Questions and Answers about Combat Robotics from Team Run Amok.

Thank you for your reply. Best regards, Jean Pierre [Provence-Alpes-Côte d'Azur, France]

A: [Mark J.] The Burkert 5404 is the solenoid valve of choice for pneumatic flipper systems because of its ability to flow a large volume of gas very quickly, but I don't think it's suited to your use. As I recall, you are building a 20 KG robot. A single Burket 5404 weighs more than a kilo and you'll need at least two valves of this type for your flipper.

The 5404 is a simple 2-port open/close valve. It can open to allow gas to flow into your actuator but when it closes there is no place for the gas in the actuator to go -- you need a second 2-port valve to open and exhaust the gas from the actuator to allow it to retract -- see the diagram. If controlling both valves from a single controller you will want the pressure valve to be the 'normally closed' type and the exhaust valve to be 'normally open' so that an actuation signal will open the pressure valve and close the exhaust.

Two 2-port valves will suffice for a flipper if you can live with a gravity or spring-powered retract. If you want a powered retract you'd need more valves to operate the retact side of the actuator. By this point a quarter of the weight of your 'bot could be valves and hoses!

Take a look at our Tips and Tricks for Pneumatic Weapon Systems page for some alternative designs.

A: [Mark J.] Who wants dibs on the name "Antisocial Distancing"?

A: [Mark J.] The FS2A receiver will failsafe correctly with your FSi6x on all channels, but the set-up process is not well described in the receiver documentation. Chinese radio gear is like that. Here's what the docs say:

Q: Hi there. I purchased an Endbots DESC lemon to use in a Beetleweight project, but am finding acquiring a DSM2 transmitter in Europe troublesome. Is it possible to add a different receiver to the project to allow me to use an alternate transmitter? Failing that, are there any other dual channel ESCa that work well for beetles?

Thanks, James [Smithton, Scotland]

A: [Mark J.] Hi James. I don't have an Endbots DESC lemon here in the shop, but I believe that it is just a Endbots DESC board with modified RX input pin locations that allow a Lemon-RX to be flipped over and soldered to the back of the board. De-soldering the Lemon-RX should allow you to wire any receiver onto the exposed channel pins. I would suggest writing to Endbots to verify this; they accept support requests at Sales@endbots.com

Failing that, the popular Beetle DESC at the moment is the Scorpion Mini from Robot Power. It is a fair bit larger and heavier than the Endbots DESC, but has a much higher current rating (6.5 amp continuous) and will handle up to 28 volts.

Some builders prefer using two of the single-channel Wasp ESCs from Robot Power. A pair of them are a little lighter than a single Scorpion Mini, and it's easier to find space in a cramped beetle for two small boards than one larger one.

Thank you for your reply. [Provence-Alpes-Côte d'Azur, France]

A: [Mark J.] I'm glad that you are enjoying Ask Aaron! You have a choice of three types of R/C interfaces to control your pneumatic valve:

• A mechanical relay with an R/C interface like the Polulu 2804. Mechanical relays are subject to damage and failure under heavy shock loading and for that reason are not recommended for combat robot use.
• A solid-state R/C switch like the Polulu 2802. Solid-state switches have no moving parts to fail under shock loading and are a better choice for combat robots. Some solid-state switches require adding a 'flyback diode' across the power output terminals when used to operate an inductive load like your solenoid valve -- be sure to check the manual. The Polulu 2802 requires no diode.
• A small ESC like the Fingertech tinyESC would provide a forward/reverse current rather than on/off if plugged into a switched receiver output. You could get around that with transmitter programming or you could find a single-direction ESC, but an R/C switch would be easier.

Q: Is the goBILDA Element-6 Radio Control System any good for an ant or beetle? [Glendora, California]

A: [Mark J.] I'm gonna say no. Take a look at the Team Run Amok guide to what radio functions you actually need. The goBILDA does not score well:

• The manual is only two pages long, and the first page is a picture of the transmitter.
• The manual makes no mention of if or how the system failsafes -- a proper failsafe is mandatory for robot combat.
• The feature list is quite basic: servo reversing on 4 of the 6 channels, standard trims, two non-standard mixes, and a very limited dual-rate switch.
• The included receiver is large for an insect robot, and the uncommon S-FHSS protocol limits the range of replacement receiver choice.

