Questions and Answers about Combat Robotics
from Team Run Amok

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FAQ Robot Weapons Ants, Beetles, & Fairys Toy Hacks & Kits Design & Construction Materials &  Components Motors & Controllers Radio & Electronics Robot Events Team Run Amok

Q: Hello! Guess who? Alright, first things first, I've got a bot still in the works. Should be done soon, hopefully before the end of the year.

Second things second, I was at school today in my Welding I class when I noticed this old cabinet. I took a look inside and I found a HUGE collection of various drill bits! There were at LEAST 100 drill bits in there, from teeny tiny to massive! Now, I have no clue what kinds of drill bits these are, but I was wondering if there was a way I could convert some of these into spinning weapons, with the bigger ones being more for Ants and Beetles and the smallest ones being for a (potential?) fairyweight.

What do you think? Do you think these bits that I have laid out would be good candidates? Also, do you have any idea on what they're called? My teacher said I couldn't take them because our school is restarting its Industrial Arts program, which I wouldn't be able to take since I'm outta there in December. Your help and advice, as always, is greatly appreciated! [Champaign, Illinois]

A: [Mark J.] Glad to hear that the robot is coming along. A lot of your questions will disappear after your first tournament, and a lot of new ones will appear.

What you have there is a cabinet full of router edge bits. The bearing on the end of the bit rides along the bottom edge of a piece of wood to control the depth of the cut while the bit carves a decorative pattern into the upper portion of the edge as it slides along. Edge router bits are expensive and delicate woodworking tools that will not hold up well to high speed impacts with metal.

Wood and metal working bits are designed to be fed slowly into material held rigidly in place relative to their motion. Jabbing one randomly into a piece of material that is free to move is not going to give any controlled cutting or drilling.

Take a look at the Ask Aaron Spinner Weapon FAQ. Spinners are flywheels designed to store up the energy output of the weapon motor as rotational kinetic energy and release it in a big destructive impact. A small diameter bit with a lot of mass concentrated near the axis stores very little rotational energy and makes a poor spinner weapon.

Q: Hey Mark, I am making a combat robot in the antweight class. The body is inspired by T-Minus and the weapon is a 4-bar lifter. Now I don't want this to be a hamburger is bad, but what kind of servo do you recommend? [Omaha, Nebraska]

A: [Mark J.] Without details of your 4-bar linkage I'll need to be fairly general. You need speed, torque, and metal gears:

  • If you have a healthy budget, the HiTec HS-7940th High Voltage, High Speed, Titanium Gear Coreless Digital Servo is the ticket. Runs at 7.4 volts with lightning 0.07 second speed and 222 oz-in torque for $120.
  • If you have a medium budget, the Hitec HS-5665MH High-Volt High-Speed Metal Gear Servo will work. It also runs at 7.4 volts and delivers 0.14 second speed with 139 oz-in torque for $40.
  • If your budget is ant-sized, the Zoskay DS3218 20KG Full Metal Gear Digital Servo is worthwhile. It can only handle a problematic 6.8 volts, but it delivers 0.14 second speed and 298 oz-in torque for under $20. Design your 4-bar for extra speed.
Note that these servos pull several amps of current -- way too much to run them from the Battery Eliminator Circuit in your speed controller, and their best performance requires voltage too high for most receivers. Follow the diagram to run the servo from a battery with a higher voltage than the receiver.
Q: Hey, Mark. I am trying to design a 150g flipper in CAD but I am struggling with component placement. I cannot figure out what is the best material/shape for the flipper part is (currently 1mm thick metal sheet) and where the hinge and snail cam should go. Here is what I have so far: [image at right] [Bristol, England]

A: [Mark J.] I like the general layout of the 'Jännä' snail cam flipper (video). You'll also benefit from studying Dale Hetherington's version of a spring flipper inspired by 'Jännä'. Note that thick flipper arms to resist the bending force without distorting are common to all designs. An aluminum U-channel arm beam could be optimal for a very light 'bot.

Placement of the hinge point as well as spring selection is likely something best determined by manual experimentation with a mock-up test rig. Make it as crude as you like and play with the layout until you get a satisfactory flip. When you have those dimensions you can design your snail cam and pick a motor to accomodate the load. Then you can put it into CAD.

Q: Hi, I watched 'Jännä' many times, but there are a few problens: it's bulkier at 450g, it uses materials unknown to me, there is a stick just connected at the top and I am wondering if it can be better designed from scratch (I have access to milling maybe welding tools etc) and finally I wouldn't want to just straight up copy the design.

I genrally understand how it works but the problem is that you want snail close to hinge with top of the snail level with it, spring is far and high. I am really stuck ao I would really appreciate if you could suggest a design for me. [England]

A: [Mark J.] 'Ask Aaron' is neither a design service nor a free engineering service -- but I'm willing to toss out some alternative design elements that you may be overlooking.

  • A compression coil spring may be placed ahead of the flipper hinge, compressed by the snail cam;
  • A bespoke leaf spring as used on 'Dead Air' can extend along the full top length of the weapon for a low profile;
  • A torsion spring (pictured) may be placed around the weapon hinge axle (like a mousetrap) to eliminate a need for the beam to extend beyond the snail cam;
  • A pair of extension springs may be placed to the sides at the rear of the weapon beam, leaving room for the snail cam between them and giving a lower profile and more compact arrangement;
  • The snail cam may be split into two cams on a single axle that act on a cross shaft perpendicular to the weapon bar, allowing the rear extension spring to be moved forward and attach directly to the bar.
Complex designs like a snail cam flipper are tests of building and design skills. They aren't easy and not every builder should attempt them. If I were building one I'd favor the torsion spring for simplicity, but a combat robot is a very personal reflection of the builder's preferences -- make it your own.

Q: I have seen all those options before but I guess I never considered them properly. I think I have an adequate design now with a lever at the bottom that utilises a torsion spring.

A while back you suggested I use gear motors like these Pololu 50:1 Micro Metal Gearmotors. I have a 50:1 Pololu to power the weapon but I need two more for the wheels. Looking through ebay for 'gear motors' you can find off-brand motors that appear similar for 20% of Pololu. Do you think they are okay, or unreliable?

Also would it be better to have 30:1 or 50:1 gear ratio for 30mm wheels? Thank you.

A: [Mark J.] The 50:1 Pololu motor is unsatifactory to power your weapon cam: output is much too fast with far too little torque. You need to:

  • Build a crude model of the weapon;
  • Test spring rates and tensions to get a satisfactory flip;
  • Measure the spring force at the proposed location of the cam.
Then you can plug the spring force measurements into the snail cam design equations to determine the needed gearmotor torque.

Chinese gearmotors from eBay are a complete grab bag. You'll get something that looks more-or-less like the photo with specs that are kinda like those given. The only performance specs given on the motors you linked are output RPM -- no torque, no current consumption. The physical dimensions are ±3mm because every batch they ship will be a little different. Maybe you get something useable, maybe you get junk. No way to tell.

The decision on 30:1 vs. 50:1 gearing will depend on multiple factors including arena size. The Tentacle Torque Calculator will run the calculations for you, assuming that you use motors that come with accurate performance specs. With such small wheels I would guess that you'll want the 30:1 Pololus for drive.

Q: If I want to enter my bot in beetleweight competitions but it weighs less than wanted, what are some ways I can add weight? Can I simply add weights? [St. Louis, Missouri]

A: [Mark J.] Knowing nothing about your 'bot design I can only make general suggestions:

  • A robot is not required to weigh three pounds to enter a beetleweight competition -- it just can't weigh more than three pounds.
  • Weight is precious -- use that weight to strengthen your 'bot:
    • Strengthen the wedge;
    • Increase weapon mass;
    • Thicken existing armor;
    • Add effective wheel/top armor;
    • Upgrade to larger drive motors;
    • Improve internal motor/equipment mounting.
  • You can simply add weights -- but mount them securely. You don't want weights to rip loose and smash around inside your 'bot.
  • Position added weight to improve the weight balance on your drive wheels. In general:
    • For a 2-wheel drive 'bot about 70% of the total robot weight should be on the drive wheels.
    • For a 4-wheel drive 'bot total robot weight should be distributed evenly over the drive wheels.

Q: What is the reasoning behind Silent Spring's saw-like attachment that he used against 'Dinner Time'? It has much less bite than his normal single tooth weapon. [Charleston, West Virginia]

A: [Mark J.] I put in a call to builder Jamison Go to get the answer straight from the source:

Everyone is hype about single tooth blades for "bite" but why? What does bite actually do for you? It is heavier engagement on a piece of material which is arguably more energy dissipated just because it has nowhere to go.

What if the opponent has no such grabbable surfaces? Say for example, a robot made of rubber or foam? The traditional STD would be ineffective unless sharpened every match and even then its likely only good to the first few hits because it is THE singular wear point.

The saw-blade is for whittling opponents who have only compliant armor or soft things at the hitting surface. Instead of going for one big impact which would normally be absorbed, I flake material away at a high rate. What happens is I end up grabbing the same amount, but only after several milliseconds of tearing deep into them.

'Dinner Time' would use his over undercutter attachment which meant the only hitable surfaces were his wheels, hence the decision for that type of blade.

There you have it -- sometimes you want a bite, sometimes just a nibble. Thanks, Jamison!

Q: Hi Mark! A while ago I had asked a question about a beetle crusher, and today I discovered these videos of an ant called Purple Haze: weapon test and fight vs. lifter 'Andrew'. I couldn't figure out how it worked, and I was wondering if you could? [Livonia Mi]

A: [Mark J.] 'Purple Haze' fought at the NERC Franklin Institute event in 2010. NERC wasn't real good about sending their event results in to BotRank, but it appears that 'Purple Haze' fought only at that event and then fell off a bridge.

From the video of the weapon test it looks like the antweight crusher was a home-built linear actuator based on a gearmotor and a threaded rod, possibly similar to the construction below but with the output rod extending the other direction.

  • The motor spins;
  • the threaded follower is pulled up the rod;
  • the output shaft pushes up on the hinged blade;
  • the blade rotates forward and down.
There is a third video on YouTube from the same event of 'Purple Haze' getting it's butt kicked by 'Bob Saget'.

Q: So it works kind of like 'Dark-Eagle'?

A: Yes, same method. Note: I have no record of a 'bot named 'Dark-Eagle' ever competing. I suggest that you build something with a greater chance of success.

Q: Hi again, I have a antweight combat robot that has a wedge leading up to a vertical spinner. The wedge is 1mm thick grade 5 titanium, and sits at a 40 degree angle, and screws thread into heat set inserts that are in the 3D printed chassis. The issue is that when I practice driving (with the weapon disconnected) I find that the cap screws are getting in the way of the dummy robot getting fed all the up the wedge. Is there anything I can do? [Great Falls, Montana]
A: [Mark J.] There are a great many types of screw heads, and you're using the wrong type. Take a look at the way the wedges are mounted on the very successful BotKits D2 wedge robots (pictured). You need to obtain suitably sized countersunk flathead screws and a matching countersinking bit that will make the beveled hole in your wedge for the screw head to set down into. There are videos and guidance articles on the 'net for countersinking thin metal that will get you started. Practice on scrap metal to get the technique before working on your titanium wedge.
Q: Hey AskAaron, I'm trying to figure out how to make use of this brushless motor I have. It's for an ant-weight that will roughly approximate tombstone. This will be my first spinner build and my second robot build ever. The motor in question is an EMAX MT2204 which is threaded instead of having a traditional "D" shaped axle. I'm not sure how I would go about either directly mounting the weapon or using a belt drive. I would like to use the finger-tech belt drive parts, but they're designed to fit on a traditional axle. Any advice you have to offer would be appreciated. Thank you very much for your time. [Ballwin, Missouri]

A: [Mark J.] A threaded shaft is common on hobby brushless motors, but it isn't a problem:

  1. Mask up the motor with tape to keep ground metal dust out.
  2. Grind/file a decent flat spot on the motor shaft where the pulley set screw will land.
  3. Clean off the tape and swarf.
  4. Add a drop of Loctite to the pulley set screw and tighten FIRMLY in place.
Note The description of the EMAX MT2204 claims it has a 3mm shaft which is a match to the FingerTech pulleys. However, the drawings of the motor show an M5 thread which is 5mm in diameter; the smaller FingerTech pulleys will not drill out to 5mm. Measure your shaft before you procede.

Q: Hey Mark, just wanted to give an update in case some future bot builder reads my question and is confused by what diameter the shaft is, I think the actual internal motor "shaft" (the on that can be seen on the bottom of the motor) is 3mm and the threaded piece that sticks off the top of the can is 5mm. Maybe that's common knowledge that I'm just now learning, still, feels like there should be better terminology / better clarification of this.

A: That helps -- thank you! That mis-match of shaft and output sizes is not a standard configuration and the discriptions on the web are confusing. It's normal for a single shaft of uniform size to run thru the motor from end-to-end. I'm a bit worried about how the transition from 3mm to 5mm is accomplished. I appreciate your update.

Q: Hey, Mark! I've returned again! This time, I have a pretty legit question: where should I test my antweight once I get it done since I don't have access to an arena, nor do I have the supplies to build one? I want to test driving with and without the weapon. I know that I'll have to be outside to test the weapon. Where are some good places to look for? How far should I stay away from my robot while the weapon is operating (the weapon is a spinning drum)? Is it ever okay to test drive the robot with the weapon inactive indoors or would you recommend keeping ALL of the driving outdoors? The last thing I need is to get injured while testing out my robot due to an avoidable mistake!

Thanks, as per usual!! [Decatur, Illinois]

A: [Mark J.] I can provide some recommendations, but I cannot be held responsible for your safety. Your safest option is to locate a suitable arena and do all of your testing therein.

Procede at your own risk -- even small active weapons are dangerous.

I would personally not hesitate to test and practice with a Saifu antweight indoors with the weapon disconnected. With the weapon neutered it's not much more than an R/C toy. Testing with the weapon running is another matter.

You must have something solid between yourself and the 'bot when the weapon is active. Your testing surface should be swept free of loose material that could be picked up and thrown by the weapon, and there should be effective barriers to keep the 'bot from leaving the test area and picking up small objects to throw. If you have access to a concrete pad in good repair that is visible thru a window or sliding door behind which you stand and operate the 'bot, I would consider that to be a reasonably safe test area for your antweight spinner. Wear eye protection as a precaution -- and two pairs of sox.

Q: I would like to build a beetleweight version of Razer, and I was wondering if I could use a high torque motor for the crusher? Or do I have to use hydraulics? If I have to use hydraulics could you please tell me how to use hydraulics? [Livonia, MI]

A: [Mark J.] There are several posts about insect crushers in this archive. Search here for 'crusher'.

A quick summary of these posts:

  • Electric servos, actuators, and gearmotors cannot directly generate the force needed;
  • There are no off-the-shelf miniature hydraulic components small enough to be practical;
  • It is difficult to build a chassis strong enough to survive the forces a crusher will generate;
  • Lots of people have tried to build small crushers -- none have had success.
A full guide on the details of hydraulic crushers in combat robots would fill a small book. If you're interested in the general principles, take a look at this video.
Q: Why doesn't my ant/beetleweight wedge get under anyone even with sharpening? Is there some technique that the other builders use to sharpen their wedge? My angle is probably in the range of 30-40 degrees if that matters. [Ashburn, Virginia]

A: [Mark J.] Which is it, Ashburn -- an ant or a beetle? Last you told me you had an ant spinner kitbot. Do try to figure out what you've got.

There are lots of different wedgebot designs: two-wheel with dragging wedge, four-wheel fixed wedge, four-wheel hinged wedge, invertible pivoting wedge, split wedge... and you haven't told me anything about your design. I can only give you some general advice.

Your wedge needs to have a lower leading edge than your opponent's wedge if you're going to 'get under' it. That leading edge must lay flat against the arena surface along its entire length, so all sharpening of the edge is done to the underside of the wedge. The final 'hone' of the wedge is done after the wedge is mounted to the robot by placing the 'bot on a flat surface and sliding abrasive paper grit-up back and forth under the wedge to remove any 'low spots'.

Just how low you can effectively go with your wedge depends on the arena surface. An arena with irregular floor section junctions has raised edges that can catch a very low dragging edge.

There are several posts in the Ask Aaron Design and Construction archive about wedge design. You might spend some time browsing.

Q: It is the ant beetleweight wedge guy again and my beetleweight is a a d2 kit, and my ant is a 2 wheel dragging wedge made out of titanium. P.S I changed bots.

A: You seem to go thru many 'bots. I would point out that many if not all of the top-rated robots are designs that the builder refined over time. Thought, testing, and gradual improvement form the path to success.

Q: Can you recommend a place where I can get the structural components for my ant? Could I just cut up a plastic cutting board and use that? [Sacramento, CA]

A: [Mark J.] You've told me nothing about your design, so I can't make specific recommendations on the materials best suited to your robot.

Plastic cutting boards are usually made of some grade of polyethylene or polypropylene. These plastics absorb a good amount of abuse by flexing, but the material is poor at deflecting attacks fron sharp spinning weapons that can dig into their soft surface. Cutting board plastics are commonly used for side panels of the chassis, with stiffer materials (aircraft quality aluminum, fiber composites...) used for the top and bottom panels. Thin strips of polyethylene are also used for flexible wheel armor in small robots. See photo of the 'Saifu' antweight kitbot at right.

Take a look at our Materials Guide in the materials archive for some general comments on the properties of common robot metals, plastics, and composites. You may want to search or browse the entire archive for ideas.

If you're on a tight budget, a trip thru your local 'dollar store' or thrift store can be very rewarding. Cheap kitchen cleavers can be cut and shaped into good ant wedges, and you can likely find cutting boards there as well.

Write back when you can tell me more about your design and I may be able to make specific recommendations.

Q: Hey, it's the guy asking about the antweight again.

What I'm looking for primarily is material for the bottom plate of my bot which I can bolt my motors and other parts onto. The design is more or less a two wheeled box with a wedge and I have all the main parts minus the chassis. You mentioned using aluminum or steel for a bottom plate; can you reccomend a place to buy these materials? I can work out the grade and thickness myself, I just need some direction where to get some.

A: So, you know enough about metals to pick the right alloys and grades and you have enough engineering experience to determine dimensional requirements -- but you can't do a Google search for metal suppliers? Let me help you with that: try "metal suppliers sacramento california". The results show that you have a variety of local sources for materials. If you'd rather pay for shipping and order on-line I have a few suggestions:

  • offers a good selection of metals and plastic in small quantities.
  • Grainger Industrial Supply sells metals and everything else that industry needs -- and they have an outlet in West Sacramento for pickup.
  • McMaster-Carr is a national industrial supplier that deals in raw materials and other interesting items. They have a good selection of Garolyte composite material, which makes a very fine baseplate material for small 'bots.
I'm entirely sure I didn't mention steel for a bottom plate -- that's a waste of precious weight in a location where other materials will do nicely.
Q: Do you know if anyone has ever used the Lumenier FXC1806 Outrunner in a small combat robot? [Gushing and unsubstantiated praise of the Lumenier motor -deleted-] I'd think they would be a good choice for someone wanting to step up from the ever-so-common Turnigy D2822, but I've never really seen them on robots. [Asheville, North Carolina]

A: [Mark J.] I don't know of any robots using Lumenier outrunners and I don't expect to see any. These motors are intended for quadcopter racing and the properties valued there are much different from the desireable attributes in a combat robot weapon motor. The Turnigy outrunners are 'ever-so-common' for good reasons. Let's take a look:

Turnigy D2822Lumenier FXC1806
Power:160 watts165 watts
Size:28mm x 22mm23mm x 18.9mm

So the Lumenier spins too fast, costs too much, and has a shaft too fragile to justify a 3% power increase. The small weight saving would largely be used up by the need for a larger weapon pulley. Use a combat proven motor.

Q: Is Lexan a good material for the top and bottom panels of an antweight, or is metal (alloyed aluminum) better for this? [Smithtown, New York]

A: [Mark J.] Lexan (polycarbonate) is a wonderful structural or armor material if you recognize its needs and limitations. Lexan gains its strength from its ability to flex on impact. Conventional use of bolts will restrict flexing and cause cracking and failure around the bolt hole. General rules:

  • Use as large a diameter bolt as is practical and drill the hole oversize; at least 50% larger than the bolt/screw diameter.

  • Do not tighten the bolt down to squeeze the plastic. You may insert a tubular spacer so that the bolt may be tightened without stressing the Lexan. The bolt should only locate the Lexan, not squash it.

  • I've had good success using rubber grommets inserted into oversize holes to provide 'shock mounting' that allows the plastic to move a bit without creating local stress.

  • A good sized washer on one or both sides of the bolt hole will help spread stress and keep things orderly.

  • Keep the mounting holes well back from the edge of the material. I recommend an inset of at least two times the diameter of the hole.

Rubber Grommets
If you'rd rather just use a material that you can bolt down conventionally, I'm very fond of Garolite.
Q: Do you have any advice for someone who's about to be driven insane by how you have to compress the tires on Fingertech's snap wheels to quark matter densities in order to get the snap ring on? If I spend one more minute with these things I'm going to fall asleep and wake up in Carcosa, if you know what I mean (and you'll know what I mean if you've read The King in Yellow). [North Carolina]

A: [Mark J.] ...or if you've read Ambrose Bierce.

Gosh, it looks so easy in the FingerTech installation video! Here are some real-world solutions I've run across on the web.

Builder Jeff Gier suggests:

  1. Stack two quarters concentrically on each side of the foam tire.
  2. Smash the tire overnight under a stack of books, toolboxes, etc.
  3. The tire gains an indentation that lasts about half a day, making assembly easy.
Builder Matt Spurk uses a pair of spring clamps to hold the retainer in place while placing the snap ring (photo at right).

Builder Robert Masek made and sold a few customized Vise Grips with specialized jaw extensions welded in place (drawing at right).

Update: Builder Alex Horne wrote in with a link to his You Tube video showing how he uses a pair of slip joint pliers to quickly install snap hubs.
The Hamburger is Bad Q: Would 1mm thick, grade 5 Ti be strong enough to replace the 1/8" thick, mild steel alloy im using for my antweight wedge? Im doing the switch mainly for weight reasons [Quebec, Canada]

A: [Mark J.] See FAQ #17. I can tell you that the well-supported wedge on antweight 'Algos' is made from 1/16" (about 1.6 mm) grade 5 titanium, but as I know nothing about your wedge design and support structure I cannot comment on the suitability of any specific material for your purpose. The hamburger is bad.

Q: Because my design requires it, I have to use 4" liteflites for my beetleweight. The issue is that the larger liteflites have a larger inner diameter and are wider than the more common liteflites, so my usual choice of Snap hubs are useless. As I have to make custom hubs anyway, I'm wondering the best way of keeping compression on the hub washer; snap ring or shaft collar? [40 miles north]

FingerTech Snap Hub A: [Mark J.] FingerTech Snap Hubs use snap rings for a couple of very good reasons:
  • they weigh very little; and
  • they don't come loose.
If your hub design is along the same lines as the Snap Hub, use snap rings.

Q: I know you aren't a fan of direct drive weapons on anything over 150g, but do you think they have a place in the newer plastic ant category? [Salem, Oregon - really?]

A: [Mark J.] I think direct drive weapons have a place in all of the lighter combat weight classes. People build combat robots for many reasons and with a wide range of skill sets. For some of those builders a direct drive weapon is a good choice. Follow along here...

Combat records show that the highest ranked spinner robots in weight classes above 150 grams are not direct drive. Restricting the materials from which the robot is made does not change the energy physics of the weapon system. If your goal is to build a highly ranked robot in a heavier weight class and you have the construction skill set required to do so, you are best advised to avoid a direct drive weapon system.

However, if your goal is to build a plastic ant to compete and have a good time you should build whatever will maximize your enjoyment. Only one 'bot wins a tournament but everybody can leave with a smile.

'Ask Aaron' assumes that our questions come from builders interested in designs, materials and components that will give them the best chance of constructing a winning combat robot. However, we recognize that builders have differing mechanical skill levels and that there are reasons to compete that do not involve winning.

The more you tell us about your expectations and skills, the better our answers to your questions become.

Q: Why are all (as far as I've seen) 150g spinners direct drive? Are there any methods of gearing down at that weight? [Saint Stephen, England]

A: [Mark J.] The engineering answer to your question is somewhat complex. Indeed, books have been written on the subject of how proportion changes with scale. The best single sentence explanation I've read on the topic is from the overleaf of "On Size and Life" by Thomas McMahon and John Bonner:

"If elephants had legs proportioned like those of mice, they would be unable to stand without breaking them."

The smaller dimensions of the 150 gram class leads to weapons with a disproportionately small moment of inertia. To obtain the same ratio of stored energy to weight as larger 'bots the small weapons must spin faster. This does create problems with weapon 'bite', but the trade-off is acceptable in this class. If you're going to spin the weapon faster, you might as well save the weight of the gearing system and devote it to the weapon rotor.

Q: I have desgined (not yet built) a beetle weight robot with a drum that lights up (with LEDs for entertainment purposes) but what if I spin my drum like so fast that it wont cause damage? I'm sure I'm going to get 'The Burger Is Bad' or 'Check the Archives'. [TCRM, Malaysia]

A: [Mark J.] The hamburger is good and you don't need to check the archives. Read thru the Ask Aaron Spinner FAQ. The 'Rotational Speed' section of that FAQ discusses the factors involved in getting the weapon to 'bite' into your opponent rather than just 'skitter' across them without doing any damage.

Read the whole Spinner FAQ while you're there -- it'll save you a lot of time and trouble.

Q: Hi, Mark. Could we turn a Viper Kit spinner into an overhead spinner? We have the V2 because V1s are discontinued as you know. Well anyway, my viper spinner keeps pulling a 'Don't Ask' (moving itself impossible directions like sideways ad by sideways I mean my bot is pointing forward and it is going sideways). Please do not make this go to 'Hamburger is Bad'. Ok, well here is the main question: (drumroll) will it work? [Herndon, Virginia]

A: [Mark J.] Well, you could just turn it upside-down and...

Q: P.S by turning it into an overhead spinner I do not mean flipping it upside down. I mean making it an overhead spinner.

A: You mean like...

Q: P.S.S *cough* Hazard, Brutality, and Justice *cough*

A: So a longer bar-blade centered on the top of the 'bot high enough to clear the wheels? I see two major problems with that:

  • You don't have enough weight allowance on the Viper for an effective spinner bar that long; and
  • Using the direct drive method of the Viper for a blade with that great a moment of inertia would both strain the motor and give a very slow spin-up.
I'd suggest finding out why your undercutter is behaving so strangely -- I've seen many Viper spinners and never one that acts as you describe. Your weapon motor may not be aligned correctly or the weapon blade may be imbalanced. Work on getting your current weapon working correctly before moving to something new.

Q: In reply to the Viper kit owner, I've had similar but less pronounced issues with 'Original Robot Do Not Steel', where the robot tends to want to drive in a slightly diagonal line when spinning up. It's probably something to do with the large contact surface between the ground and the blade hub. It's probably something to do with the large contact surface between the ground and the blade hub.

The bottom hole of the blade hub is threaded, so you might want to put a machine screw in there. [Black Mountain, North Carolina]

A: FingerTech's blade hub webpage recommends installing a screw in that threaded hole:

"The hub has a 6-32 threaded hole so that your horizontal spinner robot can rest on a screw head and not be pulled in different directions when the blade spins."

I assumed this was standard practice. I'd recommend a round-head nylon screw if you have one.

All horizontal spinners will face some newtonian 'action/reaction' deflection force as they spin-up, but once up to speed there should be little interference with mobility unless there is poor weapon alignment or poor balance; the blade should be perfectly parallel to the arena floor.

FingerTech blade hub with screw head

Q: I am the viper kit guy and I forgot to tell you that we are still working on an arena. And in the meantime we use a cardboard blade to practice. Plus we don't plan to fight the bot until spring fling 2017 so while we practice we use tape instead of the screw.

A: It seems the hamburger was bad.

  • You failed to mention your cardboard blade that will deform at speed and create odd aerodynamic effects.
  • You didn't think it was important to tell me about the the piece of tape that moves the blade hub contact point away from the center of the spin axis.
No wonder the 'bot behaves oddly! Get the 'bot in full fighting trim before you complain of poor performance.
Q: Hi, its me again. I wanted to know if using 22:1 fingertech silverspark motor at 7.4v with 1 5/8 wheels is ok for an antweight? i put all the spec in the geartrain calculator and the number didnt means anything to me.. could you help me with that? thanks a lot your work is appreciated. [Quebec, Canada]

A: [Mark J.] The Tentacle Drivetrain Calculator you referenced is a valuable tool in the selection of drivetrain components and robot design. Your understanding of the calculator's output might be improved by reading the Example Drivetrain Analysis using the Tentacle Torque Calculator that I published a few months ago.

For the gearmotor, voltage, and wheel diameter you propose: the calculator shows a too-slow top speed around 2.5 MPH with a maximum current draw near 33% of stall. Acceleration is OK with top speed is reached in 2.5 feet from a standing start. A wedge in a small arena needs better performance than that.

Most builders run the 22:1 Silver Spark gearmotors with 3-cell LiPoly batteries (11.1 volts) and wheels around your size range. At that voltage the performance of your drivetrain improves greatly: 3.8 MPH top speed, maximum current draw at 22% of stall, and top speed still achieved in just 2.5 feet. Those a good numbers for an antweight wedge in a small arena. Bump up to a 3-cell battery.

Q: hi, my antweight "wedge" is design so i can swap the attachment i put on it, for now, i have these 2 fork as the main one, but i want to have a solid wedge to fight against spinner. But, cant it be just a flat piece of steel at an angle of about 35 degree, or do i need to add the little wedgelet thingie on the side like algos and many other bots have? is it really necessary? i joined a pic of the design as it is for now [Quebec, Canada]

A: [Mark J.] Top-ranked combat robots like 'Algos' do not have design features present just to look cool and waste weight allowance. In this case, the turned-down wedge end caps serve two important purposes:

  1. Spinning weapons get excellent 'bite' on any exposed sharp edges they can find. Leaving sharp edges on the ends of your wedge where spinners can easily get to them is suicide. Builders call exposed edges like those "spinner bait". The gently curved-down ends on the 'Algos' wedge move the edges back and to the side where a spinner weapon will have a much more difficult time taking advantage of them.
  2. Extending the wedge around the side of the robot helps deflect spinners and other weapons away from your vulnerable exposed wheels. A wedge that ends right at the side of the robot gives a clear path for an opponent to 'feel its way' right down the side into the wheel. Save your wheels -- offer them a little protection!
An 'Algos' style wedge is very effective. I'd suggest imitating it closely.

Quebec's antweight Algos

Date marker: January 2017
Q: Hi Mark,

I'm a big fan of direct drive spinning weapons in insect weight classes. The concept, to me, seems absolutely genius...if done right. In my experience I've had no reliability issues with direct drive drums and the like and prefer that method to belt driven weapons. But at what weight class does the direct drive concept start to fall apart?

Thanks, David R. [Livermore, CA]

A: [Mark J.] I don't share your enthusiasm for direct-drive weapons, David. As much as I admire simplicity in design, direct driven weapons are not as successful as belt-drive weapons anywhere above the 150 gram fairyweight class.

Of the six top-ranked antweights at SPARC/BotRank on 12/20/16 there are:
  • two belt-drive disk spinners;
  • two belt-drive bar spinners;
  • one wedge; and
  • one direct-drive mini-drum spinner ('Algos' - see text below).
Of the six top-ranked beetleweights at SPARC/BotRank on 12/20/16 there are:
  • two belt-drive mini-beaters;
  • one belt-drive disk;
  • two wedges; and
  • one direct-drive disk ('Margin of Safety' - custom hubmotor).

Direct driving a spinner weapon has two drawbacks:

  1. Direct drive places large impact loads on the motor bearings, which are poorly designed for that purpose; and
  2. The motor must be oversized to provide enough torque for a decent spin-up time with high Moment of Inertia (MOI) weapons.
Note that Mike Jeffries made extensive modifications to the weapon motor and bearings used in top-ranked antweight 'Algos' to harden it for direct-drive use. You can read the details of the modification in his guest-post in the Ask Aaron Weapons archive.

In summary, weapons with high MOI are poorly suited to direct-drive. Direct-drive 150 gram fairies work well, but at antweight size your direct-drive weapon is best restricted to a low MOI design such as a small drum or mini-beater.

Q: Well, in that case...

One of the big turnoffs with belt-driven weapons for me is "The Belt Jump" after a particularly violent hit, and the belt disconnects from the weapon drive system. Do you have any tips on how to help prevent this?

David R. [Livermore, CA]

A: Two tips:

  1. Belts jump off pulleys when the chassis and mountings 'flex' under load from an impact and shift the pulley alignment. The chassis between the weapon and motor needs to be structurally stiff, and the motor mount must be placed as close to the motor pulley as possible to avoid flexing. No overhanging 'firewall mount' for outrunner-style brushless motors!
  2. A larger diameter 'pulley flange' can replace or be added to the existing flange on one or both sides for greater security.
I think it goes without saying that great care should be taken with pulley alignment during construction. Make certain that the motor and weapon shafts are perfectly parallel and coplanar, and that the pulleys have no axial offset.
Q: Hi Mark, are the VEX Robotics pneumatics kits suitable for beetle robots? If so is there any documentation on their performance in terms of speed of actuation? Also if suitable, is there any suggestions you'd make for mounting? And the most loaded question: single-acting or double-acting - which one is better?

Thanks. [Monroeville, Pennsylvania]

A: [Mark J.] Suitable? Depends on what you want to do with it. The VEX pneumatics systems are powerful enough for a lifter, but as supplied they are not quick enough to be effective flippers. The system is also quite bulky to pack into a beetle.

  • The maximum actuator force at the rated pressure is about 12 pounds. That's comparable to the discontinued Inertia Labs antweight pneumatics system, but larger and much more expensive.
  • Weight of the system is about a pound, with most of that weight in the pressure tank.
  • A Google video search for 'Vex Robotics pnueumatics' finds many videos showing these components explained and used in various robotic applications. You can judge the size of the components and the system speed.
  • A actuator speed decreases as the load increases, and decreases as the tank pressure drops.
  • The actuators come with clevis mounting brackets that allow the actuator to pivot.
  • The single-acting actuators are equipped with a spring that returns the piston to the 'rest' position when the gas pressure is removed. That spring force must be overcome by the piston when actuated, so the net available force from the actuator is reduced. If you want the full 12 pounds of force you'll need to remove the spring or switch to the double-acting system.
  • The valves supplied with the double-acting actuators keep one side of the actuator pressurized at all times. The pressurized side only de-pressurizes when the valve starts to pressurize the other side. This greatly slows the actuator. For greater speed you could use two of the single-actuator valves and two radio channels -- allowing you to independently pressurize and de-pressurize either end of the actuator.
Given the price, bulk, and weight of the system and its limited power output -- I think I'd pass on trying to use this system in a beetle.
Q: When did the insect class combat robots first appear? Where was the first insect class tournament? [a question I asked myself, since nobody else had]

A: [Mark J.] The first antweights were something of an accident. At the time of the earliest combat robot events, R/C transmitter / receiver sets came with a full set of servos, servo mounting hardware, servo 'horns', and a receiver battery pack. The builders each had a drawer full of servos and no particular use for them.

Someone figured out how to modify servos for continuous rotation which turns them into tiny high-torque gearmotors with built-in ESCs! Attach a jar lid to a one of those servo horns, screw it onto the servo output shaft, plug two of them into a receiver along with one of those unused receiver batteries and tape the whole mess onto a stiff piece of cardboard -- instant mini robot!

The first 'Antweight World Series' tournament for 150 gram 'bots was held in September of 1999 in Reading, England (video). The event appears to have been held on a scrap piece of wallboard propped up in someone's living room. I'm not sure it should count.

The first organized U.S. insect tournament I can document was the SOZBOTS antweight event in Sun Valley, California on February 23, 2002 (video).

SOZBOTS welcome

Q: Hey, Aaron! I was thinking about building a beetleweight drum spinner for a competition in Chicago. The design I want to build will have a 1-pound drum. There's only two problems:
  1. What type of design should I use that would support a heavy drum like that?
  2. How do I cut out a drum from a piece of steel?
If you could answer one (or both) of my questions, that would be excellent! [Kollier W. , Illinois]

A: [Mark J.] I can offer some help:

  1. Take a look at the photos of the Weta 1 and Weta 2 beetle drum spinners for some general guidance on drum support. They use strong, thick-section extensions of the main frame rails to support their drums.
  2. I can't teach you metal shop fabrication in a short answer. I can tell you that most builders do not start with a solid block of metal! Typically a builder will find a suitable length of thick-wall aluminum tube and will fabricate end caps and add impactors.
There are many posts on drum design and fabrication in the Ask Aaron Weapon Archive. Search there for 'drum'.
Kitbots beetle spinner kit Q: I have a Saifu v2 kit and I want to make it like 'Klazo' from near chaos Robotics with the wedgelets. The wedgelets need to be used to get under 'DDT'. Ok here is the question. Will the wedgelets work? [Ashburn, Virginia]

A: [Mark J.] The titanium wedgelets or 'horns' used by 'Klazo' and recently adopted for the Kitbots 'Weta 2' beetleweight kit (photo at left) are not added to assist in 'getting under' a specific opponent type -- the UHMW wedgelets formed in the side rails of the 'Saifu 2' are entirely adequate for that. The problem is that the thin slicing blades on horizontal spinners like 'DDT' cut thru the UHMW plastic like butter. The titanium holds up much better to that type of attack.

If you're going to add a design feature, make sure you know what it's supposed to do.

Q: hello, so I'm building my first battle bot, i was going for ant weight but my college club is doing a beetle weight so i am looking to do that, my motors are brushless 4900kv, and they are cogging on the low end when i try to use them, also I'm having issues finding a proper wheel that gets enough traction due to my lack of torque, my question is i am trying to gear down the motors to help with the cogging, i have all the parts but i have no idea how to attach an axle to a battle bot. I just get confused on how to add a shaft with the ability to rotate. [South Brooksville, Florida]

A: [Mark J.] It sounds like you jumped into the deep end of the pool before you even watched someone else swim.

  • 'First combat robot' and 'brushless drive motors' are a very poor combination.
  • You've attempted to simply attach a wheel directly to the shaft of a 4900kv brushless motor? You're lucky it's cogging and didn't just melt.
  • You've told me nothing about your motors except the 'kv', but as a guess you're going to need to gear them down about 40:1 to get adequate torque and controllable speed. That's not something you can do with a simple pinion and spur gear. The most common approach is to attach a brushless motor to a multi-stage planetary gearbox -- but I'm getting ahead of myself.
Advice: use the brushless motors for another project. The 'kv' is large for a combat robot drivetrain, and you shouldn't be using a brushless drivetrain in your first 'bot anyhow -- they're a real pain to get working well.

More advice: get out on the 'net and find some build logs for beetleweights to get an idea of what works and get some design ideas before you go any farther. Here's one to get you started: Naked Singularity beetleweight.

Still more advice: browse the shop at to get an idea of the type of components used in competitive beetleweight robots.

Q: i am the new builder who recently asked about brushless motors, im on a tight budget main supplies were bought by my school club, so i cant go and buy brushed. our club is building 4 bots for a competition, but in my team none of us have built, and teams cant help each other. any tips for gearing down my brushless motors, they are 4900 kv 19 turn [South Brooksville, Florida]

A: [Mark J.] So... tight budget, no experience, unspecified components, the other teams can't help, you're 3000 miles away, and you want to build a combat robot.

I cannot even guess at the power available from your motors from the information you have provided -- '4900 kv' motors come in all sizes and power outputs. The Hamburger is Bad. Useful information would include the brand / model of the motor and how many volts your battery provides.

As I said in the earlier post, if you want to use conventionally sized wheels for your beetleweight robot (say about 2" diameter) you're going to need a gear reduction of around 40:1. From a practical standpoint that will require a multi-stage reduction that would be complex, fragile, and (I'm guessing) beyond your capacity to produce. It's time to get creative!

Here are two high-reduction combat robot drivetrains that require no gears, pulleys, or sprockets:

  • Friction drive The shaft of the motor presses directly against the surface of the tire and relys on friction to transmit power to the wheel. You will get some slippage, but if your motor has a 2mm to 3mm shaft the reduction ratio works out about right for a fast spinning motor like yours.
  • Tiny wheels If direct-drive for a normal sized wheel isn't practical, how about a really tiny wheel? Mount a very small wheel to the motor shaft and mount the motor at an angle to put the wheel in contact with the floor. Unconventional, but a successful antweight robot used this method as a weight-saving measure.
In your situation, I'd go for the tiny wheels. The 'wheels' could be something as simple as a small plumbing washer, a short length of small diameter rubber tubing, or even a few layers of electrical tape wound around the shaft. They won't last long, but they're easy to replace.
Q: What thickness should a titanium disc for a 1 lb bot be? I am designing it to look like DDT except a rectangle [Ashburn, Virginia]

A: [Mark J.] How long is a piece of string?

