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4730 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: 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

Q: Hi Mark,
I am trying to build a 4 bar flipper/Lifter in the Antweight/Beetleweight division. I was wondering if you knew what system Menehune used? And I was also wondering if Menehune was an Antweight or a Beetleweight? Thanks, and it is understood if you may not know the system used.

Antweight Pneumatic guy again, would you be able to create air tanks from 3D printing, such as shapeways? Or would you have to machine the parts? Thank you a lot. [Bellevue, Washington]

A: [Mark J.] I don't have specific information about the components antweight 'Menehune' used, but there aren't many options. Search the Ants, Beetles, & Fairys archive for 'Robart' to find several posts about sources for tiny pneumatic components and the modifications needed to make them useful for insect flippers.

Best to check with the event organizer before making your own pneumatic components -- rules usually call for components rated for use at the pressure used in the 'bot, and home-built components don't have a rating. The Robart air tanks are useable for antweight combat.

Q: A lot of people talk about Battlebots, but it seems like so few talk about its founder's machines. What do you think about Greg Munson and Trey Roski's bots, Mark? I think they are simple but extremely efficient. [Chinese Forum]

A: [Mark J.] Well... one of them was simple and efficient. The original 'La Machine' was a remarkable robot that won the middleweight crown at the 1995 Robot Wars as well as the middlewieght and heavyweight rumbles. It was also the most hated robot in the history of robot combat. As efficient as the pioneering wedge design was, audiences at the early combat events were looking for robotic entertainment from machines with rotating saws, swinging hammers, and flame throwers. The crowd would literally 'boo' every appearance. La Machine holds a place in the Combat Robot Hall of Fame for its pioneering design.

The only other Munson/Roski robot worth mention is 'Ginsu'. There were several quite different versions of Ginsu with the sole unifying design element being the use of circular saw blades for wheels. Although none of the Ginsu versions ever won a match in open competition, they are well rememberd for their exhibition matches against Jay Leno's 'Chin-Killa'.

La Machine robot
'La Machine' - 1995

Q: And about Overkill -- I always think one of the main reasons why it could beat a lot of powerful spinning blades is that its structure could absorb the high energy of spinning weapons well and being able to survive those deadly blows. Am I right? [Chinese Forum]

A: [Mark J.] If you watch the fights 'Overkill' had against powerful spinners (Mechavore, Warhead, M.O.E.) you'll see that Overkill never actually takes a big hit from a spinner weapon. Christian Carlberg was a good strategic driver, and he new how to stay away from a dangerous weapon and wait for the right time to attack. Often, he was able to stay away from a spinner long enough for a battle-weakened weapon to fail and then move in for a victory.

'Overkill' was well built and very maneuverable, but I think Christian's driving was the the strength.

Q: A question about the famous moment when 'Mechavore' tore BioHazard's lifting arm completely off in the BattleBots 5.0 quarter final. Some say the reason was that BioHazard's lifting mechanism wasn't strong enough, but I think it was just an unlucky hit. Mechavore's blade hit the exposed arm of BioHazard at the worst time and in the worst spot. No lifting mechanism can survive that kind of blow. What's your opinion, Mark? [Chinese Forum]

A: [Mark J.] I'll agree with you on this question. It simply isn't possible to make every component of your robot strong enough to survive every possible attack and still make the weight limit. The more vulnerable pieces of the lifting arm are usually tucked safely away under protective armor, but they must be exposed in operation. Mechavore got in a 'lucky punch', but BioHazard went on to win the match and the championship.

Wacky Question of the Month!

Q: can i eat [Los Angeles, California]

A: [Mark J.] You typed 'Robot That Answers Your Questions' into Bing and blindly accepted the link that popped up, ignoring all the signs on this site that this is where I answer your questions about combat robots, and that I am not a robot that answers your questions.

Does no one in California know how to conduct a proper web search?

Q: Use the substitution method to solve the system of equations. Choose the correct ordered pair.

2x + y = 10
y = x - 5

[San Francisco, California]

A: [Mark J.] I guess that answers my question about Californians and web searches. Pro bono publico:

Since y = x - 5, we can substitute x - 5 for the y in the first equation:

2x + x - 5 = 10

Combining like terms:

3x - 5 = 10

Add 5 to each side of the equation:

3x = 15

And divide both sides by 3:

x = 5

Now substitute 5 for x in the second equation:

y = 5 - 5

y = 0

Which gives the simultaneous solution to both equations, expressed as an ordered pair:

(5, 0)

Now, go build a robot.

Q: Hi Mark, is there an equation to calculate the force in a pneumatic ram?

