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4731 Questions and Answers about Combat Robotics
from Team Run Amok
Ten Years of Ask Aaron

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

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

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

Caution   Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot. Do not operate combat robots without proper safeguards.
It greatly saddens me to announce that my son, Aaron Joerger, died very suddenly on the afternoon of October 18th, 2013 of an apparent pulmonary embolism. He was 22 years old. Aaron's obituary.

The 'Ask Aaron' project was important to Aaron, and I have decided to continue the site in his memory. Thank you for the many kind messages of sympathy and support that have found their way to me.

- Mark Joerger, Team Run Amok

Welcome to my website Recent Questions

Q: I'm making a drum of 14 cm OD,& thickness of 15mm which makes ID of 11 cm.drum weight will be around 7kg
what kind of bearing should i use for rotation of drum on rod?even if i use 11cm OD bearing it will have a bore of 80-90mm that will increase the size and weight of rod... please help [Maharashtra, India]

A: [Mark J.] There's no need for a huge bearing. Drum weapons typically have machined 'end caps' held in each end of the drum by screws. The end caps have holes to mount bearings of suitable size for the supporting rod.

Weapon drum end cap from Team Cosmos

Q: Mark, is there any real poor sportsmanship in robot combat? I mean like the Battlerat team's reaction after the decision of their fight against Nightmare announced in Battlebots 4.0. Did they really disrespected judges or was that just the magic of editing? [Chinese Forum]

A: [Mark J.] The level of sportsmanship at combat robot events is generally quite high, but I don't believe that any competitive activity is completely free of poor sportsmanship. I wasn't present at the Battlerat vs. Nightmare match and so cannot comment on any editing of the post-match comments, but I have personally seen much worse behavior at combat events. On one noteworthy occaision police had to be called in to calm things down.

One event actually encouraged a bit of poor sportsmanship. Competitors at Robot Wars Extreme Warriors were asked to 'talk trash' and be openly confrontational with their opponents during interviews. The network (TNN) was trying for a tie-in with professional wrestling and had a well-known wrestler as the host. Some teams played along, some didn't, and a few actually got kinda nasty. It really didn't work, and the trash talk was toned down for the second season.

Cartoon Fight Cloud

Q: hi
i want to build a robot for robowars (of my college) the robot should be of 30cm*30cm and no height limit and the weight limit is upto 5kgs the battery shold be of 18volt 5amps
can you give me some advice about what type of robot should i build.
what should be the design [-- Location Confidential --]

A: [Mark J.] A robot must be designed to meet the specific challenges it will face. You've told me a bit about the limitations placed on the robot, but nothing at all about the actual competition and your experience in this area. It's a lot like designing a race car; you'd build a much different car for a quarter-mile drag race than for an off-road endurance event.

Some of the things to consider:

  • Is the event full combat, sumo, an obstacle course, king of the hill, or some other flavor of 'robowar'?
  • What is the design of the arena/course, and how large is it?
  • Are there limits on the types of weaponry that are allowed?
  • How is the event scored?
  • Are there multiple ways to win (immobilizing, pushing out of the arena, pining, accumulating points...)?
  • What is your budget for the 'bot?
  • Is this your first robowars robot?
  • Do you have experience driving remote control vehicles?
  • What workshop tools are available to you, and what is your proficiency with those tools?
  • Will the robot be radio controlled, or will you be using a wired control tether?
If you can tell me more about the event, I may be able to give some suggestions on design -- but I'm not going to design your robot for you. See FAQ #4.

Nickeloden Robot Logo Q: I remember watching Nickelodeon Robot Wars, and I remember seeing Nancy Rodriguez with Loanerbot, 'Tut-Tut'. And questions kept racing thru my mind. Did she and her dad thought about making their own robot for Robot Wars? [Cicero, New York]

A: [Mark J.] I wrote to Mike Morrow of Team JuggerBot who coached Nancy Rodriguez and her dad Carlos in the Challenge Belt competition on Nickelodeon Robot Wars. He tells me that Carlos Rodriguez was the lead technician at WCMS Motors, who supplied custom electric motors to Team JuggerBot. Mike brought them along as honorary crew members for the trip to London in 2002. The teams were encouraged to bring kids along to 'Robot Wars Extreme Warriors' to drive 'bots in 'Nickelodeon Robot Wars' which filmed just after the main competition.

I don't know if the Rodriguezes had any plans to compete with their own robot at a future event, but there have been father/daughter teams in robot combat. See, for example, Lisa Winter.

