5719 Questions and Answers about Combat Robotics
from Team Run Amok

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) asked for 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 'Got Question?'
The Ask Aaron Archives Click to browse thousands of previously answered questions by category, or search for specific topics. Includes FAQ
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   
Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot.

Q: Hey Mark, I've got some paranoia with my first beetle build (2 wheeled horizontal drum) and I'm hoping that you could perhaps ease my mind with something.

In episode 5 of Robot Wars (2016) there was a 2-wheeled vertical spinning bot called Infernal Contraption. Due to the weapon's placement being close so close to its high-torque drive system, it would easily invert itself by just driving forward (a la any overhead thwackbot).

Is there a rule of thumb or formula I could use to ensure that I can maintain good torque in my drive system without ending up flopping around like a Magikarp-out-of-water?

Thanks! David R. [Livermore, CA]

A: [Mark J.] Getting a 'bot to do the whole torque-reaction overhead hammer thing requires some deliberate design work to set the center of mass close enough to the drive axle and eliminating rear overhang. The chance of doing this inadvertantly is vanishingly small, but getting the center of mass 'just right' does require some planning.

Have a look at section 2.7.7 of the RioBotz Combat Tutorial for the math on where the center of mass should be placed in a two-wheel 'bot to get optimum traction without risk of nose lift.

I like the 'Magikarp out of water' analogy. I'll save the image and use it to adorn unworkable or needlessly awkward solutions. Watch for it.

Q: How do horizontal spinners keep their weapons off of the frame? I know for example the most iconic horizontal spinner Last Rights/Tombstone has an adjustable height blade, meaning it isn't riding on the bottom frame. Is the friction of the bearing on the shaft enough to keep the blade from shifting during big collisions or is there something more to it that I am missing because that doesn't seem adequate? [Cleveland, Ohio]

A: [Mark J.] Typically the weapon hub and pulley/sprocket are made to fill the entire space between the weapon bearings. They ride against the inner bearing races or against 'thrust bearings' that take displacement loading during a 'hit'.

If the design allows additional space between the weapon bearings for blade height adjustment, tubular spacers (orange in the diagram at left) slide over the weapon shaft above and/or below the weapon hub to raise or lower its position.

Q: How does a horizontal full body spinner like 'Barber-ous' work? Is it a shell spinner like 'Ringmaster' on its side? [a server in California]

A: [Mark J.] First, a little terminology clarification:

  • Spiners are classified by the direction their impact, not by axis orientation. 'Barber-ous' is a vertical spinner and 'Ringmaster' is a horizontal spinner.
  • A 'shell spinner' has the entire exterior of the robot spinning. 'Ringmaster' is not a shell spinner -- it is an example of the rare and complex 'ring spinner' where only the outer edge of the body spins, leaving the wheels exposed at top and bottom to allow inverted operation.
Team Rotractor's original Barber-ous webpage (archived) has the worst build report I've ever seen, but I'm still grateful that it exists. The chassis photo at right came from another source. The shell and electricals have been removed and you can see that the layout is not nearly as complex as Ringmaster's:
  1. The weapon motor is mounted on the central chassis that also carries the batteries and electronics. The entire central chassis is concealed by the weapon shell when assembled.
  2. Non-rotating stub axles come off each end of the chassis. This version of 'Barber-ous' has worm-drive gearmotors bolted to the ends of the stub axles to power the drive wheels. The gearmotors are obscured in the photo by the wheels and hubs.
  3. Laying on the floor is one of the two large weapon hubs. With the gearmotor removed, the free-spinning hub slides onto the stub axle and a drive chain connects the hub sprocket to the weapon motor. The weapon hub on the far side is already in place. With the weapon hubs in place, the weapon cylinder slides on over the hubs and chassis and is bolted to the hubs. The drive-wheel assembly can then be re-mounted.
'Barber-ous' went thru many revisions and updates to the chassis and drive motors, but the weapon drive principle remained the same.

