Privacy Policy
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.
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.
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.
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.
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:
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A: Where on earth are you finding these outdated, expensive, and horribly documented electronics?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.
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:
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.
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?"
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.
A: Mark J. You didn't tell me which ESC you have so I'll just give you a generic sketch:
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.
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.
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:
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.
Reply: "Shades of Hellachopper" here -- dropping to 2:1 reduction. Thanks for the reality check.
Comment: That's dangerously close to rational, Arlington.
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.
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:
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.
A: Mark J. Someone had to count the laps. Someone had to keep the clock. Someone had to decide who left the platform first. Someone had to determine if a goal in 'The Maze' had been blocked. Someone had to award me a penalty for going out-of-bounds in 'The Speedway'.
For Season 1 that 'someone' was Terry Huntsberger, the NASA-JPL Roboticist listed in the end credits as "Robot Consultant". I mention Terry a few times as the Robotica 'tech judge' in my Robotica Journal.
Terry was not listed in the credits for seasons 2 and 3 and no one is credited as a robot consultant -- but someone had to make those calls...
I know this is a lot in one post, but I know you're the guy to ask. So let me know your thoughts on my setup. [Mount Prospect, Illinois]
A: Mark J. I see that you have made some changes to your design since your earlier post. A few observations:
A: It is not a matter of "Featherweights should be around a 20:1 drive system" -- different drive motors will require differing gear reductions for any given combination of robot weight, wheel diameter, and arena size. See: Optimizing Drivetrains.
You have the relationship between traction and gearing reversed. Adding magnetic downforce to a robot creates a need for greater torque from greater gear reduction -- not the other way around. The Team Tentacle Drivetrain Calculator includes a field to enter magnetic downforce and can calculate adjustments to the drivetrain requirements based on that added traction.
A: As noted in my answer to your earlier post, AndyMark Redlines are quite commonly run at 6S voltage in combat robots . If run with a reasonable gear reduction they can handle the heat. If run with insufficient gear reduction they will melt. Wrapping them in a TPU heatsink would be worse than doing nothing as TPU is a much better insulator than heat conductor.
A: There are essentially no differences in bearing protection. speed, or rotational inertia between a Live Shaft that spins with the weapon and a Dead Shaft that is fixed relative to the chassis. The primary difference is that a 'dead shaft' can be a structural member of the chassis that adds to both the strength and rigidity of the robot.
A: Angular contact bearings (expensive) are used where a single bearing must absorb forces from all directions. This is not the case for your weapon. A pair of tapered roller bearings (much less expensive - and stronger) will do very nicely.
Some builders prefer oilite bushings for their weapons. These bushings can absorb huge impact loads and are inexpensive -- at the cost of a bit greater friction.
A: See Frequently Asked Questions #17. Note also the difference between 'countersink' and 'counter bore'.
- sincerely, Iceywave
A: Mark J. Sincerely? I suspect you're just prompting me to post a pic of Team Run Amok's infamous antweight snapper/crusher/flipper 'Rat Amok'.
In truth a rat trap can store far more energy than is required for a properly designed antweight spring powered flipper -- a mouse trap spring should be adequate. I found an analysis on the energy stored in a typical mouse trap at the Physics Stack Exchange:
I then used τ = −kθ (torque applied to the spring arm by the weight is equal to torsional constant times the angle rotated) along with the values from one of the weights to calculate how far the spring is twisted by default [θ = (τweight / k) − θweight ]. This came out to about 73.63°.
I used this 'starting angle' to calculate how much potential energy (U = 1/2kθ2) the spring would have when totally open (an additional 180° from that last angle we found). The maximum energy that you could get out of this "standard" mousetrap is approximately 0.815 J.
A: Mark J. Depends on what you consider "heavier weight classes". Last I heard you were building a beetle and/or a hobbyweight.
Keyed hubs are the standard for combat robots above the insect classes for good reasons: compact, reliable, and widely supported by manufacturers. You need good reason to not use them.
I have used Trantorque keyless bushings (cross-section pictured) to lock pulleys and sprockets onto smooth shafts with good success. They come in a good range of sizes but are generally too bulky to use on motor shafts. They are also a bit pricey.
