Ask Aaron - Frequently Asked Questions

Q: What do combat robots do and what are they good for?

A: Take a look at the Wikipedia article on Robot Combat for a good summary of the subject.

Q: Are they dangerous?

A: Dangerous? They fight in arenas behind inch-thick ballistic plastic. They can throw each other 15 feet in the air and tear titanium sheet in half. Their weapons carry more energy than half a dozen AK-47 bullets. Yes, dangerous.

Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot. Do not operate combat robots without proper safeguards.

Q: Can you tell me how to build a combat robot?

A: There's way too much to cover in a short answer!

• The Robot Combat Wiki "Getting Started Guide" offers a overview that takes you from planning thru walking into your first competition.
• There are a great many How-To Videos covering pretty much every aspect of the mechanics. Start with Robert Cowan's Introduction to the Combat Robot Resource Guide
• Take a look at the Ask Aaron archive to get some ideas on converting R/C toys. You may also want to look at some combat robot kits.
• The RioBotz Combat Robot Tutorial covers more advanced topics. It's 367 pages of solid design and building advice from a very successful team, and it's a free download.

Q: How much does it cost to build a combat robot?

A: Whatever money you can afford and then some, all of your spare time plus any extra time you can steal, several personal relationships, and a chunk of your sanity.

Q: How can I get a sponsor?

A: If you don't have a rich uncle you're not gonna get a sponsor.

Q: How did you do all these things?

A: One thing at a time, with a lot of mistakes along the way.

Q: What design should I use for my weapon/chassis/armor? How long/wide/thick should it be? What materials are best? What type of chassis/weapon/motors will allow my robot to crush the opposition and never be beaten? How do I add a self-righting mechanism?

A: We're happy to answer specific questions about robot design, construction, and materials, but we're not going to design your robot for you.

• Answers to a wide range of design questions plus tools to help with other design considerations can be found in the Ask Aaron Archives.
• Read thru the archives, do your homework, and come back to us with specific questions that haven't already been answered in the archives.
• When you do come back with a question, please give us enough information about your design and requirements to have a chance at giving you a useful answer.

Q: How do you get started in combat robotics?

A: Read Robert Cowan's Combat Robot Resource Guide. The guide is a comprehensive listing of general information and links to resources that builders will find useful: rules, finding events, construction resources, key YouTube channels, online groups, parts sources -- everything!

You'll also want to watch Robert's Introduction to the Resource Guide where he explains his approach and recommends how best to use the guide.

Q: What is the best weight class for a beginner to start in?

A: Scout the event you plan to enter and find out what weight classes are popular. It doesn't do any good to build a robot for a class that doesn't have anyone else in it! Start in the lightest weight class that has a good number of competitors. The lighter your weight class, the less your beginner's mistakes will cost you.

Q: Can you point me to some on-line forums for combat robotics?

A: The Robot Combat Wiki maintains a good list of forums and video channels.

Q: How do you draw plans for a 'bot and get every thing in the right place?

A: Robot builders design and build 'bots all different ways. Some use computer drawing software to design every last detail before they buy parts. Some build exact models from cardboard to see how things fit. Some just buy lots of parts and see if they can fit them together like a jigsaw puzzle. I like to list all the parts I think I'll need, sketch a drawing, and add up the weights of the parts to make sure I'm under the weight limit.

Q: What's your best tip for robot building?

A: My best robot tip is to make sure the basics of the chassis and drivetrain are really well built. I see lots of 'bots lose matches because something really simple wasn't designed well: wheels fall off, battery packs break free, unsecured wires come loose. The most insane weapon is no use at all if the chassis or drive fails.

Q: I'm building my first robot and I'm going to make it just like insert name of successful robot so that I can win every match. Great idea, right?

A: New builders often assume that a given combat robot performs well entirely because of its design. The robot you mention is successful for many reasons:

• It was built by an experienced and skilled team;
• It is driven well with a carefully set-up R/C system;
• It is made from properly selected materials and components;
• It is given meticulous preparation for each match; and
• Barely noticeable details of its design have been improved over time based on combat experience.

Q: OK, so what should I build for my first 'bot?

A: Your first combat robot should NOT have an active weapon -- no spinner, no lifter, no flamethrower, no crusher. Keep it simple; build a wedge. It is both for your benefit and the best interests of the sport. See this post in the Ask Aaron archives for a summary of the reasons.