Q: Is it possible to add Fingertech's Beater bar to the Viper 2 kit? [Malaysia]

A: [Mark J.] Possible, but I can't recommend it. You'd have to fabricate weapon mounts as there are none included with the the weapon kit, but that's just the start:

  • The beater assembly plus motor & electronics alone weigh more than a pound -- the antweight Viper becomes a beetle.
  • The drivetrain supplied with the Viper is not powerful enough for a beetle -- a motor upgrade is required.
  • That starts an upgrade avalanche: motor controllers, battery, armor, chassis...
The Viper is an adequate antweight, but turning it into a beetle is a poor idea. You'd be much better off building a suitable beetle from the ground up.
Q: I was watching this video of an antweight tournament when it mentioned a robot that was controlled via a cell phone.

Pushing concerns about proportional control and reception aside, how is this even possible? Is it legal within the rules considering it has an active weapon? [A server in California]

A: [Mark J.] A friend has a Parrot drone that uses an app in his iPad to control flight via a direct Wi-Fi connection. Multi channel proportional control is good, and range is about 50 meters. It also sends real-time video back to the tablet. A quick search on Amazon for "wifi toy" brings up a bunch of flying and rolling toys controled by android and IOS devices.

The tech is available, but I don't know of a simple off-the-shelf 'plug-n-play' system suited for combat robots. It's still an electronics geek undertaking.

  • Robot Marketplace does offer a line of Renegade Wi-Fi Robot Controllers that provide the basis for a Wi-Fi robot system, but they aren't cheap and there doesn't seem to be a controller app for your phone/tablet included.
  • Hardcore electronic hobbyists can piece something together with Arduino and Wi-Fi boards, but it's not a simple project.
The event in the video was put on by the Central Illinois Robotics Club (CIRC). Legality of radio systems is generally a decision made by the event organizer. The primary concerns are that the radio does not interfere with other robots and that it provides an adequate failsafe response on signal loss. If that could be demonstrated I would have no problem allowing Wi-Fi control in a tournament.
Q: I found this when visiting the combat robot hall of fame,here is the pic: [Malaysia]

A: [Mark J.] The Ask Aaron question form does not support attachments. If you want to send me pictures or files you need to put them someplace on the web and send me the link. Dropbox works nicely.

Q: How does ant weight 'Anticide' flipper works?

A: The flipper on 150 gram British 'Anticide' uses a standard pneumatic system with tiny parts. The big red cylinder in the photo at right is the pressure tank. A breakout and description of the components used can be found in this post on the Robowars101 forum. The post is more than six years old and some of the parts referenced are no longer available.

A search for 'Anticide' in the Ask Aaron Ants, Beetles, and Fairies archive will lead you to a post discussing the merits and drawbacks to available miniature pneumatic components.

Q: Hi,its me again,me and some other team members are creating our own Combat Robot Hall of Fame and one of our team members are considering adding Run Amok into it,can i k now Run Amok's win/loss? [Malaysia]

 8 minutes later

Q: Just ignore the question,we ran into some 'problems' and cant make the page.
What does "SFK" stands for? [Malaysia]

A: [Mark J.] According to Wikipedia, 'SFK' can refer to:

  • SoundForge peak audio file extension
  • Something for Kate, Australian rock band
  • Siófok-Kiliti Airport, Hungary (IATA code)
  • SFK Lyn, Norwegian sports club
  • SFK 2000, women's football club from Sarajevo, Bosnia and Herzegovina
  • SFK Varaviksne, Latvian football club
  • ŠFK Prenaks Jablonec, Slovak football team; or
  • SFK Nová Ves nad Váhom, Slovak football team
I considered that your request might be a typo, but then I remembered that I told my readers where to find what 'SKF' stands for just a few posts down the page. I'm certain you wouldn't be so impulsive as to ask about that.
Q: What are the best motors currently for horizontal spinner type robots? Our weight limit is 85 pounds, and we're looking for something with relatively high torque and low spin-up time for the weapon bar. Also not sure whether to use brushed or brushless. [a server in Illinois...]