For the same price you can buy a full-featured FlySky FS-i6 radio with much greater capability.

A: [Mark J.] I don't know how you determined that you 'need' that particular LiPo pack, but the 25~50C version has been replaced by an improved 'Turnigy nano-tech 1300mAh 4S 45~90C Lipo Pack' with superior discharge performance.

The 45~90C pack weighs 10 grams more and is a millimeter longer and wider than the 25~50C version, but can provide 80% greater current output if needed. It's widely available and will work well in any robot that used the older version.

A: [Mark J.] Yes, that's a very dense and 'busy' illustration that was pulled straight from a CAD cross-section view. I've taken a shot at stripping it down to the key elements:

Q: I'm having trouble relating the diagram of the 'Algos' drum to the outrunner motor before it was modified. Can you give me a sketch of the outrunner in the same format?

A: Sure. The only parts of the original outrunner that are used in the finished weapon are the motor stator and the rotor magnet ring.

Q: Do you have any suggestions for funding? I am in a group currently working to design and build a combat robot, but we are all poor college students. [California State University, Maritime]

A: [Mark J.] Cinch up your Mae Wests and read Frequently Asked Questions #3. Read the rest of the FAQ while you're there.

If you're still up for it, start with a small 'bot -- learning from your beginner's mistakes will cost a whole lot less in a lighter weight class.

A: [Mark J.] There were several robot combat competitions prior to Marc Thorpe organizing the 1994 Robot Wars competition in San Francisco, but we can credit him with commercializing the sport.

Marc Thorpe created the 1994 'Robot Wars' event in San Francisco as a larger stand-alone commercial event at a venue that allowed for larger and more violent competitors. The event brought media attention to the sport and launched robot combat as we know it today. Anyone interested in the early history of robot combat should obtain a copy of 'Gearheads' by Brad Stone. It's a fascinating read and does a fine job of keeping all the parties involved very human.

Q: The RTV silicone rubber I've been applying to my foam tires for better traction works well but keeps coming off in chunks. Is there something I can do to get the silicone to stick better? Should I switch to liquid latex? [The Panhandle]

A: [Mark J.] If the silicone rubber is coming off in 'chunks' you're putting it on too thick. Clean the foam tires vigorously and throughly -- I use lighter fluid and a rag. Allow to dry completely. Apply pure silicone sealant to the tire surface and squeegee the sticky goo around the circumference with a popcicle stick or knife blade, applying very firm pressure. The silicone layer should be no thicker than a coat of paint and the texture of the foam should show thru. Wipe any excess from the tire sidewalls with a rag. Allow to cure for several hours (or days) before use.

I prefer silicone rubber, but many builders use liquid latex 'skin paint'. The technique is to first coat the tire with craft rubber cement. When the rubber cement dries you apply a couple coats of the latex.

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Q: Hi there, I'm currently trying to construct a circular arena for a Hobbyweight class competition in order to kickstart a robot combat scene here in Indonesia, do you have any specific pointers in order to make the arena safe? I want the arena to have big ring out zones like the kind of arenas you'd see in the UK in order to make flippers viable - and indirectly make ultra-high powered spinners worse because they run the risk of flinging themselves out of the arena. [Jakarta, Indonesia]

A: [Mark J.] The information I have on safe arena construction can be found in Frequently Asked Questions #38.

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Q: Personally, what are your thoughts on the viability of Mecanum wheels in combat robots in 2020? The traditional thought was that they just don't have enough grip compared to regular wheels, but has that changed in the recent years? [Banten, Indonesia]

A: [Mark J.] Can you name a Mecanum-wheeled combat robot with a winning record? The closest I can come is superheavyweight 'Alcoholic Stepfather' with a 5 win / 5 loss record. They managed to get pretty good traction, but their custom wheels cost $1000 each and were regularly destroyed in combat.