As discussed in the Spinner FAQ a spinner is a flywheel that stores rotational energy. Its size and shape is primarilly selected for the ability to store and deliver the maximum amount of destructive energy for the allowable weight.

  • Titanium alloy is not the preferred material for small spinner weapons. Robots like 'DDT' use specialized hard and tough steel alloys.
  • A weapon disk, bar, or drum is not primarilly a structural element, but it must be designed to withstand the forces of impact. Those impact forces are determined by the dimensions of the weapon and the speed at which it rotates, neither of which you have given me.
  • If it's a rectangle, it isn't a disk -- and a rectangle is not nearly as effective at energy storage as the carefully engineered single-toothed cutout disk on 'DDT'.
  • See Frequently Asked Questions #17.
  • See The Hamburger is Bad.

Q: I am the guy that asked the disc question and I need to know if a park 250 motor will do good on a 0.465 or so pound disc.

A: The performance of a given motor with a spinner weapon depends on more than the weight of the disk, bar, or drum. Suggest you read the Ask Aaron Spinner Weapon FAQ for info on weapon motor selection and spinner design. In general I can say that the Park 250 is considerably smaller than a typical ant spinner weapon motor.

Q: The CHASSIS is a rectangle not the disc it is a 4 toothed CIRCLE. The dimensions WILL BE 4x4 inches spinning preferred speed is 4,000 rpm maximum is 18,000 rpm. Is S7 tool steel ok for it?

A: 18K RPM? It sounds like you're planning to direct-drive a heavy 4" diameter 1/8" thick steel disk with a very small brushless motor. Your spin-up time will be awful, the 2mm Park 250 motor shaft and bearings are not suited to handle large impacts, and the heavy loading during the slow spin-up will cook the motor very quickly. You can direct-drive a small weapon, but not a heavy disk with a large moment of inertia. Run a belt-drive reduction to eliminate these issues.

You don't see many 4-toothed disk weapons. If you had read the Spinner FAQ you'd know that more weapon teeth = poorer weapon bite. I strongly suggest reducing your tooth count to no more than two teeth, and please do read the Spinner FAQ.

S7 tool steel typically comes from the supplier in a soft 'annealed' state so that it may be cut and machined. The final product must be heat-hardened in order to develop its hard and tough properties. Heat treating a small and thin piece like your disk is likely to warp it. The current 'DDT' disk is 6 inches in diameter and waterjet cut from pre-hardened 1074/1075 spring steel to avoid this warping issue.

Q: The size doesn't matter, is the park 250 good for an ant class robot

A: Size does matter. When I say that the Park 250 is 'considerably smaller' than a typical ant spinner weapon motor, I refer not only to its physical size but to its power output as well. It is both considerably smaller and less powerful than a typical ant weapon motor like the Turnigy D2822/17 1100KV Outrunner. As noted above, its 2mm output shaft is also too small to use with an otherwise unsupported direct-drive antweight weapon.

Q: We are never going to make a fairy so even if we will make a belt drive we have to waste a perfectly good motor? We are gonna use the can of the park 250 motor for the belt drive. A lot of questions.

A: You can spend your time and money to build a whole robot around an underpowered weapon motor just because you have it, or you can sell that motor on eBay and buy a proper motor that will give you a chance at success. I know what I'd do.

If you want to go ahead, a belt reduction of 3:1 would be about right. Using the can of the motor to drive a belt will require a large pulley on the disk to get that 3:1 ratio -- about 2.5 inches in diameter.

Q: Will a power 25 outrunner with a 3S battery work for the disc I am the disc guy. PS I asked a lot of questions in 1 day. I will maybe suck it up and build a fairy.

A: You want about 100 - 150 watts output power for your ant weapon. Your Park 250 has about 50 watts, and the E-flight Power 25 has up to 600 watts. Worse, the Power 25 weighs almost seven ounces - which combined with your seven ounce disk leaves about two ounces for the rest of your 'bot.

Perhaps you could take a couple days off to think thru your options before sending in more questions? You've used up your quota for today.

Q: Disc guy here maybe the park 270 bc on the robot marketplace the power 25 is back ordered. Has robot combat changed since 5 years ago? P.S I found a park 370 maybe it could work. What is a quota?

A: Maybe, yes, maybe, definition of 'quota'.

Q: Aaron, how good do the anti wedge rubber pad things work? How many do you need to achieve ultimate friction? Thanks, Anonomous

A: [Mark J.] I wasn't sure what you were talking about, but I asked around and was pointed to a rubber strip used by some UK antweights that rubs the arena surface when the nose of the 'bot rides up an opponent's wedge and has its wheels/treads lifted off the arena floor (thanks, Ian). You can see in this video that it works pretty well (the blue 'bot has the rubber strip). A single strip running the width of the chassis will give you all the grip you're going to get.

Personally, I think that the problem this solves is better addressed by designing your 'bot so that the drive wheels aren't lifted off the floor if the nose of the robot is raised. That keeps your drive wheels operational and gives you some ability to push back - and steer!

Kitbots beetle spinner kit Q: I'm building a beetle weight bar beater. I want to use 1/8 UHMW polyethylene for wheel protection, forming it like the Kitbots Drum Beetle Kit wheel guards. How do you get the UHMW to keep its shape and angles? [Direct Email]

A: [Mark J.] Peter Smith at Kitbots says about the Weta-style wheel guards in his kits:

"The ends where they are screwed at the front are formed using a pair of pliers and a little heat......the big curves are just held by tension."

This works for thin sheet, but it does leave residual stress in the plastic. UHMW can be heat formed to hold a shape without adding stress. See the Garland UHMW heat forming guide.

To heat form UHMW: build a form out of wood that's the shape you need, heat the UHMW to the temperature range specified in the Garland guide, wrap it around the form, and clamp it while it cools. Be careful -- don't burn yourself!

Q: I plan on using a 7.4 v lipo to power two FingerTech 22:1 motors on my future antweight. Will my bot be able to stand against all the other ones that seems to use 3s lipos? Am I just over analyzing everything again? [Quebec, Canada]

A: [Mark J.] You're not over thinking -- it's a reasonable question.

More speed isn't always a bonus, particularly in a small arena. A pair of 22:1 Silver Spark motors @ 7.4 volts have plenty of power. For an 8 foot arena you'll want to run them with about 2.5" wheels. You'll be fine.

Q: Can you suggest drive and weapon motors for 150g bot?

So general requirement I guess that they are around 15g each, and drive motors need to reverse and [brake], so obviously esc need to be availiable as well. I've heard that brushless are generally better and that series motor is better for spinning weapon, can you evaluate? I am quite new to this [Bristol, England]

A: [Mark J.] I don't follow the UK 150 gram 'antweight' class, and the US 150 gram 'fairyweight' class is not very seriously contended. I can offer some general suggestions for a new builder:

  • I don't recommend brushless drive motors for new builders. You have enough to worry about without having to deal with the tricky details of brushless ESC firmware and poor low-speed brushless torque. Leave that for a future project.
  • The 9.5 gram 'Sanyo-style' brushed gearmotors are popular in US fairyweights. Similar motors are available from many suppliers. The 50:1 gear ratio at 7.4 volts works well with 1.25" wheels.
  • The FingerTech tinyESC provides proportional forward/brake/reverse control at just 4.5 grams each. They would match well with the Sanyo-style gearmotors
  • I'm not familliar with 'series motor' for this weight class. US insect class 'bots generally use 'outrunner' style brushless motors to direct-drive a spinner weapon. Motors like the 13 gram AD-100L Micro Brushless Outrunner are typical. The 6 gram Turnigy Plush-6A ESC is a suitable controller for this motor.
Take a look at local 'bots to make sure these specs make sense with what's happening at the events you plan to enter.

Q: Thanks a ton, and would you use the same type of motor for driving and weapon loading (like the snail spring power flipper weapon)? As I understand they generate max torque at 0 speed.

A: Yes, a brushed motor is the correct choice for reloading a spring powered weapon due to its predictable torque curve. Maximum torque is produced at stall -- but because power is the product of torque and speed, a PMDC motor generates maximum power when loaded to half of its free-running RPM. For quickest reload speed you'll select a gearing that produces twice the required torque. The torque equations are covered back in that archived post on snail cam flippers.

Q: Hey Mark,

I've noticed that many, if not most, insect class drum bots use screws for their weapon's teeth. Aside from the teeth being easily replaceable, what advantage would this give you that you couldn't get with a single, long weapon tooth that you would normally see in bots like Poison Arrow or Minotaur?

Thanks, David R. (Livermore, CA)

A: [Mark J.] The advantage is that you get to eat this month instead of spending your rent money on custom software and machining.

Read thru this PowerPoint presentation that outlines the design process for the single-tooth drum used by one of the robots you mention. Then consider the machining required to manufacture said drum.

For the average thin-walleted insect-class builder who has access to perhaps a lathe and a drill press, a few hardened screws threaded into a simple symmetric aluminum holder is very appealing.

Q: Is it possible to add Fingertech's Beater bar to the Viper 2 kit? [Malaysia]

A: [Mark J.] Possible, but I can't recommend it. You'd have to fabricate weapon mounts as there are none included with the the weapon kit, but that's just the start:

  • The beater assembly plus motor & electronics alone weigh more than a pound -- the antweight Viper becomes a beetle.
  • The drivetrain supplied with the Viper is not powerful enough for a beetle -- a motor upgrade is required.
  • That starts an upgrade avalanche: motor controllers, battery, armor, chassis...
The Viper is an adequate antweight, but turning it into a beetle is a poor idea. You'd be much better off building a suitable beetle from the ground up.
Q: I was watching this video of an antweight tournament when it mentioned a robot that was controlled via a cell phone.

Pushing concerns about proportional control and reception aside, how is this even possible? Is it legal within the rules considering it has an active weapon? [A server in California]

A: [Mark J.] A friend has a Parrot drone that uses an app in his iPad to control flight via a direct Wi-Fi connection. Multi channel proportional control is good, and range is about 50 meters. It also sends real-time video back to the tablet. A quick search on Amazon for "wifi toy" brings up a bunch of flying and rolling toys controled by android and IOS devices.

The tech is available, but I don't know of a simple off-the-shelf 'plug-n-play' system suited for combat robots. It's still an electronics geek undertaking.

  • Robot Marketplace does offer a line of Renegade Wi-Fi Robot Controllers that provide the basis for a Wi-Fi robot system, but they aren't cheap and there doesn't seem to be a controller app for your phone/tablet included.
  • Hardcore electronic hobbyists can piece something together with Arduino and Wi-Fi boards, but it's not a simple project.
The event in the video was put on by the Central Illinois Robotics Club (CIRC). Legality of radio systems is generally a decision made by the event organizer. The primary concerns are that the radio does not interfere with other robots and that it provides an adequate failsafe response on signal loss. If that could be demonstrated I would have no problem allowing Wi-Fi control in a tournament.

Comment: Hi! I'd just like to chime in on this question.

I was at this competition, and I'd just like to confirm that it wasn't 'plug-n-play' - the builder wrote his own app. I belive that it used bluetooth (although wifi as you suggested probably would have faired him better). When he exited out of the app on his phone the robot immediately stopped, so it passed fail-safe inspection. [Westerville, Ohio]

Response: Thank you for the added info. With the availabilty of full-featured hobby-grade R/C systems at very reasonable prices, there really isn't any reason to develop your own control system -- except for the challenge and novelty.

Q: How does ant weight 'Anticide' flipper works? [Malaysia]

A: The flipper on 150 gram British 'Anticide' uses a standard pneumatic system with tiny parts. The big red cylinder in the photo at right is the pressure tank. A breakout and description of the components used can be found in this post on the Robowars101 forum. The post is more than six years old and some of the parts referenced are no longer available.

A search for 'Anticide' in this archive will lead you to a post discussing the merits and drawbacks to available miniature pneumatic components.

Q: After running a recent competition with lexan and falling in love with it, I was thinking of making my beetleweight with a flexible lexan outer skirt (A bit like Team Robo Challenge did with Terrorhurtz and beta), and I was wondering, which is better: Several pieces of lexan chemically welded together, or one continuous piece of lexan bent/molded into shape? [Oregon]

A: [Mark J.] General Materials Rule: a solid piece is stronger than multiple pieces welded together. A correctly welded Lexan joint has about 80% the strength of the surrounding material. Not bad if you need a complex shape, but weaker than a single formed piece.

Have you tried UHMW Polyethylene? Builders have largely abandoned Lexan in favor of UHMW except for top armor. It isn't as 'pretty' as Lexan but it's easier to mount and more flexible. It doesn't chemically weld, but it makes a very good skirt.

Hackbot 'Blizzard'

Q: Hello Mark. This time I was wondering, what is the easiest way to weigh an insect class robot without having a proper scale?

A: [Mark J.] The lobby of your local post office has an accurate scale suitable for insect-class weights. I'm not sure how the neighborhood supermarket might feel about you weighing a robot on their produce scale, but that may be another option.

Q: Also, what would be the best way to attach a D2 kit wedge to a hacked BattleBots 'Son of Whyachi' toy, or is that even a good idea? Thanks-Luke [Alabama]

A: You can purchase a replacement D2 wedge at the BotKits store, but the beetleweight D2 wedge is 9.25" wide -- way too big for your 4.5" wide BattleBots toy.

If you want a wedge I'd suggest following the instructions in the Robot Dojo BattleBots Toy Hack Guide on 'Reversing the Direction of the Bot' which gives you a tall blunt surface on what was the back of the 'bot to bolt a scoop onto.

Q: do i need to strap my lipo in my antweight if there is almost no room for it to move, just enough to expand a little.. the chassis is a UHMPWE frame millled out of a single block [Quebec, Canada]

A: [Mark J.] What exactly is holding it in place? If it has its own compartment, that's great. If it's just wedged in with other components, a good hit can shove it so hard into those other components it can crush them, or shove them into the battery to crush it. Go 'belt and suspenders' and secure EVERYTHING!

You can use zip-ties for hard-cased things like receivers and ESCs, but narrow ties will cut into a squishy LiPoly and/or crush the internal structure on hard impact. Wide straps for the battery, please.

Q: Hi lipo guy again ; ) can i use these Velco battery straps to strap my battery securely to my chassis?

A: I don't know how large your battery is or what mounting opportunities your chassis allows, but you're on the right track to use a 20mm wide strap that will spread the load out and not cut into your soft battery. You can pick up Velcro straps like these at office supply stores -- they're used to bundle computer cables and keep them tidy. The buckles aren't needed and they take up weight and space; just fasten the strap to the chassis and wrap around the battery.

Q: Hi lipo guy again, i use this battery and the space is very tight. i was just wondering, i also use 2 tiny esc and a minimixer from fingertech. can they puncture the batery? or im i ok with the strap only and the other electronic resting on it or near it

A: I like to tie down everything. The tinyESCs and mixer are small enough to mount with squares of foam mounting tape which takes very little room or weight. Good for receiver mounting, too.

Why are you running a mixer? Does your radio transmitter not have mixing options? You can save space and weight if you can switch to transmitter mixing.

If you don't mount everything will something be damaged bu a big spinner hit? I can only say that I'm not willing to take that chance and I don't think you should either.

Q: so if i unederstand well, if everything is strapped, bolted, glued or smash so hard it become one with the chassis, i dont need any foam around the battery, just the strap wll do the job well?

A: No. Every component should be individually anchored to the chassis:

  • Nice wide straps are good. Use an appropriate number - size dependent.
  • Bolts assocoated with items that have mounting brackets are good.
  • NO GLUE! NO TAPE! NO ZIPTIES! Exceptions for foam mounting tape (servo tape) to secure light electronics and zipties for wires and very small electronics.
  • A good spinner weapon hit will generate HUGE G-FORCES. Just cramming multiple items into a tight space is not acceptable. Components will compact and move in unpredictable ways, placing stress on connectors and fragile bits. Tie individual items down!
  • Foam is OK if you have one item in its own enclosed space. That's not what you've got.
This is all general advice. An antweight is different than a heavyweight, and your particular arrangement may have oddities that I don't know about. It's the little things that lose robot combat matches -- take care of them.
Antwight combat robot held together with utility tape

Not how it's done!

Q: can i replace the battery i showed u before with this NiMH battery? it is listed as 9gram on other website and since its my first robot.. im a little bit concerned about lipo fire..

A: You should be a little concerned about LiPo fires -- enough to take precautions. Unless a LiPo is crushed, cut, improperly charged, or otherwise abused they're fine.

The NiMH battery you found is a poor choice for your application:

  • The Turnigy nano-tech LiPo battery you linked to earlier can supply a peak 7 amps, which is more than adequate to allow your motors to produce their full rated power. It takes up 7 cm3 of space and weighs 13 grams.
  • The 'Dynamite Speedpack' NiMH battery you found does not list a current output but the small size of its connector wires indicates a MUCH lower current capacity -- likely no more than 1 amp. It takes up more than twice as much space (16 cm3) and, in spite of that 'other website', weighs four times as much (at least 52 grams).
Take reasonable precautions and stick with the LiPo.
Q: can i bring an antweight combat robot on a plane for a competition? [Quebec, Canada]

A: [Mark J.] The battery is the problem. On flights in the US you can carry small batteries, including LiPoly, in carry-on bags. Rules in Canada are different. The Canadian Air Transport Security Authority offers specific guidelines for air transport of batteries that vary by the capacity of the battery. The way I read it, insect-sized batteries should be fine in either checked or carry-on bags -- but the website warns:

Not all airlines allow lithium batteries carried in personal devices such as laptops or cell phones in checked baggage. Please consult your airline for more information.

So, pack your robot as carry-on and you should be fine, or check with your airline about packing in checked baggage.

Correctly designed snail cam
Q: Mark, my old antweight robot has gotten so broken that I have felt that it is beyond repair and I should build a new one. So for my new robot I have gotten a basic chassis drawn up in CAD to try and reuse any parts that I can, but for the weapon, I wanted a spring loaded flipper but the spring compression and release mechanism has been a massive pain for me so just asking if you have any suggestions for designs? [Guangdong, China]

A: [Mark J.] Are you really in China or are you just routed thru a Chinese IP address? I'd love to see some photos or video of Chinese robot combat!

Take a look at this video of a cam-driven compression/release spring flipper. There's a discussion of the design in the Ask Aaron Weapon Archive. It is the simplest effective design I've seen.

Reply: Thanks for the design. It really is brilliant and I'm going to try and construct it. And about the competition in China, well I'm in China, but I'm not competing in China, so I will ask around in the community for videos or pictures of the competition. May/June I think.

Q: I would want to build an antweight wedge powered by 2 Spark motors (22.2:1 gearing) powering 2 Banebots 1-7/8" wheels. I wanna know if this 1000 mAH HobbyKing LiPo battery could be good for this use bot.
Thx for ur answer, I hope the hamburger is not bad. [Quebec, Canada]

A: [Mark J.] The Tentacle Drivetrain Calculator estimates that the robot you describe could get along quite well with a 100 mAH battery -- providing enough juice for a full 3 minute match with a 100% safety margin. A 1000 mAH battery is much bukier and heavier than you need.

High-quality LiPo batteries with very low capacities are uncommon. If you are comfortable with HobbyKing products, I'd suggest this Turnigy nano-tech 180mah 2S 25~40C Lipo Pack.

Q: Hello Mark, it's the Deadblow to beetleweight guy again. I was wondering this time if tempered glass used in certain screen protectors would be viable for armor? I plan to possibly use it for the bottom of my chassis. I would send you a picture but, I don't know how to copy and paste it using my phone lol. [Florida]

A: [Mark J.] A 'tempered glass' and plastic laminate screen protector works well on a smart phone. It has a hard surface that resists scratches, and when supported evenly across its length and width by the phone screen it is not subjected to bending or twisting forces. But take a look at the table below:

MaterialYield Strength (MPa)
Aluminum 2014-T6400
Stainless Steel 302520
Titanium Grade 5830
Tempered Glass210

You can see that tempered glass does not have great yield strength, but worse is what happens when the yield strength of tempered glass is exceeded. If you press aluminum, steel, or titanium beyond yield strength it dents, but if you press tempered glass beyond yield it shatters. You also can't cut tempered glass to size. Not what you want for armor; you'd be better off with just the plastic bits.

My choice for bottom armor in an insect 'bot is G10 garolite. It's light, impact resistant, and tough as nails. There are multiple posts about garolite in the Ask Aaron materials archive.

Q: Hi Mark,

I'm designing a 3-lb Weaponized 4WD setup. Because of the weapon, to save weight and space, I am looking at making some kind of pulley system for [the drive wheels]. I was wondering how that is typically done? In larger bots I have seen the back wheels powered and the front wheels on dead shafts connected by pulleys. My problem with this set up is that most motors that I am looking at (e.g. 1000 rpm motor) have too short of a shaft for this. Would it be better to have a driven pulley that connects to both wheels on dead shafts or could I alter the gearbox to have a longer shaft?

Also I'm having trouble wrapping my head around how to attach the wheels and pulleys to each other. Most of the wheel hubs that are available in this class either are meant to be supported only on one side (i.e. Daves Hubs) or are too small and flimsy to properly attach a pulley to (i.e. Snaphubs). Do most people with this set up make custom hubs? Because that is the only solution I am currently seeing.

Thanks for your help. [Ohio]

A: [Mark J.] Replacing the gearbox shaft would be a real pain, and indirectly driving all wheels with belts is unreliable. Go have a look at Bone Dead Robotics' build log for Wedge of Destruction v3. Brandon doesn't write specifically about his hub solution, but there are many photos that should give you a good outline of what he did. It appears that he bolts FingerTech Snap Hubs directly to FingerTech timing belt pulleys and uses the pulley hub to support both pulley and wheel on the short gearmotor shaft. This is preferable to indirectly driving both wheels with belts.

UPDATE: I wrote to Brandon for details on his hub solution. He tells me that there are no bolts holding the wheel hubs to the pulleys -- they're just superglued in place! He recommends boring a 6.2 mm recess into the pulley hub to accomodate the nub that sticks out of the wheel hub and using that to locate and support the wheel. I'd put a couple of machine screws thru the assembly in addition to any adhesive -- just because.

Q: Hi
This is a wonderful website and I have been lurking around for a little over a year trying to gather enough info to build my own robot.
Well that time has come and I am currently working on an ant weight vertical spinner and I am having a little trouble finding a suitable blade for my spinner. The best thing I have found so far is a 3" diameter saw blade. My only concern is the fact that the disc is pretty much smooth around the edges. I'm not sure if I would get enough bite for it to be effective. Do you have any better ideas or am I just over thinking it?
Thanks in advance,
Ant-Noob [Florida]

A: [Mark J.] 'Pretty much smooth' sounds kinda ineffective. I think you want something that at least looks intimidating. The prototypical antweight vertical spinner 'VDD Kit' used the 4-3/8" Makita carbide tipped saw blade pictured at right. If you want something a little smaller, there's a similar 3-3/8" carbide tipped blade. Either of these blades will fit the new FingerTech clamping blade hub.

Current weapon design favors a spinner weapon with very few impact teeth, but I think either of these blades will gave adequate 'bite' if you spin them at a reasonable speed. If you want to upgrade to a one or two impactor disk later you can always make your own aluminum disk with a couple of bolt-on impactors, but I like the idea of using an off-the-shelf blade to keep your first 'bot simple.

Tech note: a large diameter vertical spinner has less trouble with multi-tooth 'bite' than a smaller vertical spinner. The impact angle is different, and it tends to pop the opponent up and into the next impactor rather than just tapping the opponent back.

Q: Is it possible to convert an R/C throttle signal to analog so I can use the trottle stick on my receiver to control something like a lifter? [Quebec, Canada]

A: [Mark J.] That's exactly what an Electronic Speed Controller (ESC) does -- it converts the digital output from the R/C receiver to an analog current level, with or without reversing.

To control a lifter it's handy to also have feedback on the position of the lifter. A standard R/C servo has a small ESC, positional feedback, plus a motor and geartrain all built into a single unit. Very handy for insect class lifters.

There are a variety of other R/C interfaces for other specialized purposes.

Q: Which is the more reliable hub, a set screw hub or clamping hub?

The application is for a wedge beetle using 4 drive motors. It specs out, breaking traction at approximately 1/3 of motor stall torque with a max speed of 6-7 mph in the 5X5 arena. I've only used set screw hubs in the past with less than ideal results. I was looking for your advice for which one is more advisable considering this statement made by the manufacturer:

"The [clamping hubs] offer more holding power in high torque applications. The disadvantage is that they are not as equally balanced for high speed use."

Is this a high torque or high speed situation? Does your opinion change if only 2 motors/wheels are used -- breaks traction at ~60% of stall torque, top speed ~5.5 mph? [Pennsylvania]

A: [Mark J.] You've got a high torque situation with abrupt and frequent reversing. As you have apparently learned, set screws suck in these situations. Two-wheel or four-wheel drive makes no difference. Although there are things you can do to improve the reliability of the set screw (threadlocker compound, machined 'divot' in the shaft...), all things being equal a clamping hub is much more reliable. But in this case, all things may not be equal.

The hubs you're looking at are made to mate to the Actobotics disk wheels -- which are not suitable for combat applications. From the speed and breakaway torque you specified, you're planning on 2" diameter wheels. The hubs would be difficult to adapt to combat wheels, so I'm going to suggest that you consider the BaneBots T40 wheels and matching T40 hubs. They aren't clamping hubs, but the T40 wheel/hub is far superior to the Actobotics wheel/hub combo. Use a little theadlocker on the setscrew threads and you'll be OK.

If your design has the wheels fully exposed to attack from spinner weapons, you'll need something a bit better suited to abuse. Consider the FingerTech Snap Wheels and Hubs. Again, use threadlocker on the set screws.

Q: should i consider using xt60 connectors in a antweight robot? they seem a little bulky and i have never seen any antweight using them [Quebec, Canada]

A: [Mark J.] The XT60 plugs are overkill for an ant. I've always used Deans connectors in small 'bots and never had a failure. The Deans Micro Plug can handle 20 amps and is small enough to tuck into really tight ant spaces.

Avoid the 'look alike' knock-offs -- use real Deans. They're popular for R/C stuff -- your local hobby shop probably has them in stock.

Q: Hi Mark. First, thank you for your website and efforts in educating the rest of the community that desires to learn and compete. Spending countless hours on the website I have grown to appreciate the awesome task you have undergone and the vast wealth of knowledge you possess.

If you don't mind, I have a question on behavior of servo lifters (this is for the beetle weight class). I most likely will be short on details but will try to be through without adding too much extra detail. Imagine a wedge bot (in my case a box with only one wedge). Then split the front plate into thirds, securely fastening the outer two leaving only the middle plate. Attach this plate to a servo in the traditional mounting method (no four bar lifter, just a bar going straight to the servo and attaching securely). Now in this configuration I would like to know what happens when the middle section is attacked directly by a vertical spinner before I am out a few hundred bucks and waste alot of time perfecting a flawed conception. If the section is grabbed by a vertical spinner will it be tossed like it was hinged or would it remain fixed like it was just a solid piece in the front or somewhere in-between? Would the attack cause any damage to the servo (I'm particularly worried about striping the gears despite the servo I have in mind being titanium)? Would the same be true if the plate was attempting to go down while being hit by a spinner forcing it in the upward direction?

Thank you for your time. If you could please explain the reasoning why I'd be grateful and don't want to keep asking questions that would be child's play if I understood how a servo works and why (as I assume at some point it will break and I'll attempt to frantically repair it during competition). Thank you for the difference you are making in the world. [Greenville, Pennsylvania]

Servo Saver A: [Mark J.] You're correct to be worried about what happens when a servo takes a sudden impact. An R/C servo is designed to hold the controlled surface firmly against external force -- to the point of breakage. The force of an impact from a beetleweight spinning weapon would be passed along your simple linkage and shatter gears and the housing of the servo. The problem is the 'attaching securely' bit.

Going to a four-bar mechanism offers a couple of advantages over "just a bar going straight to the servo". The path of the lift can be designed to lift in a curve forward and away from the robot, but equally important the four-bar structure itself can direct some of the force of an impact away from the delicate servo and into the more robust hinges attached to the chassis. But the servo itself is still vulnerable because of its unyielding geartrain.

The R/C car racers had this same problem when their cars ran into unyielding objects like curbs. They developed a device called a 'servo saver' to keep such impacts from destroying their servos. A servo saver contains a spring mechanism that provides allows a certain amout of 'give' to the system that absorbs some of an abrupt impact, transmitting less of the force on to the delicate servo geartrain.

I suggest that you run a web search for 'servo saver' to find several different designs. Evaluate those designs to see how well each might fit into your lifter concept. Do also consider a four-bar mechanism -- it helps.

Q: would u recommend spark motor for a 1 lbs wedge bot? are they fast and powerful enough? [Quebec, Canada]

A: [Mark J.] Yes. The Fingertech 'Silver Spark' motors are widely and succesfully used in antweight wedge robots. They come in a range of gear ratios. The correct gear ratio will depend on the tire size, the selected voltage, the number of motors you will use, and the size of the arena. Example:

  • A one-pound robot with two Silver Spark motors and 2" diameter wheels running 7.4 volts in an 8 foot arena will perform best with the 22:1 gear ratio.
The Tentacle Drivetrain Calculator is the tool of choice for calculating robot gearing.
UK beetleweight robot 'Newton'

UK beetleweignt 'Newton'
Q: Hi, Mark, I was confused that what is the weight limit in the Beetleweight. I saw the limit is 1.362kg on the FRA forum, but I saw the limit is 1.5 kg on the Kinematic website. What is the weight limit in the Beetleweight? [Guangdong, China]

A: [Mark J.] The weight limit is whatever the organizer of a specific event says it is.

  • Beetleweights started in the US where they were and still are a 3 pound class.
  • UK organizers generally approximated an english to metric conversion to 1.362 kilos.
  • Sometime in 2014 UK organizers got tired of all the decimal places and rounded up to 1.5 kilos.
It's a messy world - do your best to adapt.

Q: Hey Mark, I've been working on my latest ant, a front hinged lifter. The motors don't seem to have the moxie needed at 7.4 volts (22:1 Sliver sparks mated to 2.25" wheels), and I want to make the jump to 11.1 volts. Thing is, the servos electronics are rated to 9v maximum (the questionable HXT 12kg, linked to the lifter by a four bar assembly), and I want to ask whats the best course:
  • Replace the servo with a HV version (expensive, but more reliable choices)
  • Use a 9v regulator (adds another part in between to fail, but allows use of my current servo)
  • Lobotomize the servo and run off a spare tiny ESC (no fail safes, but allows more voltage than the servo could handle normally
  • Risk it and run the servo at 11.1 volts anyway (doesn't seem like the best option to me)
What do you think is the best way to go about things? [Portland, Oregon]

A: [Mark J.] Take a look at this previous post in the Ants, Beetles, and Fairies archive. 'Beetle Lifter Guy' is using two LiPo batteries to provide separate power to the motors and to his lifter servo. Note carefully the warning about the red wires from the receiver to the ESC.
3S lipo battery balance connector power tap diagram
If your LiPo has a balance plug you can do the same thing with a single 3S battery. Tapping into the balance connector at 'A' and 'C' (see diagram at right -- wire colors may vary) will give you a 7.4 volt output to power your receiver and servo, while you run the main power connector to the ESC for 11.1 volts at the motors.

  • No extra electronics
  • No voltage risk
  • Minimal added expense/weight/space
  • Retains normal servo operation
That seems like a 'best choice' to me.

Comment from Near Chaos Robotics: Hi Mark, figured I'd add a bit to the question on using the HXT12kg servo with a 9v regulator-

'Reptar', the antweight lifter in this video, uses a 3s lipo for the main power and the 9v regulator from FingerTech Robotics to provide power to the servo. It's a pretty nice match, though the servo gets a bit warm after a full fight. While testing it I was messing with the trims and rates to dial in the lifter and inadvertently stalled it against the frame without realizing it and fried the servo, so some caution does need to be taken when setting things up. With that said, the combo works quite well if you've got the space and weight to fit it. As it sits the bot is right at the 1lb limit and has very little air under the armor. [Georgia]

Reply: Thanks, NCR. It's good to have a 'real world' data point. In general I advise caution in bumping the voltage. I can't think of a single unsuccessful robot that was turned into a successful competitor by turning up the juice -- can you?

Q: Mark,
For my ant-weight robot I am planning on having a 3D printed chassis wrapped in 4130 Chromoly. My question is that the 3D printers that I have access too are able to print both ABS and Polycarb, which do you think would be a better option? I know that Polycarb has better properties but it also has a tendency to be brittle and I was thinking that with the holes that I would print in there for the steel covering could lead to stress points. On the other hand I noticed in a previous post that you mentioned that 3D printed ABS has issues with the layers bonding to itself. So all things considered which do you think would be a better option? [East Cleveland, Ohio]

A: [Mark J.] Printed polycarbonate has delamination issues similar to ABS plastic, and it also tends to warp a bit. The problem varies from printer to printer, so you won't know if it's an issue until you try it.

The properties of ABS and polycarbonate are much different:

  • Polycarbonate (Lexan) is NOT brittle -- it will take enormous abuse of allowed to flex, but it will crack if your mountings prevent it from flexing and create local stress points. Mounting holes aren't a problem if the armor is loosely mounted with grommets and washers.
  • ABS is a stiffer material that is less sensitive to flexing requirements. Standard mounting techniques will be more successful with ABS.
The choice depends on your chassis design. If the steel armor is providing stiffness to the structure and will take most of the impact, I'd suggest the ABS. If the armor is individual floating plates, you'll be better off shock-mounting the armor to a polycarbonate chassis.

Note: I consider 3D chassis printing to still be highly experimental. Be prepared for several design generations of failure.

Q: I've tried unsuccessfully to master 4-bar but cannot get a successful layout no matter what input values I use. For a beetle, what would some of the approximate dimension be? My overall dimensions are currently (for the robot, not arm length) 10" x 6" x 2.25". [Pennsylvania]

A: [Mark J.] Why do 4-bar questions always come in on weekends when I'm away from the computer that has the 4-bar calculator installed? I can at least give you a starting point...

Team Run Amok's beetleweight 4-bar lifter 'Zpatula' has a front bar powered mechanism with these dimensions:

  • Base (E): 145 mm
  • Front Bar (H): 90 mm
  • RearBar (F): 55 mm
  • Top Bar (G): 115 mm
  • Rear Bar base height: raised 20 mm
Proportions similar to these should give you a starting point in your calculations. Click the image at right for a full-size 4-bar output screen of Zpatula's lifter using 'inches' and 'ounces'.
T.i 4-bar calculator output

Click for large image

Note: the 'Total Insanity' website hosting the 'T.i. 4-bar calculator' has shut down. I've pieced together a mirror site to allow downloads of the calculator: T.i. 4-Bar Calculator. I'm also working on an updated version of the 4-bar calculator that will run with current operating systems -- stay tuned.

Q: Hey Mark, I'm the beetle spinner guy again [Oregon] and I have a few more questions:

1: I know you recommended ball-bearings but I've been wondering about bushings. Should I consider them? I know they have significantly more friction but I'll take reduced performance if it means I can improve dependability.

A: [Mark J.] Correctly selected small spinner bearing failures are uncommon. Bushings are fine if well aligned (and well oiled) but if they are knocked out of alignment they will bind. Unless you're very confident that your weapon shaft support is rock-solid, use the ball bearings.

2: After seeing asymmetrical spinners (such as Decimator and Banana Spliter) I want to try to fashion my own. Dimensions for the one toothed spinner would be 6"X2"x.125" of 4030 [steel] with the striking edge hardened. I do not have access to CAD software capable of finding center of gravity, so I want to know the best way to find the spinners center of gravity manually and figuring how to get it as close to the location the blade hub as possible either through calculation of a sketch, or building the weapon and adjusting it?

Finding the center of gravity for a blade A: A blade is easy:

  • Cut out your blade, but do not drill the hub mount.
  • Balance the blade across a sharp vertical surface (see photo). A ruler edge is better than your finger.
  • Mark the balance point and drill your hub mount.
  • See this post in the Ask Aaron Robot Weapon archive for instructions on getting the fine balace correct.

3: What's the best way of locking a spinner dead solid? I was considering a heavy duty bicycle lock, but what other ways are good to keeping a spinner locked?

A: Locked, as in preventing rotation in the pits? Why so important to make it 'dead solid'? I don't know enough about your design to come up with something clever, but often a simple zip-tie will do nicely for an insect class 'bot.

4: For when the Small Johnson motor becomes to weak to progress (either through stress or natural selection) what typically works better for spinners: Sensorless Brushless Outrunner or sensored brushless inrunner?

A: Inrunners will typically have stupid high RPM, so outrunner is my choice.

Sensored have a faster spin-up than sensorless, so sensored is my choice.

Of the choices you offer, outrunner sensorless is the better combination.

5: I've noticed that some one-piece spinners have are notched on the striking surface(Tombstone's red blade is a good example). Does this improve performance to any significant degree or is it just for show?

A: That's not a 'notch' -- the ends of some blades are ground to from a wedge shape at the end. That makes a sharp edge to cut into softer armored opponents. Against hard 'brick' opponents that edge is quickly dulled, so any advantage depends on the opponent you're fighting. We discussed blade choices in response to one of your earlier questions -- see the post about Tombstone's blades near the top in the Ask Aaron Robot Weapon archive.

Q:Where can one get really good beetle motors for less than $20 a motor? The ones from [supplier name deleted] I have found to be subpar and the ones on [supplier name deleted] are quite expensive at almost $30 each. [Pennsylvania]

A: [Mark J.] I'm not a fan of mixing 'cheap' and 'combat robot' -- "really good beetle motor" and "less than $20" don't really go together.

  • The best I can do at your price point is the Kitbots 1000 RPM Beetle motor. Many builders like them for their speed and torque, but they require a bit of preparation to be tough enough for combat use. Follow Kitbots' recommended 'Battle Hardening' process.

  • There is also a large selection of cheap 1000 RPM motors on EBay that have found some application in beetles, but it's a real grab bag. Maybe you get something you can use, maybe you don't. You'd get better odds at a Native American casino.

Try the Kitbots motors. If you don't like 'em you should find a cheaper hobby.

Q: Hi servo lifter guy again. I am trying to settle down finally on a servo and am stuck between the HS-7980 and the HS-7954. I need to know exactly how bar length is calculated... is it point of rotation to point where the servo bar attaches to the scoop (middle of scoop) or is it the point of rotation to the point of the scoop (the endpoint scraping the ground)? Can a servo be effective if operating at 80% of its lifting capacity (obvious slowing it substantially but how slow is too slow?) Your answer may save me $80. Thanks. [Massachusetts??]

A: [Mark J.] The bar length is measured in a straight line from the point of rotation at the servo to the point where the weight of your opponent will be applied. In most cases that will be the far end of the bar.

How much weight will actually be on the bar is another issue. If you have a short 'scoop' that will only penetrate far enough underneath to lift one end of your opponent, the lifter will - for practical purposes - only have about half your opponent's weight on it. If your lifter is designed to get far enough underneath your opponent to lift the entire robot you will need to plan for their full weight.

How quickly you need to lift will also depend on your design and your strategy:

  • If you're building to lift your opponent up just a bit to break their traction, you'll only be lifting their weight a very small height and speed is not really an issue.
  • If you're trying to tip a 'bot over from the side, you'll be lifting higher and longer while the other side of the 'bot still has traction. Speed is critical.
  • If you're getting underneath and lifting them clear of the floor, you'll need greater lifting power and a rapid start to the lift and be lightly enough loaded to hold them for an extended period without frying the servo.
In actual combat you're never sure what lifting opportunity may present itself which is why I design for adaptability using the 60% load factor discussed in our previous post (see post immediately below). Think about your design, the likely way you'll be using the lifter, how high you'll need to lift, and how long a heavy load will be applied to the servo.
Q: How is the length of a servo lifter bar determined? Is it point of rotation on servo to point of attachment or is it the full length of the bar? [Oakdale, PA]

A: [Mark J.] I believe you're refering to a previous post about lifters in the Robot Weapons archive:

...The power you'll need from [a servo] will depend on the length of the lifter arm attached to it. For reasonable speed and reliability, select a gearmotor that will stall with no less than 1.67 times the weightclass on the end of the lifter. Here's the formula to calculate the desired torque:

Stall Torque (oz-in) = length of lifter arm (inches) * weight class (ounces) * 1.67

The length of a simple single-bar lifter that plugs into the torque requirement equation is a straight-line measurement from the servo output rotation axis to the tip of the lifter arm.

