone jack and not wires. It has replaceable crystals. Now would it be posible - minus the drum?

A: Your Vex transmitter is a good start, but the Vex receiver is not compatible with combat robot components like speed controllers -- there is more difference than the connectors. Search for 'Vex' in the archive for more details.

That leaves you needing a small FM receiver, twin drive trains, a two-channel speed controller, wheels / tires, a battery / charger, a chassis, and armor.

• GWS 75 MHz pico receiver - 20.99
• GWS receiver crystal - 6.99
• Tamiya Dual-Motor Gearbox - 10.99
• Ant 100 dual speed controller - 54.95
• Tamiya off road tire set - 4.29

Q: Pyrobug again: would it be a good idea to build an antweight without a speed controller?

A: If it was a good idea, lots of builders would be doing it. You're not going to save any money by doing that -- you'd still need a pair of reversible switch interfaces to control the motors, and they will cost at least as much as an ESC.

If you convert a toy it will most likely have a combined receiver/controller with forward-off-backward control for each motor. That will take some practice to get used to, but many antweight tournaments have been won by converted toys without proportional motor control.

A: It was probably the 'Mega Bloks Battle Bloks' set. Team JuggerBot used them for a 'build your own robot' workshop at a technology festival a few years ago to let people build custom R/C combat robots in just a few minutes. They were way cool, but I haven't seen them for sale anywhere in several years.

There are other kits kinda like that. The Vex Robotics kit includes modules that plug together to quickly make an R/C or microprocessor controlled robot. There are also several versions of the Lego Mindstorms kits with similar snap-together modules. Both of these kits have been widely used in schools.

The VEX and current Lego Mindstorms NXT kits are available thru retail outlets like amazon.com. Older versions of the Mindstorms kits can be found on EBay.

A: A Fly Wheels R/C toy would make a good start on an antweight if you did cut speed and increase torque. Smaller wheels and/or more gear reduction will do the trick, but neither is easy to do. I'd suggest taking the toy apart and using the electronics and drivetrain on a new chassis that could accomodate small diameter wheels.

A: Mark J. here: It's not even close to being a 'complete kit'. You get a chassis, motors, wire, and wheels. You need to come up with radio gear, an ESC, a battery pack, charger, and some sort of weapon. The machined aluminum chassis is way cool, but not easy to repair if it gets pranged. You might want to order a spare for your pit box. I don't really consider this to be a 'first time' kit.

Q: Were can I get the 'A:1 Complete Antweight Kit' now that Composite Labs shut down?

A: Weak! I hadn't heard that Composite Labs was gone. I had been recommending their kits. They were the manufacturer and only source, so they're gone for good.

It's difficult for me to recommend any of the currently produced antweight kits for a beginner. You're going to spend $300 or $400 and end up with a marginal radio, a low-end battery charger, and a pile of parts with no specific instructions. I'm gonna go back to suggesting that a beginner find an old BattleBots R/C toy on EBay, hack the radio and drive motors, add a wedge, and go beat up some $400 'bots for $50.

A: Standard hobby servos will not work with your inexpensive toy radio system. You'll need to salvage the steering mechanism from the original toy car.

A: Why not? It sounds like it could be fun to drive. Technically, it would be a 'thwackbot' rather than a spinner -- but that's good since thwacks can get by in most tournaments with the toy AM radio that comes with the Fly Wheels. Thwackbots suffer a little from the commonly used 'damage/aggression' scoring system because sitting in one spot and spinning doesn't get you any aggression points, but I still think it would be fun.

A: PLEASE do not build anything with a spinning weapon to play around with in your garage! Even an antweight spinner can cut tendons or fling a chip into your eye like a shot. Here's my suggestion:

• Go to Ebay.
• Search for 'BattleBots'.
• Find one of the BattleBots R/C toys (there is one as I write this for $25).
• Buy it.

Q: OK, I bought an R/C car and I'm now in the process of designing the armor and weapons. I was wondering how I could make the tires get more traction. Also, I need a light armor that won't break my budget -- I've got $20.

A: Spend some time browsing our archive. You'll find posts on improving tire traction, and our Armor Guide.

Armor selection depends not only on your budget, but on your experience in working with various materials and the availability of specialized tools. You might be interested in another post in the materials archive on Garolite. Just for playing around, plastic kitchen containers can be cut up to make pretty tough and resilient 'armor'.

