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Questions and Answers about Combat Robotics from Team Run Amok.

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7010 Questions and Answers about Combat Robotics from Team Run Amok

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.

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.

Spin or No Spin
Q: I have a FlySky FS-i6 transmitter for my beetle with the weapon controlled by channel 3. I recently saw another builder with an FS-i6 who used one of the transmitter switches as a safety that kept the weapon from spinning until it was flipped down. Can you tell me how to do that? [The Heartland]

A: [Mark J.] It's easy to set this up on a FS-i6 by activating 'Throttle Hold' in the function menu:

  1. Open the 'Functions' menu and scroll down to 'Throttle Hold'.
  2. Flip the 'Throttle Hold' switch (SWD on the far right end) up to enter 'Not Engaged' mode.
  3. Tap 'Up/Down' to turn 'Hold' on.
  4. Tap 'OK' to select the 'Value' setting.
  5. Hold 'Down' to set 'Value' to 0%.
  6. Flip the 'Throttle Hold' switch down to verify that 'Hold' is off in the 'Engaged' setting.
  7. Press and hold the 'CANCEL' key to save and return to the previous menu.
The default 'power on' safety system will not allow the transmitter to become active unless all four toggle switches are in the 'up' position and the channel 3 stick is all the way down. Once the transmitter has power, the channel 3 stick is held inactive by the 'Throttle Hold' switch being in the 'Not Engaged' up position. The channel 3 stick will remain inactive until switch 'SWD' is flipped down to release the throttle hold.

More setup tricks are in my FlySky FS-i6 Combat Guide.


Push it Through
Q: I'm looking for a way to quantify material strength and I'm hoping for some guidance. I'm playing around with the idea of a crusher robot and I'm trying to figure out how much force I need to pierce through different metals. I can look up a materials tensile strength and it usually gives me a value in PSI, but does that take into account the materials thickness? Obviously a smaller tip on the crusher means a higher force over a smaller area, but how would I calculate it? Sorry if this is a little out of the scope of this site; any help would be appreciated thanks. [Paso Robles, California]

A: [Mark J.] There are a number of different standard measures of the strength of a material exposed to different types of stress and strain. Tensile strength is a measure of resistance to a force attempting to pull the the material apart along its length. That's very different from resisting a piercing force. As you go thru the list of different measures of strength you will notice that none of them directly measure force required to pierce. This is because piercing resistance is as dependent on design elements like thickness, support, and ability of the structure to flex as it is to the material itself. A simple calculation is not going to give you a useful number.

My best suggestion here is to build a mock-up of a 'typical' robot structure that you might encounter with your crusher and subject it to destructive testing with a model of your piercing tool and a hydraulic press. Sometimes you just gotta go out and break stuff.


Dead or Live
Q: Hi, I was wondering how to make sure an axle on a vertical spinner does not come out the sides but rotates, well, vertically? [Seattle, Washington]

A: [Mark J.] There are two broad types of weapon shaft design -- see: dead shafts and live shafts for a drawing and explanation. Insect class robots will typically use a 'dead' shaft that is a non-rotating part of the chassis that strengthens and stiffens the entire structure. The spinner weapon and any drive sprocket or rotor are on a hub that rides on shaft bearings. If you want a 'live' shaft that spins with the weapon you may use shaft collars on the outside ends of the shaft to hold it in place, but as a very wise builder once said, "Set screws suck."


A Kinda Lumpy Disk
Antweight drumette spinner weapon Hello, Mark! I’ve been working on and off with my ant as of late and have two design-related questions: [Naperville, Illinois]

Q1: How would I calculate the kinetic energy for this design using your calculator?

A: [Mark J.] The kinetic energy storage capacity of a given spinner weapon design depends on the speed of rotation and the Mass Moment of Inertia (MOI) of the rotor. The online Team Run Amok Spinner Weapon Kinetic Energy Calculator can determine the MOI of a rotor made up of simple geometric shapes: disks, bars, and tubes. Calculating the precise MOI of more complex shapes like your weapon is more difficult. Options:

  • Many Computer Aided Design (CAD) programs are able to calculate the MOI of an object sketched up using the program. Check to see if your CAD program has that ability. If it does, obtain the MOI from the program, enter it directly into the "Asymetric: MOI" field of the Kinetic Energy Calculator, and set all the size parameters to zero.
  • Since your rotor shape is a kinda lumpy disk, we can get a fairly good estimate of its MOI by thinking of it as a simple disk sized half way between the radius of the round hub portion and the larger radius at the outer edge of the impactor. The estimate will be a little high, but pretty close.
Let's try that last option. I'm guessing that the weapon pulley in your render is a 30 tooth Fingertech (32mm diameter) and estimate the diameter at the outer edge of the impactor to be 44mm. Splitting the difference gives a diameter of 38mm (a 19mm radius). Each diskette looks to be about 8mm thick, so double that to account for two steel diskettes. I'll assume the contribution of the aluminum pulley and fasteners to be negligible.