Q: And is the 1.67 multiplication to provide safety or is the number produced by the equation the actual minimum oz-in?

A: As it says in the referenced post, the formula provides a desired torque that accounts for speed and reliability. To understand where that 1.67 figure comes from you need to know a bit about R/C servos:

  • Servo torque is given as 'stall torque', which is the load at which the servo stops moving.
  • Servo speed is given as transit time under zero load, which effectively never happens.
At stall load you have zero speed and the servo lifter won't actually lift anything. Actual servo speed under load is inversely proportional to the percentage of stall load applied:
  • Loaded to 100% of stall torque, the servo is stalled and has zero speed;
  • Loaded to 90% of stall torque the servo has 10% of its listed speed;
  • Loaded to 80% of stall torque the servo has 20% of its listed speed...
The 1.67 multiplication factor in the equation assures that the servo will not be loaded beyond 60% of its stall torque rating when lifting the assumed maximum load. Under that load the servo will deliver 40% of its listed speed. This provides a good balance of speed and safety from damaging overload.

Q: Could this Festo actuator be used in a beetle if using a 12 grams co2 cartridge? [Connecticut]

A: [Mark J.] Not for a flipper; the gas ports are too small to allow the rapid gas flow required. The Festo actuators are also expensive -- you might expect to pay close to $200 each.

See this post for a discussion on insect class pneumatic flippers that outlines the problems with existing off-the-shelf components.

Q: What are the advantages of a weapon system without using belts but rather attaching a wheel to the brushless and spinning it that way? [Pennsylvania]

A: [Mark J.] There are many more disadvantages than advantages to mounting a weapon directly on the motor shaft. The only real advantage is simplicity of design. I'm a great supporter of simple design, but in this case I really can't recommend it. The disadvantages are too great:

  • A larger and more powerful motor is needed to spin the weapon quickly to speed.
  • Although slower to spin up to speed, the direct-drive weapon will spin too fast for good 'bite' at full speed.
  • Weapon impacts will be transferred directly to the small and fragile motor shaft, bearings, and case -- unless "extensive modifications are made.
You'll break a lot of weapon motors by trying to keep things a little too simple. It is possible to modify a brushless motor to take the extra strain of direct-drive weapon duty, but it takes quite a bit of work. Search the Ask Aaron Robot Weapons archive for 'Mike Jeffries' to see how it's done.
Q: Is there a way to calculate about how thick your weapon shafts should be? This is for a beetle fbs about 3" tall. Bowl plus teeth weighs at 1.25 lbs. It is a live shaft and I was planning on using a 6mm shaft but am worried it is too thin and will bend or snap despite the 2 spaced apart ball bearings. It is being spun at about 4000 rpm.

Thanks. [Pennsylvania]

A: [Mark J.] From an theoretical engineering standpoint -- if you know the exact force vectors that will be applied to a shaft you can absolutely calculate the required diameter for a shaft of specific material and length. All it requires is a degree in mechanical engineering and a few hours of your time.

From a practical standpoint -- figuring out the force vectors for a shaft in a combat robot that may be impacted from any angle and with unknown amounts of force is effectively impossible. As we recommend in Frequently Asked Questions #17:

Look to see what other builders with similar designs are using and learn from their experience.
If it breaks, make it stronger.

Q: Hi, beetle lifter guy again. I'm trying to get a final parts list together and need to know the following:

1. Can I hook up 2 motors on one side inorder to get them to spin in sync?

A: [Mark J.] Yes -- multiple brushed motors can be connected to a single channel of an ESC as long as their combined current draw is within the current capacity of that channel.

2. Do I need a servo booster?

A: No.

3. Do I need a servo controller or can I simply hook it up into my Sabertooth 2 x 12 RC Dual Motor Speed Controller?

A: Neither. The servo plugs directly into the R/C receiver (see next question).

4. What do I need to make my servo (HS-7954SH) work on the left stick?

A: On most transmitters used in North America the up/down axis of the left stick is channel 3 -- it may be marked 'Throttle' or just 'THRO'. Plug the servo into that port on the receiver.

5. How is this wired together -- 1 2c lipo (for servo), 1 3c lipo(for drive motors), 4 drive motors, servo, rc receiver, speed controller, switch? Thank you as always. [Pittsburg, PA]

Wiring diagram for four-motor robot with servo lifter weapon A: See the diagram at right.

  • If you buy a two-cell 'receiver pack' battery -- it will come with the correct connector to plug directly into any unused port in your receiver. You have verified that your chosen receiver will operate on 7.4 volts, right? You may put a switch into the power line or simply unplug the battery to power-down your receiver and servo. Check the event rules to see if they require a switch on this power line.

  • On the Sabertooth motor controller, clip and tape back the red wires on the leads that run to the receiver. These wires carry 5 volt power from the ESC to the receiver, but since you are powering the receiver with a higher voltage/amperage battery you don't want the ESC trying to power it as well. If you are using 'EleVon mixing' to control the robot throttle and turning from the right transmitter stick you will plug the two leads from the ESC into channel ports 1 and 2 (ELV and AIL) in the receiver.

  • Your Sabertooth ESC will come with instructions on connecting the three-cell battery and motor leads. The diagram shows a 'Dean's plug' used to connect the battery to leads from the ESC for rapid disconnection and charging. A second plug is used as a 'removable link' to power/un-power the drive. Again, check the event rules to see how they want the main power disconnect to function.

When you get it all wired up, follow the instructions down near the bottom of our Guide to Transmitter Programming for Combat Robots to get the robot to correctly respond to transmitter commands.

Q: How do you calculate what servo you need in oz-in as well as speed for this: [upper design at right]

and this design: [lower design at right]

I have [the T.i. Combat Robotics 4-Bar Simulator] but don't think it would be very helpful considering they are not traditional designs. [Pennsylvania]

A: [Mark J.] The upper design at right is Team Run Amok's inverted 4-bar lifter. The T.i Simulator cannot handle the calculation of torque requirements for this inverted design, and a force analysis of a 4-bar system is very complex. Estimation of torque required for that specific lifter has been recently discussed -- see this post in the Ask Aaron Robot Weapons Archive.

The lower design is not a 4-bar lifter, it is a simple lever arm directly attached to a servo. This is an entirely traditional design. Torque calculation for a simple lever arm has been discussed multiple times at Ask Aaron -- see this post in the Ask Aaron Robot Weapons Archive.

Before you ask -- check the Ask Aaron Archives
for an existing answer to your question!
4-Bar Servo Lifter

Simple Servo Lever Lifter

Q: Hello, beetle fbs guy again. Not a real question but rather and explanation. If you recall you suggested I use an aluminum spacer and make the bolts the impactors. What I proposed to do was cut the beam in half making a square c. Then I would run two bolts trough the roof and through the base along with about 5 bolts through the impactors along the wall. With the bowl the design will most likely finalize into an undercuter. Would I be wise to make tall impactors like that design but not mount through the roof?

Thanks as always. [Washington]

A: [Mark J.] Aha! I was picturing a much smaller cross-section beam in a different configuration and it wasn't making sense. Now I've got it.

Steel cooking pots Take your stainless steel mixing bowls back and get yourself a straight-sided steel cooking pot of suitable size. I'd leave off the angle over the top for the roof mount because spinner shells with a tall 'bracket shape' to their mass can run into stability problems -- see this previous post on spinner instability.

I'm not sure what shell dimensions you're contemplating, but to insure stability I'd restrict the height of each vertical impactor to no more than one-third the shell diameter. Example: 9" shell diameter => 3" max impactor height. That's a pure eyeball guess based on unstable spinners I've seen. You can try a taller impactor and trim it down if it gets funky at speed. You probably aren't going to hit anything more than a couple inches off the floor anyhow.

I'm assuming that you want two impactors. Using three impactors greatly reduces (eliminates?) any possible instability, but also reduces the impactor 'bite'. I think you'll be OK with two impactors.

Don't forget to put washers under the nuts securing the bolts on the inside!

Q: How do 3 impactors make a fbs more stable than 2 impactors? In my mind this makes it less balanced and therefore less stable. For a 10" fbs about 3" tall would you recommend 1,2,3, or 4 teeth. (Spinning at about 5000 rpm). Thanks.

A: I messed up the link to the previous post on spinner instability, but it's fixed now. Give that a read. The math gets really deep really fast.

A radially symmetric object with three primary masses can be perfectly balanced to spin in its axis of symmetry. Most small motor armatures have three iron poles. The trick here is that an object with three primary masses has identical moments of inertia for the two axis at right angles to the axis of symmetry. That effectively guarantees that rotation in the axis of rotation has either the greatest or smallest moment of inertia of the three possible spin axis and is therefore stable. The same cannot be said of a rotating mass with only two primary masses -- it may be stable or it may not.

Have you calculated the energy storage capacity for your shell? I know you likely don't have performance numbers for that motor that you had lying around, but you may find that it takes a very long time to spin a 10" diameter shell to 5000 RPM -- maybe too long for a small insect arena.

How many teeth?

  • One tooth: best bite, but can be a real problem to get balanced and may or may not be stable.
  • Two teeth: fair bite, easy to balance, may or may not be stable.
  • Three teeth: bite decreasing, easy to balance, almost certainly stable.
  • Four teeth: poor bite, easy to balance, probably stable.

Yes, there are tricks to increase bite for multiple impactors but I recommend staying simple, it's getting late, and this answer is long enough already. I'd go for two impactors. If it isn't stable we can fix it.

Q: Hi Mark. Beetle fbs guy again. So I took your advice and purchased a few stainless steel mixing bowls (keeping the receipts until the design is finalized). The great part is now the overall weight is down quite a bit. The bad is I no longer know how to mount the teeth I'd like to use considering that a bowl does not have a flat side to easily put bolts through or a place to mount easily on top or underneath. I was thinking about making some wood blocks and sanding them down for a easy mount for bolts but then this takes up interior space requiring a larger bowl. Any thoughts? [Washington]

A: [Mark J.] As I recall, you have hollow square steel beam that you want to use for impactors. You told me you planned to 'cut it in half' but you gave me no dimensions except the 1/4" wall thickness. I can't really picture what you're trying to do.

Bowl FBS spinner combat robots

Angle-sided 'bowl' spinners typically have fairly small impactors mounted along the lower lip of the bowl. They are long enough to allow for several mounting bolts thru the impactor and the lip. 'Sandwiching' the lip between the impactor and a fabricated metal reinforcing strip helps to strengthen the mounting.

Of course, if you want tall impactors you can always go with a straight-sided steel cooking pot...

Q: As you may remember I also am building a beetle lifter. A few weeks ago we discussed a servo lifter and you gave me an approximate lift time of 0.6 seconds. If my strategy is to box rush the opponent and back them into a wall then use the lifter this time is completely acceptable. However, I was wondering if a faster or more powerful lift was possible if I went with a traditional 4 bar design? If yes, then in four bar what bars would be extended/shortened to do this?

4-Bar Servo Lifter A: The balance between lift force and lift speed can be changed, but the product of the two will remain constant:

  • Double the lift speed by lengthening the 'H' bar, and your lift force will be cut in half.

  • Double the lift force by lengthening the 'F' bar, and your lift speed will be cut in half.

I'd suggest sticking to the approximate bar ratios I gave you in the earlier post.

Q: Your help has been greatly appreciated over this entire design process.

P.S. Would you mind if I named the fbs 'Bad Hamburger'?

A: Aaron was sure that somebody would eventually name a robot 'Bad Hamburger' as a reference to his unanswerable question analogy. Go for it.

Q: I'm the guy who's designing the spinner beetle, and now I've settled on the electrical aspect of my bot, and now I'm working the (just as if not more important) mechanical aspects. My questions are:

1) As I'm using a live shaft for my (huge, horizontal) weapon, should I use ball bearings or needle bearings(They will be epoxied into the material)?

A: [Mark J.] I don't like the sound of 'epoxied into the material'. A standard shaft design will retain a flanged bearing in place without the need for adhesives to hold it. If an adhesive failure would result in a weapon failure in your design you should consider changing it.

Weapon shafts are best supported by ball bearings.

2) I'm using timing pulleys and belts, so how tight should the belt be? I'm trying to avoid having a belt tensioner(just another part to fail), but I also know that a belt that's too tight is just as bad as a belt that's too loose.

A: Timing belts are not like 'smooth' belts in that they do not directly rely on their tension to transmit power. The correct tension is 'just enough' to keep the belt teeth from 'jumping' out of the pulley grooves under load. You have a fairly large tension range -- a belt tensioner is generally not needed.

3) I know that my edger blade will fail eventually, so I was wondering, whats better for a one piece weapon, hardened S7, hardened 4130, or hardened AR400?

A: The requirements for the impact area and the rest of the blade are quite different, which makes a single piece blade a bit of a challenge. The impact area should be very hard and unyielding for durability and impact force transmission, while the rest of the blade must have a bit of resilience and toughness to survive the high impact loading without shattering.

  • S7 tool steel is the material of choice for impactors, but it's not ideal for a long and fairly thin blade like yours. I'd be worried about breakage.

  • AR400 is a wonderful armor material but it doesn't hold up well at the weapon impact site. The repeated impacts chip away bits of material, rounding the impactor off and making it less effective.

  • For your particular blade dimensions (9" by 2" by 0.12" from an earlier post) my preference of the three materials would be the 4130 chromoly, but I would selectively harden only the tips and leave the body of the blade in a tougher and more resilient state. I'm not usually a fan of 'backyard hardening', but it is possible to perform tip hardening yourself with a torch. Take a look at this steel hardening video. The case hardening powder used in the video is required for low-carbon steels but is optional for medium-carbon steel like 4130. Do use a water quench for chromoly.

4) Because I'm using a live shaft, should my weapon pulley be between the bearings, or outside them, or does it matter?

A: Your blade hub will be the major load on your bearing system and it should be placed as close to a bearing as possible. If you can get the weapon hub closer to a bearing by moving the pulley to a position between the bearings, that would be the preferred design.

5) Speaking of pulleys, should I use pulleys for my drive system(Using a fingertech 50:1 spark motor with 3" wheels at 11.1 volts) to isolate shock, or should I just risk it and directly drive my wheels of the motor? I might not have much weight so spare, so I'm not sure if wheel guards are in the cards for me. [Molalla, Oregon]

A: Keep it simple. You said it yourself in a question above: "...just another part to fail." If you're using the 3" Lite Flite wheels the spongy tire material will offer good protection from drivetrain shock. Get an extra set of the Lite Flights for your spares kit -- they rip up a bit if exposed.

Q: Hi Mark. I'm building a beetle fbs and come with two questions.

1. I am powering this [weapon] with a 1/8 castle creations motor I had laying around. It is a d shaft. I would like to use a keyed layout for both weapon motor and pulley. Ideally it would be reduced down to about 4500 rpm. I found a few pulleys at my local auto parts store that would work but are way too heavy. The shell at this point could be live but dead if perfered. My question here is how do I power the system? I don't want to use a set screw and hub but I know of no other way to enlarge the shaft (currently 6mm and 2 in long). Also where to buy suitable parts again perfered keyed?

A: [Mark J.] Keys are not generally used for shafts less than about 1/2" diameter. It's very difficult to key a shaft much smaller than that, and the shaft is weakened too much by the process. I think you're going to be stuck with a set screw pulley for the motor shaft. Use a thread-locking compound and check tightness before every match.

Consider these MXL timing belt pulleys for your drive. You'll need to enlarge the bore diameter to match the shaft size. Robot Marketplace has MXL timing belts in suitable sizes.

2. What is the best material for the shell? I could use 1/4 in plywood for a top and 8 in PVC for walls. It would be 3.5 inches tall. I would use 3 in long deck screws around the perimeter to fasten this assembly (about 16 screws). I could also use a stainless steel mixing bowl of the same diameter but fear it would be shredded because it is quite thin. Finally would the bottom of a home depot bucket suffice? My impactors are a square steel hollow steel beam cut in half. The steel is 1/4 in thick. I would run 4 screws through the top 2 through bottom and 6 bolts through the impactors and through the wall. They would be 3/8 in diameter bolts 2 inches long.

A: Have you ever seen a plastic Full Body Spinner? Plastics have one of two problems as materials for an FBS shell: they are either brittle (low impact strength) or flexible.

  • Rigid PVC is brittle. It will shatter under high impact loading, which is exactly what it will experience as a spinner shell. It's very embarrassing to have your spinner shell explode -- I can't recommend it.

  • Plastic buckets are typically made from polypropylene. They won't shatter, but they do flex a lot on impact. Flex in a spinner shell is BAD: it reduces the impact given to your opponent and alters the balance of the shell. Picture hitting your opponent with a pillow then wobbling off out of control. Preferable to the PVC, but also not recommended.
'Best' is likely a custom machined aircraft spec aluminum alloy, but you told me in the inquiry you made on this topic a couple weeks ago that you didn't have the facilities to do that. As I suggested then, use the steel mixing bowl. Many, many successful spinners of all sizes have used cookware for their spinner shells. Pots, pans, bowls, and big woks have all seen action in combat arenas. Reinforce the impactor mounting points with plates/washers on the inside and you'll find a mixing bowl to be entirely suitable.

One final question. Does this have to have 4 drive wheels or can I use 2 inline and just use roller bearings ahead and behind this drive system? Thank you so much. I hope the hamburger isn't too bad on this one. [Internet, USA]

A: Two-wheel drive is common for FBS weapons. Simple polyethylene or teflon skids are suitable to stabilize the chassis. Roller bearings or castor wheels are overkill in a small 'bot -- keep it simple.

By the way, have you added up the weight of all these components? I'm guessing that this is running overweight for a beetle.

Q: Hey Mark, I'm designing a monster beetle spinner. The weapon is a 3mm thick steel bar, 9 inches long and 2 inches at its widest. Right now my design has a huge roadblock. My spinner motor is not brushless as most builders are using, but a simple brushed motor that I harvested from a drill with a dead battery long ago. The issue is that it's a Small Johnson motor with a 3:1 reduction and the motor demands a huge amount of starting current. I can find a battery that can supply enough amps for it, but I can't find a hobby ESC that can meet its demands even halfway and still be underweight.

I don't know if I should use a solid state relay (the cheapest I could find for my needs was 50 to 60 dollars, and is heavy), a solenoid (much cheaper, but also heavy), go with the Victor SP (which might be the best option, even if it is 60 dollars), or call it a bust and go with a lower power brushless system. What do you think is the best option? [Molalla, Oregon]

A: [Mark J.] A few thoughts:

  • The '550' size motors in cordless drills come in several different varieties that have very different power outputs. Just because it looks like a 'Small Johnson' doesn't mean that it has the same power or thirst for current. If you have doubts about the motor it might be a good investment to buy an actual Small Johnson motor so you know the true performance specs.

  • Of the options given, the Victor SP ESC is the best choice. It's small, light, cheap, and will be useful for future robot projects. The motor is only pulling 50+ amps for about 1/3 of a second during spin-up -- that's well within the capacity of the Victor controller.

  • There is a trick from the 'old days' when we didn't have ESCs with enough power handling to control big motors. Shrinking the connection wire a few sizes and making it longer (loop the excess in a coil) will add some extra resistance to the motor circuit. For a Small Johnson, using 5 feet of 20 gauge wire for connections on both poles (10 feet total wire) will drop your stall current by about half. It will also roughly double your spin-up time, but peak speed will be nearly identical.

  • You can also use a Servo Slower with an ESC to reduce the high start-up current drain. Again, this will lengthen spin-up time, but top speed will be unaffected.
I'd go with the Victor controller and keep the quick spin-up for a small insect arena.
Q: I am building a fbs with a two part body; a pvc body and a wood top connected by lots of screws. If this design acceptable? I know you will suggest using a metal but I don't have access to the tools needed to make your typical fbs shell. [Internet, USA]

A: [Mark J.] You've told me almost nothing about your robot or your weapon. The hamburger is bad.

  • Weight class?
  • Shell diameter?
  • Thickness of materials?
  • How fast will you spin it?
  • How many screws are 'a lot'?
If this is a small (insect class) robot I'd recommend a metal mixing bowl or pet dish. Many small FBS have been built using bowls and if you can find one of suitable size it would have to be better than wood, plastic, and lots of screws.
Servo powered 4-bar lifting wedge

Q: Is the HS-5585 [servo] ok to lift a 4 lb robot if directly attached (wedge/scoop hinged on top with servo attaching on inside around middle of 3 inch long by 3 inch high scoop/wedge)? All that said, do you have a way to calculate maximum lift capacity and speed to 60/90/180 degrees for a design like this because I have a few different servos in mind (some 7.4v others 6.0v with varying speeds and torque) and do not want to throw grunt work at you that I can do. Thanks. [Bellevue, Washington]

A: I'm not sure that I understand how you plan to attach the servo to the lifter wedge. If it looks like my diagram at right, it's a 4-bar mechanism and the calculations for required torque and for speed are complex. You can find posts about tools to help calculate 4-bar performance in the Robot Weapons archive -- try this post for a start.

Q: Is 1/8" AR400 sheet OK for a scoop for a mantis? [Brooklyn, New York]

A: [Mark J.] See Frequently Asked Questions #17.

I can say that AR400 steel has good impact resistance and is in general suited to armor applications.

Q: Do you know of any good websites or stores to buy weapon hubs as well as components to make an insect lifter (by geared/brushless motor/servo since you cannot make a co2 flipper with of shelf parts)? Also approximately how fast would this lift/ extension occur? Thank you. [New Jersey]

A: [Mark J.] Spend some time browsing around ServoCity -- they have everything you need to make an insect lifter of any design you may like. I'd recommend staying away from brushless motors for a lifter mechanism -- high startup loads are their nemesis.

Insect class lifters traditionally use high-power servos for power -- see examples of insect lifters in this archive. A simple direct acting servo lifter can lift in perhaps 1/4 second. If you go to more complex 4-bar mechanisms or power sources other than servos, lift times can vary wildly.

Weapon hub requirements vary greatly. Most often they are custom made, but if ServoCity doesn't have what you need you may find something you can use at Robot Marketplace.

Q: Hey Mark, I was wondering if you knew what parts this beetleweight (video) was using for pneumatics? Thank you! [Mercer Island, Washington]

A: [Mark J.] Your video is a test of a custom-made full-pressure CO2 system for British beetleweight 'Flange'. There is another video from June, 2012 of 'Flange' testing its flipper, but I'm unable to find any record of the bot actually competing. I suspect that the system did not meet British rules -- it doesn't meet US rules, although a brave [foolish] event organizer might allow it to compete.

The custom machined actuator is single-acting and self-venting with a spring return; a very inefficient design, but it does allow use of a simple 2-port poppet valve. No pressure regulator is used. The system cannot be duplicated from off-the-shelf parts.

Q: Is there any one good website that shows designs for a bunch of beetle weight robots? I know teams usually have a website but most don't list beetles. [Rockfish, North Carolina]

A: [Mark J.] Browse around The Builders Database.

Click on one of the thumbnail photos for more info and a larger photo.
Beetleweight 'Zpatula

Q: Could a 90 gram co2 tank be used to make a 4lb flipper? [Durham, North Carolina]

A: [Mark J.] A 90 gram CO2 cartridge is overkill for an insect class robot. It weighs the better part of a pound and holds 7500 cubic inches of gas at one bar pressure. That's hundreds of actuations of a small pneumatic cylinder at 10 bar working pressure. A 12 gram tank should be plenty of gas.

In addition to the CO2 tank you'll also need:

  • A high-flow pressure regulator to drop the high tank pressure (around 800 PSI) to useable levels;
  • A 3-port solenoid valve to control the gas flow into and out of the actuator;
  • A suitably sized actuator to provide the actual mechanical force; and
  • Assorted connectors and hoses to put it all together.
Finding all these components in a size and pressure rating suitable for a 4 pound robot is a BIG problem. Insect class pneumatic flippers are discussed in several posts in this archive -- I suggest you start there.

Q: About how many flips could you get out of a 12 gram co2 tank if using a 1.25 lb 6061 aluminum flipper? Is the concept ok using .25 aluminum sheets welded together or should .5 thick magnesium bolted together be better?

A: I'd estimate 'ZERO' flips. You didn't take my advice to read thru the archive. If you had you wouldn't be asking these questions.

The concept is not OK. As I touched on above and discuss in the archives, there aren't any off-the-shelf components small enough for your robot with a great enough gas flow rate to release energy quickly enough to actually 'flip' an opponent. Do you know of any insect class CO2 pneumatic flippers? If the components were available there'd be a lot of them.

The hamburger is bad! Assuming that you can find or make suitable components, the Team DaVinci Understanding Pneumatics page includes a section on calculating the number of actuations a pneumatic system will provide given:

  • 'a' amount of 'gas' in a
  • 'b' sized tank with
  • 'c' psi regulated pressure and a cylinder with
  • 'd' bore and
  • 'e' throw.
I'll get you started by telling you that a 12 gram CO2 tank holds about 1000 cubic inches of gas compressed into a cylinder about 3" by 0.7". Do yourself a favor and read the whole DaVinci page before you proceed. It will answer most of your design questions.
Q: Using 4 motors in an insect robot using 11.1v lipo on 2.875 banebots, would the servocity 624 RPM precision planetary gearmotor or the Kitbots 1000 RPM gearmotor be more reliable and/or give out better pushing performance? By my calculations the robot would be faster on the kitbots but stronger with the motors from servocity. With their performance so close (unless I'm wrong in that aspect) which ones would be more reliable; the battlehardened kitbots or the stock servocitys? [North Carolina]

A: [Mark J.] How are you 'calculating' the performance of the Kitbots motors? The only performance spec they provide is RPM @ 12 volts. No torque spec, no current consumption, no terminal resistance. That's not enough for me to model their acceleration, pushing power, or general performance in a specific robot. Note also that the Kitbot motors don't come pre-hardened -- the 'battle hardening' they describe is a do-it-yourself process that can be applied to any small gearmotor.

The ServoCity motors come with full specs. They're also a better quality motor/gearbox. Assuming a 3-pound robot (4 of either motor would be too heavy for an antweight) with 2.875" wheels at 11.1 volts, a 'bot powered by the ServoCity motors would reach a top speed of just under 5 MPH in about 6 feet. Peak amp draw would be about 2 amps per motor, and the motors would generate more than twice the torque needed to maximize the pushing potential of the robot. That's very good performance.

The Kitbot motors are an unknown quantity and the ServoCity motors are well documented. Given the choice, I'd use the Servo City motors.

Q: Hi me with my beetle fbs and scoop. My group came up with a few good questions the other day and I we cannot find an answer to them.

1. Is a more horizontal scoop (like you pictured when we first discussed this idea) better than a vertical scoop like punjar or ice cube? This is against a field of drumbots and 8in vertical flywheels with about 18 teeth.

2. For a breaker box is a overpowered 2wd system better than a 4wd with appropriate motors for the weight class? We would be using 2 hd planetary precision 612 rpm motors or 4 of the 624 rpm precision planetary motors. If 4wd, how could we make the left side motors spin in sync?

3. For a fbs, how are they driven effectively? Specifically, how do drivers know which way is forward if they can't see the wheels? Also is there a specific tactic useful against vertical spinners and wedges?

4. What belt should be used to spin the robot? I suggest a v belt for slippage but they want to use timing belts. The spinning weight will be about 2.5 lbs and the rpm about 4000 with a 1:5 gear down from an inrunner brushless that spins at 2000 kv. We will be using an 11.1v lipo battery.

Thank you for your advice. [Canonsburg, Pennsylvania]

A: [Mark J.] All good questions.

  1. A more vertical scoop like 'Ice Cube' uses is a reasonable general purpose weapon. If you're targeting spinner weapons a laid-back scoop like 'Breaker Box' uses is superior.

  2. 'Breaker Box' builder Jim Smentowski knows what he's doing. His four wheel drive adds stability, control, and pushing power. A two-wheel drive 'bot - no matter how 'overpowered' - will not match a four-wheel drive 'bot in these areas. Run same-side motors off the same ESC or from twin ESCs plugged into the same radio channel and sync takes care of itself.

  3. Full Body Spinners don't require a complex driving tactics. Spin up, position in the center of the arena, move calmly toward your opponent. An FBS will have some visible que showing the rear of the 'bot': a small flat 'tail' attached to the chassis that sticks out under the back edge of the shell, a light that is visible thru holes or slots as the shell spins, or a 'flagpole' extension of the stationary weapon axle.

  4. A V-belt is a good choice, but you're going to have a very tough time finding either the belt of pulleys in so small a size. I don't believe they exist. For off-the-shelf components that will operate at such high RPM you're probably stuck with a timing belt. It'll be fine.
I'll note here that a 2.5-pound shell on a 3-pound robot is very heavy. A typical FBS shell might be half the weight of the robot.
Lightweight spinner robot 'Ziggo'

'Ziggo' has a flagpole

Q: Hi, scoop guy again. I know you suggest using 4wd with less powerful motors but my tech teacher suggests the opposite. In our competition we can build robots up to 4 lbs and he said that there is no comparison between 2 pdx16s and 4 of the little motors from servocity. If you could explain which is better and why (maybe toss in some math), it would be greatly appreciated. It would change how we build our robots entirely.

Also is riobots right that 1/8 aluminum is a better armor than 3/8 lexan? If so, would you mount it all together by welding? Thanks as always. [Canonsburg, Pennsylvania]

A: [Mark J.] Four pounds, you say? Up until now you've been telling me 'beetleweight', which is three pounds. It would have been useful for me to know that you had an extra pound of weight allowance; it changes the calculations. Please do try to provide accurate info -- my advice is free, but that doesn't mean that you should treat my time and effort cheaply.

Your tech teacher is correct in that there is no comparison between the motors. A pair of PDX16s output 800 watts of power. In a 4 pound robot that's 200 watts per pound. That's race car power ratio that you're trying to control in a little bitty plastic box. I already 'tossed in some math' the first time you mentioned the PDX16s -- let me refresh your memory:

"Your traction is restricted by the weight on the robot's drive wheels, and the PDX16 motors would overcome that traction at well less than 10% of their output power."

Let me break it down a little more:

  • Two wheel drive; assumed weight on drive wheels: (0.7 * 4) = 2.8 pounds
  • Estimated coefficient of friction between tires and dusty arena surface: 0.7
  • Torque required to break traction, assuming 3" diameter (1.5" radius) wheels: (2.8 * 0.7 * 1.5) = 2.94 in-lb
  • Torque available from dual PDX16 motors: 182 in-lb
  • Percentage of PDX16 torque useable without breaking traction: (2.96 / 182) = 1.6%
With these motors in a four pound 'bot you'll hit the 'go' button, the wheels will break traction, one tire will get some grip, and the 'bot will dart off in an unpredictable direction into a wall. Uncontrollable. You want someplace around 35% to 50% useable torque for a robot in a small arena. The smaller Servo City motors will give you that amount of torque and will result in a powerful, controllable robot -- with a considerable weight savings.

About armor materials:

  • There are MANY different alluminum alloys. Some make quite good armor, some are junk. There is discussion about various aluminum alloys in the Materials & Components archive.

  • Lexan (polycarbonate) can be a very effective armor material if properly mounted and allowed enough room to flex on impact. This is also extensively discussed in the Materials & Components archive.

  • The suitability of one armor material over another depends as much on the armor design as on the material itself. It's an oversimplification to state that one material is 'better' armor in all cases than another material. It's like saying that pizza is always better than a cheezeburger.

  • Robot armor is generally mounted with bolts or machine screws. Much easier to repair/replace in a hurry.

Q: Would adding a tread pattern as described in the riobots handbook be useful in an insect weight class? Same with the wd 40? Finally would this be effective on banebots wheels too? Thanks. [North Carolina]

A: [Mark J.] I have great respect for Team RioBotz and the effort they put into their combat robot tutorial. That said, I don't agree with all of their advice.

  • I've never found that cutting grooves into tires improved their traction on the smooth and uniform surface of a typical combat arena. Maybe they have some particularly funky arenas in Brazil?

  • Cleaning your tires is a very good idea. I don't use WD-40, I use lighter fluid and a clean rag. It cleans oily deposits well and evaporates quickly with no residue. Be careful with it and with the wiping rag -- highly flammable!

My advice: whatever compound the tires are, clean 'em but don't cut 'em.

Q: Sorry to bug you so much on a simple topic but I just thought how would you mount colsons to a 1/2 in keyed shaft and to 6 mm D shafts. Thanks again. [North Carolina]

A: [Mark J.] That depends on the size of the Colson. Small diameter Colsons have a 1/2" bore and can be mounted to a 1/2" keyed shaft by cutting a keyway into the wheel. A 6mm shaft can mate via an off-the-shelf hub. Larger Colsons generally require custom hubs.

Q: One final question for wheels and traction. For the insect weight classes are colson wheels really better than banebots and are duallys effective? Thanks. [North Carolina]

A: [Mark J.] That's two questions. What wheel is 'best' depends largely on your design. BaneBots provide good traction and have simple mounting options, but won't handle much abuse. Colsons are more durable, but heavier and more difficult to mount. Lite Flites are easy to mount and absorb damage well, but lack a bit in traction. Consider the exposure your wheels have in your design and pick accordingly.

Extra wide or dual wheels: some builders love 'em and claim increased traction. I think not. Most 'bots I see that have traction problems are two-wheel drive layouts that didn't put enough weight on the drive wheels. Pay attention to the center of gravity and you'll be fine with single width wheels. There are many posts on this general topic in the Materials & Components archive" -- search there for 'traction'.

Q: How fast should a Motor for an antweight spinner like DDT be? [Baden-wurttemberg, Germany]

A: [Mark J.] Not a simple question. G3 Robotics' antweight 'DDT' runs a Hacker A20-20 L brushless outrunner motor at 11.1 volts, giving just a bit over 11,000 RPM -- unloaded. There is some speed reduction built into the belt drive to the spinner blade; looks like about a 3:2 reduction ratio. Finally, builder/driver Jamison Go reports that he commonly operates the weapon at about half throttle, so the actual speed of the big horizontal spinner blade in combat is around 4000 RPM.

There a many previous questions and answers about determining correct spinner weapon speed and motor selection in the Ask Aaron Weapons Archive. You may also wish to read the Spinner Weapon FAQ.

Antweight combat robot 'DDT'

Q: I'm planning to sharpen my ant wedge, and my event organizer (rightfully) requires something to cover any sharp edges to protect blades and builders alike. Whats a good, cheap material that I can quickly take on and off my wedge blade edge that will provide good protection while not dulling my edge?[Charlotte, North Carolina]

Sheath to protect sharp wedge blade A: [Mark J.] Keep it simple. The razor-sharp front wedge on our antweight 'Rat Amok' is protected by a simple strip of heavy poster board folded in half to form a shallow pouch that slips over the blade. A strip of strapping tape around the length holds the ends closed and makes for a snug fit. Make it a bright color so you'll remember to take if off before the match starts!

Q: Hey Mark, I've got an... odd design for a fairy weight I've been thinking of.
The idea is to have one wheel to push the bot forward and backwards, and using a spinning disc/bar at the front to turn it, saving weight to put into a bigger weapon while still being able to move around(kinda). My two issues with this is:
A: Can the bot move around reasonably well(I know the design won't be able to move in a straight line with the spinner going, I can live with that)?
B: How do I attach the blade in a way that I can slam it in the other direction to steer with out it coming off AND make it the primary steering device? [Aurora, Oregon]

A: [Mark J.] Hold on... you want to propel the 'bot with a single drive wheel and turn it using only the torque reaction from spinning up a horizontal disc/blade? Wow! That's easily the craziest design concept ever submitted to 'Ask Aaron' -- but if I understand your design, it's not gonna work for a damn.

  • The 'bot will be able to move in a fairly straight line with the weapon spinning. When the disc/bar is fully up to speed there will be very little weapon motor torque attempting to turn the 'bot.

  • Maximum turning action will come from reversing the weapon from full speed. This will be VERY hard on the motor/ESC/battery and may require reprogramming the ESC to allow an instantaneous reversal.

  • With the weapon spinning at full speed the 'bot will only be able to turn in one direction -- the direction it will turn when the weapon motor is reversed.

  • Turning will require slowing the weapon to a stop and spinning it up in the other direction, leaving the 'bot vulnerable during the turning process.

  • Once the 'bot is pointing in the right direction, any changes to the weapon speed will turn it away from the correct line. Very frustrating if the weapon is stopped or spinning slowly.
You get points for imaginative design, but don't bother building the 'bot. It would be a nightmare to drive, and if you can't reliably move toward your opponent you'll get very poor 'aggression points' in judging.
Interlocking finger joint. Q: Hey Mark, I've got a few questions:

Right now I'm overhauling the construction of my primary antweight, my old design had horrible weight distribution due to the heavier material being shoved up front, so I'm going to a box with a hinged wedge, made from plastic cutting boards and garolite. My issue is how the the plastic is screwed together, should the screws be parallel with the wheels (with the front and back flush with the side panels with seams) or perpendicular (the front and back being all one piece with no seams)? The wheels themselves are internal and are mounted to the base plate. [Oregon]

A: [Mark J.] Why not have it both ways? If you cut the plastic sidewalls in an interlocking finger joint pattern (see drawing) you can hold the walls together with screws in both directions. It's a stronger joint with less chance of shearing a screw by an impact from either front or side.

Q: How come there hasn't been more widespread use of multi-rotor motors [in antweight robots]? I ask this because they spin slower than similar motors of equal power and are flatter, which I think would make them more appealing to ant and beetle builders. If they were just as easy to use as normal brushless motors, then more builders would be using them, or am I just the first person to think of them? I even ran the numbers on one with a six and a half inch steel disk and the numbers were promising (over a hundred joules in half a second, surely that's a good speed and power for an insect arena). [Still Oregon]

A: [Mark J.] There isn't anything particularly unusual about multi-rotor brushless motors. They are outrunner-style (rotating case) motors of large diameter for their power rating, which does give them greater torque and lower speed. There's no reason that they should be any more difficult to use than other brushless weapon motors, and the lower RPM and higher torque make them a desireable alternative. I suspect that builders are just using well-tested motors that others have had success with. Be brave and give 'em a try.

Date marker: January 2015
Q: Hey Mark,
I was wondering if this solenoid valve [Ebay link removed] could be of any use in pneumatics?
Thanks [Washington]

A: [Mark J.] The only description given is:

micro mini pneumatic air solenoid valve
three ways mini solenoid valve for air exhaust DC3V/4.5V/6V
Tube diameter: 3.0mm(metal)/4.5mm plastic
No flow rate specs, no max pressure, no flow diagram. For $9 it might be interesting to play with, but I can't tell if it's of any insect class combat use.
Ebay micro pneumatic valve'

'Newton' beetleweight combat robot Q: hi mark
Newton - Weapon test - Beetleweight combat robot from TeamExpat
impressed in seeing their weapon. i want to know the construction of that weapon and they have used 1200kv brushless motor for their weapon. can brushless motor be used for running weapons in combact robotics [India]

A: [Mark J.] The full build log for 'Newton' is in a thread on the FRA website: Team Expat Beetleweight Adventures.

Nearly all current insect-class robots use brushless motors for their spinning weapons - see FAQ #23.

Q: Hey Mark, I'm designing an antweight spinner, I've been wondering what are some good cannon fodder objects for ant spinners to chew on, something with enough chunk to give a reasonable approximation of another ant weight, soda and soup cans can only go so far :) [Oregon]

A: [Mark J.] I made up a few targets by filling tuna cans with plaster of paris to give them proper mass. Suitably sized chunks of 2x4 lumber make satisfying targets as well. Stay safe -- keep adequate shielding between yourself and a spinner of any size!

Q: Dear Mark,
Beetleweight eggbeater 'Wave of Mutilation' I am looking into building a beetleweight Eggbeater robot. I am trying to find a place to manufacture the actual eggbeater part of the robot. Its 2.5"x3.5"x.625" made out of steel (preferably tool steel). I looked at e-Machine shop to try to manufacture it and their price that they gave me was around $600! That seemed outrageous to me. That's over twice what I am spending on parts for the rest of the robot. I know that robot combat is an expensive hobby, I've built two already, and that the weapon needs to be the sturdiest part of the robot but my question is does this price seem reasonable to you? [location withheld]

A: [Mark J.] You didn't include a link to a drawing of your beater design, so I can't comment directly. It's possible that some element of your design may unintentionally call for very time-consuming work. If the design is a conventional rectangle with simple holes for the shaft, the price is not reasonable.