A: [Mark J.] Sure - in pounds, inches, and psi:

Force = π * (0.5 * Ram Bore)2 * Pressure

Q: And is there an equation to calculate the force needed to flip a robot? Thank You. [San Francisco, California]

A: Unfortunately, no -- it takes both force and speed to flip an opponent. A ram with a great deal of force that extends slowly will lift but not flip a given weight into the air. A flipper must be able to flow pressureized gas through the regulator, valves, and ports at a very high rate to maintain pneumatic force as the ram quickly extends. The additional varaibles make this a difficult analysis. Most builders just go for as much speed and power as they can get and hope for the best.

Q: Mark, what made Tazbot being able to defeat Razer in dominant fashion in Battlebots Long Beach 99? Seems like the long weapon and low wedge cotributed a lot. [Chinese Forum]

A: [Mark J.] 'Razer' had a very specific attack -- maneuver the opponent into the jaws of its hydraulic piercing weapon and make a large hole in them. 'Taz' didn't really have any vulnerable bits that could fit into Razer's weapon, except perhaps the difficult to access wheels. The long and narrow wedge guards protected Taz's main body, and the weapon turret could safely reach around to Razer's vulnerable sides. Not much that Razer could really do.

Q: And another thing I wanted to say for a long time: in your 'Who Won' guide it states that the RG05 Middleweight winner is 'The Mortican', but your tournament tree for that event shows that the actual champion is 'Nasty Attitude' -- is that a mistake? [Chinese Forum]

A: [Mark J.]Worse than a mistake, a conundrum! It turns out that both 'Nasty Attitude' and 'The Mortician' won middleweight tournaments at RoboGames 2005.

  • RoboGames '05 hosted a standard double elimination middleweight tournament with 21 robots competing. That is the event that appears in my tournament tree for RG'05, which correctly shows that 'Nasty Attitude' was the winner.

  • Tacked onto the end of the middleweight results as sent to BotRank are six fights featuring four robots that did not appear anywhere in the earlier results. These six fights were apparently a seperate round-robin tournament that was mistakenly reported as part of the double elimination tournament. 'The Mortician' went undefeated in this event (3 wins, 0 losses) for the win.
It's not clear if the round robin tournament was an official event or some sort of ad-hoc challenge that just happened when the arena was empty -- it does not appear in the official RoboGames Results for 2005.

I think it's best if I change the 'Who Won' page to reflect the winner of the 'official' event at RG'05 -- 'Nasty Attitude'.

Q: can u please tell me how to control a servo wirelessly? [West Bengal, India]

A: [Mark J.] The simple way is to use a standard R/C radio system. See: How R/C Radios Work.

If you're looking to wirelessly control with Arduino, try this tutorial: Wireless Servo Control.

A web search for "wireless servo controller" will give you other options.

Q: Mark,a question came to my mind when watching 'The Labyrinth' fight between Jawbreaker's Revenge amd Buzz Bomb [Robotica season 3]. I know Robotica had 30 seconds limit [clamping/pining] rule about 'Fight to the Finish' segment, but does that apply to Labyrinth as well? Because Jawbreaker's Revenge clamped Buzz Bomb for the whole length of the fight without referee asking them to release. [Chinese Forum]

A: [Mark J.] The Robotica Gauntlet and Labyrinth were both race stages to see which robot could gather the most obstacle points in the alloted time. There was no clamping or pining limit for these stages as it was not anticipated that a robot could clamp their opponent and still complete any of the obstacles. Jawbreaker's Revenge was able to clamp and carry 'Buzz Bomb' only because 'BB' was a very small and light robot -- about 1/4th the weight of 'JBR'. A poor choice on Buzz Bomb's part.

Q: What will happen if the torque from a motor is greater than the traction on a wheel? [Garland, Texas]

A: [Mark J.] A properly geared robot propulsion motor should provide more torque than the wheels have traction. When torque exceeds traction, the tire will break traction and start to slip. You'll still be getting full thrust from the slipping tire, but the slippage will prevent the motor from stalling and will keep amperage consumption under control. I generally design for between 50% and 100% more stall torque than the wheels can directly use for traction.

The Team Tentacle Torque Calculator will help with the calculations to determine the best gearing for your robot's weight, motors, wheel diameter, and voltage.

See also: Optimum Gearing for Combat Robots.

Q: A quite silly question but I've been wondering for a long time:What made Biohazard became so successful upon its first ever event in 1996 to the last televised Battlebots event?No robot during that era had this kind of consistency-6 full years.I think that's because of its very good design and engineering level,isn't it? [Chinese Forum]

A: [Mark J.] Design, engineering, construction, preparation, and driving. That pretty much covers it.

