Questions and Answers about Combat Robotics from Team Run Amok.

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7792 Questions and Answers about Combat Robotics
from Team Run Amok

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Original Work Only, Please
Comment: i am very impressed with Iceywave's Robotica Competitor Roster and feel sad that he had to finish with the season 1 competitors only.

however fear NOT Iceywave i'll finish this roster for you which will include all of the Robots from Seasons 1-3 including the robotica rats, Robots from Robotica Comicpalooza 2022 and some the top 10 or more UK competitors that i would've loved to see compete in Robotica the TV Series.

You are about to witness the most epic Robotica Roster list ever in history! [Erskine, Scotland ☆]

Response: Mark J. Iceywave did a great job in reproducing not just the twelve Robotica Season 1 episode finalists as playable models for the Robot Arena 2 PC game, but also playable models of:

  • Eight of Team Run Amok's robots: antweights thru heavyweights;
  • Twelve competitors from 'Robot Wars Extreme Warriors; and
  • All eighteen entries from the 1994 US Robot Wars.
...all of which are available for download from the Team Run Amok Robot Arena 2 page.

Comment: Allright then in the attachment here you'll find a few robotica competitor .bot files right here and i'd thought that it would be nice to add into the Robotica Competitor Roster that is even if its the one from Iceywave ill add the resting which you'll see

Response: Hamerschlag, Hot Wheels, Jawbreaker, Juggerbot, Killer B, Kritical Mass, Panzer Mk1, Ram Force, Run Away, Solar Flare, Viper, Wendigo, Botzilla, Deb Bot, Rambot... These seem to be botfiles already on our Robot Arena 2 page, or existing files from other sources that I'm unwilling to use here without permission. If you have new and original RA2 models please send them in with a screenshot in the format seen on my RA2 models page.


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.


Someone Made the Calls
Q: If i remember correct: in the Robotica Labyrinth match up between Jawbreaker's Revenge Vs Buzz Bomb Dan Danknick says "The Judges said they'll be Jawbreaker's Points." DID ROBOTICA HAVE ANY JUDGES?! [Erskine, Scotland ☆]

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...


A Lot of VEX Parts
Q: Hello, I am currently designing a 30lb combat robot and have 3 main questions. To start, I have added a small photo of the design so far to give an idea. The goal is to have a vertical spinner design, that has a 4 wheels driven by two motors. I am running an 8s system, with Talon SRX and Redline 775 + 10:1 planetary gearbox for the drive. And a Castle 2028 800 Kv and Mamba Monster X 8s for the Weapon. The Talons are technically only rated for 28V, but have been tested and work at 30V while mixing the output to 40% for the 12V redlines. We do have 8s ESCs but they are almost double in size and would be much more difficult to design the plating around.

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]


First off with just the specs I would be curious any advice for the design just based off the electronics and CAD photo.

A: Mark J. I see that you have made some changes to your design since your earlier post. A few observations:

  • I'm personally not a fan of overvolting ESCs. A LiPo cell has a nominal potential of 3.7 volts, but when fully charged it sets at a resting 4.2 volts. That means your 8S system can push 33.6 volts thru your Talon SRX. I can hear the capacitors failing already. Still feel confident?
  • A Castle 2028 weapon motor is massive overkill for a featherweight -- particularly given that your weapon itself appears to be on the small size. A typical featherweight weapon motor weighs in at about 21 ounces (4.4% of the robot mass), whereas the Castle tips the scale at 44 ounces (9.2% of the robot mass). See: Brushless Motor Selection.
    Spinning weapons are flywheels. They rely on rotational inertia to collect energy from a continuous power source (electric motor, internal combustion engine...) over time and store it as rotational kinetic energy. On impact, the flywheel releases the stored energy in a blow that far exceeds the energy directly available from the continuous source.
    Having a huge motor paired to a weapon too small to store a significant multiple of the motor's output power at a reasonable rotational speed is not a path to victory. Cut the motor weight in half and add the mass to the weapon. See: Ask Aaron Spinner Weapon FAQ.
  • Your design makes VERY little effort to 'feed' your opponent up and into the rotating weapon. Your plow is far too steep and elevated to 'win the ground game'. The current spinner design 'meta' employs floating forks to get under the opponent and lift their leading edge up into the weapon path where the weapon will get excellent 'bite' and deliver a massive hit. Without forks your weapon is set up to strike a glancing and ineffective blow on some smooth surface of your opponent.
  • Can I assume there is a chain or belt drive running from the rear wheels to the fronts to provide four-wheel drive? If not, the rear wheels by themselves have very little weight on them which will result in poor pushing power, reduced acceleration, and impaired maneuverability
  • I wonder what events you plan to enter with this 'bot. You are using a lot of VEX parts that are common in non-combat robotics in preference to components in use by successful combat competitors. This seems a little odd.
I have additional comments, but they fit well into the answers to your other questions below.
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?

