1383 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 2002 my son and team member Aaron Joerger (now 17) requested a question and answer page to document our responses. Aaron answers most of the questions, but I'll step in if it gets very technical.

Aaron Joerger holding trophy at TLC Discovery Robotica, 2001
Aaron at Robotica - 2001
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Recent questions and Aaron's answers will be posted below. Answers to hundreds of older questions are in the searchable Ask Aaron Archives. Need a quick answer? Browse the articles at the Combat Robotics Wiki.

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TopRecent Questions

Q: What happened to Juilo Roquetta of Team Loki? I saw an "in memory" for him at the bottom of the Builders Database.

A: Mark J. here: it's probably best described as a traffic accident. He got out of his car at a traffic light very late one night to argue with some guys in another car. The driver of a third car didn't see him and hit him. Let's all be careful out there.

Q: Hey Aaron, is there a motor with a RS-385 mount-hole pattern? I need the same speed and torque too, but at 1.5 oz instead of 2.5 oz. Thanks.

A: If there was an exact replacement for the RS-385 that was 40% lighter, why would anyone use the RS-385? No such motor -- look for your weight savings somewhere else.

Q: Hi Aaron, great site. In your archives you mention that the main difference between a drum and a beater is the inertia each can wield. Does that that mean there are no advantages in the structure or shape when it comes to a hit?

A: With a weapon rotating at operational speed there is no advantage to the eggbeater structure on impact. The weapon is rotating so fast that penetration of the opponent into the weapon before impact is a small fraction of an inch. A shallow impact bar on a drum is every bit as effective as the eggbeater bar.

There are several posts about eggbeaters and drums in the Robot Weapons archive that deal with construction, rotational speed, and impact bars. The question you reference came in after the other posts and asked if the two designs didn't basically do the same thing, and my answer generated a good deal of off-line discussion.

To clarify my original statement, a drum weapon the same weight and diameter as an eggbeater will have greater rotational inertia. Someone pointed out that an eggbeater can be built to a larger diameter and have the same mass as a smaller drum and therefore have greater rotational inertia. This is true, but it just points out the trade-offs and complexity of weapon design. Generally speaking, an eggbeater is simpler to build but a drum is more effective.

Q: I was looking at your Combat Robot Hall of Fame and I was wondering why 'Little Drummer Boy' isn't in the Hall? LDB was very impressive in its rookie season going all the way to the finals. Granted season 4 and 5 it didn't fare to well. Also, why isn't 'Suicidal Tendencies' in the Hall?

A: Mark J. here: I don't get to pick who is or is not in the Hall of Fame -- I just collect the votes. Every two years, voting is opened for the Hall. Announcements are made on the Delphi robot combat forums and on the Fighting Robot Association forum. I tally the votes and announce the results. The Hall first opened for voting in 2003, and I do not recall ever receiving a vote for either 'Little Drummer Boy' or 'Suicidal Tendencies'.

Q: Did the winners of a Battlebots event get to keep the giant nut trophys? Did the runners-up get any trophys?

A: Yes, BattleBots winners in each weight class were awarded their own personal 'giant nut' trophies to keep. Other 'giant nuts' were awarded to runners-up, winners of the rumbles, and for several other categories that sometimes changed from event to event: 'Best Driver', 'Most Aggressive', 'Coolest Robot', 'Funniest Robot', and 'Best Newcomer'. I show a total of 94 giant nuts awarded.

Q: Did you ever have any thought about entering BattleBots before there was a Robotica?

A: Some.

Q: With Battlebot possibly returning, do you think some of the old Battlebot teams will also return?

A: I would be surprized if the old crews are not well represented.

Q: Do you have any pictures of 'Panic Attack' from Robot Wars series 2-7? What happned to Panic Attack after Robot Wars?

A: 'Panic Attack' is a member of the Combat Robot Hall of Fame and we have a picture there. A Google image search for 'Panic Attack Robot' turned up plenty more photos.

I haven't heard anything about Panic Attack since the Seventh Wars. Kim Davies (captain of Team Panic Attack thru series 6) hangs out at the Fighting Robot Association forum so I suspect any recent developments about Panic Attack are discussed there.

Q: What would be some Pros and Cons for an axe weapon and a spinner weapon?