Pumping those numbers into the kinetic energy calculator with an assumed speed of 8,000 RPM gives kinetic energy storage of... nine joules. That's pitiful. A typical antweight spinner weapon has about seven times that much stored energy. Go bigger!

Press-fit needle bearing Q2: How would I go about fitting the bearings into the weapon? I don’t have access to any fancy or expensive tools and figured it wouldn’t be very easy to just press-fit two metal parts together.

A: An interference press fit requires a high precision drilled hole -- much tighter tolerances than you might get from a waterjet cut hole. If you have a correctly sized hole a it's not all that tough to tap or vise-press a needle roller bearing into place.

I know of builders that fix bearings into slide-fit holes with Loctite 640 retaining compound. This is not the same stuff as the common blue Loctite threadlocker. The Loctite is effective -- but don't get it in the bearing!

You might consider flanged oilite bushings instead of needle roller bearings. The flange keeps the bushing in place and the bronze bushing can absorb enourmous impact loading. Correctly oiled, the frictional difference is negligible.


The Guide Says...
Q: Hi, Back again, but this time building a beetle! What brushless motor would you recommend for vertical or drum spinners of the 1.5KG weight class?
Thanks! [York, England]

A: [Mark J.] The Ask Aaron Combat Robot Brushless Motor Selection Guide will give you general parameters for weapon and drive motors for a given robot weight. For reasons provided in the guide, a brushless motor massing about 90 grams with a power output around 450 watts will do nicely for a typically sized beetle weapon. Examples:

Selection of motor diameter/length will depend on available space in your design, and selection of motor Kv rating will depend on the weapon design and drive method. Since all you've told me is "beetle vert or drum" I can't narrow it down more than that for you.
Team Run Amok
 20 Years in Combat Robotics
2021 marked Team Run Amok's 20th anniversary in combat robotics. We dove straight into the deep end of the competition pool, starting our career with a win at the nationally televised 'Robotica' tournament. In the years that followed we won more competitions, travelled to compete in England twice, and finished in the top three at more than half the events we entered.

I made several updates to the website to observe our anniversary year. Check the Team Run Amok webpage for a full list.


Flashback: an archived post from 2019
Q: How well do clamping-style shaft collars resist axial shock? Cheers. [Sydney, Australia]

Trantorque bushing cross-section A: [Mark J.] Many designs qualify as a 'clamping' collar, and some are better than others for both torque transmission and axial shock. Holding 'well enough' depends on the specific application, information you have elected to withhold. I can comment that clamping collars are generally preferable to set screw collars.

Q: If I were to machine my own clamping-style shaft collar and shaft, would there be any benefit to including a Morse taper on the mating surfaces?

A: Adding a matching shaft and collar taper will greatly improve axial shock resistance in one direction -- and entirely screw up resistance in the other direction. Unless the shock loading direction is completely predictable (and nothing in combat robotics is completely predictable) I would strongly avoid any taper.

I'm assuming that you're asking about shaft collars because your application requires axial adjustment along the shaft. If not, a simple machined groove and snap-in circlip are the standard and preferred solution.


The Miracle is...
Q: Hi again, this time having a problem with Lipos…

I bought a 2s LiPo charger from the BBB shop and when I attempt to charge any of my Turnigy 300mah LiPo batteries, the light is red for about for seconds, then flashes briefly and repeats this. I have plugged these batteries into my robot, but it’s not turning on?

Thanks for your help! [Eton, England]

A: [Mark J.] This same charger is sold on Amazon.com as the Blomiky H102. Several reviews of the Blomiky report problems similar to what you describe. The miracle is that most of these little £3 ($5) chargers actually do kinda work. Your's doesn't. Send it back to the Bristol Bot Builders shop and ask for a new one.