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.


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.

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.


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.

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.


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.

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.


Countersink vs. Counter Bore 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.

A: See Frequently Asked Questions #17. Note also the difference between 'countersink' and 'counter bore'.


More Than You Need
Q: Could a spring from a typical rat trap be repurposed into an antweight flipper?

  - sincerely, Iceywave [West of San Antonio ✪]

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 calculated the torsion constant in a Victor Original Mousetrap with a spring arm length of 4.3cm) to be approximately 0.09088 N∗m/Rad by using Hooke's Law and comparing the angle between the spring arm and the wood base when hanging different weights from the arm with the trap upside down.

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.

Using the potential energy calculator at OMNI Calculator reveals that 0.815 joules -- if perfectly converted to vertical speed -- could loft a 1-pound object just over 17 feet straight up.
Keys are the Standard
Trantorque bushing cross-section 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]

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.


Nothing Practical
Q: Is there a formula or calculator to approximate the motor power in watts to overcome aerodynamic resistance for a weapon of specific dimensions and RPM?

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. [An iCloud in Boston]

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:

Fd = 1/2 × ρ × A × C × v2

Fd – Drag force (N)
ρ – Air density (kg/m3)
A – Frontal area (m2)
C – Drag coefficient (unitless)
v – Relative velocity (m/s)
But this equation calculates the instantaneous drag on the object, not the power needed to sustain speed against that drag. Power is defined as work done per unit time so, the power calculation must multiply that work (drag force) by the velocity (distance over time) to give us Pd – Power to offset drag (Watts):
Pd = (1/2 × ρ × A × C × v2) × v =
1/2 × ρ × A × C × v3
The derivation of this equation - with extensive notes on its limitations - is available at The Physics Hypertextbook.

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:

  • You can find a successful weapon of similar design and speed. Adopting a weapon motor with output power equal to the one used by that weapon should provide you with success as well.
  • You can extrapolate the power requirement from the known power requirement of a similar weapon at a different speed as I did in the Increases with the Cube of Speed post farther down this page.
  • You can physically mock-up your weapon and see how fast you can spin it while monitoring current draw and extrapolating input watts required for your target speed:

Watts Required = Watts at Test Speed × (Target Speed / Test Speed)3


Think Wider
Q: Do people still use the FingerTech S3M belt at Beetleweight? I am working on a horizontal spinner but I don't know if the belt would be able to survive. [Sacramento-ish]

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:

  • The EndBots 'Vector' horizontal bar spinner beetleweight kit used a 0.25" wide (6.35 mm) XL profile timing belt.
  • For their 3lb Beater Bar assembly FingerTech uses a wide S3M pulley that accepts up to a 8.25 mm belt.
  • The vertical Peter Bar Weapon Kit from Repeat Robotics uses a 9mm wide 3M profile belt.

The Spec Sheet is Wrong
Q: Why is my drivetrain supposedly so close to stalling? If I drop the voltage to 11.1V then it's apparently going to be unable to drive even though I've run these motors on a Fingertech beater before at 3S. Motors in question are the generic 22mm gearmotors available on the Fingertech site. [Arlington, Virginia]

A: Mark J. You have correctly entered the motor specs given by FingerTech (and other sources) for this motor -- but those specs are incorrect . Per the spec sheet, the 12 volt stall torque for the gearmotor is 27.8 oz-in @ 4.9 amps (Kt = 5.67) but actual test results from multiple builders yield an average stall torque almost three times greater.