A: Suggest you find a copy of Combat Robot Weapons by Chris Hannold for a good discussion on weapon pros and cons. Very briefly:

  • Overhead axe weapons can attack the usually weaker top armor of an opponent but must accelerate the weapon to high energy levels in very little time.

  • Spinners can more slowly build up kinetic energy in the rotational mass of their weapon for a devastating impact, but must deal with gyroscopic forces and the large 'kickback' from their own weapon.

Q: Do you think BattleBots will go down as scheduled this April? I hope the event becomes a success.

A: Mark J. here: beats me. I've stopped believing any of the information that comes out of BattleBots because so much of it proves to be false. Their actions over the last several years have not, in my opinion, been good for the sport. I wish them well, but will not become involved.

Q: I read that Razer, Panic Attack, and Mortis competed at BattleBots. How did they do?

A: Six UK Robot Wars teams entered a total of eight heavyweight robots in BattleBots competitions:

  • Long Beach 1999: Killerhurtz and Razer
  • 1999 Pay-per-view: Killerhurtz, Razer, and Mortis
  • BattleBots 1.0: Suicidal Tendancies and Killerhurtz
  • BattleBots 2.0: Bigger Brother, Suicidal Tendancies, Panic Attack, and Killerhurtz
  • BattleBots 3.0: Little Sister and Killerhurtz
  • BattleBots 4.0: Little Sister and Killerhurtz
  • BattleBots 5.0: Little Sister and Warhead
They had an overall record of 28 wins and 19 losses. You can trace the progress of individual robots thru the tournaments in our collection of complete tournament trees for BattleBots and other major tournaments.

Q: What happened to Killerhutz after season 4 of BattleBots?

A: Simply retired, I believe.

Q: Had 'Son of Whyachi' still been a legal heavyweight do you think it could have beat 'Warhead' at BattleBots 5.0?

A: I don't predict fantasy matches, but it would have been fun to watch.

Q: Why did Son of Whyachi do so poorly in the SHW division?

A: Beating up a 220 pound robot is a lot easier than beating up a 340 pound robot. Most people don't remember that at the same tournament where 'Son of Whyachi' won the heavyweight championship, stablemate 'Whyachi' competed in the superheavyweight division and had only a 1 win 1 loss record in spite of it's 'shufflebot' weight advantage. Spinners never did all that well in the SHW BattleBots class.

Q: Hey Aaron, any idea on what the motors and gearboxes are in this picture (third down on the right)? Where can I buy them? Thanks.

A: Terrible photo, but I'm pretty sure they're Mini-EV Warriors. You can buy them at Robot Marketplace. The spur-gear reduction drive units shown are custom.

Q: What does 'Domore' do any way?

A: More than 'Dolittle' but not as much as 'DoAll'. The main weapon was a pneumatic spike, but it could also spin. You have to remember that robot combat was new in 1995 and nobody knew what was going to work.

Mark J. here: the following set of questions was sent to me in a personal email. I think the answers would be of general interest so I've reprinted my responses here, with permission from the author of the questions:

Scott LaValley's 'Domore' Q: First off, I got to say you have nice website. Do you know of any pictures of Scott LaValley's 'Dolittle'? I know it competed in US Robot Wars 1994.

A: Thanks for the appreciation. I did a lot of research on the early robot wars, and photos of the robots from the 1994 event are hard to come by. I don't have a photo of 'Dolittle', but I do have a photo of Scott's 1995 entry 'Domore'.

Q: On YouTube there are several videos from the early Robot Wars events. Do you wish the UK version stayed truer to the original US version?

A: The very early UK Robot Wars really were pretty close to the spirit of the US Robot Wars. The show producers had to adapt to what their television audience wanted, and they seem to have wanted direct combat. Some of the Techno Games events went back toward the original Robot Wars idea, but that show just wasn't as popular as the all-combat format. Personally, I really enjoy some of the non-combat events. I tried to emphasize that in the Antbotica events that Team Run Amok put on.

Q: Did any teams that competed in Robot Wars: Extreme Warriors compete in the early US Robot Wars? The only one I think did was Mike Regan.