Q: VestedMadScientist here again, this time with a more technical question. I have a Spektrum AR6210 DSMX receiver and a lightweight battlekit with F30-150s (I also have a Vantec RFDR36R, but that's still in the mail), and I'm a bit concerned with whether or not the aluminum chassis will interfere with the radio signal. Is there an optimal place to mount the receiver, or does it really matter? [North Carolina]

A: [Mark J.] The Spektrum AR6210 manual provides advice on mounting and orientation of the main and remote receivers (yes, a two-piece receiver). Keep the receiver away from electrically 'noisy' devices like the ESC and motors, and don't tape the wire antennas down directly to the aluminum -- space them up on a foam strip. As long as the receivers aren't enclosed on all sides by conductive material (metal, carbon fiber...) you'll get a good signal.

For more radio help, see our R/C Radio Reception Guide: Radio Reception Guide

Q: Also, what do you think about a double-layer of 1/8" lexan (totaling 1/4") as armor? Should I try it or should I just use a single 1/4" thick sheet?

A: I use 1/8" Lexan on my antweights -- I think you're gonna need more than 1/4" for a 'bot 60 times that heavy. Just how much top armor you need is debateable because few competitors build overhead hammer/spike/saw weapons to attack from above. However, they are out there and if you run into one with poor top armor you can find yourself in serious trouble -- video.

Lexan is able to survive large impact because it deforms to absorb the energy. You need to leave considerable room for this deformation between the armor and what you're trying to protect. For your application I think I'd recommend something a little stiffer -- consider garolite. There are several posts about garolite in the Materials & Components archive. And yes, garolite is radio transparent.

Q: Was it difficult to make your robot waterproof for the waterfall at Robotica? [Watertown, Massachusetts]

A: [Mark J.] We didn't waterproof 'Run Amok' -- it wasn't necessary. The top armor was a single, solid sheet that shed water to the edges like a roof. The only vulnerable components (steering servo, receiver, and speed controller) were all tucked up against the top armor and had their own cases that would resist any random splash. None of the 'bots at 'Robotica' had any trouble with the water.

Q: Roughly what magnitude impact force does a powerful bot like Metroid impart on another antweight when it hits it several feet into the air? Is there a way we can estimate this by using the Joules of energy stored from your Spinner Spreadsheet (assuming both bots are very rigid)? [San Diego, California]

A: [Mark J.] I went thru the math for this in a previous post. Search the Robot Weapons archive for "brag about my spinner" to find the post with equations and a diagram.

The numbers from these simple equations overstate the real world performance of the weapon, since it is effectively impossible for a spinning weapon to transfer all of its energy directly into vertical acceleration of the opponent -- but they make for nice brag numbers.

Q: Thanks for referring me to the spinner brag equations. But I was really curious about getting a Force value out of it. Something you could apply to a finite element model or hand calc in order to determine the stress or displacement in your chassis or weapon mount.

A: [Mark J.] Unfortunately, joules of energy don't - in this case - convert directly to force. A heavy but slow moving object might just gently push your robot out of the way, while a fast moving lighter object with the same kinetic energy could deliver a damaging blow. Add to that the many different angles and places of potential impact and many possible values for inertia of the robot depending on the rotational axis imparted by the impact, and you'll get so great a range of theoretical force values (many highly improbable) that the analysis will be useless.

The classic combat robot design advice is to build it strong, and if it breaks make it stronger.

Q: If you need to bolt some things to your Lexan sheets (have read the many posts about only welding Lexan, never bolt), what is the best way to prevent a failure around the hole? should you use a large washer to spread out the load? i want to use about a 8" diameter Lexan piece and have 3 bolts connecting it to it in a triangular pattern near the edges. so it will still have some space to flex between the bolts and in the middle. [San Diego, California]

A: [Mark J.] Lexan plastic (polycarbonate) gains its strength from its ability to flex on impact. Conventional use of bolts will restrict flexing and cause cracking and failure around the bolt hole. General rules:

  • Use as large a diameter bolt as is practical and drill the hole oversize; at least a 1/4" hole for a 3/16" bolt.

  • Do not tighten the bolt down to squeeze the plastic -- insert a tubular spacer so that the bolt may be tightened without stressing the Lexan. The bolt should only locate the Lexan, not squash it.

  • I've had good success using rubber grommets to provide 'shock mounting' that allows the plastic to move a bit without creating local stress.

  • A good sized washer on one or both sides of the bolt hole will help.