The hamburger is bad! A: [Mark J.] The hamburger is bad. I cannot match a weapon motor to a weapon based only on the robot's weight class and weapon type. See the Ask Aaron Spinner Weapon FAQ to find out why and to learn what information is needed to calculate weapon performance.

If you don't know whether to use brushed or brushless, use brushed. Brushless adds a level of complexity and many pitfalls for builders unfamilliar with their quirks -- particularly in a heavier weight class such as this. Brushed is simple. Simple is good.

Now, it's possible that you just want me to take a blind guess and recommend an affordable and reliable old school motor that will make your entirely undescribed heavier-than-lightweight bar spin-up and look like a combat robot. If that's the case, Robot Marketplace has found a few of the classic EV Warrior motors. Run one at 24 volts thru a 2:1 pulley reduction to your bar weapon and you're probably in the ballpark.

What event runs an 85 pound weight limit? That's not a standard US weight class.

Q: Why can't Warrior Clan launch bots into the ceiling like its previous form Warrior SKF could? [Massachusetts]

A: [Mark J.] There are no significant changes to the 'bot, so the capacity is still there. I can only speculate that they have not had opponents that are particularly vulnerable to their flipper weapon. The SKF weapon is powerful but it does not have a great deal of vertical motion; their ideal opponent would have a low structural edge close to its center of mass.

Q: Sorry sir for posting a question but can you please clear my doubt " heavier the drum,Oppenent will find difficult to Topel you" is it true???? [Maharashtra, India]

A: [Mark J.] Pure, weapons-grade bolognium. Stop asking about weapons and start building arenas to contain the weapons you have.

Q: Hi There

First off, a huge thanks for keeping this site going, it's a hugely valuable source of information and by far one of the most comprehensive sites on combat robotics on the web. I'm currently designing a heavyweight (110Kg) robot after an extended break - I last built autonomous antweight/sumo bots in 2005.

My question is about spinners - namely, getting a large bar - al la Tombstone/Last Rites - up to speed in a respectable fashion. The current Robot Wars arena is 22m x 22m, and allows for around 2.5s of spin up time (on average) before first impact occurs.

Bar specs:
1300mm x 125mm x 30mm
Weight is roughly 38Kg

Motor Spec:
8500RPM, 42Nm Peak Torque (stall torque isn't stated, nor is the internal resistance, so I've used the peak torque figure in the Run Amok spinner calculator)

Results using a 4:1 gear ratio:
1339 RPM in 7.18 seconds, storing 53397 Joules.

Now, obviously this isn't [quick] enough - is this a case of me just not working out the stall torque correctly, or a case of choose a different motor? (If it is, which ones would you reccomend?)

Thanks [Fulwood, England]

A: [Mark J.] Welcome back to combat robotics, and thank you for the kind comment.

The Team Run Amok Spinner Spreadsheet - like any modeling software - is only as good as the data that goes into it. A motor with uncertain specs or a brushless motor with a non-linear torque curve results in questionable output, but in this case I don't think the motor specs are the problem.

If we conservatively assume that 'peak torque' is the same as 'stall torque' as you have done, the power numbers for the motor are still very impressive. Let's run a comparison by replacing your un-named motor in the spreadsheet with the weapon motor 'Tombstone' currently uses -- the mighty 'E-Tek-R' at 56 volts. We'll set the reduction to 2:1 to get comparable weapon RPM from the slow-spinning E-Tek:

E-Tek-R with 2:1 ratio: 1360 RPM in 6.04 seconds, storing 55,120 joules

Not a whole lot different from your results, so motor power isn't the problem. The real issue is that you're spinning up a big, heavy chunk of steel with a huge moment of inertia and the motor needs more help on low end torque to get a quicker spin-up. Let's try modeling your weapon with increased reduction ratios at meaningful time intervals:

Reductionjoules @ 2.5 secjoules @ 5.0 sec

Energy storage in the kilo-teens range is plenty to warmly welcome hard-charging opponents, and potential energy storage that takes more than 6 or 8 seconds to obtain is effectively useless for anything but 'showboat' hits on an already-beaten opponent. Dial in some additional reduction. It will put less stress on your motor and battery, and will give you a better balance of spin-up time to useable peak energy storage.

