Questions and Answers about Combat Robotics from Team Run Amok.

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7162 Questions and Answers about Combat Robotics
from Team Run Amok

Privacy Policy
Team Run Amok receives a lot of email about designing and building combat robots. In 2003 my son and team member Aaron Joerger (then 12 years old) asked for a question and answer page to document our responses.
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.
Click to browse thousands of previously answered questions by category, or search for specific topics. Includes
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.

Significant Digits
In your Spinning Weapon FAQ it says,
"A steel bar 300 mm in length, 75 mm wide, and 23mm thick has a mass of 4 kg.

Energy storage at 2000 RPM: 710 joules"

When I did the calculation for the rotational kinetic energy, I got around 699.08 joules, not 710. I have attached my work. Could you please explain how you got 710 joules as the rotational kinetic energy? [Woburn Massachussets]

A: [Mark J.] Your calculations are correct, but you have used as an input my mass calculation output which has been rounded to a correct number of significant digits.

  • The mass of a bar of the given dimensions and a steel density of 7800 kg/meter3 is calculated by the Run Amok Spinner Weapon Kinetic Energy Calculator at 4.04 kg. I rounded the quoted mass in the example to 4 kg given the two digit precision of the input dimensions, but the 4.04 kg figure was used by the calculator. This accounts for the majority of the difference in our numbers.
  • You chose to calculate the Moment of Inertia to six decimal places (0.031875), while the calculator uses a corrected precision of two significant digits (0.032) which adds a bit to the calculated energy.
  • With an input mass of 4.04 kg the calculator provides a kinetic energy of 709 joules @ 2000 RPM, which I adjusted to 710 joules for two significant digit precision.
For real-world purposes in combat robotics, either figure will do nicely.
Annoying Newtonian Reaction
Q: Hi. Love your site! I’ve been following the Golden Dukes and built a wedge and then a flipper before my spinner, and am having a blast so far. My spinner is a 150g version of everyone’s favourite 'Huge' which has taken serious work, but is nearly there.

The latest roadblock: When I spin up the weapon, the whole bot tips forward and ends up upside down. The centre of mass of the whole bot is back, and it drives fine without the weapon, but if it's spun up quickly it flails!

Do you know why, and how I could stop it? [Walthamstow, England]

A: [Mark J.] The 'why' is easy.

"For every action there is an equal and opposite reaction."

The action of applying torque to spin-up your weapon in one direction results in an equal torque applied to your chassis that attempts to spin it in the other direction. In your case that opposite torque is strong enough to flip the chassis forward.

The 'how to stop it' is trickier.

  • Accelerating the weapon more slowly will reduce the force attempting to flip the chassis. You can insert an adjustable servo slower module between the receiver and your weapon ESC that will reduce the weapon acceleration and keep the chassis stable. The weapon will still spin as fast, it will just take a little longer to reach top speed.
  • Moving additional mass farther to the rear of the robot will increase its resistance to flipping over forward.
  • The forces applied to your chassis by the accelerating drive system oppose the action of your weapon spin-up. You can try accelerating forward with the robot drive while spinning up the weapon. The opposing forces may keep the chassis from flipping over.
  • If you fight in a steel-floored arena the event organizer may allow you to add small magnets to the tips of your rear stabilizer bars to hold them to the floor when the weapon spins up. I can't see the bars in the photo, but they must be there!

Follow-Up: Hello again. Thanks for the explanation and reminder that robots are Newtonian objects, not magic!

UK ants tend to have wood floors so magnets are out, but before messing with power curves I slapped some M4 bolts through the rear support bars which seems to have done the trick: Spinup Test.

Reply: That's the perfect spot to add a little weight, and it looks like a little weight was all it took. I had imagined that the 'bot was flipping over hard and would need more aggressive correction so I'm glad the solution was that simple!


Jeff, Mark, and Dan
Q: You recently posted about an "Ask the Builders" question and answer page on the old TLC Robotica fansite. You mentioned that host Dan Danknick had a Q&A and I believe you had one as well. Did any other builders have a Q&A on that site? [Boise Idaho]

A: [Mark J.] You have a good memory. The official TLC/Discovery Robotica Fansite (archived) took questions from viewers as the seasons unfolded. Jeff Cesnik (Kritical Mass) Took the first shift for Season 1. I took over at the end of the first season to fill the gap 'til the start of Season 2 when Dan Danknick took over as technical advisor and host.

I've got a complete set of the questions and answers from all three volumes. Give me a sec and I'll wrap a webpage around them...

Four Hours Later...