For comparision: At 12 volts, the very much smaller FingerTech Silver Spark 22:1 has a similar no-load speed and stalls at 22.7 oz-in @ 2.1 amps for a Kt of 10.8 -- the spec for the 22mm stall torque is obviously too low. See: Converting Motor Specs. Based on the real world numbers I estimate the torque constant for these 22mm gearmotors at 16.3 oz-in per amp. Plug that into the drivetrain calculator and your output will make sense.

Also, the "Torque (per motor) to spin wheels" calculation in the drivetrain calculator does not refer to the torque required to simply drive the robot across the arena. It is the torque required to provide the full pushing force and "beak traction" to spin the wheels and prevent motor stall under heavy pushing. This value should ideally be attained at no more than half the stall amperage of the drive motor. See the Optimizing Drivetrains page for a full explanation.

PS: How much leftover battery life should I pack? The spinner weapon spreadsheet tells me that I'll be using 1.03 amp hours per match, so would a 1500 maH battery work? How do I know if the margin is too small, and if the battery will start to die before the end?

A: The Spinner Weapon Spreadsheet provides a gross estimate of the battery capacity required to spin up your weapon a specified number of times and maintain top speed for the given duration of the match. Take that number with a grain of salt. It does not factor in things like excessive aerodynamic drag from spinning a weapon at stupid-fast speed. It also does not include the battery capacity required by the robot drivetrain.

Generally, rounding up capacity in the 25% to 50% range is about right. You will find out if the margin is too small by testing. Most battery chargers will tell you the mAh required to restore the battery to full charge after a match so that you may determine if the battery has too much or too little capacity.


Literal Top Post
Q: In a beetleweight bar spinner design driven by a timing belt, is it good to have one pulley be smooth? This robot seems to do that, and it would definitely make CAD work easier if I can just use a fingertech toothed pulley for the weapon and fit a smooth 3D-printed one (more appropriate for my CAD skills than a full-on timing pulley) around the motor can.

Three Minutes Later...

Just realized that the literal top post [on the Ask Aaron page] answered my initial question, oops. Do I need to worry about tensioning with one smooth side using a fingertech belt? [Ashburn, Virginia]

A: Mark J. If you run two toothed pulleys you can run a calculated fixed pulley spacing and be fine. If you have one smooth pulley you will need some method of tension adjustment -- one or two tensioning idlers as in your example photo or perhaps adjustable weapon motor mounts.

Beetleweights are still small enough to consider running two toothed pulleys with a timing belt -- you can do that and avoid the tensioning issue. Take a look at the STL files for the EndbotsVector Beetle kit. You might find it easy to modify the motor can 0.25" XL pulley from the Vector to fit your weapon motor. Consider battle hardening your weapon motor if you choose to do this.


You Need a Little Slip
Q: Hi! What do people typically use for weapon [power] transmission for 30 pound robots? Ar chains common or is it some kind of timing belt?

Thanks! [Masked Server]

A: Mark J. Is this purely a theoretical inquiry or are you constructing a featherweight robot? I ask because someone building a featherweight with an active weapon would likely have gained sufficient experience in lighter weight classes to understand why chains are not used and timing belts are commonly used with at least one smooth pulley.

The abrupt deceleration of a spinning weapon striking its target places an enormous load on the weapon motor. The larger the motor the greater the risk of motor damage from this load. Current practice for 30-pound robots favors a narrow v-belt set loose enough to slip a bit under decelleration loading for protection of the weapon motor. Heavyweight robots may use chain drive with an industrial slip clutch built into the weapon or motor hub.

There are dozens of posts on the use of chains, belts, and slip clutches for weapons in the Ask Aaron Robot Weapons Archive.


Close to the Base
Q: I'm working on a 12lb 'Tombstone' style horizontal spinner and I need some reference. My current design has the weapon motor pulley mounted to either the top of the outrunner can or around the can itself. Most reference designs I see have it mounted to the bottom with shafts that stick out underneath, but I am having trouble doing this for a non-undercutter style of robot. Would you consider the mounting solutions I am thinking of to be suitable or is it something you wouldn't trust? [Sacramento-ish]

A: Mark J. If your design does not support the shaft on the far end of the outrunner you should place the pulley as close to the motor base as possible to limit stress on the motor's internal bearing tube. Wrapping a pulley around the outrunner has the advantage of creating a very compact package and is common in beetleweight horizontal spinners -- see the Press Fit post farther down this page. Upscaling that design to a hobbyweight is fine, but featherweights and up should look to designs that do not stress the motor can.