The problems associated with Mecanum wheels go far beyond traction. Here's what the Stepfather team had to say about them in a 2015 Reddit post:

Mecanum wheels have a LOT of disadvantages: expensive custom parts (including custom shaped rollers); wheels are heavy; needs a complex control system (long time to debug); needs a suspension to ensure all wheels touch the uneven steel floor; you give up a BIG chunk of your traction; use a lot of channels of RC unit; need two different versions (only opposite corner wheels match each other) so twice as many costly spares to build.

Advantages: great orientation control (keeps our uberstrong front end pointing at the opponent). But the biggest advantage is they look really cool when you can get them to work well. That is really why we used them.

Nothing has changed since that Reddit post. If you want to look cool, by all means give Mecanum wheels a shot. If you're trying to win matches they're best left alone. There are multiple posts about Mecanum and Omniwheels in the Ask Aaron Robot Design and Construction archive.

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Q: I'm looking to make a Beetle weight hammer/pick ax bot and saw you mention a pneumatic hammer system is the way to go. Would it be possible to fit into the US Beetle class weight limit if not what is the best substitute? [Spartanburg, South Carolina]

A: [Mark J.] Did I really say that? A pneumatic system can deliver a great deal more speed and power to a hammer or lifter weapon than a direct-acting electric system -- but they are also a great deal more complex and dangerous. Whether they are 'the way to go' depends on your experience in building combat robots, expertise in metalworking, access to a machine shop, and expectations of performance.

1. Take a look at the Team DaVinci Guide to Understanding Pneumatics for an overview of the combat robot pneumatic systems. Also check with the organizers of any events where you wish to compete for special tournament rules and restrictions on pneumatic systems.
2. Search the Ask Aaron Ants, Beetles, and Fairies archive for 'pneumatic' to find dozens of earlier posts on insect class pneumatic systems. You'll find some alternatives with that same search.
3. There have been many pneumatic beetles, ants, and even fairies, but there is no 'off-the shelf' set of components currently available that will work for insect-class combat robots. You'll need to carefully modify existing pieces or make your own -- not a simple task and not for the inexperienced.
4. You can download the Team Run Amok Electric Hammer Spreadsheet and model the performance of an electric hammer sized for your 'bot -- but you'll find that the destructive energy available from such systems is disappointingly small compared to other weapon choices. A pneumatic hammer would be more powerful, but would still fall well short of other weapons.

No type of beetleweight hammer is likely to be effective at winning matches against spinners or powerful wedges, so 'the way to go' here might be to make it easy and just mount a hammer on a quick R/C servo. It won't do much damage, but neither will a more complex hammer system.

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Q: A robot that has fascinated me and a design I can’t recall being repeated was that of 'LOLCano V' (as it’s called on BuildersDB). One thing that isn’t really explained, however, is how exactly they managed to get both the drivetrain and the weapon to move on the same axle. What are some ways to accomplish this, and what am I missing with these designs that I’m most likely overlooking?

I know this design is one that’s probably better suited to show off than to be competitive, but it’s one that I enjoy and would like to put my own spin on... whenever I get around to doing so. [Joliet, Illinois]

A: [Mark J.] 'LOLCano V' (fight video) is not a unique design. It's a eggbeater variant of a "full-body drum spinner" (FBDS) of which there are several well-known examples:

• Derek Zahn competed successfully with ant and hobbyweight versions of his FBDS 'Daffodil' at NERC events in the early 2000's;
• Team Anomoly campaigned an antweight FBDS 'Tumbleweed' at NERC events in 2005-6;
• Team Rotractor's heavyweight FBDS 'Barber-ous' fought at Robot Wars series 5 thru 7; and
• Team KurTrox's 2019 BattleBots heavyweight 'Axe Backwards' is a FBDS.

You're having trouble figuring out the 15-pound 'LOLCano V' because:

1. The builders got carried away with their design software and made it overly complex; and
2. The render left off key pieces (like wheels, hubs, and belts) and included extra stuff that didn't make it onto the finished 'bot.