Down on the lower end of 'big bots' I see some builders using clamping hubs that surface-bolt onto pulleys and sprockets. A seach for 'clamping hubs' will turn up a variety of styles.
With all the talk of motors getting burned out due to aerodynamic resistance lately on the site, I don't want to waste money and time implementing a motor that melts when I turn on the blade. I'd then have to redesign the bar, chassis, and pulley to accommodate the bigger motor in weight and space.
A: Mark J. If you don't want to waste money and time you should pick a different hobby.
CAUTION: Entering the Deep End of the physics pool. If you Google "aerodynamic drag equation" you'll get this tidy little equation that calculates the drag on an object moving thru still air:
The Big Problem: Our rotating weapon is not moving uniformly thru still air. Velocity ranges from the greatest out at the tips down to zero at the hub center. How good is your calculus?
The Bigger Problem: The motion of the weapon creates a vortex of wind that changes the velocities of the weapon relative to the air. This is non-trivial and would keep a supercomputer busy for a week to calculate.
The Bottom Line: It is unrealistic to attempt to calculate the power needed to offset the drag on a defined spinner weapon at a given speed. But this is not to say that it is impossible to gain guidance on the power requirement for your weapon:
Watts Required =
A: Mark J. The 4mm wide S3M FingerTech belts are uncommon in beetleweight spinners -- particularly for a belt long enough to reach out to a horizontal weapon. The S3M tooth profile is OK but the magnitude of the power transfer calls for a wider belt:
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.
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
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:
Q: What is the usual size of an 'insect sized' arena? [Lagos, Nigeria]
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.
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.
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?
A nice image of HellaChopper - just to break up the blocks of text.
A change from a 1.5:1 reduction to a 2:1 reduction:
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.
First off with just the specs I would be curious any advice for the design just based off the electronics and CAD photo.
Q: Getting into my questions though, my first is about the drive. In another post you said that Featherweights should be around a 20:1 drive system. My first question is, if I have an arena that is utilizing a steel floor, and I add magnets for extra down force, would 10:1 be suitable? Or does the extra downforce not affect the torque?
Q: Another comment about the drive system, is when running the redlines and gearbox at 12v, they seem to get hot very fast. Besides adding a cooling fan, is there an easy way to dissipate the heat? Would 3D printing a TPU heatsink be beneficial? Or maybe it isn't a concern since the matches are only 3 mins max.
Q: Another question I have is about the weapon system. I am trying to decide whether it would be better to have the bearings spin on the inner or outer ring. The main difference in setup would be spinning the Weapon + Shaft, and attaching the bearings to a side plate. Or attaching the bearings inside the weapon and spinning it around the stationary shaft. I am not sure which would protect the bearing most from impact, as well as produce the most RPM/Inertia.
Q: Along with that, I've done a lot of research on bearings and have heard a lot of good things about angular contact bearings. But did not know the best type for high RPM yet high force.
Q: My third question [You and I count differently!] is about bolts/tapping plates connection. I currently have 1/16", 1/8", 1/4" and 1/2" aluminum to work with for plating. I also have M3, M4, M5, M6 bolts to work with. In my design I wanted to countersink my bolts so that I didn't leave an exposed bolt to be sheared off by the enemy weapon. But my main confusion is the best combination of these. Because say if we use a 1/2" plate, the bigger the bore a tap we make, the less wall material we leave to support the bolt.
Q: How do builders in the heavier weight classes go about attaching a pulley to their weapon motor shaft? I know set screws can't be the answer here. I've seen some builders reshaft their motors with a thicker shaft for a keyway but are there any other methods out there? [Sacramento-ish]
Fd – Drag force (N)
ρ – Air density (kg/m3)
A – Frontal area (m2)
C – Drag coefficient (unitless)
v – Relative velocity (m/s)
Remembering Aaron Joerger, 1991 - 2013
That's obviously
A question from your homework.
Do your own research.
how to design and build a battlebot
Copyright 2009, 2025 by Mark Joerger
All rights reserved.
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]