Questions and Answers about Combat Robotics from Team Run Amok.

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7810 Questions and Answers about Combat Robotics
from Team Run Amok
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Stop at Line Five
Q: Is the question "Is asking a question about if a question is substantive substantive?" count as a substantive question?

- couldn' t resist, Iceywave : ) [West of San Antionio]

A: Mark J. A meta-question deserves a meta-answer:

There was a young boy from the sticks
Whose Limericks went to line six.
They started OK
But then went astray
When he found himself in a fix
Toward the end.
Flashback: an archived post from 2021
Q: Somebody made a comment about the "hamburger is bad" rule on [a combat robot social media site]. Can you tell me what that rule is? [Henderson, Nevada]

A: Mark J. You came to the right place.

'Ask Aaron' has a long history of receiving requests for very specific recommendations on materials or components that provide far too little information for us to give a useful answer. We needed a name for this type of question and a way to explain our problem in answering. In 2010 we published a webpage titled "The Hamburger is Bad" that uses a fictional exchange of questions and answers about whether a 1/4 pound hamburger is good to depict the problem. The meme caught on in the combat robot community.

So, "The Hamburger is Bad" is not so much a rule as a shorthand request to provide adequate information when asking a question.

Brushless in Tunisia
Q: What are the best brushless motors for the weapon system and the drive system for a 70 kg fighting robot [Tunis, Tunisia]

A: Mark J. "Best" depends on many factors which you have not shared in your question. Additionally, brushless motors of this size require substanital expertise in adjusting their controllers to provide acceptable performance; they are not "plug-and-play". The "best" motors for your particular situation may not be brushless at all.

Further, I have seen videos of recent Tunisian robot combat (see image below). Wire mesh is wildly inadequate for the safety of the competitors and spectators. Combat robots of this size and power require a much higher standard to protect human life and limb from potentially deadly shrapenel. My conscience does not allow me to assist in creating faster or more powerful robots for use under such conditions.

How Wide Is It???
Q: My 2wd robot has the batteries and drive escs on one side. To do this I would need to lengthen the phase wires of the second drive motor a considerable amount. I have space to move one of the escs over, but that would then mean having a really long signal wire as a result to get to the receiver. Between the two, which would be the more favorable option? [Sacramento-ish]

A: Mark J. I hesitate to answer this question because I have to guess at how you define "a considerable amount" and "really long". If your robot is "SMEEEEEEEEEEEEEEEEEE" wide you might need special techniques -- may I assume your 'bot is not that expansive?

  • It is considered good practice to keep all phase wires for a given motor the same length, but the phase wires from ESC to motor #1 do not need to be the same length as the phase wires from ESC to motor #2.
  • A long receiver signal wire is not itself a problem. General advice is to keep it under 15 feet, assuming that it is routed to avoid sources of potential interference. You can always bind a second receiver to your transmitter and put it on the other side of the 'bot if you like.
  • The only critical wire length is the run between the battery and the ESCs. Those wires need not all be the same length, but they should be kept quite short.
Given the above, the preferred solution is to keep both ESCs close to the battery and extend the phase wires of the more distant motor.
So Very Close
Q: I'm making a beetleweight horizontal spinner for my first robot. I have all the electronics but I do not know how to wire it. Is there a way to wire a skid steer system on a duel esc? [SanFran Bay Area]

A: Mark J. Read the "Don't Do That!!!" post immediately below for a link to a wiring diagram for skid steer with a dual ESC -- plus several reasons why a novice builder should not construct a robot with a spinner weapon.

Then read the Ask Aaron FAQ to answer the next few questions you'll want to ask.

Q: On a skid steer with a duel esc should I power each wheel individually or is it better to create some form of a linkage between the two. If its best to individually power them do I wire two motors to each input on the esc or do I need two duel ESCs

A: You have not mentioned how many wheels your robot has. Most beetleweight horizontal spinners are two-wheeled. From your question I will guess that you have a four-wheel design with each wheel powered by its own motor. It helps to tell me things like this because my psychic abilities are weak. As shown in the wiring diagram above, it is typical to wire both motors on one side of the robot to a single output on the dual ESC. The diagram makes a couple assumptions:

  • You have not mentioned what drive motors you have selected. The diagram assumes that you are using 'brushed' drive motors -- 'brushless' drive motors each require an output from their own ESC.
  • You have not mentioned the specific dual ESC you have selected. The diagram assumes that the selected ESC has sufficient current capacity to supply both of the drive motors thru each output port.
If you require specific recommendations I will need to know the specific components selected for your robot: drive motors, drive ESC, wheel diameters, battery voltage, and battery capacity (mAh). It may also be handy to know what radio brand and model you have selected to control your robot.
I will restate my concern that you as a novice builder plan to construct a robot with a spinning weapon. I worry both for your safety (do you have a safe test box in which to try-out your weapon?) and that the added complexity of a spinner weapon will lead to a poor experience for you at your first tournament. Please do reconsider.
Don't Do That!!!
Q: My competition is on April 25th and this happened. I don’t think I have time to replace them. Can these two still work? I don’t know what happened. [Washington D.C.]

A: Mark J. What happend is that you plugged two random wires from your brushless weapon motor directly into the main power plug on your 6S LiPo battery. Brushless motors are 'dumb' -- they require a motor controller to route current thru each of the three winding circuits in the proper sequence and timing in order to operate. Plugging a pair of brushless motor wires into a battery creates essentially a dead short which pumps hundreds of amps thru one motor loop.

DO NOT connect brushless motor wires directly to a battery! You're lucky to still have fingers on your left hand and a non-burnt crotch.
The Basics: Your brushless weapon motor plugs into the weapon brushless ESC, and the brushless ESC plugs into the battery.
  • See the simplified combat robot wiring diagram.
  • Do not test 'loose' components. A brushless motor of that size will have a violent torque reaction if wired up correctly. Tie everything down securely.
  • The motor and battery may or may not be useable at this point. If the battery sleeve is no longer snug and tight around the cells ("puffy") the battery is toast and should be disposed of properly. Never attempt to charge a 'puffy' LiPo battery.
  • IF the plastic battery sleeve is still tight you may:
  1. Securely mount the motor -- disconnected from the weapon itself.
  2. Correctly connect the motor to the ESC.
  3. Plug the ESC into your R/C receiver.
  4. Cautiously attach the ESC to the battery.
  5. Turn on your transmitter with all sticks and switches in the correct start-up positions.
  6. Provide 5-volt power to the receiver.
  7. Carefully apply a little throttle from your transmitter to see if the motor responds.
Combat robots aren't rocket science, but you are dealing with potentially dangerous components, high power levels, and many opportunities to hurt yourself or others by screwing something up. This is why novice builders should build small robots without spinner weapons. Being under time pressure to complete your robot only adds to the danger.

Consider dropping out of the competition and revising your design to something more appropriate for a new builder. I'll write you an excuse slip if you like.

About So Big
Q: What is the usual size of an 'insect sized' arena? [Lagos, Nigeria]

A: Mark J. A common size for beetleweight competition is 8' by 6'. One-pound antweight arenas are often 4' by 4'.

Here is a YouTube video covering the design and building of a 4' by 4' antweight arena with a link to a parts list and design drawings.

What's Left?
Q: Build: Repeat Robotics 16mm Brushed Planetary Motors MK2 and a Scorpion Nano 2.1 brushed ESC. When starting moving one motor stops. After a restart, the motor works again. I've switched out the Scorpion Nano, the motor, and the fully charged 3S battery. The issue remains.

Looking for some problem solving tips. [Social Media]

A: Mark J. OK -- it isn't the motor, it isn't the ESC, and it isn't the battery. Tell me about your radio system.

Comment: Ooo, good call. I'll switch to another Rx and Tx.

Horrible, Outdated, and Expensive
Q: I'm building a middleweight bot with two wheels and a spinning horizontal wheel. I'm currently struggling to wire up the receiver and the weapon speed controller to each other. I have a FS-iA6B receiver and a Roboclaw Solo 60A ESC for the weapon motor. [Denver, Colorado]

A: Mark J. The Roboclaw is a general purpose brushed motor controller that can be interfaced with many control signal sources including standard hobby R/C receivers like your FlySky -- but it is not 'plug and play'. You will need to connect the Roboclaw to your PC with a USB cable and run the BasicMicro Motion Studio software to select RC input. Here's a video of the process.

Q: I figured that, and I can do all that part. I just don’t think I can plug a 3 wire into the roboclaw which is where I’m stuck. I know how to do the rest already.