  • Keep the mounting holes well back from the edge of the material. I recommend an inset of at least two times the diameter of the hole.
Rubber grommets
Rubber Grommets
Lexan is a wonderful structural or armor material if you recognize its needs and limitations.

Q: Mark, what caused Tanto to explode into many pieces when fighting Touro Maximus in the STEM Tech Olympiad in May [2014]? Does that prove that many robots who are fighting in England right now are not suitable to American competitions? [Chinese Forum]

A: [Mark J.] British heavyweight robot 'Tanto' simply took a good hit from a strong spinning weapon storing many thousand joules of energy and suffered an extensive structural failure (video). The main chassis lands out of sight of the camera. This demonstrates that 'Tanto' wasn't strong enough to survive an attack from one specific South American robot, but I certainly won't generalize that weakness to other Britbots.

British and American combat arenas differ in design, and those differences have a strong influence on robot design and combat style. We've discussed this in earlier posts, but in short:

  • British arenas have a large space between the barrier around the combat area and the arena wall which makes it practical and relatively simple to toss your opponent out over a low retaining wall for the win -- hence the large number of flipper designs in the UK.

  • American arenas generally have a small (if any) space between the combat barrier and the arena wall, making a toss-out a much less reliable tactic and leading to an emphasis on very destructive weaponry.

Many fine combat robots have travelled across the Atlantic - in both directions - only to find that their 'bot does not do well on the other side of "the pond". That isn't to say that either combat style is better than the other -- they're just different.

Q: Just thought about this when I saw the winning streak question. I remember before BioHazard's continous win which started in 2.0 of Battlebots it had already achieved an impressive winning streak from 1996 Robot Wars US season to the quarter final in Battlebots Las Vegas 99 -- am I right? [Chinese Forum]

A: [Mark J.] With an overall record of 35 wins and 5 losses, you might expect a few long win streaks. BioHazard won its first 13 matches in a streak that ran over four events, ending with a loss to 'Vlad the Impaler' at the '99 BattleBots event in Las Vegas. BioHazard's full match record at

Q: Hey Mark, I made a documentary about robot combat for my videography class a month ago, and I wanted to know what you think: Robot Combat: A Documentary [Havertown, Pennsylvania]

A: [Mark J.] You couldn't put in a clip of one of my 'bots, Nate?

I'm always happy to see outreach that may generate some interest from the public. I like your selection of combat clips, and the editing is quite professional. I also like the breakout of the video into sections on history, people, and robots. The only thing I might have wished was that your interview subjects had been a bit more animated -- you needed to interview Stephen Felk!

Q: Am using 3HP amp flow motor for my drum bot but weight of drum is 7-8 kg maximum and the length of drum is 14-15 cm..please suggest me the drum diameter and thickness of drum..which stored maximum energy.. [Maharashtra, India]

A: [Mark J.] I've spent considerable effort to put together the Team Run Amok Excel Spinner Spreadsheet that allows builders to model the performace of spinning weapons, but there still seems to be confusion about the basic physics of drum design and moment of inertia. I'd suggest that you study up on the topic before continuing your design efforts -- it's more than I can teach here.

The variables that determine the energy that a spinning drum holds at a given RPM are: mass, material density, diameter, and length. You've specified mass and length, and I'll assume that you're using steel. With mass, length, and speed held constant the energy storage will increase with increasing diameter. Examples - for a bare steel tube (no end caps or impactors):

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

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

  • 15 cm long - 25 cm diameter -  8 mm thickness: mass is 7 kg and it stores 9200 joules of energy at 4000 RPM
If your primary design consideration is greatest energy storage, make the drum as large in diameter as is practical for your overall design. There are other elements in drum design that should be examined before you get too excited about maximum energy storage -- see recent posts in the Robot Weapons on drum design.

Q: Has any bot in history had a winning streak longer than 'Hazard's? [Havertown, Pennsylvania]

A: [Mark J.] Middleweight 'Hazard' ran up an impressive 17 match win streak before losing to flipper 'T-Minus' at BattleBots 5.0, but it isn't the longest streak.

  • Hobbyweight 'Helios' completed a 19 match win streak with its championship victory at the 2004 Robolympics.

  • Antweight 'Dark Pounder' ground out 22 wins before losing to 'MC Pee Pants' in 2007.

  • 15-pounder 'Humdinger' cruised thru a 23 match win streak in a one-year period spanning 2006 and 2007. Team mate 'Humdinger 2' retired with an 18 match win streak, going undefeated in 2008. Maybe he'll make a comeback?