A: There were three US Robot Wars competitors at RWEW:

  • As you note, Mike Regan (1997 'Vicious-1') was at RWEW1 with 'The Brute';

  • Patrick Campbell (1994 'TMZ', 1995 'Cyberknight', 1996 'Terminal Frenzy', 1997 'Frenzy') was at RWEW2 with 'The Bat';

  • Dan Danknick (1996 'The Agamemnon') was at both of the RWEW series, not competing but working technical support for the event;

There were some other interesting tie-ins between US Robot Wars and later UK Robot Wars events:
  • The Tilford Clan (1996 'South Bay Mauler', 1997 'Mauler') entered a Robot Wars tournament filmed in 2000 in England as a pilot for a show for MTV. The deal didn't fly and the footage was never shown. Andrew Lindsey (1996 'Spike', 1997 'Spike II'), Patrick Campbell, and Dan Danknick were also there.

  • Eric Dickerson (1996 'WYSIWYG') became involved with the UK Robot Wars productions. 'WYSIWYG' appeared in the 1997 UK Robot Wars driven by Michelle Wheeley.

That's all I can think of, but I may have missed someone.

Q: Why did the Bigger Brother team change the bot's name for BattleBots? 'Killerhurtz' was still competing with it's original name until season 5.0 when he entered his new robot 'Beta'.

A: There was considerable confusion about legal rights to robot names between events. The contracts signed by competitors at BattleBots and Robot Wars events appeared to transfer certain rights to use of the names to the producers of the shows. Some competitors chose to avoid any possible conflicts by changing robot names and appearances when competing in different events, and some chose to ignore the whole issue.

Q: What UK Robot Wars team would have done good in Battlebots?

A: Robot Wars and BattleBots were very different events. Many Robot Wars competitors built flippers designed to throw their competitors out of the arena -- something not possible at BattleBots. Other Robot Wars competitors would suffer badly if they went up against destructive spinner weapons -- odd how 'Razer' never had to fight such a robot, isn't it? I don't like to play 'fantasy match prediction' with robots, but I suppose 'Tornado' would be a good pick to have done well at BattleBots.

Q: Dear Aaron, I've found a mini hydraulic sytem at gardentrucking.com. Tthe system has almost 40 pounds of force. Would this be a good system for builders who want to make a crushing weapon, or would a cordless drill and gearbox hooked up to a worm gear or screw and conected to a claw be better. Please help. [Anthony]

A: That mini hydraulic system is expensive! A pump, cylinder, valve and assorted lines and fittings looks like about $700, and they don't give you the weight of the system or the volume output of the pump.

Crushing weapons require a great deal of force and very strong chassis, The crushing pincer on Robot Wars heavyweight champion 'Razer' had 18,000 pounds of force -- 100 times it's own weight! So, 40 to 60 pounds of hydraulic force is not going to make much of a crushing weapon and neither is a geared-down drill motor.

Q: Would it be an effective crushing system on an antweight? Would I be able to multiply that 60 pounds of force with a lever like 'Razer' did when there cylinder force was 3 tons and now the tip of the claw has 9 tons? Sorry for bombarding you with questions -- I just really like this sport. I can't help it!!!

A: If I didn't like questions, I wouldn't have this site, Anthony!

There are a couple problems I see with using this system in an antweight:

  • Although the component weights are not given, the dimensions are. The pump alone is 6" long and 1.5" in diameter. That looks like a RS-385 motor powering it. I'd guess the pump alone might weigh half a pound. You wouldn't have enough weight allowance left to build a robot strong enough to withstand the force of it's own weapon.

  • Gardentrucking supplies components for builders of scale trucks and construction equipment. These builders are after realistic lifelike performance from the hydraulic system, and in this case lifelike means 'slow'. Adding a force-multiplying lever system to would slow this down even more: three times the force means one-third the speed.
In short, the gardentrucking mini hydraulic system is too heavy and too slow to be the power source for an effective antweight crushing weapon.

FingerTech's Viper Antweight Kit Q: What's your say on the Viper starter kit by FingerTech? Worth it? Good for an ant with a servo lifter?

A: I'm quite skeptical of the suitability of the FingerTech kit for combat:

  • The kit features a "6-Channel radio transmitter and receiver pair", but they don't say which radio it is.

  • I don't know anyone who has used the FingerTech "tinyESC" motor controllers or gearmotors.

  • The "sporty vacuum-formed lid" certainly does not qualify as 'armor'.

  • There are reasons you don't see robots using 9-volt alkaline batteries for power in combat. The 9-volt battery is not designed for high amperage draw. They can only deliver about an amp each, with a significant voltage drop at that power level.