Q: If the first design you should build is a wedge, what's the second?

A: When you have built and competed with your wedge you will better understand:

1. The magnitude of the challenges presented by differing types of weapons; and
2. How well your knowledge and skill level suit those challenges.

Your next step will be obvious.

Q: How do I search this page? The search box got me this far.

A: Use the search function in your browser to search a specific page: hit CTRL-F to bring up a page search box.

Q: The last question I asked was a follow-on to my earlier question. Don't you remember me?

A: Questions submitted to 'Ask Aaron' all come in from the same webmail address. We can trace them to their source if we have a reason, but if you don't identify yourself as 'the guy who asked the titanium question' we may not figure out that your question was a follow-on. Our psychic abilities are weak.

Q: I have an idea for a robot, but I don't want to talk about it here. Is there some way I can ask you a question about it besides here where others can see it?

A: Send it in thru the website, include your email address, and mark it 'CONFIDENTIAL'. I'll keep it between us.

Q: Are there any combat robot tournaments near where I live?

A: There are websites to check for upcoming events...

• Robot Combat Events has event notices from around the world;
• The Fighting Robot Association has listings and discussion for British events.

Q: Hey, why don't you put all your recordings of Robotica / BattleBots / Robot Wars on You Tube?

A: The Team Run Amok video library contains complete recordings of every nationally televised combat robot event. We respect and honor the rights of the copyright holder for these programs. We will not place copyrighted video on the internet without permission.

Q: What exactly happened at the fight between old robot #1 and old robot #2? I know who won, but I want you to go dig the tape of the fight out of your video library, watch it, write up a detailed summary, and then we can talk about each and every episode because I'm a HUGE FANBOY.

A: We get variations on this question a lot. 'Ask Aaron' supports combat robot builders and robot combat historians; Ask Aaron is not a fan site. See our Mission Statement at the bottom of this page.

Q: I heard that BattleBots was cancelled in 2002 because Budweiser threatened to pull all their advertising from the Comedy Central network if that didn't happen. Is this true?

A: No, but the rumor will not die. Here's what happened: during the 2002 Superbowl the Anhauser-Busch company aired a humorous Bud Light commercial that featured fictional combat robots. The robot combat community thought it was great. BattleBots, however, thought it infringed on their copyrights and filed a lawsuit. The court ruled in July of 2004 that the commercial was a fair-use parody of robot combat and dismissed the suit.

BattleBot's action in filing the lawsuit may have damaged their reputation and injured combat robotics in a way that contributed to the show's demise, but there is nothing to suggest that Anhauser-Busch extorted Comedy Central into cancelling the TV show.

Q: Where can I get really cheap combat robot parts?

A: You're going to spend a lot of time and effort building your 'bot and going to a tournament. When some component fails in combat and puts you out of the competition, you're gonna wish you hadn't gone cheap. In particular, don't scrimp on electronics! With experience you'll learn where you can save money, but it's not gonna be on key components like speed controllers and wheel hubs.

That said, some teams are willing to use the really cheap off-brand electronics, motors, and batteries available from HobbyKing. I don't recommend their products: documentation is awful, customer service non-existent, quality control unheard of, and delivery uncertain -- use them at your own risk.

Q: OK, where can I buy good parts to build a combat robot?

A: There are many suppliers of quality components for small combat robots -- here is a partial list:

A: 'Ask Aaron' is not a free engineering service. Even if we were, no competent engineer would spec material or thickness before knowing a great deal more about the design than you have told us. We do provide some advice and guidance on materials in our Armor Guide. Look to see what other builders with similar designs are using and learn from their experience. If it breaks, make it stronger.

Q: What is a 'scale factor' and how does it effect combat robot design?

A: The 'scale factor' refers to the disproportionate changes to material thickness required when a design component significantly increases or decreases in size. It is related to the Square-Cube Law.

Consider what happens when you double the dimensions of an object:

If you took the design for a successful one-pound 'antweight' combat robot and scaled up all the dimensions by a factor of six it would become a (6 × 6 × 6 =) 216-pound heavyweight -- but the strength of the shafts, armor, and fasteners would be only (6 × 6 =) 36 times as great and it would not survive in combat.