Increases with the Cube of Speed
Q: These weapon performance numbers [at right] from the Run Amok Spinner Weapon Energy Calculator are looking a bit optimistic. I used ChatGPT to calculate the internal resistance of the SunnySky 2450 Kv 2212 motor since they only have the specs up to 1400 Kv version on the site.

I'm guessing aero forces will be the limiting factor here and overload the motor, but can you weigh in on how this weapon would perform? Would it be better to go with a lower kv? [An iCloud Server in New York]

A: Mark J. I recognize those weapon numbers. You either have or are duplicating a Vector beetleweight kit. The Vector had the 980 Kv SunnySky 2212 weapon motor that would draw a continuous 8 amps @ 14.8 volts to overcome the aerodynamic drag at 6500 RPM (370 joules). That's about 90 watts and the motor is rated for a continuous power output of 385 watts -- it could do that all day.

You are correct in worrying about aero forces at high RPM. Increasing weapon speed increases aerodynamic drag with the cube of speed:

  • Doubling the speed requires 23 = 2 × 2 × 2 = 8 times the energy; so...
  • Doubling the speed of that 6500 RPM weapon to 13,000 RPM (5000 RPM below your target speed) would require 90 watts × 8 = 720 continuous watts to overcome aerodynamic drag; but...
  • The 2450 Kv SunnySky 2212 has a continuous power rating of only 450 watts; which means...
  • The motor will not hit those performance numbers and it will melt trying.
The output for the same weapon from the full Run Amok Spinner Weapon Spreadsheet (below) shows that you can probably get away with using the 1250 Kv version of the SunnySky 2212 at 14.8 volts to push the weapon speed toward 8000 RPM (520 joules) at a continuous 15 amps @ 14.8 volts. That's about 220 watts with the motor rated at 518 watts. If you want more than that you'll need a larger motor with a higher continuous output limit.

Press Fit
Q: How do robots like Sauron and Vector design their pulleys to fit around the outrunner can? Do they just build it with equal diameter and press fit it on? [Ashburn, Virginia]

A: Mark J. Typically, yes. Actually the pulley inner diameter is a few thousandths of an inch smaller than the can diameter for a tight press fit. See this post in the Ants, Beetles, and Fairies archive for a photo and a link.


How High will it Fly
Q: I have been building featherweight spinners for a couple of years now and I want to look into making a pneumatic flipper. I have experience with paintball pneumatic systems and a good machine shop. I've read the Team Da Vinci pneumatics overview and your own Pneumatics Tricks and Tips page, but I'm uncertain about the sizes of components needed to produce a good flip in this weightclass.

Is there is software that will model the performance of a specific flipper design in the way your Spinner Weapon Spreadsheet models spinner weapon performance? [Albany, New York]

A: Mark J. Spinner weapon analysis is simple in comparison to the fluid dynamics flow calculations needed to model a pneumatic flipper. Most gas flipper builders will simply max out the components and hope for the best, but I can see how a reality check would be useful in a weightclass where such weapons are few and far between.

The builders of Robot Wars flipper 'Hassocks Hog' have a Guide to Designing a Pneumatic Flipper that includes a 'Flipper Calc' Excel spreadsheet. The interface is not very user friendly, but with determination it can get you some performance answers. From the webpage:

Designing an effective flipper takes more than just scrounging any old pneumatic parts, bolting them together, and then attaching them to a flipper. You might end up with a very good flipper, but the chances are you will end up with a "limp lifter" rather that a "feared flipper".

To help me improve my own woefully inadequate flipper, I wanted some way of simulating its performance before building it. I needed to check its performance first, before wasting money buying the wrong parts. As a benchmark, I wanted to know how high my flipper would throw another robot, but after trawling the Internet for some form of simulator, I gave up and set about creating a spreadsheet for myself.

"Flipper Calc" is the result of a few months work picking peoples brains and surfing pneumatic suppliers and gurus. I won't pretend that "Flipper Calc" is a 100% accurate simulation, but none the less it gives a close enough indication of flipper performance. In any case, the theory may be all well and good, but there are practical aspects such as curvatures of pipes, the type of connectors used, etc, that will affect the performance of your flipper too. Once the theory has identified the parts you need, the practical aspects will have to be addressed as well.