Note: The Blomiky advert on Amazon estimates that the H102 will take about 5 hours to charge a 1000 mAh battery -- that's about 90 minutes to charge your 300 mAh pack. You might want to consider spending a bit more for a faster charger.

Q: About my recent question concerning chargers, I do have a fingertech, proper lipo charger, which came with the fingertech viper kit, but I don’t know how to use it, and also my £3 BBB charged batteries much faster than 90 minutes when it worked. If my fingertech charger isn’t suitable either, could you link me with a decent, working one with correct accessories and a video on how to use it? Many thanks again!

A: You have options:

  • If you're happy with the charge rate and simplicity of your little £3 USB charger, you could buy a couple more of them (one to use and one as a spare) and live with the fact that a £3 charger isn't likely to last very long.
  • The GT Power C6D Mini that came with your Viper kit is a very capable charger, but I'm not surprised to hear that you can't figure out how to use it. It has a horribly complex and poorly translated Chinese manual. Sorting thru all the available menu options for battery type, diagnostics, and charge rates is quite a challenge. I've found a video demonstrating charging with the C6D Mini, but the demonstrator already knows what he's doing and doesn't take the time to explain his actions.
  • For small capacity LiPo batteries you do not need a complex or expensive charger, but you do need something reliable. The Turnigy E3 Compact 2S/3S Lipo Charger is a very simple and inexpensive (£9) balance charger that plugs into a standard wall outlet (available in US, EU, and UK plug styles) and will charge small 2-cell or 3-cell Lipo batteries in a reasonable length of time. Just plug the battery into the correct port and charging starts automatically.
The Turnigy E3 with the UK plug is currently out-of-stock at HobbyKing, but there are other sources for this charger. Look around -- I think it's the right charger for you.
Flashback: an archived post from 2019
I had a conversation with a builder today that convinced me it's time to repost this explanation of brushless torque:
Q: I have a choice of two versions of the same brushless motor to power my weapon: a 750 Kv and an 1100 Kv. The 750 Kv version will give me more torque, right? [Everywhere]

A: [Mark J.] There are a lot of 'half-truths' about brushless motors floating around out on the 'net that are confusing robot builders and leading to poor design choices. You can find this one all over the 'net:

"A lower Kv motor has more torque"

There is a kernal of truth in that statement, but it is incomplete and misleading.

The true part -- the motor speed constant (Kv) and torque constant (Kt) are inversely proportional -- if one goes down the other goes up. Compared to a higher Kv version, a lower Kv motor will produce more torque per amp of current.

The incomplete part -- lowering the motor Kv increases the electrical resistance (Ri), which reduces the current the motor will draw.

The misleading part -- if allowed to pull unrestricted current, the lower Kv motor version will produce both less torque and less power.

Here's a real-world example comparing two versions of the AXI 2208 motor:

AXI 2208/34 Gold Line V2 motor
  • Kv: 1100 RPM/volt
  • Kt: 1.23 in-oz/amp
  • Ri: 0.260 ohm
  • Voltage: 3s
  • Max Current (60 seconds): 10 amps
  • Torque @ Max Current: 12.3 in-oz
  • RPM @ Max Current: 9350
  • Max Rated Power: 100 watts
AXI 2208/20 Gold Line V2 motor
  • Kv: 1820 RPM/volt
  • Kt: 0.74 in-oz/amp
  • Ri: 0.089 ohm
  • Voltage: 3s
  • Max Current (60 seconds): 18 amps
  • Torque @ Max Current: 13.3 in-oz
  • RPM @ Max Current: 17,280
  • Max Rated Power: 182 watts

The 1820 Kv version of this motor generates greater torque than the 1100 Kv version throughout the RPM range. When bogged down to the '60 second' current maximum it produces 8% more torque, and it does so while spinning 85% faster than the lower Kv motor -- a power increase of: (1.08 × 1.85) - 1 = 99.8%.

There are a number of reasons why you might choose a lower Kv version of a motor for a specific application, but "because it has more torque" is not one of them.


Technical K.O.
Q: Why would my combat robot be browning out when it gets hit? [Bellevue, Washington]

A: [Mark J.] It would help a great deal to know a bit about your robot and more details as to how it behaves when hit. You're asking the equivalent of, "Why won't my car start on a cold morning?" The Hamburger is Bad.