A: The black/red/white wires on a standard servo cable from the receiver (CH3 for weapon?) connect to the ten-pin CTRL port on the Roboclaw in this order:

  • Black (ground) goes to pin 1;
  • Red (5v power) goes to pin 2;
  • White (signal) goes to pin 3.
The Roboclaw provides power to the receiver via the cable -- you do not need additional receiver power. See the Roboclaw manual for a pin diagram.

Q: I'm back again since I got some really good help last time, thanks. So with my weapon hooked up I now have to set up my two wheels with a MCP263 Dual Channel Motor Controller. I assume I need to connect them to channels 1 and 2 but not sure where they should connect on the ESC.

A: Where on earth are you finding these outdated, expensive, and horribly documented electronics? One-hundred-eighty-nine pages of user manual and the only diagram for wiring in an RC receiver references connections S1 and S2 THAT DO NOT EXIST.

The only clue I have is a pin-out diagram on page 4 of the MCP26X Datasheet that indicates pulse inputs on pins 6 (P2) and 13 (P1) of the DB15 female connector. Try connecting the signal leads from receiver channel one to pin 13 and channel two to pin 6. I assume you will need to connect the MCP263 to your computer and use the BasicMicro Motion Studio software to select RC input as you did for the Solo 60A.

One Better Than Two
Q: My spinner has an XL timing pulley with a 1/2" toothed section for the belt and 1/8" thick flanges on each side, making it 3/4" thick in total. However, I couldn't find a needle bearing in that size with a 3/8" shaft diameter. Is it fine to squash two half-sized (3/8" wide) bearings in the pulley bore side by side? [Ashburn, Virginia]

A: Mark J. Is that pulley your entire weapon hub? It is better to have a wider hub that separates weapon bearings for a more stable base to improve stability and strength. Needle bearings are sensitive to even small static misalignment. Jamming two needle bearings right up against each other will magnify the effect of any installation or bore problems. You might be fine -- you might not be.

I would prefer one of two alternatives:

  1. A single 5/8" wide needle bearing. Add small spacing washers on each end to assure it stays centered.
  2. A full-width sintered bronze ("Oilite") sleeve bushing. With proper lubrication this type of bushing adds very little friction, can survive enormous impact loads, and will not wear into non-hardened shafts.
Fell Off a Bridge
Q: Ramfire 100 won 1994 US Robot Wars, then fell off Earth as far as I know. Do you know if ANYTHING else happened to it? [An iPad in Utah]

A: Mark J. Yes, I think I remember hearing something about 'Ramfire 100'...

Michael Sorenson's 'Ramfire 100' fought two matches at the 1994 US Robot Wars and won them both to become the heavyweight champion. Depressed that there were no more opponents to defeat, 'Ramfire 100' made its way to the center of the Golden Gate Bridge and leapt off - only to land on the deck of a freighter bound for Finland. After hitching a ride into Helsinki, 'Ramfire 100' worked as a forklift in a paper mill for several years and saved every penny until it had enough money to open a small cigar shop. It married a lovely girl named Helmi and had four children: a girl, two boys, and a fax machine. The family is doing well.

See also: Ask Aaron MadLibs.

Flashback: an archived post from 2019
Q: I was looking through the Combat Robot Hall of Fame and I noticed that some of the robots have more than one name and that each of those names is tracked separately on Botrank. Doesn't changing the name make it a new robot? [Reddit comment]

A: Mark J. Botrank is a service to the robotics community that tracks the competition records of combat robots and attempts to rank them within their weight class. BotRank simply tracks robots by the name they register for at a tournament. Given the number of robots and fights that they have to track this is a reasonable approach for them to take; a new name starts a new combat tracking record.

The Combat Robot Hall of Fame has a greater interest in the true heritage of a robot nominated for recognition. An increase or decrease in the weight of a robot or a name change (on a whim or to meet television production requirements) does not by itself create a new robotic entity. The Hall believes that the identity of a robot lies in its design concept. That can be a challenge to sort out.

I've put together a fairly lengthy explanation of how The Hall sorts this out - with examples: "Two robots one, or one robot two?"

Some is Good - More May Be Better
Q: Rpm's for a 1lber vertical spinner weapon [Greenville, Pennsylvania]

A: Mark J. Yes, you do need some RPMs for a spinner weapon. See the 'Rotational Speed' section of our Spinning Weapon FAQ for help in figuring out how many.