There -- all done. It took a bit of squeezing to get all the links to work; I think I got most of them. Viewer Q & A from the TLC/Discovery Robotica Fansite


Start in a Good Place
Q: Complete newbie here. What do I need to make a small simple combat robot? I went on Instructables and other websites but haven't been able to findn the info I want. What kind of motors will I need? Do I need an esc with them? What batteries will I need? If I want a receiver/transmitter how would I integrate that? Do I really need an Arduino? Is there a guide for a complete newbie that I can use which tells step by step instructions? [Social Media]

A: [Mark J.] A good place for you to start might be with a combat robot kit. Take a look at the FingerTech Viper and download the Viper Instruction Manual which diplays and describes the components, their use, and how they are assembled.

See Frequently Asked Questions #2 for additional options.


They Sell a Lot of These
I have an HK-T6A transmitter that takes 8 AA batteries, and they never seem to last as long as I'd like. Has anybody come up with a rechargeable battery that works as a substitute? [Social Media]

A: [Mark J.] FingerTech Robotics sells a lot of those radios with their combat robot kits. They sell a Turnigy 3S Transmitter Lipoly Pack that fits perfectly into the 8xAA battery compartment of the HK-T6A and will last multiple events before needing a recharge. A matching female connector to solder into your transmitter is included.


No - Not Really
Q: According to the Team Toad Website 'Windchill' sent in an audition packet to be in Robotica Season 2 but was not selected. If you watch this short clip from their audition video you'll realize that Windchill's weapon is a brushbroom. A Brushbroom!? Really!?

A: [Mark J.] I believe you have misinterpreted the events described on the 'Windchill' webpage. Windchill had a modular lifting spike that could accept attachments to suit differing tasks. That video clip simply showed the versatility of their lifter. Any number of things could have led to the show producers rejecting Team Toad's application, but I'm sure the issue was not the ability of their 'bot to push a broom.


Rats Need Love Too
Q: I don't think that the Robotica Rats from the Season 2 and 3 Labyrinth get enough love. They did a great job of keeping the Labyrinth competition going while adding a touch of mayhem. Can you tell me anything about them?

A: [Mark J.] The Rats were a great idea and they did keep things moving in The Labyrinth. In several matches the Rats were able to unstick a competitor and get them back in the game, yet they showed no favoritism and were never a deciding factor in who moved on. A few Rat facts:

  • The Rats were built by Andrew Lindsey of Robotica Season 1 finalist Team Force.
  • The two Rats (Red and Black) each weighed about 90 pounds and had modest circular saw weapons in the rear.
  • The translucent plastic rat bodies covered a welded aluminum chassis with a swivel castor wheel under the nose.
Q: The Rats still need some TLC so I gave them their own page on The Robotica Wiki.

A: Let me give you some more material gleaned from the archived TLC Robotica Fansite where host/advisor Dan Danknick answered questions from viewers:

Q: I was watching your show the other day, and I saw the mice attack the competitors. I was wondering if the mice were controlled by people, or if they acted on their own accord. They were my favorite and I thought maybe I could drive them some time.

A: Most of the technical details concerning the Robotica Rats are classified but I can tell you there is an experienced Hollywood SFX (special effects) team in control of them. Pay close attention to their behavior — not only do they impede and attack the competitors at times but they can also give them a hand in the Labyrinth!

I have added entry for "The Labyrinth Rats" at the bottom of my Robotica Competitor Galleries for Season 2 and Season 3. I credit them as 'House Robots' and include most of Dan's description of the Rats from above.
The Lips Are Synched
Q: I know that all 3 seasons of Robotica are available on the Internet Archive, but did you know that they have a new and better copy of Robotica Season 1? Improved Robotica Season 1 Videos at Internet Archive

A: [Mark J.] Very nice! Better color saturation, less screen distortion, and perfect sound synch. I've changed all the site links for Internet Archive Season 1 Robotica to point at the new uploads.


A Real Mystery
Q: Who built 'Boxster' for Robotica season 1? It was an alternate and did not compete, but I wonder about the team that built it.

A: [Mark J.] There were several robots at the Robotica Season 1 filming that were not able to compete. Some had mechanical problems, some failed in the daily qualifying sessions, and then there was the mystery of 'Boxster'. Some of Boxster's design elements are common to a well-known combat robot team, and I did spot a member of that team in the robot storage area, but I can't directly attribute the build to them. I'm not going to start any rumors that I can't back up.


...or Buy a Modern Transmitter
Q: Just built my first bot using a Viper kit. It is very tricky to drive in that moving the joystick the smallest amount makes it turn sharply, resulting in it constantly overturning. I have a transmitter called FlySky Model FS-CT6B that came with the kit. Do you know if there’s a way I can make the joystick less sensitive to turns? [Social Media]

A: [Mark J.] The FlySky FS-CT6b is a primitive transmitter that requires connection to a PC to adjust most control functions. It's awkward and outdated but it does have the ability to adjust steering sensitivity.