I'd suggest that you post your design to the Facebook 'Robotics Community' for comment and a referal to a shop to water cut your beater bar at a reasonable price.

Date marker: January 2014
Q: Hi Mark,
I am trying to build a 4 bar flipper/Lifter in the Antweight/Beetleweight division. I was wondering if you knew what system Menehune used? And I was also wondering if Menehune was an Antweight or a Beetleweight? Thanks, and it is understood if you may not know the system used.

Antweight Pneumatic guy again, would you be able to create air tanks from 3D printing, such as shapeways? Or would you have to machine the parts? Thank you a lot. [Bellevue, Washington]

A: [Mark J.] I don't have specific information about the components antweight 'Menehune' used, but there aren't many options. Search this archive for 'Robart' to find several posts about sources for tiny pneumatic components and the modifications needed to make them useful for insect flippers.

Best to check with the event organizer before making your own pneumatic components -- rules usually call for components rated for use at the pressure used in the 'bot, and home-built components don't have a rating. The Robart air tanks are useable for antweight combat.

Q: Hello. We've all seen videos of antweight full body spinners (FBS) colliding with another bot and then flying off the walls of the arena (ultimately ending upside down or outside of the arena). This is why generally [Ask Aaron] has advised to avoid building FBS at this weight class (even though it is so fun to build them!).

What do you think of mounting the spinner on a suspension between the spinner and chassis. When the spinner hits another bot it will recoil into this suspension, attenuating the impact over a longer period of time so the bot as a whole will not bounce back as far. I imagine that it will not throw the other bot as far either. The shell of the bot at least is still very rigid. it just has a soft linkage to the chassis. not sure if there is a benefit to doing this, what do you think? [San Diego, California]

A: [Mark J.] Your analysis is correct. Placing suspension between the horizontal spinner shell and the chassis could reduce the recoil to your chassis, but it would also reduce the effective impact of the weapon on your opponent. Effectively, it would help your opponent as much as it would help you! You might just as well reduce the power of the weapon - it would be simpler. I've gotta vote 'no' on this idea.

For maximum weapon impact in a horizontal spinner you want the structural path from the point where the weapon strikes to the center of mass of the robot to be as stiff as possible. Vertical spinners have a strong advantage in this regard, as the recoil path (downward) is eventually supported by the arena floor (and the planet beneath). Section 6.6 of the RioBotz Combat Tutorial discusses the importance of mounting stiffness in maximizing weapon impact -- a good read.

Q: Hey Mark,

I am building a 1lb ant weight vertical spinner bot. What is the best way to tell if a motor is adequate for a vertical spinner? I know that you can calculate what the kinetic energy in a spinning weapon. However, the motor I have (and I am trying to figure out if it is adequate) is a Rimfire 370 and is rated to 1000kV, weighs 1.4 oz and has a Burst Watts of 165. So basically, is there a way to look at the critical specs of a brushless outrunner (maybe there is a range of kV?) and know if it would be a good motor? I also know that the forces of a weapon are largely dependent on the radius and mass of the weapon itself, but I can assume that I can judge if said motor makes sense before designing the impactor. Does that make sense? If not, let me know.

Thank you very much,
New York

A: [Mark J.] You're on the right track, New York. The load on the motor when spinning up a weapon is dependent on the 'moment of inertia' (MoI) of the spinner, which does depend on the spinner shape, dimensions, and mass distribution. The challenge is in matching the MoI of the weapon to the power of the motor to assure that the motor can spin the weapon up to speed quickly enough to be useful.

If you're looking for a quick estimate of the suitability of the motor for a spinner, you'll want to look at the 'kV' and 'burst wattage' ratings:

  • The 'kV' of a motor tells you how fast the motor will spin for each volt of electricity it receives. Multiply the kV by your battery voltage for the no-load RPM of the motor. This is important because you don't want a motor that has to be 'geared down' a lot to provide a (not too fast) useful speed for your spinner. The Rimfire 370 has a kV of 1000, so with a 7.4 volt battery it will have a no-load speed of about 7400 RPM, which can be made into a reasonable spinner speed with a belt reduction of around 2:1. That's good!

  • The 'burst wattage' is an indication of the power the motor can produce to accelerate the spinning mass up to speed. Twice the wattage will spin a given weapon blade up to speed twice as quickly. The energy storage of the spinning weapon is measured in 'joules', and for an ant about 30 joules is a reasonable amount of stored energy. A joule is equivalent to one watt of power applied over one second of time, so your proposed 165 watt motor could (at peak output) store 30 Joules (watt-seconds) of energy in a spinner weapon in less than 1/5th of a second (30 watt-seconds / 165 watts = 0.18 second). That's huge overkill!
Now, in actual operation the motor has to start from a standstill and generates only a fraction of it's rated output power until well up in the RPM range - but even estimating that the average output of the motor as it accelerates is half the peak output, this motor has WAY MORE than ample power for an ant spinner. The Rimfire 370 would be more than enough motor for a 3 pound 'beetleweight -- for an ant I'd go with a lighter motor and put the saved weight into a heavier spinner bar/disk/drum. Around 50 watts output per pound of 'bot is plenty!
Q: Hi Mark, do you have any advice on the simplest ways to mount a Ring Spinner shell? My thought is the base could use 3 V-Groove Bearings at 120 degree spacing. The shell would have an internal groove in it to fit into the bearings. A motor wheel would also touch for direct drive.

However, the max RPM of these bearings (5300) is a problem since they will be going several times the speed of the actual ring. I've also found some Track Rollers that are rated for much higher rpm (64,000), so would be more suitable for this type of design, but since they do not have the V-groove (they are flat), I imagine that it would require a design with perhaps twice as many bearings (big weight cost)..

Are rollers or V-groove bearings the right idea for a ring spinner or are there some better ways to do this? Thanks! [San Diego, California]

A: [Mark J.] Have you noticed that there has never been a successful ring spinner in any weight class? Spinning just an outer ring rather than a full shell does let you make the 'bot invertible, but the design problems are considerable. I'm not sure that there is a 'good way' to do it. You failed to mention what weight class you're building, but since you're worried about the weight of a few extra bearings I assume it's an insect.

Using V-groove rollers to support and locate the ring is reasonable, but the RPM limitation on the rollers you found is a problem. Deformation of the ring (or chassis) on impact is another problem -- it can pop the ring out of the guide rollers, and if the deformation is permanent it can jam the ring and prevent it from spinning. Increasing the number of rollers can reduce the risk of ring deformation (I'd suggest six at a minimum), but you'd probably be best advised to simply not build a ring spinner in the first place.

P.S. - Friction drive on a shell spinner causes all sorts of trouble. Maintaining enough pressure and contact friction is much harder than it appears. Avoid!

Q: What's the size/weight rules for a 1lb combat robot? [Yorba Linda, California]

A: [Mark J.] For U.S. competition, the maximum weight for a 1 lb combat robot (antweight) is... ummm, 1 pound. There are no size restrictions -- if it fits thru the arena door you're good.

In the United Kingdom, a combat 'antweight' robot has a maximum weight of 150 grams, and must fit into a cube 4" on a side. Why? Don't know.

It never hurts to check the rules for the specific event you plan to enter, but these are the standards.

Q: Hey Mark, I am designing my latest ant weight bot to compete at the USATL in May. I want to continue off of the success of Hangar 11. Hangar lost five fights over its carrrier, losing two critical matches to vertical spinners (Altitude and End Game). I want to leverage more clamping ability in my next bot, and I basically want it to be a lifter/clamp bot. This idea came after I won a fight by using the lifter as a clamp bring an opponent to a push out zone. I realized the HXT 12k servo is incredibly powerful and could be effective in both directions. What are the most successful lifter/clamper bots out there? I want to find inspiration. Do you happen to have any suggestions otherwise in terms of design or something?

Thanks a ton, Mark!
New York

A: [Mark J.] Good to hear from you, New York.

You'll want to take a long and careful look at Adam Conus' antweight clampbot 'Mission Control'. Adam used a directly coupled Hitec high-torque standard servo [HS-545bb - 76 in/oz of torque] to power the lifting platform. A second servo [Hitec 'Mighty Mini' - HS-225bb] mounted on the lifting platform operates an aluminum arm that clamps the opponent to the lifting platform.

A second version of Mission Control (pictured) used a more sophisticated 4-bar mechanism for the clamp, but suffered a bit from too little lifting power.

Mission Control - antweight clampbot

It greatly saddens me to announce that my son, Aaron Joerger, died very suddenly on the afternoon of October 18th, 2013 of an apparent pulmonary embolism. He was 22 years old. Aaron's obituary.

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

- Mark Joerger, Team Run Amok

Q: Hi Aaron, the pneumatic antweight guy again. I really want to build an antweight flipper. I understand that I would need to modify some parts such as the actuator and valve, however which actuator and valve would be easiest to modify? Which actuator and valve would perform the best? Thanks in advance [Washington]

A: Many people really want to build antweight flippers, but you don't see many being built. That's because none of the available pneumatic components are easy to adapt to the purpose. They're all built for slow actuation of R/C aircraft landing gear and they will require precision miniature machine work to provide enough air flow for a 'flipper'.

Start with Robart pneumatic components. Remove the push-on hose barbs, drill out the ports to a larger size, and thread them. Locate or fabricate new, larger hose barbs and install them in the ports. The valve body itself may require some work to enlarge the air passageways. You'll also have to locate some larger diameter pressure hose to connect everything up.

It's a lot of work, and a strict event organizer may decide that the 'home brew' modifications to the pneumatics aren't in compliance with the safety rules.

Robot haiku:

Antweight flippers
Appeal to many builders.
Hard to execute.

Q: Hi Aaron, I was wondering if a 7.5 x 6 inch Antweight would be too big, or if it is a average size for an Antweight. Sorry this may seem like a dumb question , but I am just starting and would like to know. Thank You [Washington]

A: It's big for an ant, but I can't tell you if it's 'too' big since you haven't told me anything about the design or why you want to make it that size. You might have a good reason!

Common design wisdom says that a smaller 'bot is a better 'bot -- less area to cover with armor means thicker armor for the same weight allowance. A typical ant might measure around 6" long by 4" wide.

Robot haiku:

A larger robot
Must spread its armor thinly.
Is smaller better?

Q: Hey Aaron, how do you wire a Fingertech Micro Power Switch with a basic drive configuration with a battery and esc?
Thanks. [Beltsville, Maryland]

A: Take a look at the diagram in FAQ #19 for a basic combat robot wiring diagram. The FingerTech power switch will substitute for the 'Link' in that diagram.

A 'removeable link' is a type of switch made from a connector plug set with one side shorted. They are reliable, inexpensive, easy to use, and mandated for heavier weight classes in some competitions because they require no tool to shut off the power -- just yank it apart.

Robot haiku:

Master power switch
Breaks one of the power leads
Close to battery.

Q: Dear Aaron, I am building an ant-weight lifter bot. The lifter is powered by a Futaba S3305 servo. The drive train is two Gold-Spark motors each with their own TinyESC. The bot is powered by a Thunder Power 3s LiPo. I hooked up the drive and it worked fine, but when I plugged the servo in the robot became unresponsive. Sometimes it would move but it was delayed. Other times it wouldn't move at all. I don't know if it matters but I removed one of the BEC wires on one of the TinyESCs.

A: The battery eliminator circuit (BEC) on the TinyESC puts out a very tiny 100 milliamps with a 2-cell LiPo, and a dismal 50 mA when used with a 3-cell (output chart at FingerTech). That's enough to run its own electronics and the receiver, but not nearly enough to also power a servo. The additional drain from the servo drops the 5 volt feed below the voltage needed by the electronics and they become non-responsive, even if the servo is idle.

If you want to keep the TinyESCs you'll need to add a beefier BEC that can output at least a couple amps for your high-torque servo. Wire it to the battery, plug it into any unused receiver port, and disconnect the red BEC lead wire on the TinyESC that still has one.

Robot haiku:

Has a tiny BEC.
You need more current.

Q: Hi Aaron Is the Robot Marketplace Antweight robot starter package good for a thwackbot Because I think it is.Also how would I fare if I removed the battery charger.How would I charge the battery then.Thanks I hope the hamburger is Juicy. [Portage, Ohio]

A: The Robot Marketplace has two antweight starter packages -- Basic and Advanced. I'll assume you are asking about the basic package, but my comments largely apply to both.

RMP has been selling that same starter package with only minor substitutions for at least ten years. The set-up was OK at the time, but antweights have changed! The Tamiya Twin Gearbox is too slow and too fragile for the current competition standard, and certainly not powerful enough for a thwackbot.

Neither starter package is a complete kit -- just a collection of parts that might be pieced together to your own design to make an antweight. There are no instructions, and no specific design for the chassis and armor. You can do better by doing some research and selecting parts that better suit your own design.

If you run a rechargeable battery, you MUST HAVE a charger designed for that specific type of battery that can quickly bring your charge back up in the limited time between matches.

  • Soaking the battery in a jar full of electrons does not work.
  • Drilling a hole in the battery and dripping electrons in with a dropper does not work.
  • Pushing electrons into the battery by hand does not work.
Antweight builders use LiPoly batteries because they are compact, light, and deliver a lot of current to the motors. They do require special chargers, but the effort is worthwhile. Buy a decent charger.

Final note: have you noticed that there are no successful antweight thwackbots? We have discussed ant thwackbots in this archive several times -- maybe you should look up those discussions before you decide to build one.

Q: I know that antweight thwackbots aren't succesfull but I should also tell you that I am using 60:1 Copal motors and a 5 in uknown specs and thickness as I have not yet made it high tensile strength steel blade,So I can kill spinners.I already have a chassis made for thwackbot.Would it help to know it is a reverse rotation thwackbot thank you.Soon to be team 1 pound Wacko.

A: I have no idea what a 'reverse rotation' thwackbot is, but best luck to you.

Q: A reverse rotation thwackbot is a thwackbot that has its blade pointing back and i'm driving forward all of a sudden I stop and go backwards a little bit the resulting reverse rotation of the wheels sends the blade flying to hit or miss the enemy.

A: A thwackbot builds energy in its weapon by spinning up to speed over many rotations. The math doesn't work for a thwack that only rotates half a revolution. Suggest you reconsider.

Q: I already new the only succesfull Thwackbot was Trilocity.So I decided to make a flipper instead.How does a servo powered flipper work.What speed controller would you recommend with 60:1 copal motors should I use the sabertooth 5 speed controller.

A: Several comments...

  • 'Trilocity' was a beetleweight -- overall record 9 wins, 5 losses, modestly successful.

  • There are no servo powered flippers -- servos do not have the speed and power to flip. There are many servo powered lifters. Plenty of discussion on servo lifters in this archive.

  • A Copal HG16 motor at 7.4 volts pulls only about 1.6 amps at stall, so pretty much any small ESC will do. The Sabertooth 5 would be fine.

  • The Copal 60:1 gearmotor would be slow, even with large diameter wheels. You'd be better off with the Copal 30:1 motors running tires around 2.75" diameter.

Q: Thank you and sorry for be so newbish.

A: You're welcome. Happy to help.

Robot haiku:

Nobody makes a
Self-recharging battery.
You need a charger!

Opinion [Annonymous]: The antweight kit person [above] would be better off skipping the COPALs entirely and going with...

Response: Hold up, this website isn't called 'Annonymous guy disagrees with Aaron and plugs some products.' You can do that in the forums.

That said, I agree that Copal gearmotors are 'old school' and that there are more powerful options available with stronger gearboxes. BUT, the Ohio kit guy did not ask me for an opinion on Copals -- he said he was gonna use Copals, so I gently tried to steer him to the right Copals.

Opinion [Annonymous]: As for kits, the kits available from [deleted] are likely a much better deal than the RMP kits.

Response: Again, I don't allow unknown sources to come in here and talk up specific kits or components -- particularly when all the kits and components are suspiciously from the same company.

I think I made it clear that I believe the RMP kits are outdated, incomplete, and unsuited to Ohio kit guy's purpose. I wasn't asked to recommend another kit, but my reviews of other available kits are in the Toy Hacks & Kits archive for interested readers.

Opinion [Annonymous]: You seem a little out of touch with current insect-sized components.

Response: You have a lot of opinions for someone who doesn't have a name. You gave no props - you gained no cred.

Robot haiku:

Opinions gain worth
From reputation of source.
No name, what value?

Q: Aaron,
For an Antweight servo lifter, is there a required distance the servo must be able to travel (e.g. 90 degrees, 180 degrees)?

Thank you,
New York

Servo powered 4-bar lifter A: Depends entirely on your design, New York. In general, torque is WAY more important than degrees of motion.

  • For a simple lever lifter: you only need a few degrees of motion to lift your opponent enough to break their traction, but you MUST have enough torque to lift your opponent's weight out at the end of the lifter arm.

  • For a more sophisticated 4-bar lifter: careful selection of bar lengths can trade speed and degrees of motion for extra lifting power.
Figure out what your lifter needs to do, run the numbers, and the torque and degrees of motion required will fall out of the calculations. There are plenty of posts about lifter design in the archives.

Q: In a follow up to my previos question about the 4-bar servo lifter for the antweight, is the point at where the blue part connects with the servo a hinge? If so, how do I construct this? This antweight, by the way, is merely a proof of concept for a combat robotics (as well as some conventional robotics) school program I am setting up, and this bot will probably be made of wood or UHMW, so no real fighting specifications will be required (I am not going to be pushing this bot to the limits like you would normally).

Also, I am decent with math, but I downloaded the 4-bar program from total insanity, and a problem I have is that I do not know how much my arm is going to weight and I do not fully understand the program. So I took apart one of my two Biohazard Pro kits and measured the length of the arms (in the diagram it would be the red bar and the bar that is replaced with the servo) and I saw that it was 2.5" and 4". I like how the front arm extends exactly to 90 degrees, but I don't know if that is truly an advantage. Do you think that I should try to scale it down to my spec? Would that be effective? It is my understand that it is easy to mess up a four bar lifter. My servo is an HX 12k and it will be operating either off of 2 9v in parallel or 5v. Any thoughts on what the best solution could be?

As always, you guys are a huge help, and I wouldn't even have these biohazard bots if it wasn't for your recommendation (and I met Carlo Bertocchini at Robogames!) - New York

A: All of the 'dot in a circle' connections in the diagram are pivot hinges. Your local hobby shop will have a variety of pivot fasteners to fit servo horns. Websearch: 'servo horn connector'.

A 4-bar lifter mechanism can provide a very wide range of output motions from a given input. There is no single 'best solution' -- you just have to play with the bar lengths until you get a suitable lifting motion, lift strength, and reasonable servo loading. It is REALLY easy to mess up a 4-bar design, which is why the T.i. Simulator is so valuable.

Spend some time with the simulator and get the hang of it. The weight OF your lifter arm is not one of the inputs -- the weight ON your lifter arm is the input. That would be the weight of your opponent. If you can come up with a set of arm lengths you think might work, I can check your work for you.

Q:Hey Aaron,

I am getting a lot of different results and variations of servo horn connectors when I Google them. Do you know any specific ones/could you find any? I don't mean for you to be my search monkey but I am not exactly certain which variation would be beneficial.

Thank you,
New York

A:The simplest and strongest connector are probably the Z-bend and L-bend styles. Suggest you read this guide.

Robot haiku:

For good lifter speed,
Aim for twice the servo torque
The calcs say you need.

Q: I have made a 15 pound drum robot and I'm going to start the three pounders. I want to make a over head spinner or full body spinner. Which do you suggest would be easier and cheaper? Also, can I direct mount the weapon to the motor or should I use pullies? [Florida]

A: We have a HUGE PILE of information on spinner weapon design choices and drive requirements in the Robot Weapons archive, and some specific advice on insect class spinners in this archive. I strongly suggest you browse those archives. Briefly:

  • An overhead spinner is a metal bar with a hole in the middle. A full body spinner is a precision machined and balanced dome or cylinder. Which do you think is easier and less expensive? Hint: metal bars are cheap.

  • Look at successful beetleweight robots. Do you see any overhead spinners? Any FBS? Why not? It isn't because they haven't been tried.

  • I don't recommend direct driving a large spinner weapon. Direct drive places huge loads (lateral and shock) on the motor bearings. It also slows the spin-up time (important in a small insect arena) and will typically spin the weapon too fast for adequate weapon 'bite' (read the archives).
Our Excel Spinner Spreadsheet will give you spinner weapon performance data for specific spinner designs and drive options. There is a lot more to an effective spinner weapon than just getting it to spin!

Robot haiku:

Effective spinners
Take work and careful planning.
Some work - most do not.

Q: I'm designing a budget beetle weight(Less than 100 dollars, and I already have a DX5e) and I'm fairly sure about most of the robot, except one thing, how do I attach a lite flite to a B&D screwdriver? The only things I could think of is to either drill a hole and run a pin through the shaft and hub of the wheels or too take the tires off the hubs and epoxy them on.

A: There are several different Black & Decker power screwdrivers, but they all have the same output shaft design: a tube about 3/8" in diameter with an internal 1/4" hex drive. Those dimensions are WAY too large for the Lite Flite wheels (max drill out 3/16"), and I certainly can't recommend glueing the tire directly to the gearbox output shaft! You'd have no lateral support, and no way to quickly replace a shredded tire.

The best wheel solution might be to run the BaneBots 3/8" hub [now discontinued] with BaneBots 3/4" hex mount wheels. Measure your output shaft diameter carefully -- you may need to reduce the diameter a bit. The hubs are heavy, a little expensive, and overkill -- but that large gearbox shaft is really awkward. I hear that you're on a tight budget, but a hub solution is NOT the place to economize! I think I've seen more robots fail from poor/hacked hubs than any other single cause.

I should also point out that the 'bot is going to be slow. Power screwdrivers are more about torque than speed, and unless you're running serious overvoltage and really big wheels, you're gonna be at slow walking speed. I think you might be money ahead to switch to more conventional gearmotors to gain speed and the ability to use standard hubs and wheels.

Robot haiku:

Power screwdrivers?
You're starting to figure out
Why they are not used.

Q: For an antweight wedge with two B16 motors, would you recommend 2" Lite Flite wheels or 1 7/8" Banebots wheels? The Lite Flite wheels have a 3.97mm bore, can I just push them onto the 4mm motor shafts, or do I need the expensive aluminum Dave's Hubs? Thanks.

A: If the wheels are protected, I like BaneBots. If the wheels are unprotected, the tougher LiteFlites are a better choice.

DO NOT try to get away with press-fitting wheels onto motor shafts! Dave's Hubs are very strong, compact, and make it simple to replace the tires when they get chewed up. I think they're well worth their price, but there are other options. The Astroflight prop adapter makes a good hub solution if you're willing to drill out the Lite Flite wheel a bit, and the FingerTech hubs are functional and very light. Whichever you choose, check the tightness of the hub set screws before every match.

Also, consider a larger diameter wheel with the B16 motors in an antweight. A 2 1/2" wheel would give great performance in an 8 foot arena.

Robot haiku:

Lite Flites absorb hits
That would destroy the BaneBots.
I'd buy the good hubs.

Q: Well, I just got a shiny new servo today, and I was thinking of using it for my ant to power a four-bar lifter. I know the hamburger may be a little bad, but should I power the front or rear bar? The servo rotates about 180 degrees.

A: To maximize the power of your lifter, you'd want to drive the the shorter (rear) bar. To maximize the speed of the lifter you might want to drive the longer (front) bar.

The T.i. Combat Robotics 4-Bar Simulator is a very useful tool to help with the design of your lifter. You can try differing bar lengths and compare the performance of the lifter when powering the front and rear bars.

Robot haiku:
Your lifter might not.
Lift, that is. Torque specs needed
For shiny servo.
4-bar lifter animation.

Comment: I was very pleased to find the following letter in my inbox. Dennis Beck is a fine builder/driver, and we have previously discussed his dominating (23/1) antweight 'Metroid'. Dennis has written in to clarify a few points about his ant, update its history, and talk a bit about weapon theory. The earlier post and video links Dennis mentions can be found here .

Hi, Aaron! My name is Dennis Beck, from Saskatoon, Saskatchewan, Canada. I was searching for info on steel drums when I stumbled upon your page, and a picture of an old version of my antweight robot 'Metroid', as well as some questions/answers about it's weapon. I realize that I am a few years late to the party, but I can provide some info in regards to it's weapon. Everything that you posted was correct, with one exception.... the drum diameter. I believe that the drum diameter of Metroid to be similar to other direct drive antweight drum spinners, since most use the AXI 2808/20 1820KV Gold Line motor, which has a 28mm OD. Metroid has also used 28mm OD outrunners in all of the 5 versions that it has gone through. :) The OD of the drum is 1.25", and with the end of the drum machined out to accept the 28mm motor, the wall thickness is less than 2mm in that area of the drum.

Anyways, to answer some questions, the first version of Metroid used a slow turning (although very robust) Himax 2808-1160 motor which is purchased from, a local vendor to me. Here is a link to the motor on their page.

As you can see, that motor turns quite slow in comparison to the popular AXI's 1820KV. In the Kilobots XIII rumble video that was posted, Metroid had the slow Himax installed as a backup motor. I had a Turnigy 1900KV motor installed at the start of the tournament, but the glue that was securing the magnets to the can failed, so I installed the old trusty Himax motor. The low RPM's resulted in very reliable bite, but you could definitely tell that the kinetic energy was lacking (the other robots weren't hitting the ceiling, as they would if using a faster motor). Metroid still had the teeth installed off axis at that time, as you correctly noticed from the close-up picture of the drum that you had posted.

In the Metroid vs Spark Plug video that was also posted, Metroid was using a 2600KV Scorpion motor. I chose the faster motor in order to have the ability to obtain a high tip speed if needed. I noticed that the guys with the large diameter beater weapons were gearing them 1:1 with their axi motors, so I figured that I should try to obtain a tip speed as high (or higher) that them. The nice thing about the 2600KV motor is that you don't have to run at at max RPM all of the time. Unfortunately, I was running it close to max speed in the spark plug vid, as is obvious by the sound, and the fact that Metroid would gyro when turning, even with the magnets in the base plate. At one point in the video, Metroid isn't getting a bite on the vertical back panel of Spark Plug. At that point, you can hear me throttle down the weapon to about half speed, in which case the weapon was able to bite and throw the other robot into the air. Also, Metroid had dull teeth installed vs spark plug (I was too lazy to make a spare set of sharp teeth), and I also no longer had the tooth holes drilled off axis in the drum. What I had started doing at that point in time was using weapon teeth that were long enough to thread into the opposite wall of the drum. This prevented the teeth from bending over in the drum, and also clamped the drum into the weapon motor.

Dennis Beck's antweight robot 'Metroid' - version 5. I had just built a 5th version of Metroid a few weeks ago, in preparation for Kilobots XXIV. For the first time, the bot was symetric top-to-bottom, and no longer had a rear wedge. Here is a photo of version 5:

Kurtis (from Fingertech) broke Metroids Scorpion motor in the summer of 2011 using his robot 'Iron Infidel', so Metroid was built using a cheap "RC Timer" brand 2600KV motor. I switched back to 1/4-20 screws for teeth (the previous version used 5/16"), and I noticed that one of the 1/4-20 screws is now bent. 5/16 screws seem like overkill, but they might actually be necessary. Anyways, the weapon motor was damaged again in the fight vs Iron Infidel. A corner chipped off of a magnet and jammed up the weapon motor. Metroid received it's first ever loss in it's 24 fight history. :(

With two broken weapon motors in two events, I have decided to finally relocate the weapon motor to the inside of the bot, and to drive the drum with an o-ring. I'm really not looking forward to the amount of space that a weapon motor will consume inside of the bot, but I'm also not looking forward to damaging any more weapon motors by keeping them mounted inside of an aluminum drum. I'm also looking at using 4130 tube for drum material with welded on teeth (or, single tooth) for the next version, and may consider mounting the motor in the drum since the hardenned 4130 drum should protect the motor a bit better than 7075 aluminum.

Thanks a bunch for all of the time that you have put into answering all of these questions! I have only just discovered your site, and will definitely be spending much time reading through it!

Regards, Dennis
Antweight: Metroid
Kilobot: Triple Action
Beetles: Utopia, T6
Mantisweight: Zillion

Q: Hi, the Antweight pneumatic guy again. I was wondering if there is still a place to find the solenoid valve from the kit? Or if there is another solenoid valve for an air up, spring down cylinder, or a air up, and down cylinder? The valve doesn't have to be for a flipper. Lastly, is it possible to make an Antweight pneumatic lifter?

A: I assume you're asking about the long-discontinued Inertia Labs micro pneumatics valve. All sources of these valves have been exhausted -- there aren't any more. You could try a post to a robot combat forum looking for a used valve, but your chances aren't good.

Robart offers a variety of servo-actuated micro pneumatic valves suitable for both air-up/air-down and air-up/spring-down systems. The valves do not have a high enough flow rate to use them in a flipper application.

You can certainly make an antweight pneumatic lifter, but it is much easier to use servos for an electric lifter.

Q: Hi, I was wondering if these parts were suitable for an Antweight/Beetleweight robot: I would use some 4 mm OD tubing, and 2.5 ID tubing. I was wondering how big is this E-flight pressure tank, i have been looking for the size because it seems to be a small enough size.

I am thinking of using a lego pneumatic actuator, with the ports drilled out to around 2.5mm, and an OD of 4mm. Or using one of Robarts actuators. Which actuator would you recommend? Would this type of set up be able to flip a Antweight, or Beetleweight? Thank you in advance.

A: We have discussed these components in earlier posts and made recommendations. Search this archive for 'Crouzet' and 'hobbyking pneumatics'. Read the rest of the antweight pneumatics posts while you're there. Very briefly:

  • Neither of the valves you found, or any currently available off-the-shelf pneumatic micro valve, has a high enough gas flow rate to operate an insect class flipper. Lifter yes, flipper no.

  • A 3-port valve is not adequate for air-up/air-down operation -- that requires a 5-port valve.

  • The E-flight pressure tank is about 6" long by 1.4" in diameter.

  • A Robart actuator with enlarged ports is acceptable for an antweight flipper, but without a high-flow valve it won't have the speed to flip.
There are good reasons you don't see insect class pneumatic flippers in current combat, and you just found a couple of them.
Q: Is it possible to swap the motors for a hacked Battlebot toy antweight? In another antweight I built I used some Tamiya Hyper Dash-2 motors. They're the same size as the ones in the Battlebots toy. Or do you think this could cause damage either to the integrated ESC/RX?

A: The BattleBots toy Controller/RX should be fine, but the Hyper Dash-2 motors won't do well at 6 volts. The HD-2 is a 3.0 volt motor that shouldn't be run over 4.8 volts. If you want more power, I'd suggest overvolting the stock motors. I've seen BattleBots Custom Series toys run at over 9.6 volts without trouble -- but are you sure you really need/want more speed in a small insect arena? It's gonna be a real handfull to control!

Q: only 4.8v for the Hyper Dash 2? I figured since the robot marketplace sells them as a drop in for the Tamiya Tracked Chassis, and says that can be ran safely up to 7.2V...I was planning on using that chassis and putting a dual gearbox with the Hyper Dash 2 motors installed...

Mark J. here: you can run the stock Tamiya motors up to 7.2 volts. The high-performance HD-2 is wound with larger wire and less of it than the stock motor. It spins as fast at 3 volts as the stock motor does at 7.2 volts, and it draws a lot more current. Run the HD-2 at 7.2 volts and you'll likely melt the brush holders, fry the commutator, or just burn the windings. See my comments on overvolting high-performance motors in the Motors & Controllers archive.

Q: Hey Aaron, Henry from Texas again.

I'm working on a beetleweight (along with those anyweights I mentioned in my last question) [see the Toy Hacks & Kits archive]. This is my first robot with an active weapon. I'm using the sabertooth ESC for it and for the weapon I'm thinking of using the BattleSwitch 10A R/C Switch to power the 30:1 micro gear motor from Robot market place. Now, It looks like I have to have an additional battery for this RC switch, or can I splice it off my main battery using some barrier strips?

A: If your weapon motor can handle the voltage your main battery pack pumps out, and your main battery has the capacity to support the current requirements of the drive and weapon motors combined -- you can use that single battery to power everything.

Take a look at the generic wiring diagram in FAQ #19 and just replace the weapon ESC with your BattleSwitch. You can tap power for the BattleSwitch/weapon motor from a second set of wires added to the battery screw terminals on the Sabertooth ESC -- no barrier strips needed.

You don't mention what type of weapon you have planned, and I can't figure it out from the details you've given. The 30:1 micro gear motor is not suitable for a beetleweight spinner weapon -- too slow and too little power. What type of weapon are you planning???

Note that the BattleSwitch will give you simple on/off single direction motor control. You might want to consider a single-channel ESC like the FingerTech tinyESC that can provide a smaller, lighter package that offers dual-direction proportional speed control for about the same price.

Q: I was planning on making the weapon interchangable with saws or spinning blades. Thats why I was just going to use a relay instead of an ESC, looking at the stats I thought the micro gear motor would be sufficient but I guess I'm going back to my plan of using the Beetle B04.

A: You'll need to spin a 6 ounce, 4" blade at 4000+ RPM in order to have enough energy for an effective beetle spinner weapon -- and you'll need enough power to spin up to that speed quickly in a small insect arena. Take a look at the designs, materials, and motors used by successful beetle competitors for some guidance.

Q: Could I use the 30:1 Micro gear motor if I mount it to a 42 tooth pulley, to a 9 tooth pully with a 50 tooth belt? According to my math that will bring the RPM up to 4666.

A: Your math is correct, Henry -- but every gear stage you run your drivetrain thru steals power due to friction and transfer inefficiency. Your design runs the motor power thru the two gear reduction stages on the gearmotor to reduce the speed by a factor of 30, then a belt stage to increase the speed by a factor of 4.67. You've got a lot of un-needed moving parts that do nothing but add complexity, weight, and increased opportunity for mechanical failure.

Look at the designs used by successful insect spinners. They typically run a single belt-drive reduction straight from the motor to the weapon. No heavy, power-stealing gear reduction stage.

Your other problem is that the 30:1 Micro Geared Motor simply does not generate enough power to spin a reasonably sized beetleweight spinner weapon up to effective speed in a reasonable amount of time. It's an adequate antweight drive motor, but it just isn't enough for a beetle weapon.

A quick check with the Team Run Amok Excel Spinner Spreadsheet estimates that a 6 ounce, 4" diameter spinner blade powered by the Micro Geared Motor with a belt drive speed increase to 4666 RPM would take over 10 seconds to spin up to a moderate 20 Joules of energy. The weapon would have a harmless 3 Joules of energy stored up after two seconds -- enough time for an average opponent to sprint across the arena and shove you into the rail. Too little power!

Now, take that same weapon and power it with just the motor from the B04 (no gear reduction) thru a 12 tooth to 39 tooth sprocket set. Your spin-up time to 20 Joules will drop to 4.5 seconds, and the weapon will pack nearly 10 Joules of energy after 2 seconds. That's enough to be useful.

Keep it simple, use a motor with enough power, and take design cues from successful 'bots of similar design.

Q: Great advice on using just the B04 Motor without gear reduction, I was looking into using the Fingertech pulleys since I can't find sprockets that would fit the 2mm shaft on the B04. Do you think I would be able to get similar performance using the Fingertech Pulleys?

A: The FingerTech pulley system will be fine. The ungeared B04 motor was just an example; it has a very stubby shaft in an inconvenient diameter. You might find it easier to start with a motor that has a 3mm shaft to fit the FingerTech pulley. I'm not a big fan of 'Hobby King' components for robots, but an inexpensive brushless motor and a simple brushless controller might be just what you're looking for. Brushless motors have more power than a brushed motor of similar size and weight -- they are very popular for insect class weapon power.

Q: How would I go about wiring a 4wd (4 micro gear motors) antweight with 2 Fingertech TinyESCs? Can you provide a diagram? And would the amps required to run all 4 motors from the FT TinyESCs mean I need a lipo that puts out twice the amps needed? Thanks

A: The two motors on the same side of the robot are wired to one of the ESCs in parallel [see diagram]. Note that when running two tinyESCs, the red wire from one of the ESCs to the receiver should be clipped to avoid battery eliminator circuit conflict.

The combined amperage draw of all motors connected to the tinyESC should not exceed the maximum current rating of the ESC. A combined current draw above 2 amps (total for both motors) will kick in the overcurrent protection and power back your robot -- very bad in a pushing match. The Team Tentacle Torque & Amp-Hour Calculator can assist you in determining the expected amperage draw for your motors as used in your robot.

Your battery must be able to supply the total current draw for all four motors at maximum current consumption. Again, the Team Tentacle Torque & Amp-Hour Calculator can supply an estimate of that current draw.

Note: you can run multiple brushed motors from a single channel brushed motor ESC, but brushless motors each require their own brushless ESC.

Wiring diagram for two tinyESCs and four motors.

Battle Antz kit from Roaming Robots. Q: Aaron, I have friends coming over from England, and they are young (7,10 ish) and they are into, though have zero experience in, Combat Robotics. I wanted to possibly purchase them Battle Antz from Roaming Robots, but they are out of stock and IMO they are over priced for their quality. However, I like the fact they are small and are beyond RC cars since the have servo lifters, and are very 'cute' in the sense that they seem very put together.

What would be the most effective way for me to potentially build two or three 'battle ant like' bots? I want them to fight each other with servo lifters and a decent drive. At 125 Euros [about $165] I think the hacked servos on the Antz seem dubious. What parts and how would you build them? I would either build them myself or have them build them, but either way it would be nice if they were easy to assemble, and (possibly) without soldering.

Thanks a lot! - New York

A: Not willing to turn them loose with your 'Hangar 11' antweight, New York?

Antweights were invented "back in the day" by teams looking for something to do with all the un-used servos that came with radio systems. At the time a 6-channel radio came with six servos! Somebody figured out how to 'hack' a servo for continuous rotation so they could be used as cheap gearmotors, and the rest was history. Let's do this 'old school':

  • You can buy pre-hacked servos and not have to solder anything. Buy four 'hacked' servos for drive motors and two regular servos for lifters. While you're there, order two pairs of servo wheels that will bolt right onto the hacked servo shafts. You now have two complete drivetrains and two weapon gearmotors.

  • Pick up a pair of cheap and simple radio systems with mixing. The servos all plug into the receiver directly -- no speed controller needed.

  • Run down to Radio Shack and grab two 4 "AA" battery holders with switch. Terminate the battery wires with female R/C plugs so that they may be plugged into any unused receiver port to power your entire system. Duplicate the positions of the red and black wires on the servo plugs -- the third plug connector is left empty. Alkaline AA cells will be fine for your purpose.

  • Scavenge a flat, stiff piece of plastic/wood/metal to use as chassis. Lay out the components and trim the chassis to size. Fasten the components to the chassis and/or each other with servo tape. Fabricate an arm for the lifter servo from a popsicle stick and screw it onto the servo horn. Power up, sort the radio system, and have a robot fight!
Total cost: about $85 per 'bot, including popsicle stick. If the 'bots aren't fast enough for you, speed hack (video) the drive servos.
Q: do you think the 11:1 Silver Sparks from Fingertech will be a good choice for a drum bot with speed to obtain bite yet some (though not amazing) pushing power? Thank you very much, New York

A: Depends on how large a wheel diameter you plan to run. The 11.1:1 Silver Spark gearmotors are fine with 1" diameter wheels -- scroll down two posts . For larger diameter wheels I'd suggest the 22.2:1 gearmotors.

Q: Is there a torque calculator that has the fingertech line of motors? The tentacle doesn't have it.
Thanks, New York

A: Do your homework. Scroll down two posts to the question I directed you to in my answer above. There I give the motor stats for the FingerTech FK-050SH used in the Silver Spark and Gold Spark motors. Enter them into the motor spec fields in the Tentacle Drivetrain Calculator per the instructions given, then enter the Gear Ratio and Wheel Diameter you are investigating.

The motor specs are straight from the FingerTech website. I've added the FingerTech FK-050SH (ungeared) motor to the pull-down menu on the Tentacle Calculator.