Q: Hello Mark! It's said that the flipper of Warrior Clan (Warrior SKF) is powered by its spinning ring, that's amazing! Can you show me how it works? [Guangdong, China]

A: [Mark J.] Team Whyachi's 'Warrior SKF' has been around for several years and we've had quite a few questions about its design and function. Search the Ask Aaron Combat Robot Weapons archive for "Warrior SKF" and "dog clutch" to find those posts. You'll also discover what 'SKF' stands for.

The best explanation of how a flywheel flipper works is the well-illustrated build report for Dale Hetherington's 'Flip-O-Matic'. If flywheel flippers were a good idea you'd see lots of them; you don't see lots of them.

Q: How are the chains and sprockets connected to each other in the Whyachi 2-stage reduction "gearbox"? I saw pictures of the inside but I don't get how it works. [Quebec]

A: [Mark J.] The Team Whyachi gearboxes are not chain and sprocket -- their various models use spur, bevel, or planetary gears.

Perhaps you're thinking of the AmpFlow 3-stage chain speed reduction unit?

I'll be pleased to explain, but I have to know which gearbox I'm explaining.

Q: I was talking about the AmpFlow, I am so sorry I got messed up. I just don't get how the reduction can be made by using 3 chains and only 2 axles.

A: Got it. The trick is that only two of the six sprockets are attached to the shafts.

The diagram at right is a cutaway section of the AmpFlow speed reducer box as viewed from above with the chains removed. The cyan sprockets are attached to the shafts and rotate with them. The magenta sprockets are attached in pairs to 'dead hubs' that spin freely on those shafts (bearings not shown). Functionally there are four shafts, but two are hollow and co-axial with the solid shafts. It makes for a compact package! Open up an R/C servo sometime; that gear train is very similar in design.

Q: And how is the first sprocket fixed to the motor shaft? With a key stock?

A: I don't have an AmpFlow box here in the shop to verify, but since the motor shaft has a keyway it makes sense to key the first sprocket to the motor shaft. The final sprocket and output shaft are machined from one chunk of steel.

Q: Hello Mark, it's the Deadblow to beetleweight guy (yet again) with another question. I have come to the conclusion that having an ineffective active weapon for my first robot is probably a bad idea. However, using the toy chassis I have come up with a "new" idea and need answers to help with some reoccurring problems.

For this design, I would like to build an invertible wedge similar to what 'Tornado' used in their fight against 'Gravity'. What components and equipment would I need to build a wedge like that to attach to the front of my 'Deadblow' chassis?

Also, when I was designing the axe robot, you said Fingertech "Silver Spark" 22:1 gear ratio motors would be fine for drive power. Which motors should I be using to get more speed and/or torque for a four, exposed wheels, invertible, wedge design? Thanks-Luke [Alabama]

A: [Mark J.] Maybe I'm just in a bad mood today, but I'm liking this conversion of a 'Deadblow' push-toy onto a combat robot less and less.

  • The idea of an antweight hammer "tribute bot" was cool;
  • Then I found out you were building a very small beetleweight and you have no tools or budget;
  • Now the cool hammer has turned into a wedge. The use of this chassis no longer makes sense.
The plastic and 'butter steel' toy is restricting your choices for motors, wheel size, and weapon mounting. You'll be much better off to put the toy back on the shelf and bolt some motors down onto a sheet of Lexan, garolyte, or even thin plywood. Bolt another sheet on top to sandwich your components and find a bent chunk of sturdy metal to attach to the front for a wedge. That removes the dimensional restrictions of the toy chassis and gives you a chance to build something that might survive it's first fight.