  1. If it didn't come with the kit you'll need a programming cable to connect the transmitter to a PC: Programming Cable for T6A and CT6b Transmitter.
  2. You'll also need the transmitter manual: FlySky FS-CT6b Manual
  3. On page 11 of the manual are instructions for downloading the required software and connecting the transmitter to a PC.
  4. On page 17 of the manual are instructions for adjusting the 'ENDPOINT' settings. To reduce steering sensitivity you will reduce both the left and right endpoints of Channel 1. Try about 50% for both.
  5. There is a 'How To' guide for setting up the PC => Transmitter link available on the FingerTech site that is easier to follow than the FS-CT6b manual: T6A Radio Programmer Setup Win10.
When you tire of jumping thru these hoops to adjust functions on your transmitter, see Combat Robot Radio Systems - what functions do you actually need? for guidance in selecting a replacement.

Q: Why does FingerTech use this awkward transmitter with their robot kits? The full-featured FlySky FS-i6 costs about the same.

A: From a manufacturer's standpoint the FS-CT6b makes sense. FingerTech can load their standard transmitter set-up file on a large batch of transmitters in very little time: turn transmitter on, plug in the cable, press upload, next. For the FS-i6 they would need to wade thru the transmitter menu and manually enter a FS-i6 combat set-up. That takes much more time and involves possible entry errors. Most Viper kit owners just make do with that stock set-up and never change anything.


Flashback: an archived post from 2020
We've been light on technical questions at Ask Aaron for a while, so here's an explanation of an interesting mechanism out of the Robot Weapons archive:
Q: How exactly does the 'Greedy Snake' lifter mechanism work? I’ve seen it used on bots like 'SlamMow', 'Claw Viper', and 'Barróg Doom' and kinda have an idea as to how the system works, but I feel like I don’t get it entirely despite being a seemingly simple setup. Are there any diagrams, pictures, or videos that best describe how it works?

As always, thanks! [Social Media]

A: [Mark J.] The mechanism in question is often referred to as a single motor clamp lifter. Powered rotation of a spur gear (shown with a red dot) drives a clamping arm attached to a second spur gear downward until on object stops it's motion and prevents further rotation of its gear. Continued rotation of the powered spur gear will then rotate the entire gearbox and attached lifting platform around the axis of the powered gear. Reversing the rotation of the powered gear will lower the platform and release the clamp. In practice, there may be additional gears involved to provide additional gear reduction in order to gain the substantial torque needed for the lift. The animation has been reduced to only the critical components.

Note The clamping force is created by weight on the lifting platform. As the lift angle increases there is less weight pressing down on the platform: clamping force becomes essentially zero when the lifter is vertical.


Just Put Seven At The End
Q: now about robotica season 3, it ran for a marathon on TLC back in 2002 but it might have been the wrong order, so shouldn't have been this order?:

ep 1 - Juggerbot 3.0's heat, ep 2 - Ultra-Violence's heat, ep 3 - Mini-Rip's heat, ep 4 - Jawbreaker's Revenge's heat, ep 5 - Panzer Mk 3's heat and ep 6 - Rambot's heat

coz in my opinion i feel it should've been Juggerbot 1st, then Jawbreaker, Ultra-Violence, Mini-Rip, Panzer and finally Rambot after that instead of Mini-Rip to Ultra-Violence, no idea what TLC were doing.

A: [Mark J.] The original broadcast order for Robotica Season 3 episodes was:

1. Mini-Rip
2. Jawbreaker's Revenge
3. Panzer Mk III
4. Rambot
5. Juggerbot 3.0
6. Ultra-Violence
7. The Championship
I've mentioned previously that the order in which the Robotica episodes were shown had no relationship to the order of events at the competition. As long as the Championship is shown last to avoid spoilers the viewing order of the episodes is irrelevant.
Point a Camcorder At It
Q: Did you know that back in the early 2000's you could by VHS Tapes of Robotica Season 1 on the TLC Website?

YouTube user 'Flipperbots Rule' has all seven tapes of Robotica Season 1 and he recorded them by just pointing a camcorder at the screen of his TV (classic thing to do, right?) Here's his playlist. He also has Season 3 as shown on The Science Channel.

A: [Mark J.] Yes, Discovery/TLC sold VHS tapes for many of their popular shows. They were available both thru their websites and at their 'Discovery Stores' in shopping malls across the country. There weren't any 'extras' on the tape -- just the show. As I recall, they were about $15 each.