Q: I'm building my first active weapon robot. It's a vertical spinning bar. It's a beetleweight using the B04 motor from Robot Marketplace. I'm not sure the best way to attach the weapon...since it's already has a gearbox in the motor can I just attach it to the 4MM shaft? what is a suitable hub? should I use a pulley? if so I can't find pullys the right size. :/

A: A spinner weapon shaft should be supported on BOTH sides of the blade to control impact forces. If you just hang a weapon on the end of the output shaft, a couple of good hits will destroy the gearbox bearing. The shaft on the B04 gearmotor is too short to allow you to mount a weapon hub and have enough shaft remaining to support with a bearing block, so I think you'll have to run a belt/pulley to isolate the gearbox from impact loading.

You'll likely need to bore out a 3mm timing pulley to fit the 4mm shaft on your B04 gearmotor. You could save weight by eliminating the gearbox and performing the 4:1 reduction with the belt/pulley system.

The pulley itself may be suitable to use as a hub for your weapon blade -- consider bolting the blade directly to the pulley. If that does not fit with your design, a wheel hub can be used for your weapon blade. Take a look around at hub designs from other builders.

Q: I'm having a hard time deciding what gear ratio Silver Spark motors to buy from FingerTech. My antweight is a 2wd running on a 3S 11.1v 450mah 65c lipo, 2 FingerTech TinyESCs, a R410 OrangeRX with 1 inch rubber wheels. I want a motor that has decent speed but not so fast it's uncontrollable but not so slow other bots can maneuver around me. Maybe you can help with some input?

A: This is a job for the Tentacle Drivetrain Calculator! Input the motor specs from the FingerTech site:

  • Nominal Voltage: 6Vdc
  • Stall Current: 1.3A
  • Kt: 0.49oz-in/A
  • Kv: 1573rpm/V
Next, change to voltage to 11.1 to match your battery voltage. Set the wheel diamter to 1 inch, and try the gear ratios available for your Silver Spark motors.

You'll quickly discover that the only gear ratio that makes any sense for those small wheels is the 11.1 gearing. You'll have about 4.6 MPH (plenty) and can accelerate to that speed in about 4 feet (good for a small arena). Maximum current draw is less than 0.7 amps per motor, well within the capacity of the tinyESC. The calculator says your battery is way overkill, as your drive motors will use less than 100mAh for a 5 minute match.

If you find the speed too great for your liking, you can always 'dial back' the speed and acceleration via the ATV setting on your transmitter -- Spektrum calls it 'Travel Adjust' on their radios. See the Radio & Electronics archive for more info on ATV.

Q: What is a good antweight battery that has a high mAh rating? It would be best if it was as light as possible. Thank you in advanced.

A: There is more to battery selection than the mAh rating:

  • What voltage are you looking for?
  • What are you willing to spend on a battery charger?
  • How much peak amperage will the battery need to supply?
  • More capacity = more weight, so how many milliamp hours of capacity does your robot actually need?
Your selection of drive and weapon motors will determine the voltage requirement.

Different types of batteries have different charging requirements. Those with the highest mAh/weight ratio require special chargers.

Peak amperage and mAh consumption can be calculated from the specs for your drive and weapon motors plus tools like the Tentacle Drivetrain Calculator and the Team Run Amok Spinner Weapon Spreadsheet (Excel).

I can tell you that most antweights use LiPoly batteries, but that the specific battery you need will depend on your answers to the above questions. If you don't want to do the required work, just look around at successful robots with similar specs to your own and see what battery they run.

Q: Can I use PVC pipe in antweight?

A: For what purpose? There are good reasons why you don't see PVC used. In general, Poly Vinyl Chloride (PVC) is too weak, soft, and ultimately too brittle for combat robot applications.

Q: Dear Aaron,
I am entering Hangar 11 in the NERC Franklin Institute event. I am excited, but never the less worried. The competition is on the 6th of october and today is the 22nd [of September]. I am going to try to use your lipo battery idea to save weight. In addition to this modification, I was pondering the idea of installing a basic lifter on the robot:

A) by the time the servo comes (which I have not ordered), how long and hard is it to install the servo on my bot and create the lifting apparatus? There is a lot of space behind the wheels of the bot.

B) Is it possible to make this removable based on who I am going to fight next? Does this make it more challenging?

Thank you very much, New York

A: I don't know how you plan to implement the lifter, but it's certainly possible to bolt a crude arm on the servo, stick the servo to the chassis with 'servo tape', plug the servo into a free receiver channel, and be operational in 10 minutes. That's if everything goes well and you've picked the right servo. Picking the right servo requires some thought about where the servo will be mounted and how long the lifter arm needs to be: the longer the arm, the more torque the servo must provide to lift your opponent.

Making the entire lifter removeable will require more planning and design to fabricate a strong and easy to remove mounting system. More to go wrong, and more time to build. I'm not a fan of last-minute rush jobs on combat robots, New York.

Q: Aaron, can I attach the wires from a servo directly into the 2.4ghz hub that is in the robot, or do I need an ESC somewhere in there? If I do need an ESC, what is the layout of servo ESC 2.4ghz hub?

Thanks, New York

A: Hobby servos have a small ESC built into their circuitry. A single 3-pin connector from the servo plugs directly into the receiver (what you call the 2.4ghz hub) and provides power and the control signal -- no additional ESC is needed.

Note: the Battery Eliminator Circuit (BEC) in your main drive ESC supplies 5 volt power to your receiver and to other devices plugged into the receiver -- like servos. A high power servo pulls a good deal of current, and some robot speed controller BECs provide barely enough current to run the receiver. Check the documentation for your ESC and for any servo you choose. If the servo requires more current than the BEC in the speed controller provides, you need to disable the BEC in the speed controller and fit a higher output stand-alone BEC.

Q:How do the builders in the U.K. use compressed air for their antweights and can they be adapted to a beetleweight lifter and, potentially, a flipper? [Maryland]

A: There is nothing special about the principles in U.K. antweight pneumatic systems: a tank to hold a quantity of compressed air, a cylinder actuator to turn the air pressure into movement, and a valve system to control the air flow into and out of the actuator. You can learn EVERYTHING you need to know about combat robot pneumatic principles at Team DaVinci's Understanding Pneumatics page.

What U.K. builders are known for is their creative use of unusual components: tanks made from recycled aerosol cans, actuators crafted from re-purposed syringes, and valves salvaged from toy construction kits.

I can't give you the imagination and 'bodging' experience needed to put this type of system together. Even if I could, RFL safety rules and the event organizers' safety concerns would prevent homebrew pneumatic systems like these from competing in most U.S. events.

Q: Hi: I was reading some of the back posts and came across the comment: "The pressure in a CO2 cartidge is 600+ PSI, and there are no commercially available sub-miniature valves or cylinders that can handle pressure that high." FYI The Lee Valve company makes very small solenoid valves that will operate up to 800 Psi. They are called Extended Performance Solenoid Valves. A typical part number is IEPA1221241H 12v to open about 3v to hold open, they will open in less than a millisecond! The down side is they are EXPENSIVE... around $650. I don't work for the company but I do use their parts.

A: Really interesting component, but not of use to small combat robots. These valves are designed to control the passage of small quantities of fluids or gasses -- the ports appear to be WAY too small to flow enough gas to be of any use for a pneumatic flipper weapon. It's also unclear if the valve could handle the very low temperatures involved with conversion of liquified CO2 to a gas.

You'd need at least two valves to control a simple one-way actuator (slowly), and there are still no commercial sub-miniature actuators that can operate at 600+ PSI.

Q: Hi. I'm the three lb drum spinner guy again. So everything had been working swimmingly for a while, but today I discovered that the sabertooths failsafe timeout is not working. The weapon still failsafes but unfortunately the drive dosen't. Any tips or suggestion? Thanks for your help

A: Your Spectrum AR6115(e) receiver has an active failsafe only on channel 3: your weapon channel. Other channels revert to 'no signal' status. You haven't mentioned which Sabertooth ESC your robot uses -- but assuming that you are using either the 5 RC or 12 RC, make sure that DIP switch #6 is in the 'up' position (away from the number 6) to turn on the timeout feature that failsafes on loss of signal.

To test, put your robot up on blocks with the drive wheels off the ground. Power up, and command forward motion. With the wheels spinning, hold the stick position steady and turn the transmitter power off. The timeout failsafe takes about one second to kick in and stop the motors. If DIP switch 6 is 'up' and the failsafe function is not working, I'd suggest contacting the manufacturer.

Q: I am building an antweight Lifterbot and I'm thinking of using a b231 to power the lifting arm. The drive is two 22.2:1 silver sparks. The wedge lift is .375 7075 aluminum. it's an inch long from the body.

A: Do you have a specific question? As a general comment, the B231 gearmotor is heavy and overkill for an antweight lifter.

Q: My idea for an inexpensive antweight weapon works on using the opponents speed and power to attack. It involes a vertical "lever" with a pick at the top. when an opponent rams into the bottom of the lever or I ram them the pick slam into the usually weaker top armor to deal damage. Do you think this would work? Would it count as an active weapon?

A: Second question first -- no, it does not count as an active weapon. It generates no movement of its own and does not require a decrete radio channel to operate. It is a passive weapon.

Will it work? Well, kinda. The impact reaction will swing the pick downward toward your opponent, but...

  • The energy in the pick will be a small fraction of the total impact energy;

  • The action that forces the pick downward will also force the front of your robot upward; and

  • The lower lever arm will form a handy reverse-wedge to direct your opponent neatly under your 'bot, lifting it off its wheels and turning it into a passenger on a speedy trip into the arena wall.
I think you'd be serious wedge bait. I also think that you don't want to be charging at full speed into the maw of a high-energy spinner weapon. That could be your last charge.
Q: Could a soup can be used as beetle armor? My bot won't be fighting any spinners, just my brothers wedge.

A: Backyard robot fight? Awesome!!! Soup can steel is pretty soft and 'denty'. You might be better off with resilient plastic from a drink pitcher or sandwich box. Have fun!

Q: Because of very generous relatives, I now have some cash, and I want to build a new antweight. I have 225 dollars, but I want to ask an expert before I drop any amount of cash.
  • First, I want to use Li-poly, a three cell 750 mha Rhino li-poly to be more precise. Is this a good brand of battery? If not, what brand would you recommend around that price range?

  • Second, I'm want to have a hinged wedge on my bot. Which wedge type would be better: A high hinged, skirt like wedge like Gilbert, or a mid body line hinged wedge like Original Sin?

  • Third, I already have a pair of Tiny ESCs from my Viper Kit, can I run a pair of 11:1 Silver Sparks off of each ESC? Or do I need a higher amperage ESC?

  • Forth, I want to use 2.5 inch lite flights, how do I keep them on the hub? I been using plastic cement, and it's NOT working at all. Should I use CA glue, or Gorrila glue like Finger Tech recommends?

  • Fifth, is the Dynamite Passport AC/DC good? Should I drop a few extra bucks for the Dynamite Passport Ultra AC/DC, or another charger like Triton or AstroFlight and power supply?

  • Sixth (Don't worry, I'm all most done), is HDPE a good building material? I know a good portion of UK bots use it, can it stand to the likes of combat here? Would a garolite top and bottom plate be good with the HDPE, or should I use lexan? Should I bolt everything into the HDPE, or should I invest in nut strips that are becoming popular?

  • Lastly, is chrome-moly still viable in the ant world? I want to use it in the wedge, and I know it has to be very strong. Would 7075 aluminum be better?
Thank you kindly, R1885.

A: Mark J. here: Congratulations on your new sponsorship.

  1. 'Rhino' is a very inexpensive Hong Kong battery that suffers, IMHO, from a lack of quality control. Sometimes you get a good one, sometimes you don't. It's about all you can expect for the price. Some builders use them with success -- I'd spend more and get something better suited to combat. If you want to roll the dice, the best price is direct from the importer: Hobby King. More about batteries in the answer to question 5, below.

  2. I like mid-hinge wedges. Construction is more difficult, but the impact force is better controlled along the centerline of the robot than it is from a top hinge.

  3. Running 2.5" wheels at 11.1 volts will bog down the Silver Spark 11:1 motors. Acceleration will be poor and the motors will pull about 1.6 amps each at a hard push -- well above the 1 amp continuous rating of the tinyESC. Rather than switch to a higher amperage ESC, I'd suggest switching to the 33:1 Silver Spark motors. Maximum amperage draw will drop to less than 0.6 amp per motor, and acceleration/speed will be much better suited to a typical small ant arena.

  4. Didn't you ask this same tire question a couple weeks ago? Read down a bit in this archive for the answer we gave then. Different adhesives have different applications - as you have discovered. Gorilla Glue is not well suited for rubber, and regular CA is too brittle. I like weatherstrip adhesive for any application that bonds rubber.

  5. It doesn't make sense for you to spend 1/3 to 1/2 of your entire robot budget for a fancy charger to maintain a $7 battery. For your purpose I'd suggest a simple and inexpensive 'no-frills' charger like the Dynamite Prophet Sport AC Lipo or the E-Flite 2-3 Cell LiPoly Balancing Charger. You don't need bells and whistles to just 'top up' a small LiPoly between matches. Spend some of what you save on a better quality battery -- and a spare battery for back-up.

    Incidentally, a 750 mAH battery is overkill for your wedge antweight. The Tentacle Torque/Amp-Hour Calculator estimates that you'll use less than 100 mAH in a 5 minute match (with the 33:1 Silver Sparks). A good quality 430 mAH pack would be plenty!

  6. Don't use High Density Polyethylene (HDPE) -- upgrade to Ultra High Molecular Weight polyethylene (UHMW). It's a tremendous material if used correctly. It is quite flexible but also very light, so don't hesitate to use thick sections to get adequate strength and stiffness.

    Garolyte comes in different types and grades. Stick with G9, G10, or G11 grades and you'll be fine. It makes very good top/bottom plates. I don't like to use Lexan in applications where it is bolted out near the edge -- it tends to crack in these situations unless mounted in rubber grommets.

    You can bolt into UHMW, but the soft material does not hold threads well. Specialized screws designed for plastic with deep, sharp, coarse threads are good for thick plastic -- but nutstrips are likely a better option for relatively thin antweight material. Use large-headed screws and/or washers to prevent the heads pulling thru the soft plastic.

  7. Chromoly steel is an entirely viable ant wedge material -- if you heat treat it. It's stiffer and has a harder surface than than 7075 aluminum, which will help spinner resistance. It is also heavier, but - assuming that your wedge isn't huge - you can likely afford a little extra weight for a wedgebot. If you don't want the trouble of heat treating the chromoly, 7075-T6 tempered aluminum would be fine.

Comment: Wood screws also work great in UHMW. [West Chester]

Response: Wood screws work much better than machine screws in soft plastic, but screws specifically designed for plastic will hold better still and cause less damage to the plastic. I think it's worth the extra effort to find the correct screw. Follow recommendations on correct pilot hole diameter and you'll get excellent results.

Wood screws and plastic screws

Q: R1885 again, I must thank you for your help. I have a few more questions:

  1. I'm designing my bot like Original Sin, and I want to have a hinged wedge like it. Is it better to bend one piece of 1/8" 7075 into the shape I want, go with a U Channel and cut it to the right size, or to bolt several pieces into a wedge shape?

  2. I looked at Online Metals UHMW selection, and I see Reprocessed and Virgin plastics. Does it matter which I use?

  3. Are the bearing blocks sold on Robot Marketplace good for mounting my sparks, or should I go for the very expensive kit bot spark mounts?

A: You're very welcome.

  1. 7075-T6 aluminum does NOT bend well -- it fractures. The minimum bend radius is roughly six times the thickness, so you aren't going to get anything like a sharp bend. If you can get a formed shape close to what you want, go with that.

  2. There's a joke here someplace, but I'm not going to go looking for it. Reprocessed UHMW has variable physical properties that are typically less desireable than the virgin material. Stick with the good stuff.

  3. Very expensive is right! I don't know enough about your design to comment directly on the best motor mounting method. You might be able to bolt the gearbox directly thru the UHMW chassis wall and clamp the motor end down to the base plate -- no mounting plate required. The bearing block could be used to give extra support to the shaft on the outside of the chassis wall -- if your design could benefit from that.

Q: What regulator can I use for a 12 gram disposable co2 cartridge?

A: With a 12 gram cartridge adapter you can use a standard paintball regulator.

Q: what tubing should I use for the 12 gram co2 adapter? Do I need a regulator? What is a small rc valve that I could use? Is there a small pnuematic cylinder that can work with this system? All of this is for an ant weight robot.

A: You're about to find out why there aren't any CO2 antweight flippers:

  • The 12 gram adaptor is a specially machined and threaded holder which aligns the cartridge and seals it up to a standard regulator. No tubing is involved. The adaptor weighs about 3 ounces, and the full cartridge is 2 ounces.

  • Yes, you need a regulator. The pressure in a CO2 cartidge is 600+ PSI, and there are no commercially available sub-miniature valve/actuator sets that can handle pressure that high. Add another 3 ounces.

  • There are many posts in this archive about sub-miniature pneumatic valves and actuators - search for 'Robart'. The available minaiture components require some machine work to be suited to weapon use.
A small regulator, cartridge, and adaptor total around 8 ounces, leaving you very little for the rest of the weapon and robot. All the pneumatic ants I can think of use small compressed air tanks rather than a heavy CO2 system.

Q: Co2 cartridge person again. Is this whole setup dangerous for a beginner? Is there any regulators you would reccomend? How would I machine the robarts sub-miniature cylinder? Thank you very much in assisting my robot.

A: You're very welcome. Disclaimer: Team Run Amok has never built an insect class pneumatic robot and has no first-hand experience with the sub-miniature parts.

Are you really sure you want to build a CO2 antweight? The components are going to take up a very large chunk of the weight allowance, and it won't give any practical advantage over a much lighter compressed air system that would require no regulator or adaptor. And yes, CO2 will be more dangerous.

Many small pneumatic 'bots have used Palmer Pursuit paintabll regulators. A check of their website shows that they have just (June 2012) added a new 12-gram CO2 cartridge regulator -- no adapter required. That could save you some weight, but they are more expensive than the other regulators and are untested in robot combat.

As to machining the ports on the valve and cylinder, I can't teach you machining in a few sentances on-line. The ports have to be enlarged to improve the airflow and speed the actuation of the system. I'd suggest finding someone familiar with machining techniques to give some hands-on help with this.

Q: I'm finding that my Lite Flite wheels are slipping on my hubs. What can I do to stop this slippage?

A: You didn't mention which hubs you're using. If you have the FingerTech hubs, the manufacturer recommends a drop of cyanoacrylate ('super glue') to secure the press-fit hub to the Lite Flite nylon wheel.

If the rubber tire is slipping on the wheel, the tire may be glued to the wheel with weatherstrip cement - available at your local auto parts store. Regular rubber cement will do if you have that on hand, but don't use 'super glue' here!

Q: The RFL rules say that robots twelve pounds and under can only use 250 PSI. As PVC is rated for 315 PSI could I make a pneumatic system out of PVC tubing for an ant or beetle wieght?

A: Mark J. here: you have mis-read the rules. Section 7.4.1 of the current RFL ruleset says:

Robots 12 lbs and under and systems with gas storage of 2 fl oz or less are exempt from the remaining rules in this section provided that the maximum actuation pressure is 250 PSI or less and all components are used within the specifications provided by the manufacturer or supplier. If you comply with all the pneumatic rules you may run higher pressure -- although it would be difficult to comply with the full ruleset in an insect-class robot.

The pressure rating for PVC pipe and fittings varies with the diameter of the pipe. According to the ASTM D1785 standard, 1/2" schedule 40 PVC pipe has a max operating pressure of 358 psi @ 73 degrees farenheit, while 1/2" schedule 80 PVC pipe is rated to 509 psi.

Note that all components must be rated for the operating pressure of the pneumatic system and that any 'homebrew' components are allowed at the discretion of the event organizer.

Q: Aaron, what are some good examples of some ant weight flipper robots? Any videos?
Thanks, New York

A: True flippers are uncommon in US antweight competition, and I can't think aof a particularly 'good' example. Flipping an opponent end-over-end is usually a task left to a rotating drum weapon, which would be illegal in your sumo event.

There are, however, a few very nice and effective UK antweight (150 gram) flippers, like 'Anticide' (video).

Q: I watched the video of antweight pneumatic flipper 'Anticide'. I was impressed, so I did more research on it. I have read the previous tags about [Inertia Labs] Pneumatics, and I know that they are no longer made. First off, what type of pneumatic device would you use for that flipper? I looked up 'miniature pneumatics' and the first site came up with results for small pneumatic. However, for a 1lb or 3lb bot, how small and what device would you use for the flipper? would it be a cylinder of 5/16th bore? (I do not know what that is, I just saw it on Thanks, New York

A: Go read the Team Da Vinci 'Understanding Pneumatics' page and keep reading until you know what bore and stroke are and how they impact pneumatic weapon performance and design.

There are currently NO off-the-shelf pneumatic components available that are suitable for an insect-class pneumatic flipper. The Clippard components are all too large and heavy for the purpose. The Robart pneumatic components are correctly sized and light enough, but they are designed for slow actuation of scale model aircraft landing gear. 'Anticide' uses Robart parts, but they have been machined to provide larger ports for faster actuation. This is the same approach I would use for an insect flipper.

Q: Aaron, would an outfit like Whyatchi or Big Blue Saw make custom, insect capable pneumatics for me? I hope I am not laboring the question, I just thought that the performance displayed by Anticide and its capabilities are amazing. Thanks, New York

A: A custom machine shop could certainly do the work, but a full custom pneumatics setup could get expensive. If you're intent on an insect pneumatic flipper I'd suggest you find someone willing to enlarge the ports on the Robart actuator and valve set-up for you. Remember, the pneumatics are just the start of a successful flipper robot.

Q: Dear Aaron, I would like to know of an example of a really 'powerful' ant weight spinner. What would constitute as a 'far above average' ant weight spinner, in terms of the spinner power? [New York]

A: There are MANY articles on spinner weapon energy, materials, motors, drive systems, impactor design, and 'bite' in the Robot Weapons archive -- if you get all of that correct you'll have a 'powerful' spinner. If you'd like to dig deeper into spinners I suggest you read the appropriate sections in the Riobotz Combat Tutorial.

Q: Aaron, when I was asking about the powerful antweight spinner, I meant an example of a real bot that is considered a powerful antweight spinner. Sorry for the bad hamburger! Thanks. [New York]

A: I understood your question, New York -- but I was hesitant to name a specific robot for several reasons:

  • 'Powerful' implies 'successful'. A successful spinner requires much more than just power, as I pointed out in my answer.

  • A quick check at BotRank shows that the majority of the current top ten antweights are not spinners, powerful or otherwise.

  • If I name 'Robot A' as 'powerful' I'll get flak from builders claiming that their spinner is WAY more powerful than 'Robot A'. I don't need the grief.
I think you can watch a few videos and find a powerful ant spinner yourself; they're usually the ones throwing themselves out of the arena. You can also spot the spinners that spin too fast and can't get any bite.
Q: Dear Aaron will a steel 6 inch and 0.375 inch diamater /0.375 thick top /0.063 thick wall hole saw suffice for a beetle weight fbs shell please help from anthony

A: I don't think I understand your measurements, Anthony. A steel hole saw 6.375" in diameter with a 0.063" wall thickness but only 0.375" tall? That can't be right! Please clarify.

Q: Dear Aaron sorry about the measurements i was just rushing the height of the hole saw is 1 inch from anthony

A: I'm guessing that the hole saw you're thinking about looks something like the photo at right. With a few estimates, I can verify that the energy storage you'd get from spinning the saw at 2000 RPM would be better than 50 joules -- adequate for a beetleweight spinner. That's the good news.

Now the bad news. How do you plan to stuff an entire beetleweight chassis - with a FBS drivetrain - in the very small space underneath that saw? I don't think it's terribly practical, but if you have some special clever plan the shell can store enough energy to be an effective weapon.

Large diameter hole saw

Q: What battery would you prefer for an antweight wedge bot: a 7.4v Li Poly or Nimh battery? it will be powering a Tamiya dual motor gearbox.

A: LiPolys are lighter and more compact than NiMHd packs of the same capacity. Lighter leaves more weight for armor and other components. When in doubt, go LiPoly.

Q: Is 5 oz. enough for my antweight vertical disk spinner or is it overkill?

A: There's much more to an effective weapon than weight -- I can't judge if the weapon is 'enough' based on what little you've told me.

Q: Spinning disk question: the spinning mass will be mounted to a 256 1 BaneBots motor driven by a belt.

A: There are many different 256:1 BaneBots motors, and they're all way too slow to drive a spinner weapon. Read thru the Robot Weapons archive for many examples of spinner design tools and considerations.

Q: Would 1/4 inch thick carbon fiber make a good wedge for my ant? I plan to mount it to an Inertia Labs chassis.

A: That's probably a reasonable choice, although CF will show surface damage under heavy attack. See FAQ #17.

Q: How can I make a lifting spike, like 'Vladiator', with a servo?

A: I suggest you read thru this archive for general advice on servo powered weapons and servo selection. There are several diagrams of servos being used to power weapons that may give you design ideas. For a start, search this archive for "How do I make an antweight flipper".

Q: I'm building an antweight rambot. I'm running a twin-motor Tamiya gearbox with a 9.6 volt 600mAH Ni-MH battery. Should this suffice for a powerful rammer?

A: No. The Tamiya twin gearbox is a nice inexpensive unit, but it's bulky and weak compared to popular antweight motors. A practical and powerful rammer would have a gearmotor on each of four wheels for superior power, traction, and directional stability.

Nominal voltage for the Tamiya motors is 3 volts; at 9.6 volts they turn into hand grenades. A large overvolting will boost power but will also drastically shorten motor life. Good robots are reliable, and this one wouldn't be.

Q: How should I modify my drive/battery system to allow it to work well for the rambot?

A: The Tamiya twin-motor gearbox just isn't up to spec for a modern antweight. The motor output is modest, the gears are plastic, the case is plastic, the bushings are plastic and the output shafts are relatively small and weak. Ten years ago these gearboxes were common, but stronger and more powerful gearmotors have become available. I think you would be well advised to switch to different all-metal gearmotors. Take a look around at what high-power rammers are using and emulate them.

If you'd like to keep the Tamiya gearbox you could certainly make a nice little wedgebot out of it. Drop the voltage down around 6 volts, design a chassis with some wheel protection to keep pressure off those smallish axles and plastic gears, mount an extra-sturdy front scoop and go bash some other robots!

Q: Can I use a 9-volt Duracell to power an antwieght?

A: 9-volt alkaline batteries are designed for low current applications and have very poor performance at high amperage discharge rates. Current much above 1 amp cannot be reliably maintained without serious voltage drop, whereas modern LiPoly batteries of similar size can deliver more than 10 amps of continuous power and provide greater total capacity.

FingerTech Robotics recommends special Duracell "Procell" 9-volt batteries for their antweight kits and they claim adequate performance, but the test I've seen of the Procell was not encouraging.

If your motors cannot access the current needed for high-torque situations, your robot's performance will suffer. It also gets expensive popping in a new battery whenever you're uncertain of how much power your current battery has remaining. I can't recommend use of an alkaline 9-volt battery for combat robots.

Q: So I have been playing with my Viper Kit, and it seems to be working alright, but I noticed a grinding noise from one of my motors. I checked the gear box, nothing wrong there, and I even added grease to it, so do you know what might be wrong?

A: Grinding is bad. I think I'd ask FingerTech for a replacement.

Q: If I speed hack a servo would it make a suitable drive motor for a ant or beetle weight robot?

A: Ten years ago there were plenty of insect 'bots powered by hacked servos. In current competition there are virtually none. A standard servo has very little power compared to current insect class motors. Speed hacking the servo by removing two of the four gear reduction stages will increase the speed of the output shaft, but the increased speed comes with decreased torque. Total power (torque * speed) remains the same, and the same is too little.

Q: Hi, I recently built an antweight robot and I am now thinking of building a beetle bot. For the weapon, I was interested in the flip-o-matic designed by Dale Heatherington for his 30 pound bot Overthruster.

Do you think it would be possible to build it using .25 in lexan, with just hand tools and scaled down a bit?

Also do you think, if it is made out of lexan, would it hold up to the stresses of when it is triggered?

Lastly, do you think it would be effective against other bots or just put on a good show?

A: Mark J. here: I greatly admire Dale Hetherington's 'bots, but I cannot encourage builders to attempt adapting his designs. Dale is a very experienced and accomplished designer and machinist, and trying to copy his Overthruster 'Flip-O-Matic' weapon with plastic and hand tools would be folly. Take another look at the complexity, detail, and precision required for the weapon. You'll be much better off picking another design.

P.S. - Lexan deforms under high loading and is not useable where close tollerences are required. Dale had to switch up to more exotic materials on key pieces of the clutch mechanism because the 6061 aluminum wasn't up to the task. If Lexan was suitable for the purpose, Dale would have used it.

Q: What's more efficient for a drum weapon on an antweight using a outrunner motor, using a belt drive or mounting the motor inside the drum?
-Rick from Texas

A: An outrunner motor with the motor can attached directly to the interior of the drum will very likely have both:

  • too high a drum speed for optimum 'bite' into your opponent; and

  • a slower spin-up time than the same drum/motor combination with a belt drive reduction.
From that standpoint you can say that the belt drive is more effective. See the comments on 'bite' in the RioBotz Combat Tutorial and in the Ask Aaron Robot Weapons archive.
Q: How much PSI would be able to be compressed into a AXE, or LYNX bottle? I saw this video, and was very curious.

A: Mark J. here: that isn't a great 'how to' video. The only guidance I can provide on pressure is that generic aerosol cans typically operate at about 110 PSI, but that's before you go and drill a hole in the side of it for a valve.

You might get away with a repurposed can for a British antweight, but RFL rules require manufacturer specifications on all pneumatic components. I don't think you're going to produce such a specification for a recycled aerosol can that you've sealed with hot-melt glue and drilled into for a new valve. Event organizers may grant an exemption on a case-by-case basis -- check with the EO before you go this route.

For safety and reliability reasons I can't recommend homebrew pneumatic tanks. Small aluminum air tanks properly rated for 150 PSI are available for use in model aircraft. Use one of those.

Q: The axe/lynx guy again, do you have any recommendations? I drew a CAD of my model, and I need an air tank that is 3.75 in long, or less. And 1 1/2 inch diameter, or less. Can you reccommend an air tank for me?

A: It's not good design practice to paint yourself into a corner where you need a specific, hard-to-find part in an unusual size. Better to start with the hard-to-find parts that are available and design the rest of the 'bot around them.

The HobbyKing Micro Pneumatic Retract Landing-gear set comes with a pneumatic tank that looks to be about the right size, but they list no dimensions. The Robart Extra Small Pressure Tank is close to your desired size at 1.39" diameter by 4.25" in length.

Q: Hello im currently running a scorpion hx, 7.4 2s venom 2000mah 20c Lipo, 2 copal 50:1 motors, GWS 6 channel receiver & GWS 6 channel transmitter in my antweight (yet to be named) and i need help deciding what weapon esc and weapon motor to purchase.
I am planning on it being a bar/drum weapon.
I know these arent the top of the line products but just need to know if im on the right track on adding a weapon to my antweight and if you could tell me if they will work for my above setup or recommend something else Option #1: ESC & Motor

Option #2: ESC & Motor combo 1

Option #3: ESC & Motor combo 2

A: Several problems:

  1. The bar/drum has to work in harmony with the motor and ESC to produce a functional weapon system -- I can't recommend a motor/ESC for an undefined drum/bar.

  2. EBay brushless motors do not in general come with sufficiently detailed (or reliable) specifications to calculate their performance in a weapon system.

  3. Ditto number 2 for eBay brushless ESCs.

  4. I don't know how much weight allowance you have left for your weapon -- that's kinda critical!
The general process in developing a spinner weapon is to draft a design for the bar/disk/drum and evaluate the performance of that design with a specific motor and drive reduction ratio with a modeling tool like the Run Amok Excel Spinner Spreadsheet. You can model performance with different motors, change the weight and size of the spinner bar/disk/drum, and adjust the drive reduction to get a sufficiently quick spin-up time and maximize weapon energy.

All that said, a lot of entirely functional spinner weapons have been built by a 'best guess' at the critical elements of the weapon. You're not going to get an optimal combination of design elements this way, but you might get something useable.

If I had to guess at one of the weapon/ESC combinations you list given the VERY limited information you've provided, I'd pick option #1 just because it has an RPM constant (1650 Kv) better suited to a spinner weapon than the other motors while still claiming a good amount of power for an antweight weapon. Run a belt drive with about a 4:1 reduction to the heaviest bar you have weight allowance to cover and hope for the best.

Q: Is it worth the trouble to switch your weapon motor from brushed to brushless in an insect bot if this requires an extra speed controller?

How much more performance would you get out of a brushless motor with the same weight?

A: There are many variables, but you can expect 3 to 4 times the peak power from a quality brushless motor compared to a brushed motor of the same weight. That's peak power -- brushless motors cannot sustain those very high power outputs for long, but in a spinner weapon the power requirements decrease once the weapon is up to speed so a brushless motor can work well in that application.

I think most builders would agree that three times the power from the same weight is worthwhile. You see very few brushed motors in insect class weapons anymore.

Q: Are servos good for building an antweight crusher? If what is? How should I approach it?

A: There are MANY posts about antweight crushers in this archive. Search for 'crusher'.

Q: Can I use a 12 gram co2 disposable container as a co2 tank for my beetle weight?

A: Check the rules for the events you plan to enter. The current RFL rules do allow small disposable CO2 cartidges, provided that other rules covering pneumatic systems are met or that the event organizer allows an exemption. See section 7 of the RFL rule set. You will need a regulator to reduce the cartidge pressure (600+ psi) to a safe and useable level.

Q: Hi Aaron, I was wondering if the hobbyking pneumatics were suitable for a pneumatic antweight, or a beetleweight? They have a valve used with a servo and an actuator with spring return. Thanks.

A: The products you found are designed for very low-speed actuation of landing gear or similar functions on model aircraft where servo speed is too fast to 'look right'. The port size and airflow capacity are far too small for use in a flipper weapon.

Date marker: February 2012
Q: Hi i am making a Antweight do these parts work together?
  • Drive: 4-Speed Double Gearbox Clear - Tamiya 89918
  • DriveEsc: Sabertooth 12 RC Dual Motor Speed Controller
  • Battery: 9.6V - 8x 730mAh HR-AAAUX NiMH Cells at 3.75 Per Cell
  • Weapon Motor: 150:1 Mini Metal Gear Motor
  • Weapon Esc: SpeedMax-40 Electronic Speed Controller
  • Receiver: Spektrum AR6115 6-Channel DSMX Microlite Receiver

A: Well, they will 'work', but I have some comments.

  • Not many builders use the Tamiya gearboxes anymore -- they're quite bulky and a little fragile, but they work.
  • The Sabertooth 12 is overkill for the Tamiya gearmotor in an antweight. It will certainly work, but you can save considerable weight by using the Sabertooth 5.
  • 8 cells (9.6 volts) is too much for that Tamiya gearmotor. I'd suggest 5 NiMH cells (6.0 volts).
  • You haven't told me what type of weapon you plan, but the 150:1 Mini Metal Gear Motor is FAR too slow for a spinner weapon, and too weak for a lifter.
  • The SpeedMax-40 ESC has features and capacity you don't need, and it is tedious to program. It's also a single-direction controller (no reverse). Consider the BaneBots 3-9 Reversible Brushed ESC. It has ample capacity for many brushed antweight weapon motors, will reverse, and will fail-safe correctly with the Spectrum AR6115 receiver.
  • You might consider the Spektrum AR6115e receiver instead of the AR6115. The end pin output is a little easier to fit into a cramped antweight.

Q: Is the FingerTech "Silver Spark" 16mm Gearmotor suitable for a full size sumo robot?

A: I don't follow or compete in robot sumo, so I don't feel qualified to comment on specific sumo components.

I can say that these motors are used in antweight (1-pound) wedge/ram combat robots and beetleweight (3 pound) combat robots with large weapons. If by 'full size' you mean 'standard class' (3 kg) sumo, motors I have seen used in this class are considerably larger.

Q: Dear Aaron the modified saw blade is 10.85 oz (diablo brand) (plus six carbide impact teeth for better bite) with the hub aproximetly 11 0Z unmodified with hub and uses 4 large socket head set screws secured with nuts for weapon structual integrity the set srew holes were drilled out from the blade with a drill press and the blade is securely mounted to an andy mark 6061 aluminum hub with a half inch bore keyed to fit a .5 inch 4140 hardend shaft thats keyed and broched the weapon assembly consistes of used p60 gear box parts /shafts with a finger tech pulley and a matching kevlar reinforced belt with a 3.1 pulley ratio. The weapon motor is a novac 550 size terra claw crawler motor run @ 7.2- 12 volts the battery will eather be a thunder pack lipo g6 @ 835 mah or a megatech 1400 nmh pack @1400 mah. The drive motors are kit bots beetle motors attached to the cheaper 4mm daves aluminum hubs with extra screws put right through the hub and wheels... The wheels are 3.025 inch lite flights. the armor is .0125 uhmw sheet made into an L shaped 3 dimentional 8/6 box with 1.50 inch walls times four supported with a uhmw makeshift nut strip with nut and bolts. The connectors are deans ultra 20 amp connectors. and the kill swith is a team whyatchi MS05 shock mounted to the robots base plate. the drive esc is a dual sabortooth 12 and the weapon esc is a bane bots 12- 45. Thanks for your help and support p.s is this set up still too heavy? from anthony team warpz

A: Last time you wrote in you were building a beetleweight vertical spinner, Anthony. Is this that same 'bot? I haven't estimated the weights of all the individual pieces you mention, but the pieces seem about right for a beetle with a big weapon.

Q: Dear Aaron, is it possible to run a servo based weapon using a sabertooth 5 rc speed controller and a 4 channel rx, horizontal pins,futaba style reciever. Thank you

A: The Sabertooth ESC is not required to operate a servo weapon -- the servo plugs directly into the receiver. The Sabertooth will control two drive motors for an insect-class robot. Any 3+ channel receiver with proper failsafe response compatable with your transmitter will suffice for your purpose. Make that 4+ channels if you want to use the optional 'inverted' function of the Sabertooth.

Q: If it is properly bracketed, could .063 7075 aluminum make a decent beetleweight wedge? By "properly bracketed" I mean that it is mounted on four triangle shaped brackets made out of .25 inch thick 6061 aluminum. The brackets are spread out over a 5.5 inch distance relatively evenly, and the wedge plate itself, which will have two screws per bracket, will have a maximum overhang of .25 inches per side. Oh ya, one more thing: the wedge is is not the primary weapon: it is a secondary/defensive wedge.

A: We aren't an engineering service (see FAQ #17), but your design sounds generally adequate for your purpose. I'd reconsider that overhang -- it sounds like a sharp edge, and spinners LOVE sharp edged targets.

Antweight full-body spinner. Q: Hi Aaron, here is a pic of my Antweight bot so far.

How do you feel about driving a full body spinner by having a spinning tire contact it? I am worried that the rubber will wear off during a battle and provide insufficient contact, and it will also be tricky to mount it so the pressure is just right. Any specific material suggestions or other tips for this? I would much rather drive the spinner with a belt but due to height constraints I cannot mount the motor with its axis vertical, so belt driving it seems less feasible. I am using the 380 motor from Banebots.

How do you feel about Legos for Antweights? I am using them for the chassis since Lego Technic gears are really easy to use, and it is lightweight. Superglued together they seem really structurally strong. I am not worried about them getting shredded since they will be underneath the metal spinner shell. My main concern is maybe the plastic gears can't handle the stress of motors at stall torque if I get into a pushing match or something.

How low of a clearance can I go without getting caught on the floor of the Antweight arena at RoboGames?

Thanks for your help!

A: I really like to see someone building from materials they have at hand in a creative way. Is that spinner shell a modified frying pan?

I've seen spinner shells friction-driven by wheel, but they all drove the outer edge of the shell. It sounds like you want the drive wheel to contact the upper surface of the shell. From the look of your shell the contact point would have to be close in toward the center where much greater torque must be applied to achieve the same acceleration to the shell. That will put a lot of stress on the drive and create more trouble in getting the pressure correct. It sounds like trouble to me.

If you decide to try this type of drive, a polyurethane wheel would provide good grip and low wear. A spring tensioning device to maintain pressure seems like a must. Your opponent is going to be just a few feet away from you at the start of the match and will be charging hard. A fast spin-up time is mandatory!

Legos are made from ABS plastic that is reasonably strong, if a little soft. Superglue is somewhat brittle and can fail under shock loads. I'd rather use an ABS solvent cement (check your local hardware store) that will chemically weld the blocks into a solid mass. Remember, the shock transmitted to your opponent by the weapon impact will deliver an equal shock back thru the weapon to your chassis. Make it strong.