Different Builders, Different Timelines
Q: Hey, this is my first time trying to design a robot and build it completely from scratch. My competition is on April 29th and it is currently February 12th. I have done all the calculations for drive train. So now I am learning how to use fusion 360 and recently started designing.
  • Is it bad that I still don't have a CAD design?
  • Can you give me a time frame of how I should do things up until April 29th?
  • Any tips? [Chicago]

A: Mark J. Your event is on a Tuesday? Does that make this a school project?

It would help to know a bit about the robot you're building. Different designs, different builders, different shop tools, and differing experience levels all call for differing timetables -- but I can give some general advice.

  1. Delays in receiving parts or receiving faulty parts can scuttle your schedule. Order your parts as soon as possible and test them on arrival.
  2. It's a good idea to have one or more experienced builders take a look at a sketch of your design and suggest changes based on their experience. There are several online forums suited for this purpose -- as well as 'Ask Aaron'.
  3. If this is a school project the CAD may be a requirement, but many combat robots have been and continue to be fabricated without Computer Aided Design. You can gather your parts and use "Cardboard Aided Design" to construct a mockup of a robot and make sure everything fits before commiting to chassis dimensions and layout. See FAQ #7 and the photo of a cardboard chassis mockup below.

  4. Simple robots win. A chassis made from blocks of UHMW polyethyene held together with long wood screws is simple, durable, and easy to construct. Add top and bottom covers and you have a viable chassis. Below is a photo of "Cloud of Suspicion" with the top cover removed.

  5. Schedule time between completion of the robot and the event to become familiar with operating the robot and finding things that need to be changed. About a week is not too much time for this. Spend some of that time adjusting the settings on your R/C transmitter for improved control. See: Transmitter Tweeks for Better Driving Control

A True Story
Q: I found a post in the Robot Design Archive where you claim that Team Run Amok once won a competition with "a yam, four nails, and a girl in a mouse suit". Can this be true? Can I hear the full story? [An iCloud in the Mid-West]

A: Mark J. Yes, it is entirely true. The girl in the mouse suit had little to do with it, but the yam (it may have been a sweet potato) and the nails were critically important.

I prefer to not put the story in print as it is best told with a great many gestures, sound effects, and exagerated facial expressions. As I said in the original post, "...you'll need to buy me a beer to hear that story."


Too Squishy
Q: Hi Mark,

I have been pondering the usefulness of tangential drive for antweight (1 lb) applications, but have concerns regarding its compatibility with foam wheels. In particular, the Repeat Robotics Repeat Tangent motors seem to be effective on the likes of robots like "Super Space Turtle", but I have only seen them used with tires made via custom-molded polyurethane/rubber. Could it be that foam wheels are too "squishy" to create any meaningful contact points with the shaft or simply have a poor friction coefficient (if the latter, could this be mitigated using liquid latex/some other traction coating)? This seemed like a "too good to be true" lightweight 4WD solution. Any feedback is greatly appreciated. [Zanesville, Ohio]

A: Mark J. You are entirely correct to worry about this, Zanesville. Tangential drive (YouTube video) and squishy foam tires do not mix. The transfer of power from the drive shaft to the tire is the product of the coefficient of friction and the force by which the shaft is pressed against the tire. Power in excess of this power limit results in slippage, and getting enough force against a foam tire will depress the shaft so deeply into the tire that drive force vectors would no longer be 'tangential' and power transfer efficiency plummets -- with or without a traction coating on the tire.

  • Note that pressing hard against a tire may place considerable side-loading on the motor shaft. This is a type of load that most hobby brushless outrunners are not designed to accommodate.
  • Note also that the tangential drive video linked above has the test bed operating at low power and not doing any high-resistance pushing. Gears don't slip under high loading, but friction drive can. I like gears.
Extra Credit:  A tangent-drive antweight with 2.0" diameter drive wheels has a calculated top speed of 12 MPH. If the drive train is modified to accept 1.5" wheels, what will the calculated top speed of the robot be?

  1. 16 MPH
  2. 12 MPH
  3.   9 MPH
  4.   8 MPH

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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