  • A true 'brownout' occurs when the voltage supply to the receiver and ESC logic boards drops below the minumum level required for their operation. That voltage source may be a Battery Eliminator Circuit (BEC) onboard an ESC, a separate stand-alone BEC, or if running a 2 or 3-cell LiPo the receiver may be directly powered from the main battery itself.
  • Maximum and minimum allowable voltage levels vary, depending on the manufacture of the device. Some have a wide voltage operation range, others have a low tollerence for variation.
  • A brownout may cause the receiver to drop its output signal, which may in turn cause drive and/or weapon ESCs to reset and go thru their start-up sequence. This leaves your robot a 'sitting duck' until the sequence resolves. Inconvenient.
  • The brownout itself may have several causes, including but not limited to:
    • Exceeding the current capacity of the BEC, perhaps with a high current drain telemetry receiver;
    • Exceeding the current capacity of the main battery by stalling drive or weapon motors; or
    • Some specific ESCs are known to falter and reset when they take a good hit, mimicing a true brownout.
As you have told me nothing at all about your robot I can give very little direct advice. You might start troubleshooting the problem by adding a stand-alone BEC to power the receiver and disabling all the on-board BECs currently operating. The first few posts found by a searching the Ask Aaron Radio and Electrical archive for "brown" may provide some additional guidance.
Electron Maze
Q: Hi, I’m still working on my antweight spinner and space doesn’t seem to be an issue anymore which is great! I am still struggling with the wiring though so could you create a wiring diagram utilising 2 red bbb ESCs, the BBB brushless motor and Brushless speed controller for a basic antweight spinner bot?

Thank you very much! [Oxford, England]

A: [Mark J.] This previous post in the Ask Aaron archive [link fixed] has a wiring diagram and notes for the Bristol Bot Builders Red ESCs with N-20 motors. Adding the wiring for the brushless weapon ESC and motor looks like this: You'll need to add a switch in the battery line, as covered in the assembly notes on the Bristol Bot Builders website. If the weapon motor spins the wrong direction, reverse any two of the three weapon motor connections to the weapon ESC.

Note that the BBB Red ESCs are being phased out in favor of the BBB Edition Antweight Dual ESC. The wiring diagram for the Dual ESC is the standard combat robot wiring diagram as seen in FAQ #19.


Ready for Anything
Q: When I went to Norwalk Havoc (as a spectator) I noticed a sawbot called 'Whittle by Whittle'. I happened to notice that this robot - as well as 'SawBlaze' on the rare occasion they use the saw - use a certain type of circular serration saw blade that differs from the common very-serrated design. The blade seems to be much flatter and stable, however it also seems to not be able to cut as quickly. Are there any reasons why different bots use these different saw design?

As always, Go Run Amok! [Worcester, Massachusetts]

A: [Mark J.] If you know specifically what type of material you'll be cutting with a circular saw you can match the saw blade design to that material and get an optimum cutting rate. The selected saw blade might have twenty teeth or a hundred and fifty teeth, and those teeth might be steel, carbide, or something more exotic. For some materials you might choose a blade made entirely from an abrasive ceramic.

If your're planning to attach a saw blade to a combat robot you're going to face some unusual challenges:

  • A wide list of very different materials you may need to cut into;
  • Poor control of the 'feed rate' of the material into the saw; and
  • Unpredictable and potentially damaging impacts to the saw blade itself.
The single best overall blade for this environment is a general purpose 'diamond saw blade' that consists of industrial diamond particles embedded in a carbide ceramic base that is then brazed onto a segmented-edge steel disk. It isn't the best blade for cutting rapidly into soft materials, but give it enough power and it won't 'jam' while carving thru any material all the way up to hardened steel. These are the cutting blades used by 'SawBlaze' and 'Whittle by Whittle'.
Risk and Reward
Q: Do you ever think Motorama will return once Covid settles down? NHRL is cool and all but they don't run anything below 3lbers? [Richmond, Virginia]

A: [Mark J.] Your wish is granted. According to the Motorama Robot Conflict webpage, registration for the February 19-20, 2022 event will open November 14th, 2021. Fingers crossed -- check there for updates.

Q: Additionally, Fish or Carne Asada in tacos?

A: How high is your risk tollerance?