The stall torque of the motors I see in the photo should not be a problem for Lego components. Besides, if you get into a pushing match with your FBS you're doing something wrong! Spin fast and hope for the best.

According to my records RoboGames hasn't reported an antweight class since 2008 [see next question down]. If they do have an antweight class in their next event I don't know what arena they might use. I'd suggest allowing some adjustment in clearance to accomodate changing conditions.

Q: As a competitor at Robogames, I can tell you, they have a very popular antweight event.

A: <Rant Mode>

I'd love to know why this 'very popular antweight event' does not bother to report their match results. The heavier weight classes at RoboGames report, so why not the insects? It takes ten minutes to send match data to BotRank, but a few events can't be bothered to share results there or anywhere else. This is a disservice to both the competitors and the sport.

     </Rant Mode>

Perhaps some recent competitor would like to help our Legomaniac with an opinion on adequate clearance for the Robogames insect arena?

Annonymous Opinion: the floor can get pretty scuffed up by the 2nd half of the tournament. I personally think that you should have at least an 8th of an inch clearance around the wheels and a little less around the shell. Take that with more than one grain of salt, though.

Also, opinion regarding the "is combat robots declining/ a shadow of itself" issue below: The last two Robogames/Combots events have had an increase in competitors compared to their 2010 equivalents. It is not enough to be called a trend, but it IS good news. Still, don't expect a neo-Battlebots.

Response: thanks for the arena report! RoboGames/Combots are doing well -- power to them.

Q: I am the antweight fbs guy that just posted. Thanks for the quick answer!

It is indeed a frying pan with a ball bearing pressed in. I used a hacksaw and file to make the holes in it to get it lighter.

You make a really good point about the friction drive. I never considered driving it farther from the center but I think I will modify the design to have it driving the pan just outside of the edge of the holes where the top surface starts to curve downwards. This will add about a 9:1 ratio which I hope doesn't limit the top speed of the spinner too much to be dangerous.

I'm pretty sure RoboGames still has an antweight competition. This site ( and YouTube have some video of Antwieghts from RoboGames 2011. Also from reading your site I know Antweight is the most popular category so it would be absurd if they didnt do Antweights!

A: Yes, going to the outside edge will solve a number of problems with the friction drive and give better spin-up on the weapon. Guessing at dimensions from the photo, you'll still have plenty of speed from that RS-380 driven shell. You may need an idler wheel on the opposite side of the shell to counter the upward force of the drive wheel.

As noted above, BotRank does indeed continue to have an antweight competition. You can likely get some guidance on the characteristics of the arena with a few questions at the RFL Forum

Q: Dear Aaron i'm almost done with my beetle weight two wheel drive vertical disk spinner for franklin institute 2011 and i,m stompt. would the vdd gear box survive the loads that other beetles would dish out or should i support the protruding 3.2 mm shaft with a uhmw bearing block or increase the shaft size? i'm running 2 metal geared tamiya motors with mounts with a size 380 motor both are drawing 12 amps at stall plus a speed 300 motor for the weapon drawing 6 amps at stall with a vdd1 saw blade. The battery is two 750 mah nimh batteries in a series to get 7.2 volts with a sabortooth 25x25 i know this set up is too big but it was all i had to work with and the armor is 3mm 6061 aluminum plus it can operate inverted is this design going to work or is it just too heavy thanks for all your support from anthony aka team warpz.

A: A combat robot's success depends about 20% materials/components and 80% on design/construction/detail. What you have told me about your components sounds OK, but there is a lot of detail left out. I really can't comment on how well it might work.

I will point out that the VDD gearbox with Speed 300 motor and VDD1 blade make an effective antweight weapon, but it seems underpowered for a beetle. The weapon shaft on the gearbox is already supported by two ball bearings and the overhang is small. I don't think the shaft needs additional support, but I'd carry a spare polycarbonate weapon housing in my spares box.

Q: What is the least effective design for a UK antweight?

A: Mark J. here: I can't claim any expertise in UK ants, but I've always contended that any design can be successful if enough thought and craftsmanship goes into the build. That said, I think it would be really tough to make a tiny twackbot effective in a UK ant arena.

Q: I currently own a kato wedge kit with 50:1 copal gearmotors. However, the lexan mounts I use for the motors keep shattering upon impact with big blades. What other antweight motor mounts would you recommend?

A: Lexan gets its strength from its ability to flex. A single bolt holding a Lexan motor mount closed will produce a high stress load in a single spot and lead to failure. Options:

  • Add support around the outside of the Lexan mount with an automotive 'hose clamp' to spread the load.

  • Switch to a metal motor mount that cannot shatter (but may deform) like the FingerTech mount.

  • Provide a little wheel protection to deflect the spinner blade before it has a chance to destroy the mount.

Q: Hi Aaron. Would this Crouzet micro switch valve [dead link removed] work for an antweight 100 psi pneumatic system with a spring return?

A: Mark J. here: this type of valve (2-way/3-port) is correct to operate a single-acting pneumatic actuator with a spring return. I found a data sheet for this valve that shows an adequate pressure rating (120 psi) and a good flow rate for a valve this small. It's a mechanical valve that you must actuate with modest external force, say from a small servo.

The speed of your weapon will depend on design factors you have not supplied, but the valve is generally suitable for your purpose.

Q: How well does the EFL 400 920 brushless motor hold out as a weapon motor in a beetleweight? I.e. could it survive powering a 100 j weapon with a belt? (in terms of structual integrety) How many amps can it handle and for how long?

A: I have no first-hand experience with the Park EFL-400-920 motor, but the numbers look acceptable for a beetle weapon motor. Park motors are well built and should not be the structural weak link in a weapon system. The motor is rated 10 amps continuous with a 13 amp burst for a few seconds. The Team Run Amok Spinner Spreadsheet can help you calculate weapon performance with this motor and a specific rotor blade.

Q: Aaron, I had an idea! Maybe it could be possible to use a actuator that is rated for 100lbs of force on a 6lb mantis crusher! I would not be surprised if it doesn't work, but I at least want to hear your input and corrections.

A: I'd need to know more about the specific actuator you're talking about in order to offer an opinion. See: The Hamburger is Bad.

In general I see two problems:

  1. I don't know of any actuators that are small, light, strong, and fast enough for the purpose; and
  2. The last time I counted there were three active mantisweights, and they were all in Saskatoon.
I'd suggest that you pick a more workable weapon and a more competitive weightclass.

Q: [Broken Firgelli link removed] - Actually, I am going to the PA Bot Blast and the 6lb class will be there. Or, is it possible to use these on a 12 as well.

A: OK, the FA-150-S-12-3 actuator you point to weighs 2 pounds, is 7.5 inches long (closed), produces a maximum 150 pounds of force, and extends at 0.5 inch per second (at no load -- slower when loaded). You face several problems:

  1. Fitting such a large actuator into a 6-pound robot while orienting the force in a useful manner;
  2. Building a light chassis that can hold up to the force the actuator applies without bucking;
  3. Positioning the jaws someplace where 150 pounds of force will do some damage; and
  4. Holding onto an opponent while your jaws... very... slowly... close... down...
Whether 150 pounds of force will actually damage your opponent is another question. It will depend on the structure of your opponent and where you position your jaws. I'd do some testing on mock robots to see if 150 pounds of force has any real chance of damaging either 6 or 12 pound robots before I committed to a build.

There have been thousands of combat robots built, and exactly one of them was a successful crusher/piercer. Your odds of success aren't good.

A word of warning: all the mantis fights since 2006 have taken place in Canada. The PA Bot Blast may have a mantisweight class, but that doesn't mean that any will show up.

Q: Would a Fergeli mini actuator be fast enough to be rated as a flipper at a high enough voltage? -Brandon

A: Nope, no way, no how. Speed under load for the fastest Firgelli actuators is well less than one inch per second at rated voltage - a flipper should be minimally a hundred times that fast. You'd be well advised to give up on electric flippers/hammers.

Q: Would they still be useful in lifters in the 12-30lb classes?- Brandon

A: Take a look at the spec sheets on the Firgelli website. The actuators are very small, produce only a pound or two of useable force (1 Newton is approximately equal to 0.22 pound force), and typically extend only a couple of inches. Potentially useful in an insect class robot, but nothing larger.

Q: how do i get an axe weapon for my beetleweight robot?

A: You build one. We give short answers here - you need a book. Suggest you browse the Team Rum Amok Book Review page.

Date marker: May 2011
Q: How do I set up a belt reduction system for an antweight fbs? Belt drive weapon support spindle.

A: Space is tight so you're not going to have the recommeneded distance between the belt pulleys. It's tempting to direct drive the shell, but spin-up time is very limited in an ant arena - weapon performance will suffer if you do.

The spinning shell itself should be supported on a long shaft and a widely spaced pair of bearings. The diagram at right was drawn for a blade spinner, but the same support is needed for your shell. Tuck the weapon motor in as best you can.

Q: Hello i am building an ant weight full body spinner. The shell on it is going to be five inches in diameter with a 3/32 inch wall using 6061 aluminum alloy the top plate is also 3/32 inch 6061 aluminum alloy, The impact teeth will be 1/8 inch titanium bolted on. The weapon motor I will use is the park 370-1360 at a 3.6:1 gear ratio. I was also thinking to make the top plate out of 1/8 inch polycarbonate to save weight, ignoring that a full body spinner is not the best idea for a ant weight. Do you think it will be sturdy enough, and that the weapon motor, gear ratio, and shell its self will work efficiently? Is there any thing that u suggest i do to improve the design? Lastly what are your thoughts about the lexan? Thanks for all the help!

A: There are a lot of unmentioned construction details that will determine if the shell is 'sturdy enough' (see FAQ #17). I can say that your choces of materials and thicknesses are ballpark correct, and that a sturdy shell could be constructed with the dimensions and materials you list. The motor and gearing seem suitable -- but you did not tell me the voltage at which the motor will run or the height of the spinner shell.

I'm not keen on the idea of a Lexan top. Bolt holes near the edge of Lexan where it would bolt to the shell rim would be likely starting points for cracks. The weight savings would be small, so better to use aluminum for this. It would be best to machine the entire shell from a single block of 6061, but I know that 'best' is not always possible.

Make your support spindle for the shell very sturdy and keep everything precisely balanced or you'll have a wobbling, uncontrollable gyroscopic menace on your hands. Best luck.

Q: Thanks a lot for the help with the full body spinner! I don't know if it will help now but the shell is 2 inches tall and i am running it at 11.1v.

A: You're welcome. You know that I'm not a fan of ant FBS, but the numbers don't look bad for this design. I hope the components all tuck under the shell neatly for you.

Q: Oh, and by the way, could you please soften your statement regarding electric hammers in the beetleweight class. As my team has learned from the experience, the hammer can be an effective weapon in a class where most people have at least one major hole in their top armor (if not more holes or no top armor at all.) Yes, a little over 3 joules brought down a FBS and gave a tracked wedge a run for its money. In addition, the fans love the hammerbots, and other builders find them fascinating, win or lose.

A: Mark J. here: you have a 1 win, 2 loss record. If you do start to be dangerous, that light top armor on your opponents will quickly improve. Prove me wrong - earn a winning record. Until you do, my opinion stands.

We give the best advice we can to help builders win matches. If your goal is to be adored as an underdog and fascinate other builders, you're on your own.

Q: Would a dust pan from a hardware store serve as armor for my ant? Its flipped over, alowing it to be a wedge.

A: Maybe -- see the hamburger analogy

Q: So two questions, I am building an antweight rammer wedge thing (like every other person on the planet.) and I have 2 B16 motors. I have a few 2 cell 7.4v lipo batteries and 2.5" wheels. Using one of the batteries I can get a max speed of 3-ish mph. With two I can get about twice that. The logistics of havng two doesn't work out too well, namely recharging, weight. I can fit them in if It is really neccesary, but I need to know if 3mph is fast enough to be a good rammer. It will be well armored. Also for a wedge, I was thing of putting a putty scraper on the front.

A: You're going to need more than 3 MPH to be an effective rammer - go with 14.8 volts.

The putty scraper blade wedge should be fine.

Q: Aaron, I am planning on creating a 3lb 'Razer' and I need help on the crusher. I am planning on using a 256:1 Banebots motor and I haven't figured out how to transfer the torque. I was thinking about a screw in design like 'Lock-Jaw', but I don't have the resources to create a long screw like that or the box it goes through. -Brandon

A: On paper, a 256:1 BaneBots gearbox can provide a lot of torque. In practice, the gearbox is more for speed reduction than torque multiplication; it can't handle the forces involved with high torque levels and will break. I can't recommend that you use it for your crusher.

If it was simple to build a small crusher you'd see lots of them. This isn't a project for a builder with limited resources who must rely on 'off the shelf' parts.

Q: Or, could a PD264 motor on a pulley system moderately work on making the claw go down?I would have it set to about 86lbs with 2.5in travel. That pressure might harm some beetle tops.

A: Mark J. here: several points -

  • The PD264M gearmotor is similar to the BaneBots design. The gearbox is unlikely to survive at the advertised stall torque.

  • If the gearbox does survive, the motor will not last long at high torque levels near/at stall.

  • You've given no details about your proposed 'pulley system', but I can't envision a solution with the PD264M gearmotor that would actually provide 80+ pounds of force at the end of a reasonably deep crushing arm with reasonable speed.

  • Assuming that the above problems are delt with successfully, your chassis still has to be strong enough to survive they very high forces the weapon would place on it. Eighty pounds of force might harm your opponent, but might also split your chassis like a wishbone.

  • The only active crusher I know of is a 'Sportsman' class competitor that does not have to deal with high-speed spinners. A crusher arm would be real 'spinner bait' in open class competition.
Aaron is correct -- a crusher is not a design that should be attepted with 'off the shelf' components.
Q: What are the problems with using gears in antweight spinners?

A: Large shock loads are transmitted thru the spinner drivetrain on weapon impact. A belt drive has a much greater chance to absorb that shock without damage than does an unyielding gear drive.

Q: What aluminum would work best for a 4in by 3in by .5 in with a .25 in wall would work best for an ant egg beater?

A: I don't recommend aluminum for an eggbeater. Stress loading is very high, plus you want high material density for energy storage -- titanium or case hardened steel are preferable. If you absolutely must use aluminum, tempered 7075 alloy would be best at handling the stress loading.

Q: Hello, I'm building a ant weight fbs and I know it's not a good idea but I would like to give it a try. It's going to be 6 inches in diameter and 1.5 inches tall. I'm using a 1/8 inch lexan top plate. The part I am trying to decide is what I should use for the outer ring I would like to keep it under a half pound. The three options I found is 1/4 inch lexan 1/8 aluminum or 1/16 inch steel. What one would u suggest or do u have any better alternatives? And how much would it help to keep the spinners from getting bite is i make it a cone shape?Thanks alot I love your site!!

A: How do you plan to form the ring for your Full Body Spinner (FBS)? It's REALLY difficult to form a perfectly round and ballanced 6" ring out of flat stock. Do you have a source for 6" pipe in each of tha materials and thicknesses you list? Do you plan on machining the ring from a solid block of material? I'd suggest finding what range of material is available that meets your needs before getting any deeper into your design.

Most FBS shells are made from either aluminum (6061 alloy is popular) or 6Al-4V titanium. Avoid Lexan - it flexes on impact, which results in less energy transfer to your opponent.

A truncated cone might be a little harder for some spinners to impact, but it would be more difficult to manufacture. Find your materials first, then design around what's available and your skill level.

JuggerBot 3.0 'UpEnder' weapon. Q: Aaron, I am trying to design something like a 3lb Juggerbot 3.0 with some slight alterations. I am thinking of using servo with bent arm the will hook into the lifting wedge and act similar to how the Juggerbot 3.0 lifter worked. The point where it connects to the servo allows it to turn. I made the rear end with a flatter edge so I can bolt on a rear guard like 'Pinball'. My concerns are that the servo's drive to the flipper wedge might be able to shift to much and lose power. Thank You.

Servo powered lifting wedge illustration. A: A servo-powered beetle lifter wedge is entirely possible, although you aren't going to get the type of performance from a servo that Team JuggerBot got from their High Pressure Air (HPA) 'UpEnder' weapon. What you describe is a type of 4-bar linkage, widely used in lifters. Getting the angles and lengths of the bars correct may take considerable effort. There are diagrams and information about 4-bar linkages in the Robot Weapons archive, plus a link to the 'T.i. Combat Robotics 4-Bar simulator' that may be of use to you.

Your local hobby shop can sell you servo hardware and a threaded pushrod to make sure there is no 'shifting' in the link from servo to wedge.

Q: I forgot, I also needed to know what type of thickness would be suitable to make a rear end strong enough to cope with robots like 'One Fierce Roundhouse' or Thomas Kenney's 'Misdirected Aggresion'

A: See FAQ #17.

Q: Would it also work to have the wedge at a single flat wedge with a pivot point in the middle and use the servo arm to either push it down or pull it up like J3's original design.

A: You can put the pivot point wherever you like, but getting a large range of motion with enough force to be useful will take careful design and a high-torque servo. Don't let impact load transfer to the servo -- strong end stops on the lifter and a 'servo saver' on the output shaft are mandatory.

Lego pneumatic components. Q: Hi Aaron, I was wondering if these parts would work for a antweight pneumatic system
  • Lego Ram ports drilled to 2mm
  • Technobots tubing
  • Lego air tanks (2)
  • 4mm 3/2 poly tube NC roller lever valve [broken link removed]
  • Lego pump(to refill tanks)
Would that work?

A: I'm confused by the operating diagram published for that valve page. It claims to be a 3 port 2 way valve, but the drawings show only 2 ports and the flow schematic is unlabeled and uses non-standard symbols.

If your design calls for powered extension and retraction, you would need two 3 port 2 way valves or a single 5 port 3 way valve. How do you plan to operate the valve -- with a servo? Why did you choose a valve actuated by a roller lever?

We have discussed Lego pneumatic components previously in this archive. I can't guess at how quickly the ram might actuate. The flow coefficient (CV) of the valve is small (0.055) so I don't think you're going to get 'flipper' speed. If you do, the Lego ram probably isn't up to handling that type of loading. You can always try it and find out.

I'm going to label this idea 'Not Combat Ready' - experiment at your own risk.

Q: Could I use half a soup can for my beetles rollover top armor?

A: Getting a passive rollover system to work is more difficult than bolting half a soup can to the top of your 'bot. The only stable position available to the robot as it rolls has to be 'back on it's wheels'. This takes some thought and experimentation.

Q: Is there a way to use a servo to lift straight up or will i have to use a linear actuator?It's for an ant weight.

A: That depends on exactly how 'straight up' it has to be. If you'll settle for 'kinda straight up and a little forward' I can recommend a 4-bar lifter with one bar powered by the servo. This is diagramed in a previous post in this archive: search for "How do you implement a four bar lifter for an antweight using a servo?"

If it really has to be 'straight up' there is a conversion kit to change specific Futaba servos to linear output: E-Clec-Tech.

Q: Is it true that antweight robots have to be able to fit in a 4 [inch] by 4 [inch] by 4 [inch] cube?

A: Previously answered in this archive. The 4" cube rule applies only to the 150 gram antweight class in the United Kingdom. None of the RFL combat weight classes in the US have specific size limits; if it fits thru the arena door it's good.

Q: How do I add drop skirts to my antweight robot.I plan to mount them to the sides of an Interia Labs chassis.

A: Drop skirts have to be mounted securely, yet be free to hinge downward to remain in contact with the arena surface. Large robots require strong mechanical hinges to hold drop skirts in place, but insect class robots can often attach the skirts with a full-length strip of tough 'hinge tape' used for model aircraft control surfaces. Check with your local hobby shop. Do not be tempted to use duct tape - please.

Q: How do people make antweight flippers if there aren't any pneumatic systems small enough for them?

A: Inertia Labs used to make antweight pneumatic components. Some builders are lucky enough to still have these components in their parts drawer. Some builders are experienced enough machinists to make their own pneumatic components. A few builders are innovative enough to adapt components originally intended for other purposes. Building an antweight pneumatic flipper is a difficult task reserved for advanced builders.

Q: Could I use a beyblade metal fusion wheel as a spinning disk or flywheel for an ant or beetle?

A: I wouldn't. The Beyblade appears to be cast from a soft, weak, and brittle 'pot metal' zinc alloy. It would be poorly suited to spinning up to a couple thousand RPM and crashing into hardened tool steel, aircraft aluminum, or tempered titanium.

Q: Hi Aaron, how do I make a wedge for my robot? It's a ant. Thank you.

A: A simple wedge is just a rectangular piece of strong material mounted securely to the front of your robot at an angle. There are many posts in this archive that discuss wedge materials, construction, and mounting.

Q: Hi Aaron, I was wondering how to mount my 30:1 Copal gearmotors? I have the mounts, could I superglue them down, or should I try and drill the down?

A: Mark J. here: I know it says in the description for the Lexan Copal motor mounts that you can "hold in place with your choice of adhesive", but we have rules about mounting motors at Team Run Amok:




Unless you plan to chemically weld the mounts to a chassis of the same material I'd very strongly advise you to drill holes up thru the chassis, tap the motor mounts, and secure with suitable screws. You shouldn't take chances with critical items like mounts.

Q: Hi Aaron, what kind of chassis would you need for a antweight? A stick frame?

A: Take a look at some antweights. You'll see all kinds of chassis: stick, platform, box, tray, perimeter, you name it. Anything goes with insect class 'bots. Proper design, materials selection and construction technique are more important than style.

Q: Hi Aaron, I was wondering if 4 COPAL 30:1 Gearmotors would work for an antweight? Would it have enough speed and torque? Just wondering.

A: There have been a great many antweights powered by two Copal gearmotors, so four is more than enough power. Speed and torque will depend on tire diameter and voltage. I suggest examining those possibilities with the Team Tentacle Torque & Amp-Hour Calculator.

Example: an ant with four 30:1 Copals and 2.25" wheels at 11.1 volts has a top speed of 3.8 MPH that is reached in less than two feet in under half a second. Current drain per motor at maximum push is only 0.33 amp. Sounds pretty good to me.

Q: would the vex robotics pneumatics work for an antweight robot

A: I'm gonna say no. The air tank weighs eleven ounces all by itself - too heavy to use in an antweight. Worse, the connector plugs for the solenoid air valves are compatable only with the VEX radio system receiver, which does not have the failsafe capacity required for an active weapon like a flipper.

Q: What Is your favorite ant weight esc? What Is your favorite 1lber Drive motor? I notice that alot of people like the banebots 3-9 and the finger tech tiny esc.

A: Horses for courses. Different designs have different space requirements and call for very different performance factors from the drivetrain. Also, we make it a point at Ask Aaron to avoid general endorsement of any commercial product. We aren't comfortable labeling any product as our 'favorite', although we will recommend specific products for specific applications.

We haven't used either the BB-3-9 or the tinyESC and cannot directly comment on their performance.

Q: Hi I'm building a beetle weight with 4 wheel drive powered by 2 motors with belts and pulleys and slave shafts. It's going to be a wedge so I need pushing power also I'm trying to design a fly wheel for the top or maybe a lifting arm, I don't have any questions about that part.

I have been jumping from brushed to brushless with the design over and over. I found options either way for brushed or brushless. brushless esc 'ezrun-25a-l-brushless-esc-for-rc-car'. Brushed esc most likely the sabertooth 12, mabey the scorpion or robo claw or for the cheap way out on the brushed esc, 4 hobby king esc's

I need a motor with a 3mm shaft either brushed or brushless with alot of pushing power and speed. for brushess a motor like the hobbypartzm 96m05, or for brushed a motor like this Mabuchi RS-380SH-4045 7.2VDC Motor. the mabuchi probly wouldn't work because the shaft is a little big and I'm not sure how much power it would have being under $3. Maybe you know of a better motor with a 3mm shaft?

I'm looking for an expert opinion on this someone with more experience on this subject. Thanks.

List Of Part's I Already Have
6x BaneBots Wheel, 1-7/8" x 0.4", 1/2" Hex Mount, 30A, Black/Green
4x Hub, Hex, Series 40, Set Screw, 3mm Bore, 1 Wide
2x Hub, Hex, Series 40, Set Screw, 3mm Bore, 2 Wide
4x 16mm Slave Shaft Kit 1.5 inch long 3mm shaft
half inch aluminum angle (to go around the polycarbonate)
sheet of polycarbonate (for the chassis)
big roll of aluminum flashing (for armor, also might add a sheet under the polycarbonate)
Spektrum DX7 remote

A: See FAQ #23 for an explanation of the difference between brushed and brushless motors and a short discussion of correct use of each type in combat robots. Many additional posts on this topic are in the Motors & Controllers archive. We contend that brushless motors are not suitable for combat robot drivetrains. Available hobby brushless motors just aren't designed for the demands placed on them when pushing around a combat robot. Neither are hobby ESCs designed for use in cars or airplanes - for brushed or brushless motors. I strongly recommend that you stick with combat proven components.

You're going to need more gear reduction than a single-stage belt system will provide. The Team Tentacle Torque & Amp-Hour Calculator can model your drivetrain and help you determine the gearing needed for those 1-7/8" wheels. The simple way to handle gear reduction is a strong planetary gearbox for the motor.

You don't need massive power in order to get maximum pushing force from your 'bot. Pushing power is limited by the weight on the driven wheels; in your case, that's the full three pounds of the robot weight. Power in excess of what is needed to spin the tires freely will simply be wasted. As for speed, the realistic maximum speed depends on the size of the arena and the skill/preference of the operator. Anything much over 5 MPH in an insect-sized arena is unuseable.

I'd suggest a pair of BaneBots 28mm RS-385 16:1 gearmotors [now discontinued] direct-driving wheels (6mm hub) with timing belts running to the other end of the robot for your 4-wheel drive. Top speed with 1.75" wheels is 5+ MPH and the motors have about 8 times the torque needed to spin the wheels with the robot pushing an imoveable object. More power than that is wild overkill. Maximum amperage draw at full push is less than 3 amps (per the Tentacle calculator), so a single Sabertooth 5 RC Dual Motor Speed Controller should handle the controlling work for both motors nicely.

By the way, the aluminum angle and flashing you buy at the hardware store is a very soft alloy intended to be easily bent and machined. It makes really lousy armor. The polycarbonate by itself is much better.

Q: I'm trying to find a way to use the pulley system instead of the gear motors. I found an RS-380 motor and I could run it with the sabertooth 12 [ESC] and Fingertech pulleys. I'm thinking a 15 tooth on the motor and a 42 tooth on the slave shafts. Do you see any chance of this setup working? Do you think the pushing power be low?

A: Several problems with your proposed setup:

  1. The fingertech timing pulleys and belts are too narrow to reliably handle the amount of torque that this drivetrain can produce. They will skip and slip when pushing and you will have real trouble keeping the belts on the pulleys. If you do pop off a main drive belt, you're sunk.

  2. A speed reduction of 2.8:1 (32:15) with 1.75" wheels is not nearly enough to provide optimum acceleration, amperage consuption, and speed in a small arena. Optimum gearing would be around 10:1 which, as noted in the answer above, cannot be done with a compact single-stage belt drive.

  3. Maximum amperage consumption when pushing with the proposed motor, gearing, and wheels comes in at about 14 amps (per the Tentacle Calculator) which exceeds the published capacity of the Sabertooth 12 ESC. With a 10:1 gear reduction the maximum amperage consumption drops down below 4 amps.
There are good reasons why builders use gearmotors instead of belts and pulleys for the primary drives in combat robots. I'd suggest that you consider these reasons carefully before proceding with your planned design.
Q: What are the best motors for a 2-wheel drive Beetleweight wedgebot?

A: The 'best' motors will depend on the arena size, wheel diameter, how exposed the wheels are, and your driving style. The balance between speed, control, and power is largely a personal choice.

The Team Tentacle Torque & Amp-Hour Calculator can provide performance estimates for a wide variety of motors and wheel diameters in arenas of any size, and provides a peak amperage estimate to help in selecting a speed controller. A pair of BaneBots 16:1 24mm gearmotors [now discontinued] might be a good place to start your search.

Beetleweight hammerbot Q: Based on the photo, do you think my beetleweight will be able to win a match? If so, yay! If not, explain why not. In particular, I am wondering how effective the hammer will be.

The drive is two banebot 16:1 motors. Armor is 2025 aluminum side plates that are .25'' thick, and top and bottom armor that is .1" thick. Two more banebot 16:1 motors power a hammer. The hammer can put a small punch mark in steel, a larger one in softer metals, and can crack the copal lexan motor mounts.

A: If I could tell which gelding was going to win a race by looking at pictures of horses, I'd be a very rich man. A few comments:

  • A hammer that can't hit its target is not of much use, no matter how powerful. Is the 'bot maneuverable enough to hit a fast moving target? Is your driving that good?

  • A good spinner is going to have a field day with those exposed hard edges.

  • A good wedge will be under you and have you hammering air all the way into the nearest wall.

  • You seem to have placed you 'top' armor 'underneath' your weapon motors and drive. That could be a problem.

  • How about some protection for the exposed wires and a cover for that switch?
Overall, I'd say the outlook isn't great. I can't think of a single successful beetleweight hammerbot.

Q: What should I do about the issues you brought forward?

A: It's kinda too late to do much about the major design concept of your 'bot after you built it. You could add a little light protection to cover the exposed weapon bits and at least keep stray junk from jamming the open gears or tearing away your wiring. Even a thin sheet of flexible plastic would be helpful. I'm guessing you don't have much weight allowance left - probably not enough to build shields for your exposed wheels - but maybe enough to add a small wedge to the front of the 'bot?

Q: Well, should I even bother entering it in a competition? All I want is a single win. It doesn't matter if it loses all the other matches. One win is all I need.

A: Absolutely you should enter! Like I said, I can't predict winners from photos, and I haven't seen your competition. Winning is all well and good, but the satisfaction comes from building and competing. Practice your driving skills, run the 'bot into stuff to see what breaks, replace the broken pieces with something stronger, then get out there and fight!

Q: How do you make a wedge?

A: In your case, I'd just extend the bottom armor plate forward a couple inches and hone it to a sharp edge. Your opponent will run up the wedge into your front armor and be in perfect position for the hammer.

Q: Thanks Aaron! After listening to the input of both you and other builders, I think I have a good "shopping list" of modifications I can make. Fortunately, there are actually quite a few areas to cut down weight.

The main reason I built a hammer in the first place was that I decided it was more important to be unique than it was to be destructive. Diversity is a good thing, and I will be a sacrifice in its name.

It also helped when I noticed the thin, plastic top armor many beetles have.

A: Diversity is a good thing.

Precision control is going to be critical if you're going to make best use of the hammer weapon. Tweak your radio settings until the response feels natural to you. Consider reducing the maximum turn rate (via 'ATV' or 'travel adjust') to retain precise control in hectic combat situations. And of course, put in a lot of driving practice.

Remember that scoring is on both damage and aggression: keep pointed at your opponent and keep moving forward for maximum aggression points.

Q: Aaron, do you know where I can get a Beetlewight spinning disk? and can the VDD gearbox and blades work anyway?

A: Spinning disks are generally made, not purchased. You might find something at the hardware store that could be adapted, but I don't know what type of design you're thinking about.

A beetleweight blade is available to fit the VDD gearbox -- it requires a hub adaptor. The VDD gearbox has a good record in antweight robots, but I would prefer a belt drive for beetleweights and heavier classes.

Q: What kind of a servo would you recommend for a beetleweight lifter?

A: There is ample discussion on insect class lifter servo selection in this archive.

Q: Do beetleweights need stick frames? If so, will screws be enough to create a sturdy one?

A: Most beetleweights do not have a separate frame structure, and certainly don't require one. With proper material selection and construction technique a sturdy 'stick' chassis can be built using mechanical fasteners -- triangulate everything and/or gusset the corners.

Q: Hi Aaron, I am planning on building an antweight full body spinner. I will direct drive a brushless outrunner to the shell. Basically, I'm looking for a motor with lots of torque, but not too high of a kv. Using the formula to find the N-m of brushless motors I have found that the Hacker A20-26M looks to be the best outrunner for my purposes. What would you recommend?

A: For a start, I don't recommend direct drive for a spinner weapon. The design places too much stress on the small motor shaft and gives too high a spin rate for the shell. The design is simple and tempting, but it just has too many drawbacks to be reliable. There have been many direct drive spinners tried, but you will not find them near the top of the rankings at

About the motor: I really can't make a good recommendation for a specific motor without knowing the explicit design details of the weapon shell and drive -- see FAQ #29. I'm going to suggest that you put design numbers into the Team Run Amok Spinner Excel spreadsheet and see what type of performance you get from different motors. As a pure guess, the Hacker A20-50S might be a better choice. It's a smaller motor with less torque, but its less aggressive power consumption will make a more reliable weapon.

Q: Do you have any suggestions on how to build a beetleweight dome spinner on limited resources (no titanium, budget of $200)?

A: Radio included?? A decent radio for an active weapon beetle is going to eat up 60% of your budget. You really can't go cheap on your R/C gear -- see the previous post on the Exceed radio. A speed controller for your drive and weapon is going to eat up the rest of that budget. Even if you use a hacked toy for the chassis and a steel salad bowl for the dome, you're still in need of a weapon drive. We've said this before: you'll get a much better result if you design a robot you can afford to build from good components rather than a larger or more complex 'bot that will be cobbled from make-do materials. My suggestion is to build something you can afford to build well.

I know you didn't ask for an opinion on an insect-class full-body spinner (FBS), but for the benefit of others reading this I have to mention that they don't work well in small insect arenas. An FBS needs spin-up time that you just don't have in a small arena. You've got no place to hide and no way to shield your weapon to get those critical seconds you need. If you do survive long enough to get a hit in, the rebound can send you bouncing off multiple arena walls. Not recommended.

Q: Would it be logical to build a thwackbot beetle? I have been thinking about this idea, but does it count as an active weapon?

A: Twackbots are not big favorites of judges. It's very difficult to show 'aggression' since you can't move toward your opponent while spinning, and aggression is a big part of the current scoring system. See multiple posts on thwackbots and 'melty brain' in the Design & Construction archive. A thwackbot is not considered to be an active weapon.

Team Velocity did compete with a successful thwackbeetle named 'Trilocity'.

Q: Thanks for the info on thwackbots, but I noticed my bot does tend to move while spinning. Does this mean that if I positioned it right it would move towards the target getting aggression points?

A: I think a little experimentation will show that your spinning 'drift' tends to be downhill along a imperceptable slope. Your motion will vary according to the arena and judges will not be impressed by an uncontrolled drift. If your opponent is dense enough to sit still and wait for your 'bot to drift in the right direction, they deserve to lose.

Q: Would I get aggression points if I put a spike on the end of the weapon and used it as a ram?

A: Yes. You'd also get your head handed to you by a robot with a real weapon.

You don't actually even need the spike. 'Agression' is scored simply by moving toward your opponent. See our You Be the Judge page for some other surprizes about combat robot judging.

Q: I'm building an antweight wedge/pushy bot It will be .05 7075 aluminum on a frame made of either .125 stainless 316 or .25 6061 aluminum. Which would be better? The wege goes about 6 mph.

A: See FAQ #17.

I can tell you that stainless steel alloys are designed for corrosion resistance and high temperature stability -- not for structural strength. There are much better materials for combat robot purposes. I'd go with the 6061 aluminum.

Q: Would kevlar wrapped around lexon plastic make a good composite armor for an antweight? Otherwise, would kevlar streched over a sturdy metal frame work?

A: As discussed in the Materials & Components archive, the materials used to form composite armor must be carefully selected to compliment each other's properties. Stacking random materials together in hope that they become stronger than either of the individual materials has a very small chance of success.

Lexan makes excellent armor because of its ability to flex and absorb large amounts of energy without permanent deformation. Kevlar fabric has great tensile strength -- a property not greatly valued in robot armor. As a flexible fabric, the material would transfer impact to the framework supporting it rather than absorbing the energy itself. It could also be prone to being 'caught' by a spinning weapon -- not a good thing! I don't see any synergy in combining the two materials, or much benefit in using Kevlar alone for robot armor.

Q: Could .018 [inch thick] T304 steel be used as antweight armor? well supported.

A: T-304 stainless steel is not a top choice for armor. Although it has good 'toughness', it is also quite ductile and will show damage easily. Since any sign of damage scores points for your opponent, I wouldn't recommend it at any thickness.

Q: How fast does a servo lifter need to move to [flip] an antweight 6" up [into the air]?

A: Mark J. here: a classic physics problem! Here's the formula:

Maximum Altitude = Initial Vertical Speed2 / 2g

You can cheat and use the calculator at the HyperPhysics Trajectory webpage. It turns out that an object going straight up at just over 12 feet per second (about 8 MPH) will rise 6 inches before falling back.

Converting that to the type of speed figures given for servos: you'd need a servo that could travel 60 degrees in 0.04 seconds while accelerating a one-pound load vertically at the end of a 3 inch lifter arm. *** There is no such servo! *** Servos simply aren't fast/powerful enough to 'launch' an antweight. They are useable as lifters, not flippers.
Chart of servo speed versus load
Q: Although it may not flip an antweight 6 inches, the Hitec HS-7940TH Servo has good torque and a blazing fast speed. Could you use this servo to "flip" the other antweight robot? Does the length of the arm change the amount of speed a servo could deliver? Couldn't you use a 4 bar linkage to double the speed, while reducing half of the already large torque rating?

A: Power is calculated as the product of speed and torque: you can't gain power by playing with linkages, arm length, or gearing.

That 'blazing fast speed' is at zero load. When you load a servo to half its maximum torque, the transit time doubles -- cutting the speed in half. Using a linkage to increase the zero-load speed will give an equal increase in torque needed under load, resulting in a nullifying speed reduction.

The Hitec HS-7940TH could accelerate a one-pound weight vertically at the end of a 3 inch arm thru 60 degrees of arc in about 0.18 seconds. That's very quick for a servo, but a long way from flipper speed.

Q: Can I run a 3" bar weighing 2 oz directly off a speed 400 motor? Spin-up time is not a problem except over 8 seconds. It will be for a verticle antweight spinner, but the spinner is facing directly off the bot. Like a horzontal flipped on it's side.

A: Read thru the Robot Weapons archive for a full explanation of why direct drive bites. Briefly:

  • Attaching that heavy bar to the small diameter shaft of the Speed 400 is a real problem;

  • The first good hit you get will very likely bend the motor shaft and render the weapon useless;

  • A bar spinning at 15000 plus RPM will have VERY little 'bite'.
The Team Run Amok Spinner Excel spreadsheet can calculate spin-up time and stored energy for your weapon -- a 7.2 volt Speed 400 has about 0.04 N-m stall torque and 16,000 RPM -- but there is much more to good weapon design than getting the thing to spin.
Q: Where can I find Titanium or alluminum in a disk shape? Small like diameter of 3"

A: That's something you're likely going to have to make for yourself or have made for you. I'm sure that Team Whyachi's Bot Shop would be happy to make a disk to your specifications. Depending on the thickness you need, you might find something useful by tearing apart an old computer hard disk drive.

Q: Disk guy, how about a disk made of carbon fiber? Otherwise how thick should a antweight spinner disk be( at 3") Just a rough estimate.

A: No! Carbon fiber is light, stiff, and strong -- but it isn't 'tough'. It shatters under heavy impact, exactly NOT what you want your disk weapon to do.

No competent engineer would spec a material thickness knowing so little about the design -- see FAQ #17. I don't know how fast you're going to spin it, what additional weight will be added for 'impactors', which alloy you will use, or how strong the hub will be. Therefore, I absolutely cannot tell you to make it roughly 0.125" thick.

Note that there are considerations other than strength to the design of a disk weapon. The purpose of a rotating mass weapon is to store energy for release on impact. The design of such a weapon calls for a balance between motor power and rotational inertia to store the greatest energy possible within a reasonable time period. The Team Run Amok Spinner Excel spreadsheet can assist you in evaluating these design tradeoffs.

Q: How would I go about making an antweight overhead hammer? As in what power source.

A: The first question is why you would want to build an antweight overhead hammer. An overhead hammer is one of those things that does not 'scale' well -- search the [DESIGN] archive for the previous post on 'scale'. Worse, overhead axes aren't all that successful at any size. I'd strongly suggest another weapon design.

Search this archive for 'pneumatic' to find a great many previous posts on antweight pneumatic parts sources. The short answer is 'there aren't any'. You'd pretty much have to build or modify your own actuator and valve system.

Q: Do you know where I can get a pneumatic acutator suitable for antweight use?