Flashback: an archived post from 2023
Under the Cover
Q: I'd like to cut away the plastic wrap around my brushless weapon ESC to see what's inside, but I don't want to break anything. Do you have a drawing to help guide me? [Fort Collins, Colorado]

A: Mark J. You didn't tell me which ESC you have so I'll just give you a generic sketch:

Shades of HellaChopper
Q: I am the same person who asked the question
Nothing Practical
[archived here]. My design is based on the quintessential, exposed wheel 2WD bar spinner that you no doubt have seen several hundred times. I'm already aware of the glaringly obvious issues with this weapon, such as the fact that I will need to drive like Gary Gin crossed with Ray Billings to avoid the lightning-fast modern vertical spinners for 3.9 seconds with a massive whirling gyroscope trying to send me into the arena side rails, and the difficulty of squishing a 430g, 10" bar into 3 lbs. The former issue is compounded by the fact that events like NHRL have you start in the corner of the arena, halving my dodging angle from 180 degrees to 90 despite the increased length across the diagonals. I'm basically using the Last Rites design philosophy of "I don't need armor if I knock out the other guy first."

My motor (SunnySky X series V3 2814 1400 kv) has a max output of 1,180W, so using the Vector bar statistics in this post for a rough reference, I should be okay in terms of air resistance. By using these newfangled LiHV cells I found, I was able to push even more power than my planned 14.8V into the weapon for the same weight, giving me 15.2V. The pulley would be 3D printed nylon with a central hub containing a bearing running through the hole in the bar. With two Dartbox Viper motors for drive, I should have more than adequate speed for the weight class. Chassis setup is probably going to be 0.25" UHMW sides with 3mm carbon fiber top and bottom panels/weapon supports.


A nice image of HellaChopper - just to break up the blocks of text.
Is there anything I'm not considering here? Of course, I won't get 2.5 kJ in real life, but even 2,000J is nearly an order of magnitude stronger than your average beetle spinner. Maybe 3.9 seconds is long enough to bog the poor brushless outrunner motor and catch it on fire before I even get the chance to unleash my >2 kilojoule impact? Or is it a safety concern, in that insect arenas may not be equipped to handle the impact of this out-of-control tactical nuke of a robot? With some driving practice to counter the gyro on spinup, I'll take 4 vulnerable seconds (Probably even less, as the spreadsheet has me at 1kJ at 1 second, which is still hugely damaging) for 2:56 of a bar that can probably take out the other bot in one hit, and then half of the arena with it like a modern-day Blendo. (Hyperbolically speaking, of course)

Recoil is a consideration, but it's a 3 lb bot, and beetleweights are known to hockey puck across the arena like crazy without much internal shock damage. Suffice to say, I won't see the catastrophic failures of modern Tombstone. Plus, shallow wedges won't reflect the full force of my weapon back into me, and anything that engages heavily enough to do so will end up obliterated.

There's also bite, but in my opinion, a shallow engagement isn't the end of the world on a horizontal spinner that doesn't need to grab and toss like a vert. Hell, the high engagement that allows verts to toss their opponent 15 feet into the air can even be bad, as it will contribute to sending me flying back in a horizontal that can't push energy into the ground on impact. Just look at Last Rites vs Whoops from Robogames 2017 where Ray was kicking Whoops' ass until he got a big engagement strike that sent him recoiling violently. [Arlington, Virginia - no iCloud this time?]

A: Mark J. When you're atop a determined horse that manages to work its bridle into a position where it can grab the bit with its teeth, you can pull that bridle in any direction you like but the horse will pay you no mind and keep to the path it chooses. I don't think my input will effect your design decisions, but perhaps other builders will benefit.

You may want to stop reading at this point and click this button:

Your image attachment was lost in an internet eddy, but from the numbers you gave I was able to back into some of the numbers you did not supply. It looks like you're planning to use a 1.5:1 pully reduction to spin your weapon bar up to an attempted 14,200 RPM with a 425 MPH tip speed and store 2500 joules. I believe you are minimizing multiple issues. Here are a couple:

Consequences of Poor Bite

Stored energy is only as useful as the ability you have to transfer that energy in an impact. At 14,000 RPM a weapon would be fortunate to transfer a tenth of its stored joules to your opponent. Most likely would be a series of little "bump backs" as the blade skitters across a surface. What that stored energy will be effective at doing is to provide a prolonged sequence of pinball rebounds once you start bouncing off the arena walls.