Q: Do you think that rubber cement will give R/C car tires better traction? It's all I have.

A: I'm guessing that your R/C car has the common flexible vinyl tires. No, I don't think that rubber cement would help for long -- when it dries out it becomes hard and stiff. A tube of silicone sealant costs about $3 and would help traction a whole lot.

A: Mark J. here: most of the antweight 'kits' on the market are simply a collection of individual components stuffed into a box. Most require additional materials and lack specific instructions on the design and construction of the armor and chassis. This can be difficult and frustrating for a novice robot enthusiast as the competitive quality of the resulting robot is dependant on getting these design factors right.

I think the best choice for a first-time builder would be the A:1 Ultimate Complete Kit from Composite Labs. The kit is well designed, entirely complete, ready to assemble, and comes with an instructional DVD covering the building process. Add-on kits for lifter and drum weapons are available to upgrade the basic wedge kit if you want to try an active weapon later on. Composite Labs also supplies on-site support for their kits at major events. The price is comparable to the Robot Marketplace advanced kit.

Update: Composite Labs is no longer in business. The A:1 kit is no longer available.

A: Thanks for the info!

Some combat events do not allow toy R/C systems -- even on an antweight. The 2007 RFL rules allow robots 12 pounds and less with passive weapons to use AM / toy radios at the discretion of the event organizer. However, the rules also require a 'bot to have at least two radio frequencies available on which to operate -- not really possible with most toy systems. Check with the events you plan to enter to make sure your 'bot will be allowed to compete.

A: The first thing I'd check would be the transmitter. Toy transmitters often use cheap contact switches on the control sticks that can get dirty or misaligned and result in no signal. Check and clean the transmitter switch for forward motion on the right side before you start looking for problems with the main controller board.

I don't think the motor is the problem. When a motor fails it will almost always be inoperable in both directions. You can check this by removing the motor leads and connecting them directly to a battery to check for rotation in both directions.

A: I don't think so -- too fragile, wrong gearing, poor traction, and no good weapon mounts.

A: Take a look at the A:1 Ultimate Complete Kit from Composite Labs.

A: Rat traps really don't make good combat robot weapons. They are dangerous to handle, may not be legal for your local event, and are probably too heavy to add to a 'Fly Wheels' and stay under weight. A good wedge would be a better choice.

I don't have a 'Fly Wheels' yet. Has anybody weighed one?

A: Putting armor on a micro R/C car is only a good idea if you're trying to be underpowered target practice for the other fairyweight 'bots. Have you considered building an antweight? It's cheaper and you'll find more tournaments to enter.

A: The 'toy' radio system is the problem. The Robot Fighting League rules allow 'toy' radio systems to compete in all weight classes up to 12 pounds (hobbyweight) if the 'bot has no active weapon. Check the RFL rule set for other restrictions. The local event organizer can overrule this, so check with them, too.

A: For $50, the Fly Wheels is a good start. The rest is up to your imagination and how good you are at making things. I think I'd start with a sturdy front wedge.

A: The short answer is 'no'. R/C toys don't have interchangeable frequency crystals like hobby R/C components, and changing from 27 MHz to 49 MHz is completely out of the question -- it would require extensive modification and tuning reserved for electronic tech specialists.

A: You can compare the motor with photos and dimensions at robotmarketplace.com.

A: So many Fly Wheels questions -- I'm gonna have to get one just to keep up!

Robot builders love to overvolt motors to get more power! The trick is to stop before you smoke something. The Fly Wheels toys have some version of the 130 size motor. That motor in the BattleBots toys could take a lot of voltage -- for short periods. How much voltage the rest of the toy will take is another question. I'm guessing 9 volts would be do-able, but more power always comes with reduced lifespan.

A: I don't have a 'Fly Wheels' here to look at. I suspect you can drill a small hole thru the center of the wheel into the hub and insert a small self-tapping screw and washer. Anybody have one handy to look at and tell me if this will work?

A: Neither tape nor glue will work.

A: EBay.

A: Technical question - Mark J. here: Don't increase your radio voltage! Batteries aren't your problem, as long as they're fresh. Range problems are often a result of too short a receiver antenna, or not having the antenna wire stretched straight.

Different radio frequencies have different optimum antenna lengths for both the transmitter and receiver. Try a nice straight receiver antenna first, then try doubling it's length.