  • The best tacos I've had were fish, but so were the worst. A lot of very different types of fish can go into a taco (wahoo, haddock, pollock, mahi mahi, grouper, flounder, halibut, cod, snapper, tilapia...) and there is a lot of variability based on preparation. It's a risky choice.
  • Carne asada is beef. It all comes from the same sort of animal and preparation is fairly standard. I've never had a really bad carne asada taco, and neither have I ever had a really great carne asada taco. It's a safer bet.
I'm gonna count this as a robot question -- the choices involved in choosing a taco are a lot like the choices in building a robot. That's life for ya.
Out At The End
Q: Does the shape of the ending of the vertical spinners matter or is it best to keep it at a standard shape? [Daytona Beach, Florida]

A: [Mark J.] See this previous post in the Ask Aaron Archives about spinner impactor shape for guidance.


Nerf or Nothing
Q: Do you know if I can buy 22mm gearboxes (like the one's used in D2 kits) without the motors? I want to mess around with some high power 130 size motors for my next build and I'm just going to toss the stock ones anyway. [Roseville, California]

A: [Mark J.] When you buy the 22mm gearmotors from ServoCity or BotKits the gearboxes are 95% of the expense; the brushed motors only add about $1.50. You'll need the pinion gears from the stock motors for the conversion, so just buy the whole package so you can back-convert if you don't like those fancy Nerf motors.


Fitting It All In
Q: Hi, Still working on this second antweight and after will definitely move up to a beetle, but still after 4 design revamps am struggling to fit all of my electronics inside my robot - I have looked over multiple designs on the internet but am still having trouble trying to fit everything into a 4’ cube - bearing in mind this is a spinner. I was planning to make something not too dissimilar from the pictured robot but was wondering how all of these electronics were fitted in. Probably not a very answerable question but any tips you can give me would be much appreciated. Thanks! [Oxford, England]

A: [Mark J.] Note for unseasoned American builders: antweights in the United Kingdom are restricted in both weight (150 grams) and size (must fit in a 4" cube). Some general tips:

  • Standard combat robot components are too large. Specialty UK Ant components are available from multiple suppliers, like Bristol Bot Builders. Go tiny.
  • Wires and connectors can take up a lot of room. Cut wires to length and solder connections to eliminate connectors whenever possible.
  • UK ants can get by with surprisingly small capacity batteries. See what similar 'bots use.
  • Stack components upward as needed; battery/motors/ESC/receiver.
  • Squish.

Q: Hi, about my recent question involving a quest for space, you mentioned batteries - I am currently running a turnigy nanotech 2S 300mah battery and I know it is extremely overkill. Where could I find a (much) smaller battery and what mAh rating would be nescessary? I think the BBB site recommends a 180mah battery but browsed the entirety of google and could not find any of those at all. Thanks!

A: The battery capacity requirement depends on details of your drive train and weapon. The BBB battery recommendation of 180mAh is for their drivetrain kit without weapon: adding a spinner weapon may put you back close to 300mAh. Run some simulated matches with your 300mAh battery - strapped to the outside of the 'bot if necessary - to see how long it provides power and downsize as appropriate. If your charger tracks amp-hours needed to recharge your battery after a standard length match you can use that as a guide.

Small capacity LiPo batteries have become scarce. A search for "E-Flite 180mAh 2S" turns up a good number of responses. They are not cheap, but they are half the size of your 300mAh Turnigy.


Two Into One
Q: Can I splice the signal and ground wires of two ESC's (brushless in my case) and have them plug into the same channel in my receiver? I want to be able to drive them both simultaneously, but they don't need to be perfectly in sync with each other. [Parker, Colorado]

A: [Mark J.] It would help to know exactly what you're doing but in general, yes. You can drive two unsynched ESC/motors from a single receiver output port signal. Do not try to drive a single brushless motor with two ESCs.


Very Different Properties
Hey, I just realized the sheet of UHMW I thought I bought is actually a sheet of acetal copolymer. I’m not too familiar with plastic properties, and I’m looking to make saifu kit-style rounded wheelguards. Is acetal copolymer a bad choice for something like that? [Philadelphia, Pennsylvania]

A: [Mark J.] There are very good reasons why builders use UHMW-Polyethylene for those Saifu-style wheel guards: it's light, slick, bends easily, flexes to absorb a lot of energy, and stretches rather than breaks. Acetal Copolymer (POM-C) has very different material properties:

  • POM-C is 50% heavier;
  • It's several times stiffer;
  • It's difficult to form; and
  • It's hard enough that it breaks before it stretches.
That makes POM-C a poor choice for bowed wheel guards. Buy some UHMW and save the POM-C to make gears, hubs, or internal mounts.