  • FingerTech mentions that the chassis is aluminum, but they do not mention the alloy used or the thickness.
I'd ask FingerTech a lot of questions before I bought, and I'd be ready for some extensive upgrades to get the little bugger 'combat ready'.

Q: I'm not sure about some of the parts, but the motors in the kit are the discontinued 54:1 Banebots 16mm gearmotors, and the receiver appears to be the vertical pin variation of the GWS pico receiver. Also, I have used the TinyESCs in my ant wedge driving two 17:1 Maxons each and they work great.

A: Thanks for the info, but that still leaves a number of issues:

  • If the motors are the discontinued BaneBots 16mm spurgear units, you'd best buy some spares while you still can.

  • The receiver pictured does appear to be the GWS pico, but that doesn't mean that's what you'll get with the kit -- it's unspecified. The transmitter is not pictured or mentioned.

  • The price of a pair of the 'TinyESC's (one with BEC, one without) is $58.65. For another $1.34 you can buy a Sabertooth 5 RC Dual Motor Speed Controller with greater current capacity, a flip channel, mixing, exponential control, and a proven track record. Guess which one I'd buy?


I've exchanged emails with Kurtis Wanner of FingerTech Robotics. He has provided some details on the Viper Starter Kit that he says will be added to the website soon:

  • The transmitter provided with the kit is the GWS 6-Channel 75MHz GWT-6A. This is a very basic transmitter -- no mixing, throttle volume, or exponential response.

  • The receiver is a 6-Channel MKS that uses standard crystals.

  • The motors are the discontinued BaneBots 54:1 gearheads on FF-050 motors. FingerTech is looking for a continuting source of similar gearmotors to fit the Viper chassis.

  • The 'Tiny ESC' units are very basic, but are also very small (tiny) and very light (8 grams for the pair). I'm not sure how much that helps you with this kit that has plenty of space and weight allowance.

  • The chassis is 5052 aluminum, 1/16" thick.
Offering an antweight combat robot kit for under $160 does call for some compromises, and FingerTech has shaved every dollar to meet this low price point. Kurtis defends the use of the 9-volt alkaline batteries for power, citing that they have proven adequate in testing. I've run some calculations and found that a pair of fresh, high-quality 9-volt batteries can provide marginally enough amperage for the twin FF-050 motors and a lifter servo. Perhaps they are adequate for a low-budget starter package?

I'm not a fan of 'going cheap' and buying robot parts you'll need to upgrade to move upward in robot combat, so I would have made some different component choices. Based on retail component prices, another $20 would upgrade the kit to a Scorpion ESC and a Spektrum DX5e radio that would be useful in the next robot you build and that would retain good value when you did sell them to upgrade further. Still, with this kit you'd be able to simply and quickly put together a robot platform that you can tank-steer around under radio control. Add a simple wedge or servo lifter and you could get into competition for a rock-bottom price.

Q: BattleBots registration is open on Builders DB What do you think? Are you gonna enter 'Run Amok'?

A:Mark J. here: I'm always pleased to see another robot combat competition added to the calendar. However, there have been many false starts and a great deal of misinformation circulated about the return of BattleBots, and many builders have been alienated by the actions of the organizers. I wish the event well, but we will not be entering a robot.

Q: I'm thinking of building a beetleweight with a vertical spinner. What type of metal do you think I should use for the structure?

A: Hard to comment since I have no idea what type of structure you plan to build, what your budget is, or what tools and skill level you have. In general, aircraft aluminum alloys like 6061 are popular for structural elements.

Q: Would the components from the 'Advanced Antweight Starter Package' from Robot Marketplace be good for a beetleweight?

A: I don't think the Advanced Antweight Starter Package is good for an antweight, let alone a beetle. The radio is not current specification, the charger is really marginal, and the power supply is overkill. The actual robot components are not a kit but just a collection of pieces without a plan or instructions. The motors, hubs, speed controller, battery, and wheels are fine for an antweight but there is no chassis -- just a pile of assorted carbon fiber pieces. An experienced builder could turn this pile of pieces into a functional antweight, but unless you plan a beetle with a huge weapon that you just want to push slowly around the arena it just wouldn't work.

Q: Can I connect batteries having different current ratings? They are same type ones.

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

Q: What is GPS?

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

Q: Is there any more Robot Wars Extreme Warriors clips coming in on youtube yet?

A: We are not involved in posting copywritten material on the internet and we have no knowledge of the actions of those who are.