Conversely, if you took the design for a successful 220-pound 'heavyweight' combat robot and scaled down all the dimensions by a factor of six it would become a (220 × 1/6 × 1/6 × 1/6 =) just over 1-pound antweight -- but the strength of the shafts, armor, and fasteners would be much greater than needed. Those components should be resized so that their unnecessary mass may be allocated to weapon and drive systems to make the robot more effective in combat.

Q: What are the minimum radio system requirements for my robot?

A: Radio System Requirements from Section 6 the SPARC Robot Construction Specifications are widely accepted. Check with the event organizer for any variation from these requirements.

Spread spectrum 2.4 gHz radios have almost entirely taken over the hobby R/C market and are accepted at all combat robot tournaments -- if they failsafe correctly. When the receiver signal is lost, a correct failsafe response will shut down all robot motion -- drive motors, weapon motors, actuators, everything! There are three common responses by R/C receivers when they loose the transmitter signal:

Unacceptable Continue to send the last position signal received before signal loss to each device -- also known as 'hold position'.

Acceptable Stop sending any signal to the connected devices. This relies on the individual devices to correctly interpret 'no signal' as 'off'.

Preferred Send an output signal to all connected devices that will return them to a user-set stick position (off).

Make sure the radio and equipment you select is able to give an acceptable or preferred failsafe response!

Q: I bought all the parts I need to build my robot (battery, drive motors, Electronic Speed Controller (ESC), weapon motor, weapon ESC, transmitter, receiver) but just realized I don't know how to assemble everything! Can you briefly describe how everything connects?

A: Very briefly, with a number of assumptions:

• The power input pads for drive ESC, brushless weapon ESC, and power indicator light connect in parallel to the battery via a plug so you can disconnect the battery to charge it. Get the polarity correct! If you want to add a charging plug, see the charging jack post.
• Drive motors connect to the motor output tabs on the drive ESC -- brushless weapon motor to the weapon brushless ESC output leads.
• Two three-wire R/C input cables attach to the drive ESC signal inputs, and one R/C cable for the weapon ESC. They may already be attached. If not, double check the correct connection of the three wires (power+, power-, and signal) -- if you get it wrong you'll fry something.
• Drive ESC R/C cables plug into whichever channel ports you'll be using on the receiver: typically 1 and 2 if you're mixing, 2 and 3 if you're not. The brushless weapon ESC R/C cable plugs into a spare channel of your choice.

If everything works, but the controls aren't correct, try the on-line Run Amok Mixer Fixer to get a quick solution, or sort thru the problem manually with our Mixing Setup Guide.

Q: I put the robot together but it's acting weird. It starts and stops, and control is jerky. When I turn on the weapon everything stops and twitches. What's wrong?

A: LiPoly batteries are stored and shipped with only a partial charge. The load from your drive and weapon motors are pulling the battery voltage low and your electronics are suffering a 'brown out'. Put a full charge on your battery and try again.

Q: Where do I go to learn about radio control for combat robots?

A. You're already there:

• For a quick technical summary see How R/C Radios Work.
• Read the Run Amok Combat Robot Radio Function Guide.
• Browse our Radio Control Systems for Combat Robots page for a list of our combat robot radio guides, troubleshooters, and tips.

A. See our Beginners Guide to Combat Robot Gyros.

Q: What motors should I use for the drive on my insert weight class here robot?

A: The motors you will need depend on the style of 'bot you're planning to build and your expectations. A 'bot with a massive weapon that just needs to push itself around the arena will need a lot less drive power than a ramming brick or wedge. It comes down to matching the power-to-weight ratio of your 'bot to the type of attack strategy you're planning.

Some maniac builders pack way more than 100 watts of power per pound into their ram 'bots, but there really are limits to how much power can be used in a small arena. Current 'bots average around 40 to 50 watts per pound, and I've built three champion robots with less than 5 watts of power per pound, so there is a wide range of power that can be used with success.

You'll find the Team Tentacle Torque & Amp-Hour Calculator very useful in selecting motors for your robot. It has data on most popular motors and will quickly calculate the performance of your robot with any motors, gearing, and wheel size you choose. See also our guide to Optimum Gearing for Combat Robots for help in picking the best gear ratio and wheel size to optimize the performance of your motor.