A: Search this archive for 'pneumatic' to find a great many previous posts on antweight pneumatic parts sources. The short answer is 'there aren't any'. You'd pretty much have to build or modify your own actuator and valve system.

Q: Couldn't you use Robart valves and pistons for an antweight flipper? Would this give enough airflow to be able to flip well? I have all the parts but am curious to see what you think. I also believe that Go Flip Yourself uses these parts too.

A: I've been asked about Robart pneumatic components previously -- search this archive. The ports on the Robart valves and cylinders are really small. They're built for realistic slow-motion actuation of landing gear and such on scale aircraft, not for speed and power. If Cutting Edge Robotics is using them on 'Go Flip Yourself' I suspect they have been modified extensively for better air flow.

Q: Hi I'm the overhead axe guy. Im switching to a lifter. I'm using the Spektrum A6030 Digital Aircraft Servo. Its an antweight with a 3 inch arm.

A: Very nice servo, but overkill for your application. With a 3" arm on an antweight you won't have any real use for more than 100 oz-in of torque -- the A6030 pumps out 278 oz-in and has a price tag of about $85. The Spektrum A6020 Digital servo is $40 less and still gives 146 oz-in. Yes, the A6030 has titanium gears, but I don't think you'll need those any more than you need the extra torque.

It certainly won't hurt to go for the high-end servo, but in this case I think I'd save a few bucks and opt for 'plenty good enough'.

Q: Servo lifter guy (again) I forgot to tell you that in the near future I will be putting it to use as a cluster bot vs beetle weights. Sorry.

A: In that case, great servo choice!

Q: I'm building an antweight lifter using carbon fiber for the top and bottom plates. (sort of like Shaz-bot) The side wall is made out of .25" UHMW. I'm looking at .041" CF for the top and bottom. Will this be sufficent? Do I need larger or smaller? Thank you.

A: We get a lot of questions asking how thick the material should be for a specific robot part. The required strength for a specific chassis element will depend on the size, shape, mounting method, additional stresses placed on the chassis by your lifter, and exposure to abuse from opponent weaponry. No competent engineer would spec a material thickness knowing so little about the design -- see FAQ #17.

With that said, I can tell you that you're in the right ballpark for your CF thickness. I commonly see antweight top/bottom plate thickness in the 0.03 to 0.09 inch thickness range. If it fails, make it thicker.

Q: hey i wanna make a full body spining ant like super megabyte. how do i get it to spin while having a stick come from the top of it?

A: That 'stick' that emerges from the top of Megabyte is an extension of the 'dead shaft' axle that the shell spins on. Such a design in an antweight would require an offset belt, friction, or gear drive to spin the shell -- not a direct-drive from a motor, as is common with antweight shell spinners.

Q: How can i make an antweight spinning robot like desire or MBY? Desire and MBY are robots that competed at AWS so why is Desire or MBY a walking robot?

A: Sorry - I don't follow the UK Antweight World Series competitions, don't know either of those robots, and can't find them on the web. I do know that 'walker' rules are very different in the US and UK.

Q: Would the Electrifly 280 motor with a 4.1:1 or 5:1 gearbox work well for an antweight weapon motor in general to direct drive a disc? Which motor would you recommend, the T280 or the S280? I couldn't find the specs on any of the motors, but my design would be similar to the original ''Ultra Havoc'.

I am leaning toward the T280 motor, but I'm not too sure about the gearbox reduction. What is your opinion?

A: You may have noticed that few spinners use a model aircraft gearbox. There's a good reason for that: the abrupt stress of weapon impact destroys them. I assume that is why 'Ultra Havoc' abandoned the gearbox for their 'latest version' -- A belt drive absorbs shock much better.

Motors without specs are a problem -- everything you do with them is a guess. You'll end up doing a lot of experimenting, which can be both expensive and time consuming. If you want to try one of the motors you mention, the T-280 is the more powerful of the two. Gearing is dependent on your blade diameter and weight, but 5:1 is a reasonable starting point for a 3" blade. I'd much rather start with something that has specs!

Q: Hi, Aaron. I'm in the process of building a new Beetle and I'm in need of parts. It's going to be a 4-motor driven wedge/rambot and I wanted to know what motors/speed controller would you reccomend for it?

A: You must not be very far along in the process if you're just getting to motor selection. Proper motor selection depends on other design and use factors like arena size, wheel diameter, chassis layout, and performance expectations. See FAQ #21. The BaneBots 25mm 10:1 FF-180 gearmotors might be a good starting point. A single Sabertooth 5 RC Speed Controller could handle four of these motors driving 2" diameter wheels.

Q: What would be a better weapon motor in general for an antweight: I have built a couple robots before and was wondering which one has the most power? I think I am probably going to go with brushless as they have better power to weight ratio and are more efficient.

A: Mark J. here: there is more to being a good weapon motor than power. A weapon motor must be reliable and must have enough information available to allow the needed weapon calculations. Without a full set of motor specifications you're just guessing.

As is typical for inexpensive Chinese brushless motors, the motors you reference come without the specifications needed to calculate their output power. If the specifications did exist, there would still be the question of their reliability in combat. The motors are made for model aircaft -- an application which places much different stress on the motor than spinning a robot weapon. My recommendation is to use a motor that has a proven track record in robot combat -- so, of the motors you list, I'd have to go with the Speed 300.

Q: Okay, you would suggest the Speed 300 brushed motor. But how come most insect builders use Hobby King brushless motors now? For example, team Twisted Sick Robotics uses Turnigy brushless outrunners with good results. Also, what about the Axi's? Because the Axi's are so expensive compared to the Hobby King motors, would it be a better idea to use the AXI 2208/34 SILVER LINE? What is the difference between the gold line and the silver line, besides having slightly lower specs?

A: The Hobby King motors are false economy, IMHO. Insect builders think they're saving money, but the experimentation and failures are not worth the few dollars saved. Twisted Sick Robotics had poor results from their first experiments with the Turnigy motors. They stuck with them and learned how to best use the Turnigy, but I suspect they would have been better off to have started with a proven motor. Do yourself a favor and save yourself the frustration.

The Axi "silver line" motors are the same design as the 'gold series' but have less expensive magnets which results in somewhat lower performance and efficiency. I would much rather use a silver line Axi than a chinese knockoffs because the Axi comes with accurate specs so you know what you're getting, but if it were me I'd go for the best I could buy. We've said this often: 'Cheap' and 'Combat Robot' don't go together. You'll kick yourself when that cheap motor fails and knocks you out of a tournament.

Q: Hi, one last question. Would it be a better idea to use an Axi 2208/20 gold series motor and gear it down by around 5:1 to spin my sawblade, or use the 2208/34 gold series and gear it down 3:1? I would be running it at 11.1 volts. It seems like the 2208/20 uses more amps and has a higher current capacity than the 2208/34, so which one would have a higher starting torque with the given geardowns?

A: The Axi 2208/20 has both more torque and more speed than the Axi 2208/34 at the same voltage -- even if geared the same the /20 would provide greater starting torque than the /34. I would suggest using the Team Run Amok Spinner Excel spreadsheet to examine weapon parameters and to select optimum gearing and blade dimensions for a given motor and voltage.

Q: Can you suggest a cheap (under $20), neutrally timed speed 300/280 motor that turns at least 20,000 rpm at 7.4V?

A: Mark J. here: you aren't interested in torque or power consumption? The Speed 280 and 300 motors are generally used for model aircraft or combat robot weapons where neutral timing is not required. I don't believe that any of the Speed 300 motors are neutrally timed, and the one Speed 280 motor that I know of that has neutral timing does not meet your speed requirement. If I knew what you plan to use the motor for I could be more helpful.

Background for readers: motor timing relates to the alignment of the commutator and brushes to the magnetic field of the motor. A neutrally timed motor will operate in either direction with equal speed and efficiency. A motor with 'advanced' timing will gain speed and efficiency in one direction and sacrifice both in the other.

Q: I am looking to replace the stock motors on the B-16 gearmotors with something more powerful and since I plan on using ~1.5" wheels, I need a motor that has pretty high rpm in order to have decent speed.

A: For wheels that small I think it would be both easier and better to switch to a different gearmotor. Consider the BaneBots 9:1 24mm RS-370. With 1.5" wheels at 7.4 volts, a pair will give about 8 MPH top speed and break the wheels loose when pushing at just over 3 amps apiece.

Q: why is the robot meteroid 2nd place ant so efective? its drum can't produce that much energy because it's diameter is not very big, can it? thanks

A: We've said this before: the weapon is perhaps the least important system on a combat robot. Drivetrain, radio set-up, general construction practice, and balance are all much more important. Too much emphasis on the weapon will result in a poor robot. Antweight 'Metroid' has a weapon well balanced with the rest of the design.

Q: Can you have an antweight that have only 2 drive wheels and 2 free rolling wheels that is effective?

A: Most of the top ranked antweights at are two-wheel drive, but they all have a skid or castor rather than a second set of unpowered wheels. Trying to drag unpowered rubber tires sideways to turn will severely limit the maneuverability of a robot. A two-wheel drive robot may not have the pushing power of a four-wheel drive machine, but if you've got a big weapon you don't need pushing power.

Q: Would the Pololu TReX Jr Dual Motor Controller be a suitable ESC for insect class robots? Would it be something comparable to the Barello Ant 100?

A: I have not used the Pololu TRex Jr ESC but specifications are quite similar to the discontinued Barello Ant 150 -- both have a third channel for weapon control that the Ant 100 lacked. It appears to be suitable for insect class robots.

Somebody out there must be using one -- write in a review.

Q: Hi, which design do you think is better for an antweight lifter using the Inertia Labs Chassis: [a small servo driven finger as on] Warpig (video), or [a wider blade able to rotate 360 degrees around the robot body like] Wizard Beard (video)?

Which design would you rather have?

A: The servo-powered lifter on 'Warpig' is simple to build, easy to drive, and reasonably effective. I would recommend that design for builders new to building and driving lifters.

Personally, I would rather have a design like 'Wizard Beard'. Their lifter wedge itself could use a makeover into something more like the scoop on Team Nightmare's 'Breaker Box' to avoid being such spinner bait, but the flexibility of lifter action makes for a versatile and tenacious robot.

Q: If you made a much wider tip on the lifter of Warpig, would it increase its effectiveness?

A: A wider tip would change the characteristics of the lifter, but I can't gaurantee that it would be more effective. A narrow tip can follow the contour of the arena floor more closely and may be better at getting under low wedges, while a wide tip might offer more lifting opportunity and less chance of the opponent slipping off. Changing to a 4-bar lifter might be the best option.

Q: Why can the beetleweight 'Sting' spin its drum at over 30,000 rpm and still get decent bite? I thought you said that anything spinning real fast would just skitter along the surface of the other robot?

A: Mark J. here: the greater the spin speed of a rotary weapon, the faster it must approach the target in order to get a chunk of the opponent deep enough into the weapon for good 'bite'. The only video I've seen of 'Sting' has a single 'weapon-to-weapon' impact against an eggbeater. The relative closing rate between Sting's drum and the opponent's spinning eggbeater would be very fast, which would allow enough bite for a powerful impact. This is a special case.

If you listen carefully to the video you can hear the weapon speed on 'Sting' change throughout the fight. I assume the operator knows that hitting an armor panel at full speed would not be effective and he is moderating weapon speed to match the target opportunity.

Q: what type of ant weight spinners do you think are most successful drums, vertical spinners horazontal spinners or egg beaters I know that drums store the most energy, but horazontal spinners cause the most damage. I have built 2 wedges and a vertical bar so I am some what of experienced builder and ready to take a step up which one should I build?

A: The experience of the builder is more important than the type of weapon. If you keep jumping to new designs you will constantly be in new territory and will have to make new mistakes to learn from. Stick with what you know. Take a good look at your most recent design, evaluate its strengths and weaknesses, and design an improved version.

Q: Do you know of any insect robots that use the torxis ultra high torque servo? Do you believe that with an extremely sharp tip, a piercer arm could go through normal insect tops using this servo? I know you say its basically impossible, but the torxis servo is pretty cheap, doesn't weigh very much, and has massive torque!

A: Doesn't weigh very much? Pretty cheap? Are we talking about the same servo? The only Torxis Ultra Torque servo I know of weighs almost two and a half pounds and costs almost $300. It is horribly slow and will deliver only about 25 pounds of force at the end of a 4" long arm attached to the output wheel. Try pushing a sharp nail thru 1/8" Lexan with 25 pounds of force - not gonna happen.

Q: What do you think of the fleaweight Anticide? I'm shocked to see how much power the builder packed in 150 grams! Do you think it would be competitive in the US fleaweights? Also, is this more powerful than the other fleaweight [flipper] you pointed out, the one using syringes and some other stuff as part of its flipper?

A: The UK 150-gram antweight 'Anticide' is beatifully designed, superbly made, and tremendously effective. I don't have a way to directly compare it to Chris Sherwood's 150-gram flipper so I can't comment on which is more powerful, but both are powerful enough to be effective.

The 150-gram class in the US is neither as well supported or competitive as it is in the UK. Top 150-gram UK robots would rule at US events.

Q: Is it possible to create a 4 part antweight clusterbot?

A: Why not? Nanoweight 'bots are 50 grams apiece -- you could have nine of them cooperate as a one pound (454 gram) antweight. I'm not saying it would be a good idea.

Q: Hi, I am currently using a cheap Towerpro sg90 servo for my antweight's flipper, but I want to switch to a stronger/faster servo. What would be the best choice in your opinion? Is the Hitec HS-81 a good choice? Thanks!

A: I would be a poor designer to recommend a servo knowing so little about your lifter design.

Q: could I mount a door hinge on to the front of my bot as a hinged wedge?

A: I'll assume we're talking antweight here? Sure, why not. Trim away excess material and file the leading edge down flush with the floor. Put in a stop to keep it from folding back under and lifting the front of your 'bot.

Q: about my door hinge question, could that be used on a beetleweight? I'm thinking about getting the tonka flip over racer to turn ito a hackbot.

A: Would that be the Tonka 'Bounce Back' racer you're planning on using? Do you know that it only goes forward and backward -- it does not turn? I'd pick something else to hack.

A door hinge would be pretty small for a beetle wedge, and I'm not sure how you're planning on mounting it securely on an invertible hackbot.

Q: I am building an ant with a 3.5 oz. Drum using two speed 300 motors what should I gear them at? I was thinking 2:1, 3:1 or 4:1. What timing belts pulleys should I use?

A: Mark J. here: calculation of best gear reduction requires more information than you're giving me. Gearing is dependent on the rotational inertia of the drum design as well as the weight. See the previous post on this topic in the weapons archive for information on how to calculate best gear ratio and spin-up time.

I ran some approximate calculations assuming a 1.5" diameter aluminum drum 3" long weighing 3.5 ounces. A 2:1 drive ratio gives a spin-up time to 30 Joules in 0.5 second. I'd go with that. A significantly larger drum should be geared lower.

The small 2mm shaft diameter of the Speed 300 motor is a problem when selecting pulleys. The smallest available timing belt pulleys and belts I know of are for 3mm diameter shafts. You'll need to shim your motor shafts out to the required size. Brushless outrunner motors have larger shafts, which is one reason for their popularity as weapon motors.

Q: Aaron, what kind of system can a beetleweight use to make the lifting forks like Vlad the Impaler? And which ESC?

A: High-power servos are a simple and popular choice for insect-class lifter power. See Wallop for an example.

ESC selection is dependent on more factors than just robot weight. Run your drivetrain design thru the Team Tentacle Torque & Amp-Hour Calculator to find out how many maximum amps your motors will consume, then select an ESC that can provide that many amps.

Q: Why do people use Deans Pole connectors for insect classes? Are they more reliable and effective than the JST connectors? I have a JST connector for my antweight and was wondering if it's better to replace it with a Deans connector.

A: The various Deans connectors are highly regarded in all weight classes. Teams usually have an assortment in their pit boxes. The Deans Micro Plug has become the standard in the insect classes because of its very low connection resistance, tight fit, tiny size, and high amperage rating (20 amps). The JST connector (8 amp rated) is OK. I wouldn't replace it if it was working well for me, but don't push it beyond its rating.

Q: is there a size limit for beetleweights?

A: There are no size limits for any U.S. weightclass. As long as you can fit it thru the arena door, you're good.

Q: Hi I am making my 3rd ant and I was going to make a drum using 2 speed 300 motors found at the robot marketplace, and I was wondering if a drum like MowBee's would work good. The drum with the motors in it would weigh about 6 1/2 oz. My dad's friend works at Briggs and Stratton he said he would cut the stuff for me. Do you have any other ideas that would work better than the drum like moebee's? Thanks

A: Mark J. here: if the design for the weapon on 'MowBee' was a good one, you'd see many imitators. A drum with motors wedged inside and direct-driving the assembly supported by their shafts works fairly well with outrunner brushless motors that spin at relatively low speed (~4000 RPM) with a lot of torque, but is really not suitable for high-speed (12,000 RPM) low torque brushed motors like the Speed 300. Your spin-up time would be too great for a small insect arena, and a drum spinning that fast will just skitter off the surface of an opponent rather that 'biteing in'.

Also, the shaft and bushings on the Speed 300 are too small and too weak to adequately support the forces generated by the drum weapon impact. One hit and the shaft and/or motor end plate would likely fail. A better solution would be a belt-driven drum, geared down to spin in the 3000 to 4000 RPM range. This is a much more common and successful design which will isolate the motors from impact damage and provide a much batter spin-up time.

Q: I'm on a tight budget, so would it work if instead of giving my bot tank steering, could I give it two wheels with one motor, then add a dragger so when I drive back it spins, like a cheap R/C car? I'm gonna be at HORD 2010.

A: While you're backing up in a circle, your opponent is going to be all over you. It's also possible to get stuck in a corner, unable to turn in the direction needed to free yourself. Don't even consider this design.

The insect class robots at HORD are quick and maneuverable. If you're on a really tight budget, you'll be much better off running a hacked R/C toy with tank steering. Take it apart if you like and extract the radio, controller, and drivetrain for your own chassis.

Q: Would a wood wedge or scoop work for an antweight? I'm on a small budget.

A: There are many inexpensive materials that would be far superior to wood for a wedge -- many of which can be obtained at a dollar store. See previous questions in the Materials & Components archive.

Q: Would you reccomend the "CKRC WIGGLE" Hi Torque Servo for an antweight lifter? Do you think its a good servo compared to the Hitec 645mg? Also, for servo mounts, would you go with these fancy anodized aluminum wedges or these complicated bent brackets?

A: Mark J. here: the 'CKRC WIGGLE' is a re-branded Cirrus CS704MG Servo. I've used other Cirrus servos and found them to be reliable. I have not had 'hands on' this servo, so cannot compare it directly to the Hitec 645MG. The specifications look very good and the chatter on the web about them is good -- but I don't know any robot builders using them. YPYMYTYC.

You don't neen anything fancy to mount your lifter servo - a couple of blocks of UHMW polyethylene, polycarbonate, even wood will do nicely depending on your design. Spend that money on something more critical.

Q: The tires on my antweight are kinda smooth now, and I was wondering if it would be a good idea to put a thin layer of pure silicon on them. I am using ultra light wheels sold by inertia labs. Does it matter what the tire material is like, or can you put silicon on any tire to increase traction?

A: Traction in an antweight arena is an elusive goal. Dust, oil spray, and other contaminants on the arena floor will spoil traction for any set-up, so don't expect miracles. That said, a thin layer of RTV silicone rubber applied to the tread surface can give a significant traction boost under some circumstances.

Silicone is gooey stuff to work with, and you have to work quickly and with a steady hand to get a satifactory job. If you've never worked with silicone before, practice applying a thin layer to some scrap objects before setting to work on your tires. Silicone bonds better to some materials than others, and you may get some peeling in even the best cases.

Clean the tire surfaces very well with alcohol and let dry. Apply a very thin, even layer to the tread of each tire and set aside to cure for at least 24 hours before use.

Q: Hi, I was wondering if you knew what motors the antweight "Gilbert" uses? It seems VERY fast.

A: 'Gilbert' is very quick, but I'm not sure how fast. MH Robotics does not share much info on their robots - I don't know what motors 'Gilbert' currently uses.

Q: Hi Aaron. I have an Inertia Labs chassis. I am wondering what a good weapon would be for an antweight using the chassis. I can't make a succsesful wedge, because the other antweight wedges are using much more powerful motors than then my Sanyos. I would be underpowered if I made a wedge.

I was thinking about a lifter, but I don't think it would be very effective either. Most antweights are invertable and I'm not using a 4 bar linkage so it would be hard to flip. Could you use a VDD polycarbonate gearbox kit and put a small S7 bar instead of the discs? Would that work on the inertia labs chassis? Thanks a ton.

A: Don't sell the pushing power of your Inertia labs setup short. Motor power alone does not make a good wedge. Pushing power is limited my the weight pushing down on the driven wheels and the coefficient of friction between the tires and the arena surface. Adding more power beyond the traction limit only succeeds in spinning the tires without generating additional pushing power. An all-wheel drive chassis like yours is a good bet to out-push a 2-wheel drive 'bot of equal weight with any amount of motor power.

Also don't underestimate the effectiveness of a simple lifter. Take a look at the results of our What Weapons Win research. The raw data shows that lifters had the highest win rate of any weapon. Our own beetleweight Zpatula is an electric lifter. Simple lifters are about control and opportunity, not just turning your opponent over.

Most builders want to believe that spinners are the way to win, but the numbers just don't show it. I'm sure you could get a VDD spinner gearbox working with a steel bar weapon, but it might not produce the results you're looking for.

Robot Dojo's Holy-Moly robot Q: I have 7.55 oz left for a scoop on my antweight. I want to go with 6AL-4V titanium. How should I mount it, how thick should it be, and how do I bend it? It is for a BattleBots toy.

A: Browse around builders websites and look for wedge mounting methods that would suit your design ideas. In general the mounts should extend well back into the chassis and be fastened at multiple points. The answer to 'how thick' is always 'as thick as you can make it and stay under weight'. Making a smooth bend in thick sheet metal is something that requires specialized equipment - make a friend at a local sheet metal fabrication shop.

Q: Way down the Toy Hacks & Kits archive there is a picture of a hacked Battlebots toy with a scoop. Do you have a side view picture of it or do you know how it was mounted? I'm making basically the same thing with my toy.

A: The robot is Holy-Moly from Robot Dojo. The scoop is chrome-moly steel and I suspect that a mounting bracket is welded to the back out of sight. Such a bracket should reach as far back into the chassis as possible and mount with machine screws and nuts thru the plastic with large washers or a reinforcing backing plate.

Q: I want to make a scoop for my first antweight. Should I focus on the scoop, chassis sidewalls, or the top and bottom plates for thickness? I want a grade 5 titanium scoop, carbon fiber plates, and Lexan sidewalls. Sound good?

A: I like the materials list - good choices all around. I'd fasten the top and botton plates only at the corners to give the Lexan some freedom to flex under impact.

Thickness? A chain is only as strong as it's weakest link, and the same applies to combat robot armor. Don't scrimp anywhere, but the top and bottom plates won't be taking a lot of load in most situations.

Q: How would I make an antweight scoop? Should I get sheet metal and bend it, or get a tube and cut what I don't want out? Thanks!

A: That depends on the equipment you have available and the type/thickness of metal you want to use. I think most builders would form the scoop from sheet unless they just happened to have some tube scrap.

Q: Would arrow tips work for an antweight spike-rammer?

A: I don't know much about arrow tips, but I do know there are many different types. Pick something designed to punch a hole in something more sturdy than a soft target and you should be OK.

Q: Would Deer County 100 grain broadheads be good for the arrow tips? Also, could I take the blades off for weight purposes? Thanks so much, I love the site!

A: It sounds like you know a lot more about arrow tips than I do. Sorry, can't help.

Q: I'm building an ant with a curved plow on the front for pushing other bots around. It will be supported very well in all areas but I do not know what material to use, and how thick.

A: There is considerable discussion on armor materials and thickness in this archive. When in doubt, look at what other sucessful robots of similar design are using.

Q: Also, I'm using 2 Copal 50:1 gearmotors at 7.4v. Is this going to be fast enough?

A: Depends on your wheel diameter and the size of the arena in which you'll be competing. The 6 volt Copal motors are usually run with a 3-cell LiPoly battery at 11.1 volts. With 2" wheels and 7.4 volts you're gonna be slow: less than 2 MPH. With 2.5" wheels and 11.1 volts the speed climbs to a reasonable 3.4 MPH; adequate for a small arena.

Q: Hi I'm building an antweight with spinning drum. I'm going to mount the motor inside the drum. I have have 4.92oz in electronics,wheels, everything but the chassis and weapon and armor. Note that the weapon motor is not included in that. Is 11.08 oz enough for the rest??

A: I think you're in good shape, but it's kinda a funny way to design a 'bot - buying assorted parts and then worrying if you can cram the rest in underweight.

Q: Is 0.125 UHMW behind 0.04 7075-T6 aluminum a good composite armor for an antweight?

A: There are a number of comments about composite armor in the Materials & Components archive and further down in this archive. In general I don't like composite armor because it is so difficult to match materials that compliment each other's strengths rather than amplify their weaknesses.

In this case, you're combining a material that makes good armor because it is so flexible (UHMW polyethylene) and limiting that flexibility by combining it with a hard and stiff aluminum alloy. The UHMW is too flexible to offer any support to the aluminum -- you'd be better off to go with either of the materials alone.

Q: What material would you recomend for an Antweight parallelogram wedge?

A: There is considerable discussion on wedge materials in the Materials & Components archive and further down in this archive.

Q: Hi Aaron. I have an Inertia Labs chassis with 50:1 Sanyo gearmotors. When I drive it around, it slowly drifts to one side. How do I correct that? Thank you.

A: So, when you try to drive in a straight line it slowly turns to one side? Several possible solutions:

  • If your radio system has 'subtrims', check them to make sure both drive channels are synchronized. See the Run Amok Transmitter Programming Guide.
  • If you're using twin-stick tank style control, the 'ATV' function on your transmitter can be used to limit the top speed on the faster spinning motors.
  • A peizo gyro can be added to your 'bot to self-correct any directional drift.
  • You can move motors from one side to the other to see if some different combination of motors and sides improves the tracking.
  • Live with it.

Q: Could I use 'Crest Spinbrush' motors in my bot?

A: If it's a small 'bot, sure. I think the Spinbrush uses the Mabuchi FF180-SH motor -- fine for an ant or beetle. I don't know anything about the gearbox. It could be worth a try.

For a price comparable to the Spinbrush you can buy the BaneBots 25mm FF-180 Gearmotor [discontinued] that has all-metal gears and might be easier to mount.

Thomas Kenney's beetleweight Cloud of Suspicion Q: How is the beetle 'Cloud of Suspicion' so fast? What does it use for drive?

A: No secrets here - Thomas Kenny packed four 16:1 BaneBots RS-385 gearmotors into his compact beetle wedge. The motors, gearboxes, and wheels make up half the weight of the robot!

Although not all that fast at about 6 MPH, 'Cloud of Suspicion' is terrifyingly quick in a small arena.

Currently ranked 5th among active beetles at, 'Cloud of Suspicion' has a 8 win, 4 loss record.

Q: Would Robot Marketplace 1/4" keyed stock be OK for a beetleweight weapon live shaft?

A: You want a keyed shaft, not key stock. Key stock is the sliver of metal that slides into the key of the shaft and the hub/gear/sprocket to lock them in place. The smallest keyed shaft available at Robot Marketplace is 1/2" diameter. The lack of suitable small diameter keyed shafts is why I recommend dead shafts for insect class robots.

Q: What's wrong with using the 1/2" keyed shaft????

A: Massive overkill for an insect class 'bot. It's heavy, and the 1/2" bearings to support it would also be heavy and bulky.

Q: I'm thinking of adding this magnet to the inside of my antweight to give it a bit of extra traction on steel floored arenas. Will I overstress the four 17:1 Maxons @ 11.1 volts with 1" wheels?

A: First, check with the event organizer to see if traction magnets are allowed. Some events allow them, some do not.

You're correct to be worried about overloading the motors. The added traction you get from use of magnets will increase the load on the motors before the wheels start to slip. Everytime you double the traction you also double the amperage draw at maximum push, stressing the motors and the ESC.

Calculating how much extra traction you can get from a specific magnet has too many variables, but those Maxons are currently breaking traction at less than 1/10th their stall torque -- you can add a good amount of traction and still be fine. Experiment!

You might also consider using axial magnetic rings to replace your wheels. This set-up has worked very well for insect robots like 'Wallop'. Note that 'Wallop' was designed for the magnet wheels and runs a high gear reduction to avoid over-stressing the motors.

Q: How would you suggest attaching the ring magnets to the shafts of the 17:1 Maxons? It looks like Wallop used a prop adapter for his magnet wheels, but I only have about 1/2" of space for the width of my wheels.

Also, if I chose to just put a square magnet on the inside of my robot, would there be any chance of the large magnetic force messing with any of my electronics?

A: It sounds like you'd need custom hubs. Magnet wheels are best used on robots designed from scratch around them, but you might have been lucky enough to get away with it.

A stationary magnetic field is unlikely to create electronics trouble. It's more likely to stick you firmly to an arena upright support and leave you spinning your wheels in the air.

Q: Would 4 of the 50:1 copals at 14.8V with 2.5 inch Lite Flites and the Lexan mounts and aluminum hub accessories available at the Robot Market Place make a good drive system for a beetle? Also, I've never made a beetle or competed in the tiny insect weight arenas, so what is considered fast, average, and slow speed for an ant/beetle?

A: I'm assuming that you're talking about the 6 volt version of the Copal 50? Four of them with 2.5" wheels would give entirely adequate performance for a beetle. Top speed would be around 4.5 MPH and that speed would come in about 3 feet from a standing start. This would be a fairly average top speed for a beetle, but acceleration would be excellent for a small insect arena. The popular B16 16:1 motors would give a top speed closer to 6 MPH which would be considered fast. Down under the 3 MPH zone is getting pretty slow, but the need for speed depends on your weapon system.

Be aware that the Copal spur gearbox is a little fragile for use in a beetle. I would strongly suggest good wheel protection and I'd carry a couple spare motors in my pit box.

Q: So, the wheels should be fully protected and the lexan mounts in addition to the all metal gears should protect the motors, right? Spares are nice in between fights but I dont want to need one during a fight! Also, how big is an average insect arena and what should I be aiming at for an average 'distance to top speed'? This will be a lifter which will need good speed but also quite maneuverable and quite acceleratory (is that a word)?

A: Yes, protect the wheels. A good hit from a beetle weapon could destroy the Copal gearbox. The gears are all metal but they are small, and a spur gearbox is not as strong as a planetary gearbox with the same size gears.

A typical insect arena is about 6' by 6', but there is considerable variation. Check with the events you plan to enter to determine the size of their arena. Top speed versus acceleration is subject to personal preference, but if you're close to top speed in half the distance across the arena you're in the right ballpark. And yes, acceleratory is a word.

Q: I'm building a beetle an I'm stumped. Do most beetles have exposed wheels or wheels mounted inside? Do most beetles use foam or solid rubber or air-filled tires?

A: Have you never been to a beetle fight, or were you just not paying attention? Try stopping in at Builders Database and browse pictures of beetles from recent events. I think you'll see a fairly even mix of exposed and protected wheels that depends on the overall concept of the robot. You'll also see a mix of foam and solid tires.

Q: Hey Aaron, I thought a beetle was 1 pound so I am actually building an ant. Sorry for the mistake -- thanks.

A: So, you don't know how much a beetle weighs, and don't know what type of wheels to use or where to put them, but you think you're ready to build your robot? I'd suggest doing quite a bit more research before you start ordering parts.

Q: Hey Aaron, I have 7 ounces left on my beetle. What is the most effective weapon I can put on it? I don't want a spinner. The beetle is a fast and powerfull wedge but I want some type of weapon. Thanks.

A: An effective weapon is integrated into the structure of the robot. The time to think about a weapon is at the start of the design process, not after the 'bot is built and you discover that have a little weight allowance left.

I'd spend the extra weight on armor, but if you're determined to tack on a weapon you'll need to take a look at your design and component layout and think about what type of weapon would make sense. Consider if there is room for a servo-powered lifter and if that would make sense in your design.

Q: Hi again -- I had the 7oz beetle weapon question. Is it possable to build an effective beetle spinner with 7 oz? Thank you!

A: I'm gonna say no. You'd want at least 5 ounces of rotating mass for an effective beetle spinning weapon. That doesn't leave much for motor, drivetrain, and support structure.

You really need to decide what your robot is going to be in the design phase and build the robot to meet that goal. If you just keep adding things on 'til you top out on weight you're going to have a robot that tries to do too many things and ends up being good at nothing. Use that extra seven ounces of weight allowance to make the robot better at what it already does well.

Q: What are suitable Maxons for beetle drive? I will be doing two wheel drive.

A: Maxon makes a large range of high-precision high-cost motors. Once in a while some of their motors are available on the surplus market at prices affordable by combat robot builders. I don't currently have a source for any surplus Maxon motors suitable for insect class robots.

Q: Hey Aaron, what are the best beetle drive motors out there? I heard that BaneBots motors are bad -- is this true?

A: I say this all the time: 'best' depends on your expectations and design needs. There is no single 'best'.

There's nothing wrong with the BaneBots gearmotors, but they aren't indestructable. Many builders stick a pair of wheels on the end of the shaft, bolt the motors down, run with the wheels unprotected and without additional support, and are disappointed when a spinner hits a wheel and destroys the gearbox. Protect the wheels and/or add a support bearing to the axle shaft outside the wheel and the BaneBots motors are great.

Q: Is the BaneBots 2 7/8" wheel sturdy enough for a beetle weight?

A: The Banebots wheels are fine for a beetle. I'd use the 0.8" wide version if the wheel is exposed, and carry a few spares in your supply box. You might want to have a look at the Colson Performa Wheels as well.

I'm not a big fan of the BaneBots hubs. Using set screws to hold a hub to a small shaft on a combat robot is a weak point that will sooner or later give trouble. You'll need to check the tightness before every match.

Q: Would the Beetle B62 Gearmotor 62:1 be a good choice for beetle weight drive motors? I was really hoping to get a right or left side shaft gearhead, but I couldn't find one that would work. If you know of one of those, please recommend.

A: The gear ratio on the B62 is too large to give good speed for a beetle. With 3" wheels and running on 12 volts, the top speed would be under 3 MPH.

Pololu has small right-angle gear motors, but their output is much too small for a beetle unless you're just moving a huge weapon around slowly. I don't know of any suitable high-power right-angle gearmotors of the correct size.

Q: What are the best beetle motors? I have 7 ounces of weight allowance per motor. I will use one motor per side on 2.25" wheels. My battery is 7.2 volts.

A: 'Best' depends on what you want from the motors and what your design calls for. A good general purpose gearmotor for a beetle is the BaneBots 16:1 28mm RS-385 [no longer available]. It weighs 5.1 ounces and has a nominal 7.2 volt rating. With 2.25" wheels the top speed would be near 7 MPH with top speed reached in less than a second -- just about perfect for a fast wedge in a small arena.

Q: Could a modified hard drive disk be used to make a beetle weight spinner or would it shatter on impact?

A: Mark J. here: Hard disk platters are made from thin aluminum or a glass composite material. They are designed for loads very different from the sudden impact they would receive as a spinning disk weapon and they are unsuitable for that purpose.

As a general rule I recommend that the spinning mass for a primary spinner weapon equal at minimum 10% of the robot weight. That's just about what the small VDD3 blade is when used on an antweight. For a beetle, you're looking at about 5 ounces worth of blade.

Hobbyweight spinner 'Fiasco'. Q: I'm getting my beetleweight horizontal spinner's frame waterjetted in a style similar to that of the hobbyweight Fiasco's. Should .0625 Aluminum be sufficient, or will I need something thicker?

Update: sorry, you can scrap that question. I looked back through the archive and after reading some other answers in which you said "Make it as thick as you can and still make weight", I'm just going to do that. Thanks.

A: Mark J. here: thanks for checking the archive. The 'make it as thick as you can' rule is generally a good model to follow. I don't think that .0625 aluminum would be thick enough. 'Fiasco' uses .375" 7075 aluminum. For a beetle you won't need to go that thick. The application of some very sketchy engineering formulas leads me to believe that a high-strength aluminum alloy at least 0.125" would be in the right ballpark. Thicker would be better if you have the weight to spare.

Date marker: January 2009
Q: What are the basic components of an antweight robot? Could you show me in a diagram or picture how they are put together?

A: The basic components for a combat robot are pretty much the same for all weight classes. Take a look at FAQ #19 for a diagram that shows the components and how they connect.

Q: I'm building my first UK antweight and was wondering what design to use. Would a simple wedge be competitive? I live in Ireland. Would it be worth the journey to England to compete?

A: I always encourage first-time builders to keep their robot design simple. You'll have enough problems to sort out without adding an active weapon into the mix. A well-built wedge or scoop is always competitive.

I can't tell you if a trip to England for an antweight tournament would be worth your while, but I can tell you that I've travelled greater distances for a good robot fight. You'll either love it or hate it, and the only way to find out is to go.

Q: Hello Aaron, my name is Troy. I am 11 and I have not yet competed any of my bots but I know a lot about robot combat. I have built the Inertia Labs kit and I have some 15-3 titanium armor. I also have the Inertia Labs pneumatics kit.

I have the 75 MHz Pico receiver right now but I am going to upgrade to 2.4 GHz. Do you know of any ways to fit the Spektrum BR6000 receiver into the Inertia Labs chassis and still be able to drive inverted? Can you strip the BR6000 of any excess plastic so that it can fit?

A: There isn't a lot of space inside the Inertia Labs chassis. The guys at Dimension Engineering have some photos of the standard set-up with the GWS receiver. They compare fitting the components in place to a game of Tetris.

You're not going top save much room by modifying the case of the BR6000. The problem isn't the thickness, it's the rather large footprint. Unless you come up with some creative solution to reduce the footprint of the battery (custom NiMHd pack?) I don't see a way to cram everything into the chassis and get the lid on.

Q: Dear Aaron, my name Anthony. I am 18 years old and a beginner in combat robots. My dad suggests that I build an antweight dome spinner like 'Shrederator'. Is this robot style sturdy to use in battle? Is it possible to make it effective?

Another question: I have a Sabertooth ESC. Is it possible to connect this ESC to a 7.2 volt battery on the brushless system without an enternal ESC battery?

A: Hi, Anthony. I can't recommend that a beginner build a Full-Body Spinner for their first robot. It is possible to make an effective FBS, but there are very few that are successful and a whole lot of them that are not.

The spinning shell must carry as much weight as possible and be very well supported. When the weapon makes contact there will be as much force placed on your robot as is transmitted to your opponent. It's likely that your 'bot will fly off in an unpredictable direction and bounce off several walls in a small arena. The 'bot must be very well constructed to survive this sort of treatment. Just bolting a mixing bowl to the shaft of a motor is not going to be nearly sturdy enough.

If this is an insect-class 'bot you've got another problem. Insect arenas are very small and you will have very little time to spin your weapon up to an effective speed before your opponent is on top of you. You'll need to be very good at dodging their first attack if you're going to survive long enough to stay in the match.

There are several previous Q&A about spinners in the Robot Weapons archive that should be helpful to you. I'd also suggest reading the FAQ #26 for my answer to the question about what type of weapon is best.

I'm not sure I understand the ESC question. If you're asking if you can hook the Sabertooth up to the same battery that powers the brushless ESC for the weapon -- yes, you can do that. Just make sure the battery has enough capacity to power both systems. There is a wiring diagram in the FAQ (#19) that shows how everything goes together.

Q: Dear Aaron, it's Anthony again. I decided to build an antweight horizontal disc spinner instead of an FBS. How do I make it effective? Is the new polycarbonate VDD weapon gear box sturdy anough for competition? If it isn't, will I need a tougher shaft then the kit shaft from the Robot Marketplace?

A: We have LOTS of information on spinner weapons and how to make them effective in the Robot Weapons archive. Browse around in there. Horizontal spinners are a bit of a challenge because they 'kick' off to one side on impact just about as far as they 'kick' the opponent the other direction. Not very popular for that reason - sure you want to build one of those?

The VDD weapon parts are all combat tested and will perform well.

Q: How exactly does 'Micro Nightmare's main 14.8 volt battery power both the Hacker brushless system and the SozBots speed controler at the same time? Can the same be done with the Scorpion HX? I'm confused.