Q: We are working on a research project for the Space Elevator. We are using a A28-150 Ampflow motor . Any recommendations on what type of motor controller to use? I'm pretty new to all this and don't know where to start.

A: Mark J. here: climbing a ribbon is a little different than combat robotics, but I think I can point you in the right direction.

Ampflow A28 torque/ampere graph A few basics: you're controlling speed on a single motor and I assume you will want to control it in both directions (forward/reverse), so you will be looking for a single-channel dual-direction permanent magnet DC controller. A key factor in motor controller selection is knowing how many amps of current the motor will be consuming, and for how long. For example, here are the ratings for a popular line of robot controllers:

  Max Surge 30 Seconds Continuous
RoboteQ ax1500XC 250 amps 60 amps 40 amps
RoboteQ ax3500 500 amps 120 amps 80 amps
RoboteQ ax2550HESC 1000 amps 280 amps 160 amps

If you exceed the maximum surge rating of the controller it will likely destroy the device. Exceeding the 30 second or continuous ratings will (for the RoboteQ and most other controllers) cause the controller to cut back the amperage output and reduce motor power.

The S28-150 Magmotor, like all permanent magnet direct current motors, consumes amperage in direct linear proportion to the torque it is producing. At zero (free running) torque, the motor draws only 3.5 amps. At maximum efficiency the motor produces one horsepower and draws 37 amps. At peak output the motor produces three horsepower and draws about 185 amps. At maximum (stall) torque, the S28-150 motor can draw close to 375 amps.

Once you have examined the torque demands your design will place on the motor, you can match up the amperage demands to a suitable controller. It does no particular harm to go 'overkill' here -- better to have a controller with too much capacity than too little.

Q: If Robotica came back, what would be the best Robot Wars full-body spinner to enter?

A: Terrible idea! 'Robotica' and 'Full-body Spinner' go together like 'Ice Cream' and 'Anchovies'. In three seasons of 'Robotica' nobody entered a full-body spinner and no sane competitor would. Even die-hard spinner builders like Brian Nave and Terry Ewert built non-spinners for 'Robotica'.

Q: I plan to use a two wheel differential drive for my 22 pound robot. What motor specification should I use for my drive?

A: Mark J. here: I guess it's time to put this question in the FAQ . The motors you will need depend on the style of 'bot you're planning to build and your expectations. A 'bot with a massive weapon that just needs to push itself around the arena will need a lot less drive power than a ramming brick or wedge. It comes down to matching the power-to-weight ratio of your 'bot to the type of attack strategy you're planning.

Rule of thumb: 4 watts of drive output power per pound of robot will adequately maneuver an active weapon robot around the arena. Rammers and fast wedges require about 16 watts per pound.

Some maniac builders pack as much as 40 watts per pound into their 'bots, but there really are limits to how much power can be used in a small arena. I've built three champion robots on the 4 watts per pound formula, so please don't tell me that it can't be done.

If a motor supplier does not provide output power numbers for their motors, you can get an approximation of output power with the following formula:

Peak Output (approximate watts) = Voltage * Stall Amperage * 0.25

You'll find the Team Tentacle Torque & Amp-Hour Calculator very useful in selecting motors for your robot. It has data on all popular motors and will quickly calculate the performance of your robot with any motors, gearing, and wheel size you choose.

NiMH discharge voltage chart Q: What is the voltage where NiMH batteries don't work properly?

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

Chaos 2 Q: Which machine did you like best in Robot Wars UK?

A: Chaos 2.



Q: Should I buy a motor having high torque or high RPM for a spinner weapon??

A: Either will have to be geared down to perform well with most spinner designs, but it's generally easier to work with a high torque motor. This is why the high-torque 'outrunner' style brushless motors are popular for spinner power. High RPM means high gear reduction and potential problems keeping drive belts in place on small drive sprockets.

Q: Hey Aaron, can you use stepper motors to drive an ant or beetle?

A: Not a great idea. Commonly available stepper motors are a type of brushless motor designed to rotate in precise increments to position something accurately -- like the read/write head on a disc drive. They require special driver circuits and are not designed for high power output.

When brushless motors were first being used in model airplanes, some hobbyists found ways to convert specific stepper motors for aircraft applications. Now that brushless motors designed for the purpose are widely available there is no need to go thru the trouble. I'd suggest sticking with more conventional motors.