A: The BattleBots pro-series toys weigh about two pounds stripped down and make a pretty good platform for a beetleweight. I'd stop there. The tiny 130-size motors are awfully small to be pushing 12 pounds of robot around a combat arena, and toy radio systems are not allowed in hobbyweight 'bots with an active weapon. By the time you replace all that, you might just as well have started from scratch.

A: There isn't much to learn, and there isn't much to hack. Trace the wires -- you'll have two power leads (+ and -), an antenna wire, and a pair of leads to each motor.

Toy receiver/controllers don't come with specifications, so you'll have to guess how much power they'll handle. It's probably not smart to use motors much more powerful than the ones that came with the toy.

Also, check with the organizer of the event you plan to enter. Some don't allow toy radio systems, and others place restrictions on their use.

A: There was a really good description of how to hack the BattleBot R/C toy at the Robot Dojo site, but the site is down. Fortunately, the Web Archive has a pretty good copy! Try: How to Hack a BattleBots Toy [archived].

A: Mark J. here: Inexpensive toy R/C cars do not have standard servos. Most just slide a magnet back and forth with wire coils -- no rotary steering servo motor to modify.

There is a good article on modifying hobby grade servos for robotics use at the Seattle Robotics Society website.

A: The only toys I've seen hacked for beetleweight competition are the larger BattleBots Pro Series R/C toys -- Diesector and Biohazard. Like the smaller custom series toys, they are no longer available in stores. Your best bet on finding one is at EBay.

A: Technical question - Mark J. here: Most people build their combat robots from scratch, but four different robot kits are available from Battlekits.com. They may be used to construct 'bots ranging from the 30-pound feather weight class to the 340-pound super heavy weight class. The featherweight comes fully assembled except for the electrical connections and radio gear. It also has armor and a simple wedge weapon, but the larger kits require you to supply such 'finishing touches'. The price of the featherweight kit is close to $1200 -- plus the radio gear.

There are a few sources for less complete and less expensive kits for lighter weight classes. Check the Robot Kits Page at the Combat Robot Wiki for an up-to date list.

A: You can learn a lot and have some fun by converting an R/C toy into an antweight combat robot. Lots of small 'bots have been based on the BattleBots R/C toy. Those toys are now hard to find, but if you can find one [try EBay] there is a nice description of how to convert it into a combat robot here: How to Convert a BattleBots Toy [archived].

I've seen a new toy called Fly Wheels that sells for less than $20 and looks like it would make a good starting platform for a combat robot.

Look around your local toy shop for something that turns by changing the speed of one side versus the other [tank steering]. You might find something no one else has used!

A: It's a little like making a statue of an elephant: you start with a big chunk of rock and carve away everything that doesn't look like an elephant.

Seriously -- there are all types of R/C toys. Some have steerable front wheels and some steer by making the wheels on one side turn the opposite direction from the other side. That later type is more maneuverable and might make a better robot, but either type will work. Just start taking off things that don't look like they belong on a robot -- the body, bumpers, wings, roll bars, whatever. Get it stripped down.

The next step is to weigh the stripped-down toy to see how much armor and weapon weight you can add without going over the maximum weight for the class of robot you want. Toys make good 1-pound and 3-pound weight class robots, and larger ones can fight in the 12-pound class. Bolt on your armor to protect the wheels and other delicate stuff. Tough plastic is good, or fairly thin metal. Bolt on a wedge or a couple of spikes and you're a roboteer! You'll learn a lot from the things that go wrong with your first 'bot, and you'll have fun. Be careful with anything sharp, and don't attack your cat/dog/hamster!

The picture at the right is my beetleweight 'Zpatula', a converted BattleBots toy. It works great!

A: There are eight 'custom series' BattleBots toys:

• Blendo
• DoAll
• Dr. Inferno Jr.
• El Diablo
• KillerHurtz
• Minion
• Son of Whyachi
• Vlad the Impailer

'The Gap' has it's own webpage with several pics: The Gap

A: Tank steering takes two motor control channels - one for the motor(s) on each side of the `bot. A toy R/C car has a one motor control channel and a second channel that operates only the steering servo. Find something that already has tank steering, like the `Fly Wheels' R/C toy.

A: Sorry, but I just can't get excited about a combat robot that you could put two stamps on and mail to a competition. Fifty grams is less than two ounces. It would take nine of them to make one US antweight! Check out the Antweight Forum at Delphi for good tips on antweights, fairyweights, and fleaweights.