Motors: the Silver Sparks were marginal for a beetle but they were about all that would fit in the chassis. Real beetle motors are kind of a problem to buy at the moment. Most builders are using motors they find on eBay by searching for "1000 RPM motor". Individual suppliers come and go -- some of the motors are good and some are awful. You want something that resembles the picture at right: output shaft in the center of the gearbox, preferably 6 volt, price around $10. Most builders run the 6 volt motors at 11.1 volts for increased power and speed.

I still think the Deadblow toy would make a fun little antweight, but you're trying to make too much out of it.

Q: Well,i quit the Battlebots robot idea cause i agree that Battlebots is more of a TV reality show,like when Stinger smashed Mego Tento face TWO times and Mega Tento gets the win.

Anyways... im thinking of buying one of the light weight Battlekits set to compete in the same weight class as K2(i dont know what weight class K2 fights in) Can you compare the Light weight Battlekit with combat robot K2?

A: [Mark J.] You can look up basic information about pretty much any US-based robot via the BotRank Unique Name DataBase. There you will find that 'K2' is a lightweight combat robot from Team Velocity that last fought at RoboGames 2015. Overall record: 38 wins, 12 losses. Currently ranked #3 among lightweights.

The chassis layout if 'K2' is similar to the lightweight version of the BattleKit but there are design and material differences:

Drive Motors:2X 18v DeWalt
Rear Mounted
2X 'short' Ampflow
Center Mounted
Frame:1/2" 6061-T6 Aluminum
about 26" by 24" (w/o wedge)
1/4" 6061-T6 Aluminum
about 18" by 16"
Drive:4-wheel, by timing belt4-wheel, by chain reduction
Weapon Motor:S28-150 Magmotor- not supplied -
Wedge:0.33" 6AL-4V titanium- not supplied -
Weapon:S7 tool steel spinner- not supplied -

Q: And can you show me a video of 'Cyclone Bot' that the bot used it self too full potential?
Thanks. [TCRM,Selangor] (Now i dont type our full team name cause im very busy,so yeah :P) [Malaysia]

A: No.

  1. I'm not running a video search service. You can search on-line videos as well as I can.
  2. If you scroll all the way down to the bottom of the BotRank history score for heavyweight robots you'll find two sad robots with scores under 1100: 'Pandemic' and 'CycloneBot'. Neither of them have anything that I could call combat 'potential'.
Pick successful 'bots to emulate.

Q: Are there any R/C cars you can recommend for an antweight hack? [Utah]

A: [Mark J.] We have an entire archive devoted to questions we're answered about Toy Hacks and Kits. Many of the toy hacks talked about there are no longer available from retail sources, but you might find them on eBay. The current crop of R/C toys don't really have much promise for antweight hacks.

Six questions down this page is an extended discussion with a builder hacking a Tonka Trickster toy that is still available from some sources. Aaron had recommended this toy to a builder who wanted to hack a toy just for some backyard 'bot action, but the builder in the recent discussion is modifying the toy for actual tournament use with a full electronics replacement.

Q: How popular is the 12 pound weight class? I want to graduate past ants and beetles but I'm not sure I'm willing to put the money into a 60 'pounder [Virginia]

A: [Mark J.] The table at right shows the number of active robots and fights for popular classes 60 pounds and below as reported to BotRank in the last two years.

NERC has good turnout for hobbyweights at the Motorama and Franklin Institute events in your region, but none of the heavier classes are nearly as popular as the insect classes.