Q: During the post fight interview after Vladiator vs Maximus fight in Battlebots 5.0 Gage Cauchois attibuted his narrow win to the fact that Vladiator had an active weapon,while Maximus did not.Does having an active weapon in your robot can help you win the match when it really can go either way around?I read Frostbite's report from BB 3.0 and it said something like that as well.

A: BattleBots matches were supposedly judged on aggression, damage, and strategy. Aggression and damage are failrly easy to define, but strategy is a bit more subjective. I think the judges generally did believe that having an active weapon was a good 'strategy' -- good for a tie breaker point.

Q: And some questions about Ziggo:Johnathan Ridder said during Batttlebots 4.0 Ziggo's drive motor and speed controller got burnt after destroying Wedge of Doom in quarterfinal,since then the speed controller and drive motor got burnt after every match,and in the final it showed that tendency again so Ridder had to save its weaponry for points.What could have caused that problem?And why do Ziggo "pull off a Mauler" so frequently in 4.0?

A: As I recall (but cannot confirm as is not archived) 'Ziggy' upgraded their spinner motor for BB 4.0. The higher speed and greater power consumption could account for both the reduced reliability and the greater tendancy to go unstable and 'Mauler' tip up on edge. Sometimes an intended 'upgrade' doesn't work out.

Q: And about Biohazard vs Voltarc in 1.0,I read Carlo's old post in BB forum and it said Bio's hole in the bottom got caught up by Voltarc's spike in the arm,so there's no escape, that was enough to make judges thought it wasn't stuck?Sorry for asking so much questions in a row,and I greatly appreciate your patience,Mark.Very thanks.

A: I can't comment on what the judges thought, and don't have anything to add to my previous comments on this match. If the 'bots were entangled, they should have been separated. It Voltarc had control of the situation, the judges should have required a release after 30 seconds. It was an odd judging decision.

Q: And a question about gear changing system:Is that common for robots?Because I saw Panzer could change its gearing to deal with different opponents. [Chinese Forum]

A: No -- very few combat robots have the capacity (or need) to change gearing between matches.

Q: So...Could Biohazard change its gearing? Because I saw Battlekits which designed upon it could change gearing

A: Gear changes for 'BioHazard' (or for the BattleKits which have similar but not identical drivetrains) would require partial disassembly of the drive modules and replacement of the motor and first stage sprockets. This is not a task that you would want to take on between matches.

A combat robot correctly geared for a given arena really has no need to change gearing during a tournament. The 'Robotica' competition was an exception, as the tournament took place in four different arenas with differing performance requirements.

Q: Mark,after watching Robotica 3.0 finals I have a question:Do Robotica allow entanglement weapon aimed for spinning weapons?I saw Juggerbot 3.0 used that to stop Ultra Violence's blade in Laybrinth. [Chinese Forum]

A: [Mark J.] Our Who Won page has links to rule sets for all of the major combat robot tournaments, including the rules for Robotica 3.0. Those rules state:

All weapons located on a Robot must be cleared in advance with Show's Producers. This includes, but is not limited to, any and all hydraulic systems, projectiles of any kind, flamethrowers, buzz saws, hammers and entanglement devices. While no particular weapon is expressly forbidden, Show's Producers, in the interest of safety, reserve the right to limit the use and design of weapons.

Team Juggerbot received approval for their entangling net and put it to good use against 'Ultra Violence'. Other robots also attempted to use entanglement weapons at Robotica, but with less success.

Q: And why do a lot of competitors,even well seasoned ones like Panzer Mk3 got stuck on the bricks or buckets during Gauntlet?Are there any effective ways to solve this problem?

A: Hitting a wall of bricks, blocks, or other loose items at speed sends them in all directions and can bounce the robot up on top of them. Lots of designs were tried, with mixed success.

  • A front wedge just collects a big pile of debris that builds up and stops forward motion.

  • A boat-like front prow combined with slow speed and a lot of traction/torque could get you thru reliably, but an opponent taking a chance on speed stands a good chance of beating you to the finish.

  • A whole lot of ground clearance will get you over the debris, but huge ground clearance doesn't go well with the other Robotica challenges. Adding larger diameter wheels for additional clearance on the obstacle course was tried, and worked well for season 2 winner 'Flexi Flier' -- who also had a chassis that hinged to help 'step' over debris.

A little thought and testing will go a long way, but there just isn't a foolproof solution to obstacle debris.