If you're interested in the three seasons of Robotica you don't need to suffer thru Flipperbots' second generation analog copies. The Internet Archive has nice clean digital copies you can stream, cast, or download: see this archived post.


First Find a Hockey Puck...
Q: Antbotica - what was the shuttle race like and how did it work?

A: [Mark J.] From the Antbotica rules:

3.1 Shuttle Race

3.1.1 – Two robots start on opposite ends of the 4 foot by 8 foot Shuttle Race field within their 'goal zone'. A regulation hockey puck (or substitute) is in a marked area in the center of the field. Points may be scored in two ways:

  • The robot may traverse the length of the field and touch the end-board at the back of their opponent's goal zone for 5 points. The robot may then return to their goal zone and touch the end-board for another 5 points. This may be repeated to a maximum of 100 points.
  • Should any part of the puck be within a player's goal zone at the end of the game, the opponent will be given 20 points. The line designating the goal zone is placed 8" from the endboard and is considered a part of the goal zone.
3.1.2 – A puck that leaves the playing field will be retrieved and replaced at its starting place in the center of the field by the event marshal. The clock will not be stopped while this takes place.

3.1.3 – The Shuttle Race is over when either robot scores 100 end-board points, or 2 minutes have elapsed. Maximum points for the game: 120.

The challenge of the race is to judge your braking point so you tap the end wall of the arena and quickly reverse to the near wall in your goal zone.
  • Slow too late and the slam into the wall may set you sideways or even flip you out of the arena. The arena wall is less than 2" tall. The general event rules allow an out-of-arena 'bot to be replaced but the clock continues to run.
  • Reverse too soon and you may miss tapping the end wall and get no points.
The hockey puck is a distraction. Some 'bot designs will have no trouble shoving the puck from its starting position into the opponent's goal, but it is typically more difficult to maneuver the puck out of the tight quarters of the goal zone. Often the puck will be left in a goal zone until the final seconds for an attempt to push it clear.

Robotica Top Five
Q: I found a channel on YouTube for Nash Entertainment, the production company that made 'Robotica'. They call it 'Crazy 8 Videos'. They have a pair of Robotica clip compilations: They haven't released a 'Top Five Fights to the Finish - Season 1', but if they do here's my prediction:
  1. Episode 1 - Run Amok Vs Killer B
  2. Episode 2 - Kritical Mass Vs Hot Wheels
  3. Episode 4 - Ram Force Vs Solar Flare
  4. Episode 5 - Juggerbot Vs Hammerschlag
  5. Episode 7 - Run Amok Vs Juggerbot Vs Ram Force
What would your Season 1 'Top Five' be?

A: [Mark J.] Great find! The videos are better quality than I've ever seen for 'Robotica', but of course Nash Entertainment has the original tapes. Are you ranking those matches in decreasing or increasing order???

I watched five of the seven season 1 'Fight to the Finish' matches from either the studio floor or the drivers' platform, so I had a different perspective than the TV audience. I could hear all the screaming metal and smell the smoke. Let me give my top three in decreasing order - best first:

  1. JuggerBot vs. Hammerschlag Episode 5: This should have been an easy victory for JuggerBot, but they made an error in calculating the required thickness of their tianium front wedge. An early strong hit from Hammerschlag bent their wedge downward enough to lift their front wheels off the ground -- creating serious maneuverability problems and negating half of their power and traction. More than once they were on the brink of elimination, but driver Tom Vaeretti kept finding new ways to get the disabled robot to respond.
  2. Panzer Mk 1 vs. Viper Episode 6: The battle of the six-wheeled pushers. Panzer was a terrifying competitor with great gobs of speed and power. Viper was the only 'bot at the event with enough traction to have any hope of standing up to Panzer. After Viper proved to have the lower wedge, the two went blunt tail-to-tail in the middle of the arena, leaving arcs of dark rubber across the surface and filling the air with acrid tire smoke. Panzer chose to trust their superior power in a pushing match rather than maneuvering away and taking a risky speed-ramming approach. In the end, Viper's tires were better matched to the arena surface and delivered enough pushing force to derail Panzer's first try for Robotica glory.
  3. Run Amok vs. Juggerbot vs. Ram Force Episode 7: The season 1 fight to the finish platform was less than half the area of the one built for later seasons and there really wasn't enough room for three robots -- but there we were. As much a three-way chess match as a fracas, it came down to who found the best position before the rails dropped.

Wait... WHAAAT?
Q: Allright... I've won the Metal Warriors tournament in Robot Arena 2 as 'Run Amok', but I've also enjoyed playing as 'Run Amok' in a game you should check out called "MetalMania".