Here's how it works:

• There is a solid, structural 'dead shaft' running thru the robot and terminating on either end at a squared wheel guard plate that prevents shaft rotation.
• The internal chassis is mounted to that shaft and does not rotate.
• Chassis-mounted gearmotors belt-drive long hex-ended wheel hubs that rotate freely on the dead shaft.
• The belt-driven beater-bar rides on bushings that bear on the round-section portion of the extended wheel hubs.

Summary There is a 'dead shaft' with wheel hubs rotating on it, and rotating independently against the outside of the wheel hubs are bushings supporting the beater bar. Very messy.

In a more common FBDS design layout as used by 'Daffodil' (archived build report):

1. There is no continuous shaft thru the robot -- a structural chassis fits inside the drum and carries wheel and weapon forces.
2. The drum rides on bearings supported by hollow 'stub' axles on either end of the chassis and is powered by a friction drive wheel running against the inside of the drum.
3. The wheels are powered by chassis-mounted gearmotors with shafts extending thru the hollow stub axles to the wheel hubs.
4. The stub axles also support one or more firmly mounted arms that press against the arena surface to prevent the chassis from spinning around inside the drum.

See this Full Body Drum Spinner post in the Ask Aaron Archives for a photo and description of the layout of 'Barber-ous'. The chassis shown there is unusual in that it has the drive motors mounted externally on the trailing arms with the wiring running to the chassis thru the stub axles. Later versions of 'Barber-ous' moved the drive motors to more common internal mounts on the chassis.

Q: In that "Actual" pic of "LOLcano" it looks like the wheels don't even touch the ground. Am I seeing that right? [Wellesley, Massachusetts]

A: [Mark J.] No wheels are shown in either the 'Rendered' or 'Actual' pics of 'LOLcano V'. Large diameter wheels mount to the hexagonal section hubs you can see in the 'actual' pic, and square guards then mount to the shaft outside the wheeels. I've added a screen grab labeled 'Complete' that shows the whole robot.

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Q: In a recent post you mentioned that there are specific transmitter adjustments that could help with keeping a two-wheeled robot running straight instead of weaving or veering from the target. Are there things other than adding a gyro? Can you list some specific adjustments? [Way Up in the Rockies]

A: [Mark J.] I wasn't trying to be cryptic. I've covered specific transmitter tweeks that can help with straight tracking in assorted posts and radio articles and I assumed that I'd tied them all together in a single place. Apparently that is not the case, so I've created a new transmitter guide covering this topic:

Transmitter Tweeks for Better Combat Robot Control

Note that transmitter tweeks aren't going to solve mechanical issues with your robot. If your chassis isn't straight, a gearbox is binding, or a motor controller is faulty, you need to address those physical problems first.

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Q: We're having no luck pairing our Turnigy T6A-V2 transmitter to an Endbots Lemon RX DESC. Do we have to use the Turinigy receiver/transmitter as a pair or is it possible to connect the new Endbots DESC to our transmitter? [The Aether]

A: [Mark J.] The Lemon receiver and your Turnigy transmitter operate in the same frequency range, but they speak different languages.

• Your Endbots Lemon RX DESC requires a transmitter operating on the DSM2 radio protocol;
• Your Turnigy transmitter sends signals in a 'flavor' of the AFHDS protocol that is compatible only with the HK-T6Av2 receiver.

Several manufacturers make transmitters capable of communicating via DSM2/DSMX, but they'll cost a bit more than you paid for your entry-level T6A.

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Remembering Aaron Joerger, 1991 - 2013 The 'Ask Aaron' project was important to Aaron, and I continue the site in his memory. Thank you for the many kind messages of sympathy and support that have found their way to me. Aaron's obituary - Mark Joerger

Q: how can robots help us deal better with hurricanes and why? [Ontario, California]

A: [Aaron] Few people in Nebraska are threatened by hurricanes, so send a swarm of killer robots into low Atlantic and gulf coastal areas to drive the puny human inhabitants toward Nebraska. Problem solved.

Robot haiku:

That's obviously A question from your homework. Do your own research.

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