  • But the current streak record belings to beetleweight 'Gutter Monkey', who put together an astounding 25 consecutive wins over six events in 2009 - 2010.
Middleweight robot 'Hazard'
Middleweight champion 'Hazard'
Other memorable streaks include lightweight 'Wedge of Doom' who ran up a 15 match streak that ended at BattleBots 3.0 with a loss to 'Gamma Raptor', and heavyweight 'BioHazard' who would have had a 20 match streak if the judges had given it the controversial decision in the championship match at BettleBots 3.0 against 'Son of Whyachi'.

Q: Mark, I know lighter weight is always a big disadvantage in Robotica (due to less traction it will provide), but what makes Deb bot go so far in season 2.0? It's literally a middleweight robot. [Chinese Forum]
A: [Mark J.] Several light robots did well at Robotica. Season 1 champion 'Run Amok' was nearly 40 pounds under the weight limit. 'Deb Bot' weighed less than half the max weight, but it had a small frontal area and a lot of power. Its small size allowed it to pick its way effectively thru the rubble in 'The Gauntlet', its nimble performance allowed it to pick out a few key obstacles in 'The Labyrinth', and its low wedge was able to get underneath a tall tankbot in 'The Fight to the Finish'.

Traction was generally difficult to find at Robotica. The special effects fog machines coated arena surfaces with an oily mist that caused trouble for many types of tires. The slick surfaces leveled the field for large and smaller 'bots -- you needed more than just weight to get pushing power.

Deb Bot - too light or too fast for Robotica?
'Deb Bot' at Robotica

While I was looking for video of 'Deb Bot' for the question above, I came across this video:

Alexander Kerr's 'Tribute to Run Amok - Robotica Season 1' (link corrected)

Never had my own video, and with an Ahmet/Dweezil Zappa soudtrack! Thanks Alexander...

Q: A general competition-related question, but besides Vlad the Inhaler were there any builders that entered under a nickname or alias? -- VestedMadScientist [Asheville, North Carolina]

A: [Mark J.] Builders are generally proud of their accomplishment and pleased to have their name associated with their robot. 'Vlad the Inhaler' wasn't actually trying to hide his identity at Combots Cup VII. Ownership of the entered 'bot was well known, so perhaps they were just having a bit of fun.

I don't know of other instances of a driver alias being used at a robot combat event, but it isn't something that I track.

Q: mark how the touro get its gyroscopic effect of spinnin? [Poona, Maharashtra, India]

A: [Mark J.] I'm not sure I understand the question. A vertical spinning weapon will exert a force that will attempt to lift one side of a turning robot. The more powerful the weapon, the stronger this gyroscopic force will be. It's not something you 'get', it just happens.

Q: hey hi mark how r ? lucky here i hav a doubt about supply input and output of motor . motor 's power is max at near about half of actual speed rpm so i thought couldnt we make make arrangement to make it to rotate at this rpm?
i am talking about ampflow e30 motor [Poona, Maharashtra, India]

A: [Mark J.] I'm rather sad, Lucky -- but thanks for asking.

I've previously answered your question. Search the Motors & Controllers archive for "typical PMDC" for the explanation of why this doesn't work.

Q: I noticed a lot of comments on the net thought The Big B was robbed of it's lightweight title during the [BattleBots] 4.0 final, my opinion is that Ziggo showed enough strategy to win that 24-21 decision. Your thought towards this fight, Mark? [Chinese Forum]

A: [Mark J.] I won't re-judge a match based on edited television video. I've been present at a number of matches that were later televised. It was easy to agree with the judge's decision having seen a match live, but working only from the video I might have come to a different conclusion. Unless I saw the match live, I'll always give the judges the benefit of doubt.

Q: hi mark if i want 5000 joules energy at 5000 rpm what thickness should be drum's outer dia and thickness if mass is limited upto 13 kg?
i am confused about it i cant exceed outer dia more thn 15 cm please help me [Tamil Nadu, India]

A: [Mark J.] There seems to be a lot of confusion about stored energy in rotating weapons. Stored energy in a cylinder rotating around its radius center is a function of:

  • Rotational Speed (RPM)
  • Drum Diameter
  • Drum Length
  • Drum Wall Thickness
  • Material Density

You've given me a desired output and only two of the five variables (rotational speed and diameter). By selecting values for material density and drum length, I can give a design solution for any wall thickness to meet your criteria. For example:

  • A steel cylinder 15 cm in diameter, 100 mm in length, and solid to the center will weigh 11.5 kilos and will store 5000 joules of energy at 5000 RPM.