A: [Mark J.] Wait... There's a indie Robotica video game with 'Run Amok'? And it's been out since 2018? And finally a fan tells me about it? How did this slip by me? My palms get sweaty just watching the demo video -- Thank you!


Follow-Up I've exchanged messages with the developer of MetalMania. Development of the game has continued, but under another title: it has become Robot Rumble 2.0. There is a strong community of players on a Discord server who are developing replica 'bots from all parts of the sport using the in-game tools. Go take a look, but there is no longer a Run Amok or Maze.

It's a Quarter of a Tenth
Q: I could use some advice on what R/C car or vehicle I might use to put under my Micro Run Amok model. I tried 1/10th scale R/C but that's way too big. What would work?

A: [Mark J.] The Micro Run Amok model is a 1/10th scale version of Run Amok, but Run Amok is about 1/4th the length of a small sedan. That makes a suitable R/C car chassis someplace around 1/40th scale. Small R/C cars have a lot of speed and little pushing ability, but something like the WOWRC 1/32 Scale Mini R/C Car could be a start for something just to drive around. You can enlarge the paper model a bit in printing if required.


A Note From a Fan
Q: I know that 'Killer B' (Silver Team) was the first robot introduced in the first episode of Robotica season 1. However, in the other five preliminary episodes of that season the Red Team robot was the first to be introduced. In my heart I believe that Run Amok (Red Team) is rightfully the first ever robot not only to win Robotica but to appear on Robotica!

A: [Mark J.] Thank you for the nice note. I think I should do something in return: here is a link to a scan of the trading cards that four Robotica competitors published for their fans: Run Amok, JuggerBot, Silverback, and Death By Monkeys. Each card has a robot photo on the front and robot/team info on the back. I hope you like them.

Robotica Competitor Trading Cards (PDF)

How Massive Is It?
Q: Hey Mark, happy New Year!

I’ve been working on the idea of a full body drum spinner for a while now on and off and I keep getting stumped. No matter how I design this thing I can’t seem to have enough weight to spare. I always seem to have about 250g left in weight whether I go short and large OD drum or wide and small OD, and I can’t for the life of me figure out how to make a drum that keeps this darn thing under 1lb. Do you have any advice on building a massive drum that’s still lightweight and easy to assemble/disassemble? Any advice on where I may be able to lose weight?

Thanks in advance! [Davenport, Iowa]

A: [Mark J.] A prosperous and fulfilling New Year to you, Davenport.

Given that your chassis design leaves more than half the weight allowance available, I don't quite understand what problem you're trying to solve. You didn't include dimensions, materials, or possible drum designs; are you fishing for a compliment on your clever spring-loaded friction drum drive cradle (it is very nice) or trying for the first "Bad Hamburger" of the year?

If you're really having trouble getting a full cylinder wrapped around the full chassis, how about a short cylinder just to pick up the friction drive? Attach that to a pair of long beater bars anchored to bearing carriers at each end? It's a little sketchy on torsional rigidity, but it's certainly easy to assemble.

One Note: Your 'massive drum' is going to produce a whole lot of gyroscopic lift in turning maneuvers. You may want to run some numbers thru the Total Insanity Gyro Force Calculator before you settle on a design. A full-body drum standing on end lacks intimidation.


Complex System = No Simple Answer
Q: For a 4-bar lifter, if I have servo arm functioning as the rear bar, what effects will that have on the lifter’s performance? [Foxboro, Massachusetts]

A: [Mark J.] The impact of powering the rear bar ("crank") instead of the front bar ("rocker") in a 4-bar lifter sounds like a simple question, but the full answer takes up a couple chapters in a mechanical engineering textbook. I'll try to summarize:


As you can see in the 4-bar animation, the crank travels thru a greater arc when raising/lowering the lifter than does the rocker. I make the crank travel in the example to be about 140 degrees verus about 80 degrees for the rocker. This allows a servo powering the crank to perform its work over a longer arc, which lowers the torque requirement compared to powering the rocker.

Servo speeds are usually given as the time required for the unloaded servo to rotate 60 degrees. As the crank must rotate farther to raise the lifter than does the rocker, the lift speed for an unloaded lifter will be slower for a lifter with a servo powered crank than for a rocker powered by the same servo.

Powering the crank may or may not result in a slower actuation for a weight bearing lifter. Servos slow down from their unloaded speed in proportion to the load placed on them:

  • a servo loaded to 25% of its stall torque will slow to 75% of its unloaded speed;
  • a servo loaded to 50% of its stall torque will slow to 50% of its unloaded speed;
  • a servo loaded to 75% of its stall torque will slow to 25% of its unloaded speed;
  • a servo loaded to 100% of its stall torque will not move at all.