Consequences of Heat Saturation

The motor has a claimed max current of 80 amps for 30 seconds -- assuming that it is starting from a cold zero amp condition. During your prolonged calculated spin-up your motor is being bogged down far below its design operating RPM and pulling a lot of current. If your weapon spin-up is interrupted by a series of slowing impacts the motor will remain in that amperage danger zome for an extended period of time. Worse, your weapon motor will expend a continuous ~900 watts of power to maintain 14,000 RPM against weapon aero drag, which will place it (and likely the ESC) fairly close to heat saturation. Having to spin back up from this condition by drawing an average 160 amps over four seconds is a sure-fire way to blow the motor/ESC/battery.

You certainly are not the first builder to decide that massive weapon power is the path to glory. If that worked the arenas would be filled with such designs. They are not. You might want to read up on the failed BattleBot entry HellaChopper.

Reply: "Shades of Hellachopper" here -- dropping to 2:1 reduction. Thanks for the reality check.

Comment: That's dangerously close to rational, Arlington. A change from a 1.5:1 reduction to a 2:1 reduction:

  • Cuts sustaining motor power by 60%;
  • Cuts spin-up time by 40%; and
  • Improves bite by 33%.
Don't hesitate to throttle the weapon back if your hits aren't effective against a specific opponent. Bite wins matches.
The Pulses Don't Match
Q: Theoretically, would I be able to drive a brushed motor with two escs wired in parallel to split the current load? The signal wires would be spliced together as well to share the same input. [McClellan Park, California]

A: Mark J. No. ESCs operate with internal frequency generators to produce the current pulses used to control motor speed. The pulse generators for two ESCs -- even from identical sources and receiving identical receiver signals -- will not be 'synched'. At times the full current of the motor will be passed thru one unit, then the other. This negates their ability to "split the current load" and will very likely smoke both ESCs. Equally bad, while they survive you will get irregular pulsating speed variances rendering consistent control impossible.

Don't do it.

Before someone writes in to tell me that 'back in the day' some builders used two ESCs to "split the current load" on high-current Magmotors and Bosch GPAs, let me clarify. Those motors had a system of four brushes set 90 degrees from each other, and each of the ESCs were wired to a different pair of those brushes. This was a special application for specialised motors and the outputs of the ESCs were not "spliced together".

See also this previous post in the Ask Aaron Motors and Controllers archive.

Malenki Weapon Voltage Boost
Q: I would like to get more power from my fairyweight spinner, but I use a Malenki-Nano dual ESC/receiver that limits me to a 2S lipo battery. I don't need more drive speed but my spinner waepon would be much better at the higher voltage. I know there is a high voltage version of the Malenki but is there anything I can do that will allow me to run my Malenki-Nano on a 3S battery? [Social Media]

A: Mark J. There is a similar situation that involves operating a lifter servo weapon at 2S when it is plugged into a receiver that can take no more than the voltage from a Battery Eliminator Circuit (BEC). The two situations have similar solutions.

With your Malenki, it is possible to use a battery with more than 2S to provide power to your brushless ESC by tapping into the balance plug of the same battery to obtain 2S power for the ESC/receiver and your drive motors. A diagram for a 3S battery is provided below.

There are a few drawbacks to this solution:

  • You will need to switch
    S
    the positive leads to both the weapon ESC and to the Malenki. DO NOT ATTEMPT to use a single power switch on the ground wire! Removing the battery ground causes a 1S reverse voltage to both the Malenki and weapon ESC.
  • Make certain to use the same ground potential for both the Malenki and the weapon ESC. See this archived post for details.
  • The three battery cells will not drain at the same rate. Balance charge the battery every time.
A Motor Spins a Thing
Q: how does vertical spinner works [Ontario, Canada]

A: Mark J. This is a job for the Google A.I.: How does a vertical spinner weapon on a robot work?. The A.I. is much more patient in answering this type of broad question than I am. Each time you ask it generates a slightly different answer, but the answers I've seen for this particular question have all been reasonably complete and accurate.

If you want more detailed technical information, see the Ask Aaron Spinner Weapon FAQ.

If you have specific questions I'm glad to help.

No Steering Wheel
Q: drive train [Madhya Pradesh, Bharat]

A: Mark J. I've never actually tried, but it shouldn't be very hard. You can only go where the rails go, so just give it a little throttle and toot the whistle once in a while.

 
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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