Q: What kind of wheels should I use to make a mousetrap car for speed: big or small? Thin or thick? CDs or toy tires?

A: Why do people write to a combat robot site with mousetrap car questions?

Most mousetrap cars are designed for distance, not speed. The best distance moustrap cars creep forward very slowly -- speed is inefficient. For distance you want large, skinny wheels like CDs or even old LP records.

If you're building for speed you have other considerations. If it's a drag race style event for lowest time over a fixed distance you'll want the entire energy of the moustrap to expend itself in about the first 3/4ths of the course and then coast the rest of the way. Size the wheels accordingly. The tires will need enough traction to avoid power-wasting wheelspin, so some type of rubber tire may be needed. Experiment!

You can find more help for mousetrap cars of all types over at the Doc Fizzix website.

Q: Are there any drill motors that weigh no more than 8 oz? I need the ones with the motor attached to the gearbox.

A: I don't have a weight chart for drill motors with attached gearboxes, but BaneBots planetary gearmotors come in a wide range of sizes and start at under 3 ounces. Their 28mm planetary gearbox with RS-385 motor weighs in at less than 6 ounces.

Q: Several times in your archive you state that you feel that polypropylene is inferior bot armour. Could you elaborate?

A: Mark J. here: I believe I only say that only once. I consider it to be inferior to other plastics like polycarbonate or UMHW polyethylene and I have numbers to back that up. Take a look at the table below: the mechanical properties of polypropylene are far below those for polycarbonate. Both polycarbonate and UHMW polyethylene have much greater ability to absorb impact without failing, as shown in the 'Tensile Elongation' and 'Izod Impact' tests that reflect the 'toughness' of the material.

  Polypropylene Co-Polymer Polycarbonate Polyethylene UHMW
Density (lb/in3) 0.033 0.043 0.034
Tensile Strength (psi) 4,800 9,500 3,100
Tensile Modulus(psi) 195,000 320,000 125,000
Tensile Elongation (%) 23 60 No Break
Flexural Modulus (psi) 160,000 375,000 125,000
Compressive Strength (psi) 6,000 12,000 2,000
IZOD Impact (ft-lb/in) 7.5 13 No Break

In thin sections for an insect class robot polypropylene can be put to good use. I've used it myself for my antweight 'Rat Amok' because I happened to have a polypropylene box just the right size for my purpose. If I had a polycarbonate box that same size, I would have used it instead.

Q: What is the best motor rating for a spinner weapon? My weapon weighs 3 kg and bot weight is 10 kg.

A: See the FAQ, about 20 questions down. A good place to start with a weapon around that size would be the brushless Axi 4130/16 or the DeWalt 18 volt drillmotor.

Q: I've built a spinner weapon similar to 'Son of Whyachi'. It weighs 7 lbs. The total bot weight is 22 lbs. What is the ideal motor rating for my weapon? The maximum voltage I can use is 24 volts.

A: More power is better for a spinner motor, so 'ideal' is as much power as you can reasonably get. The Axi motor I referenced above would be a good choice. Geared down about 3:1 and running at 24 volts it would give excellent performance. Use the Team Run Amok Spinning Weapon Excel Spreadsheet to check performance of your specific weapon with various motors.

Q: What is the best way to keep NiMH batteries?

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

Q: What is a good RC toy to hack for a Fairyweight combat robot?

A: With only 150 grams of weight allowance, you don't have many choices. I've seen a few fairyweights made from the standard Micro R/C cars, like Mouseasaurus, but they are pretty weak. Pivot steering and gearing for speed over torque makes for a poor fairyweight.

I haven't had a chance to play with one, but the Air Hogs Zero Gravity Micro looks like it could make an interesting combat robot. It has differential steering and a suction fan to stick it down to the arena surface. The problem is the infrared R/C controller: they don't work very well in sunlight or thru Lexan arena walls. Some event organizers may not allow their use. Check with the event you'll be entering: if they'll let it run I'd give it a try.

Q: Can a Speed 400 motor fit a Whyachi T-box gearbox? Where can I buy gearmotors that are 1.25" square?

A: The Speed 400 motor has different mounting hole spacing than the Whayachi gearbox, and the gear reduction is not correct for the Speed 400. The BaneBots 28mm gearmotors are 1.1" wide and high by 2.8 inches long.

Q: What were the most controversial robot battles?