The torque required to power either the crank or rocker varies as the lift progresses. The screen grab below is from my Run Amok 4-Bar Lifter Spreadsheet -- a free Excel spreadsheet design aid. The spreadsheet is modeling a mechanism with a three-pound load on the lifter arm. The blue lines in the torque plots show the torque requirements for a powered crank and a powered rocker over the full lift for this specific design:

  • A powered crank will require an average torque of around 60 oz-in -- peaking at 82 oz-in.
  • A powered rocker will require an average torque of around 135 oz-in -- peaking at 150 oz-in before straining for the last bit of lift.

If the servo used in this specific design has a stall torque rating of 160 oz-in it will breeze thru the lift if powering the crank, but will strain at very slow speed if powering the rocker. A more powerful servo might result in a faster rocker powered lift than if used on the crank.

You may find value in reading thru the Ask Aaron Electric Lifter FAQ.


NOTE A typical servo controlled by a standard hobby R/C system has a motion range of about 90 degrees. If your application requires more rotation you need to make sure that:
  1. Your transmitter can be adjusted to provide an extended rotation range signal via an 'Adjustable Travel Volume' (ATV), 'End Point Adjust', or 'Travel Adjust' function; and
  2. Your selected servo has the mechanical capacity to move thru the desired range of motion.

I Just Can't Wait
Q: Ask Aaron answered its first question in 2003. You had a 10th anniversary Haiku contest in 2013, and a 15th anniversary Mad Lib contest in 2018. Are you gonna have a contest to celebrate Ask Aaron's 20th anniversary in 2023? What's it gonna be? [Petaluma, California]

A: [Mark J.] I'm mulling over several options to celebrate Ask Aaron's 20th anniversary, possibly including a contest like we had five and ten years ago. While I make up my mind, here's a fictional post based on one of the entries in 2018's Mad Lib Contest:

Q: I need a brushless speed controller for my hobbyweight robot 'Pork Chop Jr.' but I only have $300 to spend on the whole robot and can't waste it all on the electronics. What do you recommend?

A: Do what all the 'cool' builders do...

  1. Go to Hobby King and search for brushless speed controllers.
  2. Sniff suspiciously at the specifications, then order the cheapest one they have.
  3. Wait three weeks for it to arrive, or longer if it's the Lunar New Year.
  4. Open the box to see if what they shipped looks anything like what you ordered.
  5. Download a new user manual for this ESC because it was revised three times before it shipped.
  6. Throw the manual away because it's an indecipherable collection of poo that makes your head hurt.
  7. Flash the latest firmware onto the speed controller 'cause old firmware sucks.
  8. If flashing fails and bricks the controller, go back to step two and order a couple more.
  9. Flash the original firmware back onto the ESC because the new firmware turns it into a peizo gyro for a quadcopter.
  10. Post to reddit/battlebots to see if anyone knows how to get the bloody thing to stop beeping and calibrate.
Write back and let me know how this works out for you.

The Perfect Weapon
Q: What’s the idea behind a projectile weapon like Double Jeopardy’s? When I see them on TV, it never seems to do anything to the other bot. What is such a weapon supposed to do? [Richardson, Texas]

A: [Mark J.] Double Jeopardy's projectile weapon has done exactly what it was supposed to do, and it did so before it ever fired a shot:

  • The current incarnation of BattleBots is not a combat robot tourament or a sporting event -- BattleBots is 'reality' entertainment. The producers of the show want to maintain a variety of interesting designs to keep their audience entertained.
  • Prospective competitors must submit an application to the show producers that includes detailed design drawings, an explanation of the features of the proposed robot, and a summary of the resources and skills available to the build team.
  • If your proposed 'bot and team look and act like robots and teams the audience has already seen you're simply not going to be accepted to appear on the show.
A robot with a pneumatic cannon campaigned by three lawyers in suits? They aren't like any other team, so they're 'in'. Is the weapon effective? It doesn't need to be -- for TV it just has to be different.

See also: BattleBots is a television show that looks like a sports tournament.


Bought a Bargain Bot
Q: I bought a robot someone built: twin 24v motors and two 24v Victor 883 ESCs. No transmitter or receiver, but supposedly plug and play to put in. I'm researching that and have found a 6-channel system that may work - just waiting on few answers from the manufacturer.

There is an on/off switch harness that the last user did not use. He says that he found a way to do whatever it was doing with the transmitter he used. The on/off switch has only two wires, not 3-pin so I guess it does not plug into the 3-pin connector on an ESC. Seller mentioned where it went in quick discussion but my brain did not record it so now I'm lost on where to put it.