Spindizzy
Q: Are there any Heading Hold Gyros that you could recommend? I just read your page about them and they sound like the perfect thing for my bot, however I don't know what I should be looking for in a gyro when buying one. [Yuba City, California]

A: [Mark J.] It's been a few years since I wrote the Beginners Guide to Combat Robot Gyros and your question gives me a good excuse to update the page. I've re-written the "Gyro Types" section to better discuss the merits of 'heading hold' versus 'rate' gyros in the modern era of powerful spinner weapons.

Particularly with lighter weight classes, a good weapon hit can send a 'bot spinning so violently that a 'heading hold' gyro can lose its directional lock and behave erratically. Many builders have switched to 'rate' gyros that do not try to keep a heading lock because they are less susceptible to this type of confusion. You lose some of the 'on rails' feel a heading hold gyro provides, but your 'bot won't go crazy if it takes a good hit.

What you're looking for is a single servo gyro with a remote gain control. These used to be fairly common, but with R/C aircraft moving toward integrated 'flight controllers' they are now hard to find.

  • I can recommend the Futaba GY4400. The GY4400 allows you to switch between Normal (Rate) and AVCS (Heading Hold) modes, so you can try both to see which you prefer. Futaba makes great products that come with detailed manuals.
  • On a smaller budget, you might try the SKYRC GC301. This is an R/C car gyro that claims to be heading hold, but I suspect it's actually a rate gyro. You can expect the instructions to be sketchy and poorly written, but for the price you can afford to play around with it.

What Goes In the Box?
Q: Do you have any sort of guidelines on how many spares you bring to tournaments of each part? Obviously it depends on the bot design and tournament format, but I have no baseline estimate for how much damage I'll expect to take on each part and what's most likely to break. I'm using a Viper wedge kit in a double elimination tournament, so I assume it's reasonable to have at least one spare of everything going into the arena, but what needs to be prioritized? At the moment I'm thinking extra spares of wheels and the front polycarb/metal wedge are a must, but are motors and ESCs likely to break? What about the receiver? [Philadelphia, Pennsylvania]

A: [Mark J.] Repair time can be a limiting factor at a tournament. Highest priority for spares are components that:

  • Will prevent the 'bot from operating when damaged; and
  • Are likely to take damage that cannot be quickly repaired.
There are a LOT of Viper wedges out there. Builders who have competed with Vipers can tell you which specific parts commonly damaged. I've never campaigned a Viper, but my minimal spares box for a local tournament would have:
  • A replacement drive gearmotor (a spinner hit to the protruding shaft can kill the gearbox);
  • A pair of ready-to-mount latex-coated foam tires (spinners shred the tires but the hubs are well protected);
  • Zip ties, duct tape, 5-minute epoxy, a soldering kit, and every tool I could stuff in my carry bag.
A spare wedge would be 'nice'. Electronics in a stock Viper are unlikely to fail, and if they do you can always stand on top of your pit table and yell, "Who's got a spare tinyESC?"

If I were going to BattleBots I'd have two complete spare robots ready to pull out of their crates and toss into the arena, plus enough parts to build one more 'cause that how TV works these days. Your spares list should probably fall in-between these two extremes.


Not Gonna Update Them All
Q: Also, I noticed in your old Armor Guide you mention that 6061-T6 Aluminum and mild steel are both solid choices to hold up against spinners, but in your discussion with the "Xmas Viper Guy" you say that both these materials aren't worth our time. Have spinners just become too powerful for those materials in the time between those answers, or what's up? And if so, would it be worth putting out an updated Armor Guide so people don't make the mistake of using any other outdated materials from that guide?

Thanks for your time, man. [Philadelphia, Pennsylvania]

A: [Mark J.] Yes, spinners are MUCH more effective now than they were fifteen years ago when the armor guide was written, but I think you should re-read it. The guide states that mild steel and 6061-T6 aluminum are cheap and easy to obtain, but that other alloys are stronger. There's nothing about 'solid choices' or holding up to spinners. It also says that you should do your homework and:

Look at 'bots with designs similar to your own and use their experience as a guide to your own project.
That's the best timeless advice I can offer.