If all else fails, find a successful robot in your weight class with a design similar to your own and blatantly copy the drive train.

Q: How much battery capacity do I need for the drive motors in my insert weight class here robot?

A: Current use by the drive motors depends on how heavily they are loaded. The Team Tentacle Torque & Amp-Hour Calculator will estimate the battery capacity need from the drive train specifications (type and number of motors, voltage, gearing, wheel diameter, and robot weight) for 3 and 5 minute match lengths. Give yourself a little extra capacity (~20%) to allow for unexpected conditions.

Q: What Electronic Speed Controller (ESC) should I use?

A: The speed controller amperage capacity requirement for your motors will depend on design factors such as:

• robot weight;
• wheel diameter;
• drivetrain gear reduction;
• battery voltage and current capacity; and
• percentage of total weight supported by the drive axle(s).

Once you have settled on motors and drivetrain details, the Team Tentacle Torque & Amp-Hour Calculator will calculate the peak amperage the drive motors can consume with the robot pushing at full throttle against an immovable object [Amps (per motor) to spin wheels]. Use that number to select an ESC with suitable capacity. Give yourself a little extra capacity (~20%) to allow for unexpected conditions. The merits and deficiencies of specific ESCs are discussed in the Motors and Controllers Archive

Q: Electronic Speed Controllers are expensive. Can I use relays or solenoid switches to control my robot?

A: You can, but the results will be poor and you won't save much money. See the

Q: I don't know how much power a insert motor name here has. How do I find out?

A: If a motor supplier does not provide output power specifications for their motors, you can get an approximation of output power with the following formula:

Q: What is the difference between a brushed and a brushless motor?

A: A brushed permanent magnet direct current (PMDC) motor has a rotating 'armature' of wire coils, typically wound around iron pole cores. The armature is positioned in a field generated by stationary permanent magnets. Electrical power applied to the wire coils by conductive 'brushes' sliding across contacts on the armature causes the coils to be repelled from one side of the permanent magnetic field and drawn toward the other, creating rotation. As the coils reach the side of the magnetic field to which they are attracted, the polarity of the applied electrical power is reversed as the rotation of the electrical contacts places them in contact with a different set of the sliding brushes. The brushes sliding across the electrical contacts create friction, wear, and inefficiency. There is a good diagram and an animation at Wikipedia: Brushed DC Electric Motor.

A brushless PMDC motor has stationary wire coils and rotating permanent magnets. Since the coils are stationary, sliding brushes and commutator are not required -- however, the switching of electrical power to the correct coil windings must be handled by an external 'intelligent' motor controller that senses the position of the rotating permanent magnet field and adjusts the electrical polarity as needed.

See also: Wikipedia: Brushless vs. brushed motors.

Q: What is the difference between an 'inrunner' and an 'outrunner' brushless motor?

A: If the rotating magnets are outside the wire coils, the motor is an 'outrunner' or 'rotating can' design. If the rotating magnets are surrounded by the wire coils, it is called an 'inrunner'. An inrunner motor generally spins faster and produces less torque than a comparable outrunner.

Q: Should I use a brushed or brushless motor for my robot drivetrain?

A: Hobby brushless motors are generally designed for model aircraft or R/C racecars. They pack a great deal of power into a package smaller and lighter than comparably powerful brushed motors, This makes them ideal for spinning weapon power, but for drive there are some drawbacks.

Combat Robots typically spend a good portion of their matches pushing hard with their tires spinning and the motors under heavy load. Selecting brushless drive motors that will survive under these conditions can be tricky: see our page on brushless motor selection.

Brushed motors and controllers are generally "plug and play" with few complications. Brushless motor controllers often require a fair amount of "tuneing" to provide proper motor response. This may be both frustrating and time consuming.

Your first few robots will be challenging enough without the added complexity of brushless drive motors. Stick with brushed drive motors until you have all the other aspects of your robots figured out.

Q: Can brushless Electronic Speed Controllers for brushless motors be used with brushed motors and vice versa?

A: Short answer - no. Speed controllers for brushed and brushless motors are very different in design and cannot be interchanged.

It is possible to laboriously decode and rewrite the software controlling a brushless ESC to enable use with brushed motors, and there are a very few 'dual purpose' ESCs that can be switched between brushed and brushless operation. These are exceptions.