The only place I see a possible two-wire connection is the Brake/Coast jumper. Is this where it goes to turn the ESC off? [Franklin, Ohio]

A: [Mark J.] There is no place to wire an on/off switch on the Victor 883 ESC itself. The brake/coast jumper controls how quickly your motors come to a stop when the ESC gets a stop command from the radio -- keep it on 'brake'. Power is controlled by adding a switch to the positive input wire from the battery (see diagram). You will need a high capacity switch or removable link capable of handling the full current demands of the motors -- which may be substantial.

Q: I want to put a master switch in between the battery and ESC. How do I wire an on/off switch? Do I use 3 or 4 post switch?

A: The device labled 'Removable Power Link' in the diagram is the master switch. In large robots this switch is usually a 'removable link' for safety purposes. A removable link is just a two-pole connector with one side shorted by a loop of wire -- pull the connector apart and the circuit is broken.

Smaller class robots can use a simple single pole single throw (SPST) switch of suitable capacity, or you can make a removable link out of a small two-pole connector.

See also: Frequently Asked Questions #19 and Combat Robot Radio Systems - what functions do you actually need?

Q: A follow up question on the Bargain Bot. The bot has two 24v motors each attached to their own 24v Victor 883 motor controller. Seller of the bot said I just needed to hook up an RC Receiver and matching/bound transmitter and it would be good to go. Well I've bought two transmitter/receiver sets now.... just tried the second one. Same issue with both (beside poorly translated Chinese manuals): 883's flash that no PWM signal is found. I have hooked each 883 to different channels on receivers and turned on the transmitter before powering up the bot: no change. I reversed the cable with signal wire on different pin: no change. The ESCs always flash orange indicating no PWM signal.

Am I missing a part? Do I need to power the receiver separately? I was thinking it got power from a regulated voltage circuit built into the 883, but could be wrong on that.

A: Some ESCs have a built-in voltage regulator called a Battery Eliminator Circuit (BEC) to power the receiver. The Victor 883s do not have a built-in BEC so you do need to power the receiver separately. If your robot is as old as I think it is the builder may have used a separate receiver battery pack for this purpose. I would suggest adding a 'stand alone' BEC to power the receiver: something like this.

The diagram below shows how a stand-alone BEC is wired in parallel to a generic motor controller. You may plug the BEC output into any unused port on the receiver. You want and need only one BEC for your system.

Q: Do I need a converter of some sort from RC type control signals to PWM signals of these larger motor controllers in bots??

A: The Victor ESCs were originally designed to work with a special control system that had a higher voltage magnitude Pulse Width Modulation (PWM) signal than typically comes from an R/C receiver. For best signal reliability they require an IFI PWM Signal Driver to boost signal voltage. I see from a photo included with your question that signal drivers are already installed on your receiver cables. Keep them in place and you'll be fine.

Q: The BEC you linked to says it is a "Brushless Receiver Servo Power Supply". I think my motors are brushed so should I get a brushed version?

A: You do have brushed motors (they look like Bosch GPA 750s) but there is no difference in BECs for brushed and brushless applications. The BEC just provides 5 volts to the receiver power buss. I suspect that the BEC manufacturer added 'brushless' to the description in hopes of getting a few extra search hits.

Q: I see BECs in 5 volt, 6 volt, and adjustable voltages. Are receivers 5 volts these days?

A: Acceptable receiver voltage ranges vary with manufacturer, but I know of no receivers that cannot handle 4.8 to 6.0 volts. The 6 volt BECs may be preferred by R/C aircraft builders to get a little more speed from their control surface servos. For your purpose either 5 or 6 volts will be just fine.


Gotta Get Down to Go Up
Q: I have been seriously thinking about getting into combat robots for a few months now so obviously I have been reading this website for a few months. I just became a father this year and I am so sorry to hear about Aaron! I wanted my first bot to be a vertical spinner but reading your website (FAQ #8) and some other forums (NO SPINNER) I settled on a 4 bar lifter. If it fails I still essentially have a wedge bot but before that I can try to do stuff actively. Anyway I have it all drawn up in CADD and I ran the 4-bar Calculator but ...
  1. The graph showing the start position is very different from the drawing. It seems the negative on the "rear bar base rise up" causes the big issues.

  2. I can extend D a little...but no way could I get to 26mm.

  3. Do you have any ideas how I could improve the lifters performance?
"New Dad" [Slidell, Louisiana]

A: [Mark J.] You stopped reading FAQ #8 on 'first bot' a little early. After it says no spinner it continues with no lifter, no flamethrower, no crusher. Keep it simple....