If I go back to the start of Ask Aaron and update one old question every day it will take me nineteen years to get back to this question -- I'll never catch up! The archives all have date markers every year or so to help readers judge the age of the question they're reading, but I can see the merit in posting a specific warning notice in the armor guide. I've added a note.


Into the Briar Patch?
Q: Hey Mark, just stumbled across your "You be the Judge" page and found it super interesting. Have you considered making a similar one for the Battlebots ruleset? I imagine this type of thing would be a great teaching tool to link when people claim the judges are idiots, but I doubt using the old Robot Fighting League D/A ruleset would do a very good job of explaining the current TV rules for the uninitiated. [Philadelphia, Pennsylvania]

A: [Mark J.] I'm happy to hear that you enjoyed my judging guidelines quiz. The RFL guidelines attempted to be very specific but caused some unexpected outcomes if they were closely followed. The purpose of the quiz was to point out those odd decisions in hopes that the guidelines could be adjusted to eliminate nonsensical results.

Jump forward a decade. The judging guidance for the BattleBots reboot is less specific and has corrected many of the problems I had with the RFL guidelines, but a number of controversial judging results have appeared each season. The guidelines are constantly updated in response to builder input, but there is still a lot of heated discussion on fan sites that official BattleBots explanations have done little to resolve.

I appreciate your suggestion, but I don't believe that throwing myself into that particular briar patch would help the situation. I'll pass.


Weakness Leaving Your Robot
Q: This question feels obvious enough that it must exist somewhere, but the keywords I was searching with turned up no results. What do you think the best at-home testing you can do for a finished robot is? Obviously there's no true replacement for competition, but is there anything you typically do to your bots to attempt to replicate mid-fight scenarios? Maybe things you use to simulate impacts from different directions and see how well your bot handles them? [Philadelphia, Pennsylvania]

A: [Mark J.] I have known builders who took their heavyweight robots up onto the roofs of their homes and threw them off onto concrete driveways -- repeatedly and at all angles. While this may or may not be effective at uncovering weakness, it is not a common practice as most builders like to show up at an event with a pretty robot. Anything with enough impact energy to properly test is gonna leave a mark, and by the time you hit your 'bot from all possible angles you're not gonna have much of a robot left.

Get your robot out and fight. Creating a great robot is an iterative process: build, fight, evaluate, improve, repeat. Take a look at Jamison Go's blog post on the evolution of his Hall of Fame beetle 'Silent Spring' for some of his tips on testing and improvement.

I'll leave you with a quote from Team Juggerbot:

"Damage is weakness leaving your robot. If it breaks, make it stronger."

- Team Juggerbot

Robotica on Paper
Q: I've been watching the Robotica series on YouTube and some of the robots are wild. Were there any toys or models of the Robotica competitors? [Sacramento, California]

A: [Mark J.] Yes, kinda...

"Cut and Fold" paper models of combat robots were a thing at the time. I know of three printable paper models from the Robotica series:

  • Robot Dojo has printable paper models of all six of their heavyweight robots -- Robotica Season 2 champion 'Flexy Flier' is pictured: Robot Dojo paper models.
  • Team Run Amok has an easy-to-make 1/10th scale paper model of Robotica Season 1 champion 'Run Amok' to print and assemble: Paper Model Run Amok.
  • An Infernolab fan made a very simple paper model of Jason Bardis' Robotica Season 1 competitor 'Mini Inferno': Paper Mini Inferno.
Paper models of robots from other competitions are also out there. Image searches for "robot wars paper models" and "battlebots paper models" will yield a surprising number of hits. Maybe I should make a list...
All Messed Up
Q: I'm having trouble with my R/C mix on my beetle. I have an elevon mix, but when I pushed the stick forward it spun to the left. I tried to fix that, but now when I push the stick forward it spins to the right and when I push the stick right it backs up. How do I sort this out? [A Horse with No Name]

A: [Mark J.] I get a fair number of questions about fixing R/C mixes. In the past I referred such questions to a multi-step process to diagnose and correct the mix. It worked, but it took a while and the diagnosis sometimes had you changing things and then changing them back. Inefficient.

I recently finished an online javascript 'expert system' to handle this type of question. The Run Amok Mixer Fixer asks just three questions about your mix and then tells you exactly how to fix it -- no trail and error! Give it a try.


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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