Q: The brushless ESC for my spinner weapon motor makes beeping noises when I power it on. When I flip the weapon switch on my transmitter it beeps more but does not spin up the weapon motor. What's wrong?

A: Hobby aircraft ESCs will typically have a safety 'arming sequence' that looks for a specific sequence of transmitter commands before they will activate. This prevents unintended actuation of a dangerous spinning propeller -- or in our case a dangerous spinner weapon. Check the manual for your specific ESC to find the arming sequence.

Q: How do I reprogram brushless motor controllers to add reverse and make them useable for brushless drive motors? Is it easy?

A: Builder Robert Cowan has a nice video that covers the entire process of 'flashing' the reversing SimonK firmware onto brushless ESCs. I wouldn't call it either simple or easy: SimonK Firmware Flashing Tutorial.

Q: How much can I overvolt a insert motor name here?

A: It is common practice in combat robotics to run weapon and drive motors at higher voltages than they are rated in order to obtain greater power. How far a motor can be overvolted depends in part on how much load is placed on it. If allowed to bog down close to stall, an overvolted motor will not survive long. Better results will be obtained by setting up gearing and wheel diameter so the motor can provide enough torque to spin the wheels before it slows below about half the free RPM of the motor. The Team Tentacle Torque & Amp-Hour Calculator can help you select wheel sizes that will keep the amp load reasonable at elevated voltages.

Also, be aware that while motors from industrial equipment or consumer products will usually take a large voltage increase in stride, high performance hobby motors are already being stretched about as far as they can go on voltage and will have a VERY short life if pressed higher.

Q: What type of combat robot weapon is best?

A: If there was one type of weapon that was 'best', everyone would be using it. Although the highest ranked combat robots generally use high-powered spinning weapons, those teams are very experienced and well financed builders. Overall, you might be surprised by what weapons win the most matches.

Q: I want to build a robot that combines a insert weapon type 1 and insert weapon type 2. Is that a good idea?

A: If you split your weight allowance between two weapons, neither will be strong enough to be effective. It has been tried many times. Commit to a single weapon type.

Q: Is insert weapon type here a legal combat robot weapon?

A: Check the current SPARC Robot Construction Specifications for details on allowable weapons. The final authority for weapon approval is the event organizer for the specific event, so check there as well for non-standard weaponry.

How does insert flamebot name here's flame weapon work?

A: You can search the archive for 'flame' to find our many previous posts on flame weapons. Briefly:

• Flame weapons are ineffective in any weight class.
• Flame weapons are built by very experienced builders who just want to show off.
• We will not discuss flame weapon construction here because we don't want novice builders hurting themselves.
• By the time you are experienced enough to safely build a flame weapon you won't need to ask us how to do it.
• That flamebot that you're about to tell me is successful was built by a very experienced and well financed team and would be just as successful without the flame weapon.

A: 'Ask Aaron' gets a lot of questions about designing spinning weapons for combat robots. I've gone thru the archives and pulled together a selection of Q&A that should answer the most common spinner questions. See: the Team Run Amok Spinner FAQ.

Q: Does insert robot team name here still or ever have a website?

A: Pretty much everybody has or had websites. Here's my trick:

• Go to the RobotCombat.com Links Page and click on the link to the team you want. Click 'U.K. Robots' at the top of the page to list British teams.
• If the site no longer exists or no longer has robot info, copy the URL and go to The Wayback Machine.
• Paste the URL into the search box and hit the 'Take Me Back' button.
• You'll get a dated list of archived 'snapshots' for that site you can click up.

Q: Where can I find the combat record for insert robot name here?

A. Complete combat records for North American robots up to 2022 can be found at the archived BotRank.com. Enter the robot's name, then click on its 'history' link.

Full tournament trees for the major robot competitions can be found at the Team Run Amok tournament results webpage.

Q: What ever happened to some obscure old robot that fought only once and lost?

A: More than 4000 robots have fought in organized combat events in North America alone. Most of these robots have uninteresting stories -- they were built, they fought, they lost, and their builders moved on. We have very little interest in most of these obscure robots, but if you are interested and willing to dig thru old website archives and combat records, see the two questions immediately above.

We get so many variations on this question that I've started entertaining myself by playing 'Mad Libs' with the answer:

You can read the complete collection of 'Obscure Robot Mad Libs' in Aaron's Greatest Hits.