Before I get to your questions, I spotted a couple errors in your spreadsheet inputs:

  • Base [Frame]: A is measured in a straight line from the Base of the Rear Bar (Crank) to the Base of the Front Bar (Rocker). As your Crank Base has been dropped below the Rocker Base, the measurement is just a bit longer than their separation along the X-axis. I make the correct measurement to be about 33.9 mm.
  • As shown in 'Figure 1 - Elements' on the 4-bar spreadsheet, Extension: R includes the length of Top Bar [Connector]: C. That makes the correct value for your design as drwan 79.0 mm rather than 57.48 mm.
To your questions:

1) The problem you've encountered is not directly due to setting a negative value for the Rear Bar Base Rise. The geometry of your design causes the rear end of the Top Bar [Connector] to start its rise faster than the front end, which causes the front tip of Extension: R to briefly dip down below the base of the Front Bar [Rocker]. This negative relative height of the Extension tip breaks the calculation engine formulas and crashes the spreadsheet. The giveaway is the #NUM! Error that appears below the 'Front Bar Torque Chart': Shortening Rear Bar [Crank] to 12 mm will prevent the initial 'dip' and allow the spreadsheet to run correctly, but the performance of the system is not very good: there is a very limited range of servo motion combined with a high torque requirement. 2) The recommended lengths for Front Bar [Rocker]: D are critical for getting best lift height from lifters powering the Rear Bar [Crank] over a full range of motion. Lifters powered by the Front Bar [Rocker] may ignore the recommended Rocker length range, but should note that Rocker motion may be limited by very short Rear Bar [Crank] lengths.

3) Four-bar design is as much art as science. Keep playing with values 'til you get a workable design. A couple suggestions:

  • It is desirable to place the Front Bar [Rocker] much closer to the lift point than you have it. This will reduce the torque loading on the servo and place less stress on the entire system. Flipping the servo end-for-end will place the servo output shaft about 12 mm farther forward in the 'bot and change the geometry of the mechanism for the better.
  • Take a look a successful small 4-bar lifters like 'Pad Thai Doodle Ninja' to get a general idea of bar positions and ratios. This is much easier than earning a degree in mechanical engineering from MIT. Are you sure you don't want to build a wedge?
One last note: You're currently entering measurement values in grams and millimeters so the units for torque are expressed in g-mm. If you enter the lengths as centimeters the torque output will be in the standard g-cm. Yes it's easy to convert, but I suggest staying in standard units to avoid confusion.

Update - After working with the Run Amok 4-bar Calculator to answer the above questions from "New Dad", I noticed a few things that needed improvement or clarification. It all made sense to me three years ago when I wrote it, but the passage of time now allows me to see it with new eyes. I'm pleased to announce the release of Version 1.3:
  • Pop-up reporting of errors caused by trigonometric violations;
  • Rocker and crank end point angle display for both front and rear bar powered lifters;
  • Instant warning and display of impending 'retract lock' condition for powered front bar designs;
  • A new selectable option to reduce distortion in the linkage display plot; and
  • Re-written documentation.
A lot of late-night coffee and head scratching went into this version. I think you'll find it to be a big upgrade!

Variations on a Theme
I've been playing with multiple websites that use an artificial intelligence driven graphics engine to create an image based on text inputs and an optional starting image. Just for fun I fed an image of Team Run Amok's namesake robot into one of these engines and asked for variations on the theme. Thirty seconds later it spit back the images you see below: You can do the same with a render or sketch of your robot. More information on the process is at our Team Run Amok page.

View, Cast, or Download
Q: I'm a big fan of the TLC Robotica series, but I'm having trouble finding some of the season 2 and 3 episodes. Would you consider uploading these seasons from your library to one of the video services? [Tempe, Arizona]

A: [Mark J.] We won't upload copyrighted video to the internet services -- see FAQ #13. However, I've recently learned that the Internet Archive has a complete set of Robotica episodes from all three seasons available to view, cast, or download:

Consider clicking on the Internet Archive's "donate" button and chipping in a couple bucks to support their work.


They Don't Get It
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]

A: [Mark J.] My robots don't care. My robots don't spread, suffer from, or die from Covid-19 -- but you can. Don't be selfish. Follow the science. Stay safe.



Two photos of Aaron Joerger Remembering Aaron Joerger, 1991 - 2013

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

- Mark Joerger   
Killer Robot drawing by Garrett Shikuma

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.

Aaron's Greatest Hits! More of Aaron's Poems Aaron at Nickelodeon Robot Wars Aaron's Minecraft High Dive Video Aaron's World of Warcraft Player Guide


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