A: Two pop to mind:

  • Tornado vs. Razer in the Sixth Wars final: Tornado won by use of a special 'anti-crusher' framework added to their robot to keep Razer's piercing crusher away from vital parts. The device was pre-cleared with the technical crew, but many fans were outraged.

  • Biohazard vs. Son of Whyachi in the BattleBots 3.0 heavyweight final: SoW used a rule-shaving 'shufflebot' propusion system to gain the additional 'walker' weight allowance for their monster spinner. The fight was tremendously destructive with both robots taking major damage. The judges' decision went to SoW, but a lot of fans saw it differently.

Q: What do you think about the fan-made Robot Wars series on YouTube?

A: I remember being 8 years old and playing with Legos and a box on my bedroom floor. Why anyone would want to watch videos of someone doing this puzzles me.

Q: Hi. My beetle horizontal mid-cutter had its bar mounted to a 1/4" live shaft by an M Type Shaftloc. At a recent event I had a weapon to weapon collision with a drum. The nut on the Shaftloc was ripped off, stripping the threads and making the entire thing useless.

At Motorama I'm going to run it as an undercutter. What other similar components could I use for mounting the weapon to the shaft? I could use the Shaftloc again since an undercutter won't be taking the same kind of vertical hits, but I'd rather use something more proven and reliable. Thanks.

A: Mark J. here: you don't have a lot of options for securing a hub to a live shaft that small. Hobbyweight mid-cutter Fiasco uses a custom hub that clamps the blade in place and is held to the shaft with four set screws. I'm not a fan of set screws! Given the options, your current solution may be the best choice; it sounds like that hit you took would have broken something else if the Shaftloc hadn't failed.

The most reliable method of securing a hub or other item to a round live shaft is to broach a keyway into the shaft and the hub and inserting a key to prevent rotation. This isn't practical for a 1/4" shaft, and neither is cross-drilling a hole thru the shaft and hub and inserting a hardened pin. I recommend using a dead shaft in insect class spinners for just this reason.

Q: Out of the fights that you guys have been in with 'Run Amok', 'The Gap', 'Zpatula', and the others, what was your favorite fight?

A: We liked all the fights we won -- hated all the fights we lost. The final platform match at Robotica had to be the best.

Q: I remember watching the USA Robot Wars series and seeing 'Matilda' with her chainsaw tail that she stopped using after UK 4. I understand that it is interchangable, but how come she kept using it in parts of the US series and never in the later British series?

A: Once Matilda switched to the very effective flywheel weapon in the late summer of 2001, the weapon was never changed out for the old chainsaw.

The first series of 'Robot Wars Extreme Warriors' for US competitors was filmed in June/July, 2001 and Matilda was still using the chainsaw tail. This was after the UK 'Fourth Wars' and before the 'Fifth Wars' filming in August 2001 where Matilda appeared with the flywheel weapon.

The second series of 'Robot Wars Extreme Warriors' for US competitors was filmed in January, 2002. Matilda was still using the chainsaw weapon here, so the chainsaw was used in RWES series 1 and the flywheel was used in RWEW series 2.

Q: My team has an Ant/Beetle Arena (6'x6' fully enclosed by 1/4" Lexan) that we carry about for various fights. The destructive power in these weight classes has increased dramatically since this thing was built. For a spinning type weapon, at what kind of energy would you start to be concerned for survivability of the arena & safety of the drivers/spectators?

Love the site. [BDsquint- FOBOT]

A: Mark J. here: thanks for the love, BD.

We both understand that the integrity of an arena depends on more than the thickness of the Lexan. The type of framing and fastening is critical in determining how much abuse an arena can put up with. That said, a well-constructed arena with 1/4" Lexan walls should keep you well ahead of beetleweight spinners for some time to come.

I can't give you a specific number of Joules beyond which I'd start to worry, but it's unlikely that your containment will fail abruptly and catastrophically. Lexan will deform and absorb a really enormous impact. You'll notice severe marring and obvious damage to the polycarbonate well before there is danger of a breach. As long as your framing keeps the edges of the Lexan from parting, you'll have plenty of warning when spinners get close to dangerous energy levels.

Many arenas have a 'bumper strip' of material set in just a bit from the polycarbonate walls about spinner-high. This dissipates a good amount of the energy from a spinning weapon before it can reach the outer wall. Good idea!

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