August 2014 to August 2016
1 pound2961,770
3 pounds2681,566
12 pounds2994
30 pounds26130
30 (sport)27146
60 pounds2284

Q: I've been browsing around, and for some reason I cannot find a hub that can connect a Team Whyachi M3R gearbox to a 5"x2" Colson wheel. Do you know of any or will I have to find a different wheel? [North Carolina]

A: [Mark J.] If you're paying $1400 for a pair of gearboxes I think you can afford to have Team Whyachi make a pair of custom hubs for your Colsons. Drop them a line and ask if they have a design on file -- I'd guess that they do. If not, sketch up a drawing and send it in with your gearbox order.

What are you building that can use just a 2:1 gear reduction with 5" wheels?? The M3 gearbox is a useable 7.14:1 ratio, but the M3R is only 2:1 and is usually used for weapons or with an auxilliary chain reduction -- not direct-driving a wheel.

Q: Well, I was going to use the TWM3Rs for a 250lb robot, but the guys on r/battlebots already let me know that they're not sufficient for drive. I've decided to switch to TWM3Ms

As for the hubs, I'd rather use off-the-shelf parts due to availability.

A: Building with whatever's available 'off-the-shelf' isn't going to get you accepted to ABC BattleBots. Best luck.

Q: Thanks for your tech support, I design a drum bot for the 2016.9.15 FMB(Fighting My bots) in Shanghai, I will send the video to u after the match : ) [Yunnan, China]

A: [Mark J.] Awesome! I don't often get to see the robots from builders who seek our guidance. Thank you, and best luck at the tournament.

Comment: It`s my drum spinner build video : )

A: Wow -- it looks first class to me! Get in some driving practice and you'll be set. Looking forward to seeing the tournament video.

Q: So, apparently some of the people on Reddit got the smart idea to build 250 antweights and enter them into battlebots as a single entry. Now, I know that's most likely a bad idea, but how bad of an idea do you think it is? [North Carolina]

A: [Mark J.] It's bad on many levels.

First - you can't have 250 simultaneous users on 2.4 GHz spread spectrum R/C. The bandwidth tops out around 80 users - depending on the specific system. Whether it's a good idea or not, it just won't work.

Second - ABC BattleBots is all about violent destruction. They aren't going to accept an entry that would fight like termites nibbling at a log.

Assuming you could overcome those deficits I think you're still sunk.

  • There isn't physical room around a heavyweight for that many attackers;
  • Ants don't have the speed to keep up if the heavy wants to 'run and gun'; and
  • Ant weapons just can't make any headway against any part of a heavy.
Q: Weird Question Aaron - instead of rewinding brushless outrunners I was wondering if stacking the cores and outrunner magnet shells on one shaft and wiring each set of motors core in series would give an advantage over running them in parallel.

The idea would be instead of trying to combine three brushless outputs I would give the three a common shaft and use two end bells for a really long motor. I know the windings of the three motors would increase resistance but that should also allow me to increase voltage to get my current back up where optimal should be?

I figured it would be lighter (one gear reduction instead of a three motor combiner and then a gear reduction).
Only two end bells vice three.

Thanks - Team Boom Bots, Stafford USA. [Virginia]

A: [Mark J.] Why do 'builders want to make things so effing complicated? Complex is the enemy of good.

Buy an outrunner with three times the power of your small motors that runs at whatever voltage you want and be done with it.

Oh hell no!

Q: I like to make things difficult and they don't make a motor in the size and shape I am contemplating.
Thanks :-)

A: Everybody likes to do things their way, but if you like things complex and difficult you're writing to the wrong guy for advice. Two motors on a common shaft isn't a bad plan to eliminate a 'combiner', but adding a third motor and series winding the whole stack is asking for grief. Best luck.

Q: So I've been looking at the 'Tonka Tricksters' Aaron recommended in the archives however several of the reviews seem to complain about the range of the toy. They claim the signal drops at around 5 feet from them.

Now, with the goal of hacking it into a bot, I can live with a range of five feet. However, won't the signal worsen once it's put inside a lexan box? Would it still receive input? [Roseville, California]

A: [Mark J.] Lexan is just as transparent to near IR as it is to visible light. You'll be fine.