Q: Mark,what's your opinion on the STEM event held early in this month?I think it's great!Saw a lot of intense fights form lightweight to heavyweight category,maybe robot combat in America is not really "dead" yet?Also could you comment on Team Toad's new machine Polar Vortex?I think using the entire body of the robot as a lifting weapon is clever,and it seems very successful as well. [Chinese Forum]

A: [Mark J.] The 2014 STEM TECH Olympiad featured a wide range of robotics, programming, and engineering events. The 'Battling Robots' portion of the event featured robots from 150 grams thru 220 pounds. The combat was well organized and had a number of memorable matches, with a good turn-out in some of the weight classes. I'm pleased to see a well organized and successful national-scale event.

I'm also pleased to see Team Toad competing with a new heavyweight. 'Polar Vortex' was certainly recognizable as a Toad design, with large exposed wheels and a clean profile. The lifting action has the advantage of being simple and robust, but the lifter must generate enough force to lift both the opponent and a good portion of PV's own weight. Overall, a well designed and built robot -- typical for Team Toad.

Team Toad's heavyweight 'Polar Vortex'

Q: Hi Mark,

I dug out a couple of the old Battlebots RC toys from the garage. They ran awhile and then stopped. I turn them off, then on and the LED on top lights briefly and then goes out. New batteries don't change this behavior, so I followed the instructions on your site to take one apart and remove the impact spring with a pair of pliers, thinking it was stuck to the side. It wasn't but I took it out anyway.

At this point, there's no change - the LED lights briefly and then goes out, and the toy is unresponsive. They both do this after having run awhile. Any idea what I should look at next? [Old friend, California]

A: [Mark J.] The first thing I'd look at is the interlock that keeps the robot from operating when the weapon module is removed. That may have oxidized/corroded over time and may be causing trouble. Try cleaning those contacts, or just short around the switch (see the Robot Dojo BattleBot Toy Hacking Guide, just below the section on the impact spring).

A drop of oil on the motor bushings couldn't hurt -- they may be binding a bit and overheating the motor controller, causing a shut-down. Make sure everything turns freely.

I'll keep thinking -- write back if no joy.

Reply: That was it - the interlock was oxidized, scraping it fixed the problem. The odd part is that they both worked for awhile and then stopped. I hadn't taken them apart, but then again they're several years old and hadn't been run in a long time, so maybe dust built up and eventually blocked the contact. I'll take the other one apart later and it's probably the same thing.

Q: hi, i m planning to make a razer bot of 50kg, so for that hydraulic weapon , i have purchased a double acting hydraulic cylinder of 1ton with 35-40mm bore and 150mm stork , so for that can u give me what should be that psi of hydraulic pump(which pup is suitable)? and for up & down motion i m using 12v solenoid valve , is it okay? and pls tell which motor i used to drive hydraulic pump? [Gujarat, India]

A: [Mark J.] Several thoughts:

  1. Your questions are very basic -- I'm guessing that you have no prior experience with pneumatics.

  2. Many very knowledgeable teams have tried to build 'Razer' style hydraulic weapon robots, but 'Razer' remains the ONLY succesful hydraulic robot. A hydraulic crusher is a very difficult weapon to get right.

  3. If you knew enough to safely build a hydraulic weapon system, you wouldn't need to ask me how to do it.
Sorry, but I don't think you have enough knowledge or experience with pneumatics to take on building a complex and potentially dangerous crushing weapon. I certainly can't give you that knowledge in a few paragraphs here -- pick a different weapon system.

Q: hi mark lucky here how should i join my drum's impactor with my drum because i have made drum composite of mild steel and aluminium from inside as aluminium will cause major damage if i use the bolts while impacting ? [Tamil Nadu, India]

A: [Mark J.] You haven't told me nearly enough about your weapon drum for me to recommend an impactor attachment method. For example:

  • How thick is the drum?
  • How much of that is steel?
  • What aluminum alloy is the rest?
  • How much does the drum weigh?
  • How fast do you plan to spin it?
  • What is the drum diameter?
  • What do you plan to use for an impactor?
If I guessed wrong about any of these things I could give you a poor recommendation!

Q: lucky again steel hollow cylinder with 5mm thick and aluminum solid inserted in it i am thinkin to run it at 4000 rpm and material for impactor is mild steel and aluminum 6001

A: A solid core drum? Not efficient at storing energy -- the farther from the spin axis the mass is placed, the greater the energy storage. But you asked about impactor attachment...

You can certainly bolt thru the steel cylinder into a solid aluminum core, but bolts are not good at handling the shearing forces the impactor will be encountering. Ideally the impactor should be prevented from shifting on impact by insetting it into a groove machined in the drum and holding it in the groove with bolts. That takes the shear loading away from the retaining bolts, but a groove may not be practical given your composite design.

I'd be tempted to bolt down the impactor, then run a weld along the trailing edge to take some of the shear force off the bolts.

Shear forces applied to a bolt

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.

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