A: I pointed you to the wiring diagram in the FAQ last time, Anthony. The diagram there shows how to wire a weapon ESC and a drive ESC to a single battery pack. They are wired in parallel: connect both '+' inputs on the ESCs to the '+' battery terminal, and both '-' inputs to the '-' battery terminal. That will work just fine with your Scorpion HX.

Q: Can you get the Inertia Labs Micro Pneumatics Kit now that neither Inertia Labs or the Robot Marketplace sells it? If so can you please tell me where?

A: This question keeps popping up and I keep answering it.

Inertia Labs was the manufacturer of the micro pneumatics kit. They no longer make them and all stock is gone.

Q: Can you rig something up so that you can control a Lego pneumatics set with a remote control? Also, can you recommend any good sites to buy these sets or to learn more about them?

A: Sure -- you can use a nano servo to operate the Lego pneumatics switch and control the system. However, the Lego pneumatics components do not provide enough power to be very useful in even an insect class combat robot. CSSOH'S Lego Pneumatics Page (archived) has many examples of Lego pneumatics construction and a primer on Lego pneumatics. I can't recommend a articularly good place to purchase the sets, other than the usual places like

Q: I recently asked about Lego pneumatics and you said they didn't provide enough power for an antweight fliper. Well, I searched and found that the larger Lego pump can supply enough force to lift about 3 pounds. How much more do I need for an antweight flipper?

A: Mark J. here: Power is the product of two components: force and speed. The Inertia Labs micro pneumatic system delivers 16 pounds of force and delivers it very quickly thanks to a high-flow valve and pressurized storage tank. The Lego system operating off of an electric air pump is designed for slow and safe actuation; it takes way too long to develop force and move it over enough distance to make an effective flipper. The best you'd get is a slow and very gentle lifting action -- absolutely not a flipper.

Q: How do make a crushing weapon for an antweight robot?

A: Scroll down a little to the 'Grabby' question for a discussion on antweight crushers. Nobody has built a successful antweight crusher yet, and it may not be possible. It certainly wouldn't be easy!

Q: Is there a good pneumatic / CO2 system for a beetle with all the components together weighing 5-6 ounces? Thank you.

A: Sorry, no off-the-shelf CO2 systems that small. Inertia Labs made a small low-pressure air pneumatic system for insect-class robots, but they are no longer produced.

Q: Hey Aaron! Would the Tamiya 72001 Planetary Gearmotor be a good motor for a beetle clamper? If not then what would be? Thank you for your help.

A: Mark J. here: let me take this one, Aaron.

It's really difficult to discuss just one part of a weapon system. A motor that would work well for one clamper design would be completely unsuitable in another. That said, the Tamiya 72001 is not really 'combat quality'. The gearbox housing and gears are plastic and the output shaft is poorly supported and of too small a diameter to properly fasten a clamp arm. You'd be much better off with a more robust gearmotor like the Beetle B231.

Q: How does the claw mechanism on the antweight 'Grabby' work?

A: The photo of Grabby at the Inertia Labs website shows a single standard-size servo connected to twin pushrods that activate the claw mechanism -- pulling back to close the jaw and pushing forward to open it. Two pushrods are needed because the ends of the claw mechanism diverge as they move. There is a second 'thin wing' servo attached to an arm apparently used as a SRiMech.

Given the lever advantage, the claw will actuate quickly, but will not have much grabbing force. Certainly not a crusher.

Q: Have "Grabby', 'Lifty', and 'Cutty' competed or are they just examples on the Inertia Labs website?

A: All three robots are credited as being built by The Machine Lab. I'm not sure that they were built as combat robots, and I can find no record of any robots from 'The Machine Lab' in combat competition.

Q: You said that Grabby's design was meant for speed, not force. What design would work for force? What would it take to build an antweight crusher with the Hitec 645-MG servo implementing the design of Grabby? Would the servo supply enough power of would you have to use something else like small hydraulics?

A: Mark J. here: contrasting Grabby to a crusher was a facetious exaggeration. Direct servo-powered clampers can have a large range of travel and little force like Grabby, or you can change the lever pivot point to reduce the range of travel and increase the clamping force. Every time you double the clamping force, you cut the amount of jaw travel in half. By the time you got enough force to do any damage, the jaw travel would be unuseably small.

You could modify the servo for continuous rotation and design an external gearbox to multiply the available force. The problem then becomes that force and speed are a trade-off: more force gives less speed and vice versa. Jaws with significant force and travel would be agonizingly slow.

There is nothing magical about hydraulics; you still have the problem with the inverse relationship between force and speed. If such tiny hydraulic components existed, their only advantage would be that high force can be generated without the need for heavy gearboxes and linkages.

An additional problem with crushers is the enormous stress placed on the chassis of the robot deploying the weapon. A force equal to the force applied to your opponent must be borne by your own chassis. I've seen several would-be crushers that succeeded in ripping themselves apart.

Q: Would you suggest building an antweight from the Inertia Labs chassis with an arm about 3.5 inches long connected to a Hitec 645-MG servo?

A: Good servo choice. The 645-MG will deliver 38 ounces of lift at the end of a 3.5" arm. That's plenty to give quick and reliable lifts.

Q: Would it be a good idea to do something like the 2.2 pound robot 'Mars Attacks' for an antweight? Merci.

A: The kilobot version of 'Mars Attacks' was a thwackbot spinner made to look like a shell spinner. A thwackbot can't move when attacking (unless you have some fancy melty brain electronics) so all it can do for offense is sit and spin. There have been very few successful thwackbots -- judges hate them -- but they are fun to drive.

Q: Hi Aaron. Does the HXT 12KG servo have Hitec or Futaba splines? Can it be modified for 360 degree rotation?

A: The HXT 12kg (AKA Towerpro MG995) has Futaba splines and is quite inexpensive, but I strongly recommend that you buy something else.

All the reviews I've found say they're junk. They're heavy, poorly made, unreliable, and don't come close to meeting their advertised performance figures. One review thinks they may be the "world's worst servo." I wouldn't modify one of these to throw itself away. Avoid.

Q: What is a good motor or servo for a beetleweight clamper? How should I mount it?

A: If you want to keep it simple, try the Hitec HS-775MG servo. It's reasonably priced, has 200 oz/in torque, full metal gears, and easy mounting tabs.

Q: Which will be better for a beetle clamp: the servo you sugested running at 7.2 volts? or a BaneBots 28mm 25:1 gearmotor at 7.2 volts? If I use the BaneBots should I support the shaft?

A: I considered the BaneBots motors before I made my recommendation. The Hitec servo will hold better at a lower amperage draw, is an easier shaped package to mount, and requires no external speed controller. If you use a clamping arm that has some side flex (Lexan, maybe?) and mount close to the output bearing, either the Hitec servo or the BaneBots gearmotor should be OK with no additional shaft support.

Note that the Hitec servo is rated only up to 6 volts. I've never used this servo, but suspect it will be OK at 7.2 volts.

Servo powered 4-bar lifter
Q: How do you implement a four bar lifter for an antweight using a servo?

A: Mark J. here: there are several posts on the design of 4-bar lifters in the Robot Weapons archive, including a link to design software.

For an antweight the servo output can replace the entire rear (or front) bar of the mechanism to simplify construction. The diagram at right shows one possible configuration.

Q: Can you make fairyweight armor using a cardboard, aluminum foil and ducktape sandwich? It is thick like 1/4".

A: Composite armor is tricky -- you can end up with the worst properties of the individual materials rather than the best. Even if you got the best properties of those three materials you still wouldn't have much. If you have to stick with stuff you find around the house, polypropylene plastic ('PP' in the recycling label) from snap-on lid kitchen storage containers is quite tough and easy to work with. It would be a better choice.

Q: Dear Aaron, what is the best way to make a simple antweight lifter using a servo? Four bar linkage is not an option: it has to be self contained besides the servo connector.

A: I'm not sure what you mean by 'self contained', but there is a discussion on different servo powered lifters in this archive. Search for "using a servo". The simplest approach is to just attach a lifter arm directly to the servo output wheel.

Q: Dear Aaron, leaving everything aside, would the Hitec 645MG analog servo work well as a antweight lifter? What other inexpensive analog servos with around 100 oz/in would you recommend for an antweight lifter?

A: The Hitec 645MG is a great servo for an antweight lifter. The Futaba S3305 is comparable: a little lighter and a little less expensive with all metal gears and dual ball bearings.

Q: Dear Aaron, do you have any suggestions for 1" to 1 1/8" wheels and tires that fit the 12mm long shaft of the Sanyo 50:1 gearmotors and an Inertia Labs chassis?

A: The wheels usually used on the Inertia Labs chassis are the 24mm diameter Ultra-Light wheels. They are a press fit onto the 3mm diameter Sanyo shaft -- no hub needed.

Q: Is it OK to run two 28mm Banebots RS385 motors in a beetle with 2.25" Lite Flites? I'm using the Ant 150 ESC with one motor per side. Battery is 7.2 volt, 1500 mAH NiMH.

A: Sounds like a good choice. For use in an 8-foot arena, I'd go with the 20:1 gear ratio: 0 to 5.5 MPH top speed in 3.5 feet, and cross the arena in 1.2 seconds. Maximum power draw would be about 2.2 amps per side, well within the Ant 150 capacity. If your arena is larger, consider the 16:1 gearing for a little more speed.

Q: Dear Aaron, would 21 gauge 15-3 Titanium work well for antweight armor? Should 15-3 be easy to bend in its annealed form? Should you harden it?

A: Mark J. here: we've never worked with 15-3 (AKA 'Timetal'), but I've looked up it's properties and it appears to be an excellent armor material. Complex metal forming can locally 'work harden' titanium and lead to cracking under later stress; keep the bends simple and you should have no problems.

In aerospace applications, Timetal is re-annealed after forming, 'age hardened' at high temperature, then air cooled. This is the ideal treatment and it will add about 40% to the strength of the finished piece.

A 21 gauge sounds appropriate, but armor performance depends on factors other than just thickness. The size and shape of the piece, mounting method, and support from other chassis elements all count toward performance, but unless you're doing something odd the 21 gauge should be great.

Q: I am thinking of building a antweight with an aluminum and tool steel blade spinning at 30,000 RPM. It will be powered by 4 sanyo 50:1 gear motors connected to Lite Flite wheels and tires. The frame would be made out of a solid piece of 6Al-4V Titanium. I'm guessing it would cost around $1,500. What do you think?

A: Mark J. here: a few thoughts:

  • 30K RPM is WAY too fast to spin a rotating blade -- see previous question on blade speed in this archive;
  • the drivetrain sounds fine;
  • a solid machined titanium antweight chassis is expensive overkill.
There is a great deal more to a successful combat robot than materials and components. I've seen antweights armored with cardboard and duck tape win tournaments, defeating high-end carbon fiber and titanium 'bots along the way. I'd suggest that you stop thinking about designing expensive robots and attend a few tournaments to see what actually wins.

Q: What happens if you spin a blade to fast?

A: Like I said, see previous question on blade speed in this archive. Search the page for 'too fast'.

Q: Are you allowed to use magnets for an antweight to hold your robot down? It doesn't say in the RFL rules.

A: Chassis or wheel magnets are left to the discretion of the event organizer. Some allow them, some do not, and some arenas don't have a magnetic floor so it doesn't matter. At least a few builders provide their 'bots with a set of magnet wheels to use where they are allowed and a set of rubber wheels to use elsewhere.

ICE antweight Kanundrum
Q: Did team Inertia Labs build a ICE powered drum antweight?

A: Yes. Inertia Labs had an ant named 'KanunDrum' with a internal combustion powered drum. The 'bot was never mentioned on their website. It fought at the Marin Ant Wars in 2004 and 2005. shows 1 win and 3 losses.

Q: How does KanunDrum's weapon work? Does the ICE power the wheels too?

A: The drum is belt driven by a model aircraft internal combustion engine. It looks like a servo is used to engage the belt with an idler wheel. The engine is manually started via an extension of the shaft that sticks out to the left of the 'bot. The wheels are driven by electric motors.

Q: How high in volts can a Tamiya 4-Speed Double Gearbox be run at?

A: See my warnings about overvolting in FAQ #25. The FA-130RA motors that come with the Tamiya gearbox are particularly vulnerable to melt-down if allowed to overheat. I would not run them higher than 6 volts even with a low enough gearing choice to spin the wheels well before stalling.

Q: Are antweight full body spinners effective? Do you need to gear the motor that would go to the shell of the antweight spinner or could you attach the motor directly to the shell. What would be a good motor to spin about 5 ounces of shell at a reasonable speed for an antweight?

A: What is it about an FBS that makes it so attractive to builders? If you take the time to research the combat record of FBS robots you'll find that, as a group, they have a very poor win percentage in any weight class. They are often as dangerous to themselves as to their opponent -- ricochetting off at odd angles and into trouble. I can't recommend building one.

Your design questions all depend on specific information about the dimensions of the shell, the material used, the torque of the motor, and the size of the arena. The Team Run Amok Spinner Spreadsheet for Excel can perform the calculations you'll need to determine the power and gearing requirements for a specific shell design. I have seen direct-drive antweight FBS, but they had small diameter shells and very powerful motors.

Q: How come there are not many full body spinner antweights?

A: Read the answer above: there aren't many ant FBS because ant FBS have a poor win percentage. Most builders want to build something that they think can win.

Q: Why don't you think flippers are that effective for antweights?

A: Several reasons:

  • No high-pressure pneumatic equipment is available in antweight sizes;
  • Antweight 'bots can generally survive repeated flipping without damage;
  • Damage/aggression scoring systems don't give credit for flips;
The combat record shows overall poor results for ant flippers. If you compete in a SozBots-style arena where you can win by flipping your opponent out of the ring, a flipper might be worth considering.
Inertia Labs' Pele and Hummer antweights Q: What do you think about Inertia Labs' antweight drum spinner 'Hummer' and pneumatic flipper 'Pele'? Do you think it would be good to do something like 'Pele' with the Inertia Labs chassis and flipper kit?

A: 'Hummer' is a beautifully designed and constructed antweight. It is also very successful: 26 wins and 6 losses, seventh in the Botrank historic rankings. 'Pele' is more of a show-off 'bot -- fun to look at and an interesting challenge to drive, but not really competitive: 10 wins and 14 losses.

I don't believe that the Inertia Labs pneumatic parts are available anymore. If you could scrounge enough pieces to put a system together I'm sure you could have some fun with it, but don't expect to win tournaments.

Q: Dear Aaron, I am building a wedge robot with the Inertia Labs kit. Where can I find small hinges about half an inch long for antweight wedges? Is it a smart idea to put hinges on your front wedge?

A: I don't like a hinge on a front wedge. The hinge would be a weak point in the wedge mounting, and a hinged wedge can fold back under the robot and lift the wheels of the robot off the floor. If you want the wedge to scrape the floor, you can build a subframe for the wedge and pivot it from the center or rear of the robot, like the scoop mount on Breaker Box.

Small hinging mounts for antweight side skirts can be made from heavy package tape or from small mechanical hinges available from your local hobby shop. The hobby shop will also have special 'hinge tape' used for model aircraft control surfaces. You could also use small metal jewelry box hinges available at craft stores.

Q: Are there any antweight wheels available that are 3/4" in diameter with a 6mm bore, or would I have to make my own? I'm making a overcutter and would like it to be as low to the ground as possible.

A: I don't know of any ready-made wheels that small in diameter with that large a bore. It's time for a trip to your local hobby shop to see what they have. Check slot car wheels and R/C airplane landing gear wheels. You're going to have a hard time finding a small wheel with enough material in the hub to allow enlarging the bore to 6mm.

You've probably figured out that you aren't going to get much speed out of 3/4" diameter wheels on standard ant gearmotors, but I thought I should mention it.

Q: In your opinion, what is the best weapon for an antweight bot. [pyrobug]

A: Oddly, there seems to be some argument about what 'best' means. To me it means the weapon that gives you the greatest chance of winning. Other builders would rather put on a spectacular display of destruction, even if it means they seldom win a tournament.

We did some research to find out what weapon types win the highest percentage of matches. Overall, robots with passive weapons (wedges, bricks, rammers) win more often than robots with active weapons (spinners, flippers, lifters). However, if you look carefully at all the sub-classes of weapons, it's lifters that do the best. They don't win many matches by knock-out, but they can dominate a battle and make an oponent look weak and ineffective.

Antweight lifters are relatively easy to construct because R/C servos have enough power to function as your lift motor.

Q: I was wondering if I should skip the antweight an go straight to a larger bot? I know it will be more expensive but maybe I can save up. Will I find more or fewer competitions? [pyrobug]

A: Generally, the heavier the 'bot, the harder it is to find a match. In 2007 the number of RFL sanctioned matches by weight class looked like this:

My advice is to save up and build a proper antweight with components that you can use when you graduate to larger 'bots. A good computerized radio system, for example, will serve you well for any robots you build in the future. Good components can always be sold should you decide to move on, while cheap stuff won't likely be worth anything.
Date marker: March 2008
Q: Can any of the Robart R/C airplane pnumatic kits be used for an antweight flipper?

A: Mark J. here: the large scale R/C airplane guys use pneumatic systems to raise and lower landing gear in a realistic, slow manner. Their pneumatic cylinders can produce good force, but the critical ports and valves flow air too slowly for a flipper.

Q: How do I calculate how much my servo will be able to lift with its arm length, weight, and oz-in ratings?

A: The amount of force at the end of a simple arm attached to a servo is:

Force = Torque Rating / Length of Arm

Example: a servo with 60 oz-in torque with an arm extending four inches from the central axis of the servo will have:

60 oz-in / 4 inches = 15 ounces of force

Note that the servo would be able to 'hold' 15 ounces at the end of the arm. It would be able to slowly lift 14 ounces, speed increasing with lessened weight.

Q: Would the GWBLM001 2205/15T brushless motor sold by BaneBots be good in an antweight spinner at a 4:1 reduction spinning a 10 inch titanium bar?

A: Mark J. here: as noted in the FAQ all the tools you need to evaluate spinner motor performance with specific weapons are in the archives. In particular, the Team Run Amok Spinning Weapon Excel Spreadsheet will detail and graph the performance of a specific motor spinning a specific weapon at a specific gear reduction.

There's an infinite number of combinations of motors and spinner weapon designs. I've provided the tools, you run the numbers. Fair?

P.S. -- You'll need to know the width and thickness of the bar in addition to the length and material.

P.P.S. -- Oh all right: assuming that the bar is 1" wide and 1/4" thick (about 6 ounces), the GWBLM001 2205/15T geared 4:1 will spin it up to about 2500 RPM and 45 joules of energy in ~4 seconds. Killer. But seriously, that's the last spinner analysis I'm gonna do!

Buy a couple of those motors -- BaneBots is closing them out at a very good price.

Q: I'm building my first antweight. Is the Tamiya 70097 Twin Motor Gearbox be a good start for a drive system?

A: I've seen many competitive antweights built around the Tamiya Twin Motor Gearbox. It is inexpensive, sturdy, and provides adequate power for an ant. The main drawback is that it's a little bulky.

Q: Do you think that the Complete Micro Drive Kit from Robot Marketplace would be a good starter ant platform for a first time bot builder?

A: Mark J. here: It's not even close to being a 'complete kit'. You get a chassis, motors, wire, and wheels. You need to come up with radio gear, an ESC, a battery pack, charger, and some sort of weapon. The machined aluminum chassis is way cool, but not easy to repair if it gets pranged. You might want to order a spare for your pit box. I don't really consider this to be a 'first time' kit.
Hacked BattleBots R/C Toy
Q: Were can I get the 'A:1 Complete Antweight Kit' now that Composite Labs shut down?

A: Weak! I hadn't heard that Composite Labs was gone. I had been recommending their kits. They were the manufacturer and only source, so they're gone for good.

It's difficult for me to recommend any of the currently produced antweight kits for a beginner. You're going to spend $300 or $400 and end up with a marginal radio, a low-end battery charger, and a pile of parts with no specific instructions. I'm gonna go back to suggesting that a beginner find an old BattleBots R/C toy on EBay, hack the radio and drive motors, add a wedge, and go beat up some $400 'bots for $50.

Q: Do you think I could use a soup can for an ant scoop?

A: Way too flimsy. The first spinner you came up against would shred it. Try titanium, and three times that thick.

Q: Can I use a servo to power a 4-bar lifter for a antweight?

A: Sure! There are many good antweight lifters powered by servos. See previous posts on selecting an antweight lifter servo and designing 4-bar lifters.

Q: Can the Victor 883 speed controller be used in a beetleweight?

A: Match the cooling fan to your voltage and it'll work, but it's overkill. A pair of them would weigh half a pound -- a big chunk in a three pound robot. Why would you want heavy 60 amp ESCs in an beetle?

Q: I'm interested in building a flamethrowing antweight. I know that it won't be that competitive, but it's mainly designed to be showy. How would I build the flamethrower part? How is it wired? Where do I get the parts?

A: I won't post information here that could lead an inexperienced builder to injure themselves. See the previous post on flamethrowers for reasons to build something else.

Q: I've seen people use magnetic wheels on their 'bots. Are they effective? How do I make them?

A: Magnetic wheels are extremely effective -- if you happen to be fighting in an arena with a steel floor. I've only seen them used on insect-class bots. See Team Nightmare's beetle page for some good photos of the 2004 beetleweight national champion 'Wallop' with its magnet wheels.

The wheels are simply round rare-earth neodymium magnets with a hole in the center. These can be very expensive, unless you happen to find a suitable set at a surplus outlet.

Don't leave magnet wheels exposed. Put them under your armor or use side guards to keep them from clamping onto steel rails or other vertical structures. It would be embarrassing to end up stuck to a railing. Also, be sure to check with your local event organizer to see if magnet wheels are even allowed!

Q: I went to a hobby shop to look for servos. The cheapest one they had was a weak one for $20. They said it would take 3 of them to push around my one pound bot. Do you think I should buy it or look somewhere else? Do you think servos are worth it or should I buy motors, and speed controller?

A: First, find another hobby shop - one that knows something about 'bots. Second, servos make poor 'bot drive trains. Save up your money and buy a real speed controller and drive motors. See the servo discussion for more info.

Q: Tiny 'bots bite! Do you agree? [I had to substitute 'bite' for what they really said.]

A: I like to fight big 'bots! The bigger the 'bot the better -- but even tiny 'bots rock.

Q: Would Mini Run Amok converted into a mini Run Away make a good 6-pound mantisweight?

A: The side-wheel spinner design on Run Away is unique and showy, but a pivot steer 'bot like Run Away would be very difficult to maneuver in a small arena.

Q: Have you seen any gas powered beetleweight bots?

A: No. Internal Combustion Engines (ICE) are tempting, but getting them to work well and reliably in combat can be a huge problem. Also, not many insect class competitions allow ICE. Check the rules for your competition before you commit.

Q: I am building my 1st ant. What parts should I get? Thanks, Nick.

A: You could do a lot worse than the components used for the Robot Marketplace Basic Antweight Starter Package, Nick. The Tamiya dual-motor gearbox is quick and tough, and the 56 mm 'sports tires' slide right onto the shafts of the gearbox. The Ant 100 ESC is reliable, but I'd upgrade to the Ant 150 ESC for a weapon control channel that could come in handy on a later 'bot.

Radio and battery/charger are up to you. I use inexpensive NiMHd cells for ants because chargers for them are available and cheap -- but LiPoly cells are lighter. Bolt everything down to a simple flat chassis, add your armor and a sturdy wedge. Keep your first 'bot simple and have fun!

Q: I'm looking for a flat servo to power my antweight. It doesn't need to have much pushing power, just be fast and under $25 each. Do you think a Futaba S3110 Micro servo is good? Will it allow me high speed?

A: Servos are slow! The speed of a typical 'fast' servo modified for continuous rotation is about 60 RPM. With a 2" diameter tire that gives you about 32 feet per minute, or less than 0.4 miles per hour. That's not even a crawl!

It is possible to 'speed mod' a servo by locking the first and third reduction gear clusters together and eliminating the second reduction stage altogether. That will improve the speed by a factor of fifteen or more, but will reduce the torque by the same factor. It will make the motor prone to stall and an early death. It isn't worth the trouble -- don't use servos for drive motors.

The Futaba S3110 is a really tiny servo. The gear train is way too fragile to even consider using it as a drive motor in an antweight. It would be slow, weak, and vulnerable.

Q: What is the absolute best servo for a antweight if that is your only option?

A: Mark J. here: I can't figure out why a servo would be your only option, but if you wanna do the servo thing right my choice would be the Hitec HS-5996TG.

  • The titanium gears are next to indestructible,
  • A beefy 111 oz/in stall torque is un-stallable,
  • 60 degrees rotation in 0.10 seconds is nasty quick (for a servo),
  • Hardened gear pins and intermediate oilite bushings with ball bearings on the output shaft will take serious punishment, and
  • The coreless motor shaves the weight down to 63 grams.
One sweet servo! Drawback? Price tag: $95 each.

Q: Is there a good servo to power a 'bot for less than $40?

A: It's funny how fast a price limit gets set when somebody finds out what 'absolute best' actually costs.

I really don't want to encourage you to build a servo-powered 'bot - they're really slow! For less than the $80 you're willing to pay for a pair of servos you can buy a Tamaya dual-motor gearbox and a good speed controller that will run rings around any servo-bot. Reconsider?

Q: How do I make the cheapest possible antweight from scratch?

A: 'Cheap' and 'robot combat' really don't go well together. You're gonna spend your time and effort to build something that's going to let you down in battle. Why bother?

If you insist: buy a Futaba '2DR' 2-channel AM R/C setup. It comes with a transmitter, a receiver, two servos, crystals, mounting hardware, and a battery holder for about $40. Hack the two servos for continuous rotation. Find the centers on two plastic mayonnaise jar lids and mount them to the servo horns with self-tapping screws that come with the radio -- instant wheels. Stretch a wide rubber band around the outside of each jar lid for tires. Foam tape the receiver, battery holder, and servos to one of those free AOL CDs that come in the mail. Insert 4 AA cells in the battery holder and 8 more in the transmitter.

Congratulations, you've just built the world's cheapest scratch antweight. Now, throw it away before you embarrass yourself.

Q: In a earlier post you mentioned the complete Futaba 2DR AM R/C set for around $40. Where can I buy one?

A: Futaba 2DR at Tower Hobbies. This is a two-channel AM system. Check with your local event rules to make sure they allow AM radios for the weapon type and weight class you plan to build. FM radios are more expensive for a reason: they work better.

Da Vinci Days Antweight Champion - Rat Amok Q: What is the cheapest active weapon you can make on an antweight?

A: Rat trap - $1.79.

Q: How can I make the rat trap into a weapon?

A: Don't be too anxious; the rat trap is cheap but I'm not saying it's good. Set the trap and drive toward your opponent -- you get one shot. Check legality with your local event organizer and watch your fingers!

Q: I'm having trouble with my rat trap weapon. Every time I bump something the trap snaps shut. Is there a way to make it less sensitive?

A: Examine the way the trap latches to the trip plate. The bar is held by a very narrow dimple of bent metal. Bend the dimple to make it deeper, and reshape it to hold the bar more firmly.

My dad's antweight has a tiny servo that latches the trap shut 'til he releases it -- but that adds too much expense for it to qualify as the 'cheapest active weapon'.

Q: How did you turn Rat Amok into a flipper 'bot?

A: You must have seen the 'Rat Amok' video. Rat Amok isn't designed to be a flipper, but if an opponent climbs far enough on top they can be thrown forcibly upward then the trap is released. Other times, the trap ejects the opponent out the front of the trap at high speed and Rat Amok may flip over backward in reaction (she drives fine upside-down). Only occasionally does the trap actually 'catch' a part of the other 'bot. Teeth or a rubber 'gripper' added to the trap bar would modify the effect of the impact.

Q: What was the total cost of Rat Amok? What servos did it have?

A: Mark J. here: Let's see --

  • Rat trap - $1.79
  • Futaba T6XAPS R/C system - $229.95
  • 2 Futaba S3004 ball bearing servos - $0.00 (came with R/C system)
  • Cirrus 'nano' servo trap release - $29.95
  • 5 700 mAH NiMHd cells - $9.95
  • 2 front wheels from Tamiya R/C dune buggy - $7.95
  • Dollar Store knife for front blade - $1.00
  • Polypropylene cheese box from thrift store - $0.50
  • Assorted hardware - $2.58
Grand total: $283.67

Q: How do I make an antweight flipper using a servo and where can I get the materials?

Simple servo lifter. A: Servos are way too slow to directly power a flipper. I suppose you could use a servo converted to continuous rotation as a winch to wind a spring for a flipper, but that's too complicated to write about here.

You can use a servo to power a small lifter for an insect-class 'bot. You can simply connect an arm directly to the servo output wheel, but you'll have more interesting leverage options if you connect the servo to the lifter with either a rod link or a full 4-bar linkage. Search down the page for "4-bar" for tips. Your local hobby shop will have everything you need.

Q: What should I look for in a servo that's gonna power an antweight lifter? How powerful should it be (in/oz)? Are there any successful antweight lifters?

A: Mark J. here: I've looked around at ant lifters and the only things their servos have in common is high torque. The drive gears are usually well protected so metal gears are not needed. Speed isn't really an issue either. You don't need to spend a lot of money here.

Assuming that you're using the servo on one end of a simple lifter arm, you need to have enough power at the end of the arm to lift 16 ounces. Example: if you have a 3 inch long lifting arm, you need 3 in. X 16 oz. = 48 in/oz torque, plus about 25% to keep it from stalling. More torque will lift faster. There are other factors to consider, but that will get you in the ballpark.

My favorite (and very successful) antweight lifter is Adam Conus' Mission Control. Technically it's a clamp-bot since it has a second servo on the lift arm that clamps the other 'bot in place. Adam uses a Hitec high-torque standard servo [HS-545bb] with 76 in/oz of torque for the lifter and a Hitec 'Mighty Mini' servo [HS-225bb] for the clamp.

Q: In an earlier post you mentioned that a servo could be used as a winch to wind a spring for an antweight flipper weapon. How would you put that all together?

Servo winch layout. A: I also mentioned in that post that the winch was too complicated to write about here. I guess you didn't believe me!

The servo must be converted to continuous rotation and a small bobbin added to wind in string. The string passes around a pulley and attaches to the front edge of a mousetrap bar to pull it down. The complicated part is disengaging the bobbin so that it will spin free when the trap is released and re-engage when you're ready to reset the flipper. That requires a second servo and a better drawing than I can make. A pneumatic flipper would be less trouble.

Q: I found an English robot builder's site that describes a tiny pneumatic flipper 'bot built from a 3-way pneumatic valve, two 5 ml syringes, a plastic egg, and a microswitch. Can you show me how to make one of these?

A: Mark J. here: Chris Sherwood has been building robots in England for a long time. He was able to build his 150-gram pneumatic 'bot out of odd bits and pieces because of his extensive building experience. You can find pictures of 'Flipper': here. I don't believe his design would be legal (or competitive) in the U.S. under current RFL rules.

Very briefly, Chris uses a plastic egg for an air pressure reservoir and syringes for pneumatic cylinders. The system fires the 3-way pneumatic valve when a robot hits the microswitch on the flipper. Take a look at the Inertia Labs Micro Pneumatics FAQ and read the Micro Pneumatics PDF for info on building a similar system that would be safe and legal.

You might also be interested in using Lego Mindstorm Pneumatics parts for a low-budget insect flipper 'bot.

Q: I have a price limit of $200. What type of 'bot should I build and where do I get the supplies to build it from scratch?

A: If this is your first 'bot, keep it simple. An antweight wedge would be a great choice for a first scratch-built 'bot. Search down the page for an antweight parts list and lots of tips. You can get all the supplies you need at Robot Marketplace. I just counted, and that's the 18th plug for Robot Marketplace. Doesn't anybody read the old questions?

Q: My fairyweight design is just a flat-like armor on the flat chassis. What motor should I use?

A: That's not much of a description. The motor must fit in with all the design elements of the 'bot and work with them as a whole. What's your weapon? How large is the arena you'll be fighting in? What is the arena layout? Is speed more important to you than pushing power? What's your budget? Two wheel drive? Four wheel drive? Wheel size? Are you willing to make custom hubs, or do you want off-the-shelf parts only? Do you plan to use a lithium battery, or NiMH? How much weight allowance is available for the motors?

You can search down the page for 'fairyweight wedge' for a general recommendation of a motor that would make a good starting point for a 'bot.

Q: Do "Lite Flite" wheels need to have hubs? The hubs I've seen are expensive. Are there other wheels with a 3mm bore that don't need hubs?

A: You really have to make sure your wheels are securely fastened to the gearbox shaft. Having a wheel fall off is pretty much the most embarrassing thing that can happen in combat, so I really can't advise scrimping on hubs. Robot Marketplace has nice 3mm aluminum hubs to fit Lite Flights and other wheels for about $5 each. If you're really cheap, Tamaya wheels come with 3mm press-on plastic hubs for both round and hex shafts -- but if they shatter or just fall off, don't say I didn't warn you.

Q: I just built a antweight from scratch and I have one question: is car steering effective on the antweight level?

A: We used car-style steering on our heavyweight 'bot 'Run Amok'. Car steering is better than tank-style 'differential' steering at holding a straight line course and at making smooth turns, but tank steering gives much greater maneuverability in tight spaces. Car steering can work in a wedge or rammer in any weight class, but it certainly isn't popular.

P.S. - Alex Udanis wrote to tell me he thinks car steering bites. He didn't actually say 'bites', but I don't want to use the word he picked.

Q: Can I use fiberglass instead of plastic as armor on an antweight robot? Can I make a good wedge out of it?

A: Mark J. here: just like there are different alloys of metals, there are lots of types of fiberglass. The type of resin used is very important to the properties the material as a whole exhibits. Some resins are hard, but brittle. Others are more resilient. See the earlier post on garolite in the archive.

Q: I have three Electronic Speed Controllers (ESCs) in my antweight. What kind of product should I buy to split the two battery leads into six? What kind of connectors do you recommend for antweights?

A: No 'product' needed -- just solder three ESC wires to each output pin on the battery connector plug. I use Deans Micro Plugs for ant and beetle connectors, but any good R/C hobby power connector is fine. Buy them at your local hobby shop. Don't use automotive connectors (bullet connectors) -- they give trouble in robots.

Date marker: February 2006
Q: What's the maximum size for antweights? One competition site it said it was 4" by 4". Do fairyweights have a maximum size?

A: Neither SozBots nor RFL rules specify a maximum size for U.S. antweights or fairyweights. It's the British '150 gram' antweights that must fit in a 4" cube.

Q: I'm making an antweight vertical spinner with an outrunner motor. How do I mount the outrunner?

A: Tech question, Mark J. here: Outrunner style motors are a problem to mount because the entire outside 'can' rotates. Some outrunners (like the AXI) have a shaft that runs thru the rear mounting plate that makes for a simple mount. Others (like the Park) don't have a shaft in the rear and you have to get creative.

Take a look at Team Basenji's antweight 'Bitsy Blade' at the Robot Riots 5 photos page. It's an ant vertical spinner with an outrunner. They simply mounted the rear motor plate to the chassis and left the rest of the motor and pulley drive dangling in the air! It isn't good engineering practice, but it works for them. A better solution would be to add a support to the motor shaft as close to the weapon pulley as possible with a bearing on a strong support anchored to the chassis -- kinda the same as their weapon support.

Q: Is the Park 370 Outrunner motor strong enough to spin a 7 oz bar weapon without gears or belts?

Technical question, Mark J. here:

  • claims that the Park 370 Outrunner has "awesome torque" and that "in most circumstances" the motor can be used direct drive for an antweight weapon. I'm not able to find actual torque figures for the motor to back up those claims.
  • The power needed to spin a 7 oz. bar depends on the length of the bar. A short bar has less rotational mass than a longer bar and will require less torque to 'spin up'.
  • A spinning bar weapon needs to spin slowly enough for the bar end to grab and catch your opponent. The Park 370 Outrunner has a no-load speed close to 10,000 RPM at 7.2 volts! That's much too fast to spin a bar weapon.
Gear it down -- it'll be way more effective. The Team Run Amok Spinning Weapon Excel Spreadsheet can give you some help in modeling the performance of weapon/motor systems.
Q: Dear Aaron, I am making an antweight with a spinning drum weapon. Should I attach the motor directly to the drum or should I use a pulley system?

A: Unless you're running a very powerful weapon motor or a very small drum, you will need some gear reduction to spin the weapon up properly. The Team Run Amok Spinning Weapon Excel Spreadsheet can give you some help in designing your weapon For a reasonable motor and a mid-sized drum, try a belt drive with about a 3:1 reduction for a starting point.

Q: How many flips do you get when you build a antweight pneumatic flipper, and are flippers effective in causing damage?

A: The number of flips you get is dependent on the size of your air storage tank, the volume of your pneumatic actuator, and the pressure of the air in your system. You can design in as many flips as you like.

Antweight flippers are not generally effective at causing damage. They are popular in 'Sozbots' style arenas where a 'bot that leaves the platform looses. Flip 'em over the low arena wall and you win!

Q: All the antweight battery packs I find need both a charger and a high amperage DC power source for the charger. Is there a cheaper option?

A: Lithium polymer battery packs require special chargers that generally run from an external DC power supply. If you want to get off cheap, you can use the battery from your car as that DC power supply. Alternately, you can run NiCad or NiMHd cells that are less picky about charging and buy an inexpensive AC/DC charger from EBay.

If you want cheaper still, run AAA alkaline cells and replace them every few matches.

Q: Can't you just use servo motors to drive an antweight and save money on a speed controller?

A: A few years ago it was common to see antweight robots that used 'hacked' R/C servos as drive motors. Inexpensive R/C servos contain a small speed controller, a small DC motor, and a reduction gear train. They can be modified to provide rotating output rather than the stock back/forth motion (see: hacking a servo). Bolt on a wheel and you were in business!

Servo drives are nearly extinct now. They are slow and weak compared to other drivetrain options. You can build a robot with them, but you won't win many matches.

Q: I want to build an antweight with a flipper but I don't how to make one. How do you make a flipper?

A: Flippers are powered by compressed gas. You'll need a cylinder to store the compressed gas, an actuator to move the flipper arm, an electric control valve to release gas into the actuator (and vent the pressure to lower the flipper), an interface to control the valve with your remote control, and hoses/fittings to connect everything up.

Getting all of this equipment small and light enough for an antweight isn't easy. Inertia Labs makes a 'full pneumatics kit for antweights' [no longer available] and they have a FAQ page that answers a lot of questions about antweight pneumatic systems. Give it a read!

Q: Aaron, I want to build an antweight robot, but I have no idea how to do it. Could you tell me where to start?

A: Gee, everybody wants to build an antweight! I really like modifying R/C toys for antweights -- see the Toy Hacks and Kits section of the archive.

If you want to build from scratch you'll need an R/C radio set-up, a two-channel motor controller (three if you want an active weapon), two motors with gearboxes, a small battery pack, a battery charger, and wheels. You'll need to make a chassis to bolt all that stuff onto -- aluminum, Lexan plastic, and carbon fiber panels are popular. Then you'll have to get enough armor together to keep it from being cut in two. This is getting expensive!

There's an antweight discussion forum at -- dig thru the information there for more tips.

Q: What armor is best for antweight bots?

A: The same armor materials used in larger 'bots works great on antweights. Titanium is the top-of-the-line, but is expensive, not easy to find, and can be difficult to work with. Polycarbonate plastic (Lexan) is inexpensive, widely available, and simple to cut and drill. I've used ultra-high molecular weight (UHMW) polyethylene plastic with good results on my beetleweight.

Q: How big should a small robot be?

A: Combat robots are usually built to a maximum weight rather than size. Popular weight classes for small 'bots include:

  • 1-pound (antweight);
  • 3-pound (beetleweight); and
  • 12-pound (hobbyweight).
Antweight 'bots may be nearly small enough to fit in your pocket! Check with the organizers of events you're interested in to find out what weight classes are eligible to compete.
Q: What lightweight and strong metal would you recommend to use in an antweight robot, which has to weigh a maximum of 150g? (Rachel Mumby)

A: Wow -- that's really light! In the U.S. we get a full pound for antweights - 454 grams.

I live near some places that build parts for airplanes and I can get scrap pieces of thin titanium that are great for robots. Titanium is light and very tough, but it's usually expensive and hard to find.

You might want to consider thin carbon composite material instead of metal. marketplace sells small sheets of it. It's very stiff and strong.

Some types of plastic make good armor for light robots, too. Polypropylene is used for kitchen storage containers and is very thin, light, and tough.

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