Q: So I went out and ordered one, and the reviews were not exaggerating about the range. It performs well enough but the range, especially around other objects drops drastically. I've tried running it next to some other R/C toys and the signal becomes real spotty around them. I'm not sure how to send you pictures of it, but inside the toy, the IR receiver is actually pretty separate from the rest of the electronics. Any tips to increase range? How feasible would it be replace the transmitter and receiver with an FM one? [California]

A: [Mark J.] Control range on these toys seems to vary from one to the next - I've seen examples of these toys with very good range. Get that receiver exposed -- you want line-of-sight between it and the transmitter. I'd also pull the transmitter apart to make sure the IR emitter is correctly mounted. Here's a tip: human eyes can't see the IR signal, but digital cameras can! Point a cell phone camera at the transmitter and you can see if the IR light signal is strong and pointed in the direction you asssume it is.

If you can't get the range you need, you can replace the control electronics with hobby grade radio gear. You'll need a pair of motor controllers as well -- the simple H-bridge toy controller's won't interface to the radio receiver output. Very simple and inexpensive motor controllers like the VEX 29 would be great. You'd gain improved speed control sensitivity along with improved range and reliability.

Q: Exposing the transmitter gave me improved line of sight range, but that's about it: line of sight. Even having the bot facing away from the controller is causing some problems.

A: The technology is the same as your TV remote -- the receiver has to be able to 'see' the signal, or at least see a surface illuminated by the light. I'm not sure where the IR receiver is on the chassis but I'd consider moving it to a prominent location on top of the toy/bot.

Q: Okay, assuming I plan to modify the car to an FM radio, is there any specific receiver and transmitter you could recommend? I have a quite a few hobby grade R/C cars; could I use their receiver and transmitter instead?

A: I'm assuming that your R/C car transmitters are 'pistol-style' rather than 'twin-stick'. That adds a little complexity because your 'bot requires a separate channel to control each of the two drive motors. Your 'trigger' throttle could control one motor and your 'wheel' could control the other, but coordinating the two to drive the 'bot would be a nightmare.

There is a solution: you can purchase a 'V-Tail Mixer' that will sort out the inputs from the two transmitter channels and send the correct information to each motor controller -- with this interface you can drive the 'bot just like an R/C car. If you're used to a pistol-style transmitter this is a good option. Your local hobby shop likely has these in stock.

Q: So if I have the diagram from your FAQ correct, it's drive motor to motor controller, motor controller to v tail mixer, mixer to esc, then esc to receiver? Anything I'm missing before I actually purchase the parts?

A: Motor controllers are ESCs -- you've got them in there twice. I like to start with the battery and follow the power:
  • Battery to receiver;
  • Receiver outputs to the V-tail mixer;
  • V-tail mixer outputs to the VEX 26 ESCs;
  • VEX outputs to the motors.
The VEX 26 ESCs are unusual in that they pull their power thru the receiver rather than directly from the battery. That makes the wiring diagram a bit unusual.

Once you get everything hooked up you may find that some adjustments are needed to get the control response correct. The Run Amok Transmitter Programming Guide has a section on sorting out mixing problems that will step you thru the process to get everything right.

Q: Okay, final question (Hopefully): The battery charges via a connector soldered onto the main logic board. Once all the new radio equipment is in place, how do I charge the battery?

A: I'm really trying to keep this from being a 'just one more thing' project. If we're not careful there won't be anything left of the original toy and we might as well have started with a blank slate. You have several options:

  • You can save the original transmitter and 'logic board' and clip the original battery leads back onto the battery in the robot to charge. Awkward, but it will work.
  • You mention that you have some hobby-grade R/C cars. Perhaps you have a charger that would be suitable to recharge what I assume is a very small 6 volt NiCad?
  • You can remove the existing battery pack and substitute AAA cells, allowing you to replace rather than recharge. Four AAA alkaline cells would last a full tournament and then some.

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.
Killer Robot drawing by Garrett Shikuma

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