  • A steel cylinder 15 cm in diameter, 300 mm in length, with a 6.7 mm thick wall will weigh 7.1 kilos and will store 5000 joules of energy at 5000 RPM.

  • An aluminum cylinder 15 cm in diameter, 300 mm in length, with a 31 mm thick wall will weigh 9.6 kilos and will store 5000 joules of energy at 5000 RPM.

  • An aluminum cylinder 15 cm in diameter, 2600 mm in length, with a 2 mm thick wall will weigh 6.7 kilos and will store 5000 joules of energy at 5000 RPM.

I suggest that you download the Team Run Amok Excel Spinner Spreadsheet to model the performance of various spinner dimensions and designs.

I also suggest that you browse thru the Robot Weapons archive for several recent posts about drum weapon design.

It is quite odd to specify a weapon diameter, speed, and energy storage as starting parameters, and to then back into the other dimensions. In particular, specifying such a high rotational speed is detrimental to the overall performance of a spinner weapon. Were it my weapon, I would design it to maximize energy storage at the slowest possible speed -- something like:

  • A steel cylinder 15 cm in diameter, 380 mm in length, with a 10 mm thick wall will weigh 13 kilos and will store 5000 joules of energy at 3760 RPM.

A 5000 joule weapon does you no good at all if it's spinning too fast to have decent 'bite' and the ability to transfer that energy to your opponent in a single, huge impact. Slow it down a bit. A larger diameter drum would be able to store the same energy at an even slower speed -- example:

  • A steel cylinder 20 cm in diameter, 390 mm in length, with a 7 mm thick wall will weigh 13 kilos and will store 5000 joules of energy at 2780 RPM.

Or even better:

  • A steel cylinder 25 cm in diameter, 360 mm in length, with a 6 mm thick wall will weigh 13 kilos and will store 5000 joules of energy at 2175 RPM.

Don't compromise weapon performance with dimensional restrictions that you can avoid, and design for the lowest weapon speed that will store enough energy to be effective.

Q: Then another question about your team in Robotica. Who would be the bigger threat to 'Run Amok' in the Fight to The Finish: 'Mini Inferno' or 'Killer B'? From your previous answers it looks like Jason's bot would be much less dangerous, I think. [Chinese Forum]

A: [Mark J.] Jason Dante Bardis was building a 'bot from scratch to compete at Robotica, but he ran out of time and decided to substitute a very light 'bot that was essentially the chassis for 'Dr. Inferno Jr.' with a carbon fiber wedge added. Although the drivetrain was very powerful (four DeWalt 18v gearmotors running at 24 volts), the robot weighed weighed only 37 pounds. At the weigh-in, Jason walked onto the scale carrying 'Mini Inferno' and was still under-weight! Powerful though it was, Mini just didn't have enough pushing power to be a threat against any of the robotica finalists in a sumo match.

Jason did finish his original Robotica entry and fought with it at BattleBots seasons 3.0 thru 5.0 with limited success. He remarked on a forum post that after he finished 'Towering Inferno' he realized that it would not have been a successful Robotica competitor.

'Killer B', on the other hand, was a very dangerous sumo competitor. Had they put the blunt end of the robot into use instead of the wedge end, they could have used their powerful drivetrain to simply shove 'Run Amok' off the platform. Lucky for me, they didn't choose that option.

Q: From your point as a Robotica reigning champion, do you think 'The Killa Gorilla' (aka 'Silverback' in Battlebots) built by Rob Farrow is a good design to compete in Robotica, Mark? Because from the only episode in the net including it (2.0 Final) it seems like it's very hard to drive,and will fall off platform by mistake very easily. And which kind of stage layout is more challenging - the new format in later seasons or the 1.0 format in which your team competed? [Chinese Forum]

A: 'Robotica' called on competitors to answer several differing performance challenges, making it difficult to put together a single optimal design. Rob chose a short wheelbase and a responsive, torquey drivetrain to overcome the 'Gauntlet' and 'Labyrinth' challenges. Although those design choices made the 'bot difficult to control, its maneuverability and power made it a strong competitor in the non-sumo parts of the competition.

I didn't have the opportunity to drive the courses for Robotica 2.0 and 3.0, but given the success of competitors returning from Season 1.0 I'd have to guess that the level of challenge was similar.

Killa Gorilla - got banana?
Killa Gorilla

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.

More of Aaron's Poems

Aaron's Minecraft High Dive Video

Killer Robot drawing by Garrett Shikuma

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