If you are interested in stories from early robot combat, drop whatever you're doing and go find a copy of 'Gearheads: the turbulent rise of robotic sports' by Brad Stone. Great reading!

Q: Who do you think would win if robot name #1 ever fought robot name #2?

A: We don't predict fantasy matches not involving our own robots. In fantasy matches involving our robots, we always win

Q: Your photo at the top of the Ask Aaron home page is really old! When are you going to replace it?

A: I'll replace it when I win a bigger trophy.

Q: If Robotica ever gets rebooted, would you create a new version of Run Amok and compete in honor of Aaron?

A: Mark J. Much though Aaron enjoyed competing, he had a greater love of helping people and sharing his knowledge. I believe that Team Run Amok has had a beneficial impact on combat robotics through our efforts to support combat robot builders, and I believe that continuing with those efforts is the best public way for us to honor Aaron.

I would be pleased to support the production of a Robotica reboot, but our team lost its competitive heart. We will not return to competition.

Q: Our Robocup robot can see in all directions and it is attracted to a red ball i.e. it drives to it. At the same time it is repelled from blue walls, i.e. when it comes too close to it, it moves backwards. Now assume the red ball lies in front of the blue wall. Describe the resulting behavior! Can you enhance on it? How?

A: We get this same question, word for word, several times a year. Could you slackers at least re-word your class assignment before you send it in to us?

The behavior is classic approach / avoidance -- the robot will effectively 'lock up' and do nothing. The common solution adopted in sumo robots is to lock out the edge detection routines whenever the object detectors report you're heading toward your opponent.

Your Robocup robot can use a similar strategy: if the red ball is in your path, override the blue wall avoidance routine AND move toward the ball. A more sophisticated approach would utilize an elevated video camera looking down on the field to verify the relative positions of the wall and ball and determine action accordingly.

Q: Does insert name love me?

A: Beats me, but we love people who ask questions about combat robots.

Q: Why are you no longer accepting questions about UK Robot Wars events or competitors?

A: Mark J. For many years Aaron and I did our best to answer any and all questions on the broad topic of robot combat. A few years ago we were flooded with a large volume of trivial UK Robot Wars questions that were well outside the mission and focus of this website. 'Ask Aaron' is not a fan site and we are not interested in investing our time in this area. We regret having to cut off all UK Robot Wars questions, but the fanboys proved themselves to be both persistent and incredibly rude.

Q: Why are you no longer accepting questions from builders competing in India?

A: Mark J. Although I very much wish to support the technical aspects of robot construction in the energetic and expanding Indian subcontinent, I am also greatly worried that I may be contributing to an extremely dangerous situation for builders and spectators.

The best enclosed arenas in India would be considered inadequate for 30 pound robots in Europe or the US but are hosting events for 132 pound 'bots. Aaron certainly wouldn't approve of this reckless endangerment of life and limb, and I will not contribute to the development of more powerful weaponry for Indian robots until their arenas are universally able to safely contain them.

Q: How do you build a safe robot combat arena?

A: I know of four resources:

• SPARC Arena Construction Best Practices (PDF) provides construction considerations, cost estimates, material recommendations, and example arena photos.
• The Robot Fighting League (US) provides arena plans and a materials list (PDF) for 30 kilogram robots. Additionally, their 'Resources Page' (archived) provides guidance on robot safety inspection and match judging.
• The Fighting Robot Association (UK) has a comprehensive FRA Guide to Event Safety (PDF) that includes arena specifications and procedures for events of differing weight classes and weapon types.
• Team Just 'Cuz Robotics offers a full set of plans for an antweght arena than can be made with simple tools. Video: Build a Combat Robotics Arena with these Open-Source Plans -- Download Plans: Just 'Cuz Store.

Q: How would I go about building a safe and functional test box where I can practice and test my insect-class robot?

A: I know of several guides on the construction of insect-class test boxes:

• FingerTech Robotics has put together a very nice set of step-by-step plans for an inexpensive antweight test box, including a parts list you can fill from your local home center.
• Absolute Chaos Robotics has an outline of the construction of their new beetleweight test box that includes a bill of materials.
• Just 'Cuz Robotics offers a 12 minute video that includes a bill of materials in the comments section.