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Steve's Guide to Building a Featherweight

This is not meant to be comprehensive guide on how to do everything this is just meant to be an overview of what you need to get started and where to go to find more information.


Combat robots are dangerous that is one of the reasons why putting them in an arena and watching them destroy each other is fun. This means that they are also capable of destroying you. Despite this building robot can be done in a safe manner if you think about what you are doing and take a few precautions. All the weapons you can build basically rely on the transfer of large amounts of energy into the other robot whether by spinning, flipping, launching, ect. So simply don't test these sorts of weapons in situations where you are not adequately protected. Do it in an arena or equivalent area with safety measures in place to ensure you don't get hurt!

Secondly a driving robot (even without a weapon) running into your ankles could easily break one, or cause sever damage, so make sure your robot can be properly controlled and have some form of barrier it can't drive over between it and yourself before letting it loose for testing. When testing your robot on the bench you should always have your wheels elevated.

There is many other things which I haven't covered here but if you have any doubts before doing something don't do it.
I take no responsibility for any injury sustained by building anything shown in this guide. If you don't have the skills, tools or patience to do it properly and safely STOP NOW

We now return you to your regular program.


Most events now use the standard RFL rules set. Jump to the Rules Section and have a read before you go much further.

Just quickly before you ask. "Why can't I build an EMP or use radio jammer or use a gun on the robot?" Have a think about what would happen...
With an EMP you would put the two robots in the arena one would set off EMP... other robot would sit still. Not going to be the most interesting thing to watch. There is a reason why there is restrictions on the weapons. Whether it is for safety, to keep things interesting or just prevent undue damage to the arena. The rules have been refined over 10 years so they are pretty well thought out. So just ask yourself why before complaining about the restrictions.

What will you need?

This guide aims to cover really what you need to make a wedge style robot which can just drive around and might be a good entry for your first comp. Its a bit boring but keeping things simple when you start out is a good idea.

Radio controller
Drive train
Speed Controller

Radio Controller

You will need some form of radio controller.

If you don't have one already

Jump on HobbyKing and grab a 2.4ghz any model you like should pretty much work these days. A Hobbyking T6A V2 6channel radio is <$50 including shipping and is a good place to start. Just don't forget to grab the PC programming cable.

For more info on radio choices then jump to the Radio Control section

If you already own a radio

The important question now is "Is it a digital radio?"
Any 2.4ghz radio will be digital and some of the older radios have digital signal encoding which make them much more robust to interference. These should all work fine in a robot.

The question those of you who are unsure or who don't have a digital radio are asking is can I use my old 36mhz or 40mhz radio from my RC car or plane? Short answer NO. Technically you can still use your 40mhz radio in most Australian events however there are some which will require you to have a digital one. Personally why I say you can't use one of these radios is because there is always issues with interference. Something that works fine at home may just completely fail when you put your robot in the metal arena or there is other radios around. I remember back when I had big antennas sticking out of my robot and had made special tuned coils to try and reduce my radio problems. Even then half the time it would just sit there as soon as I got it in the arena.

Just a few years ago a digital radio would have set you back $300+ however now you can get one for <$50 which you just put in your robot and it works. No making antennas, no sitting there scratching your head as to why the robot isn't working. So my advice is save yourself the pain and just spend the few dollars on a proper radio. It is well worth it.

Drive Train

There is many options out there for the drive train.

This being your first robot the easiest option is probably drills. Drills from Bunnings or K-mart these days are ~$40+ which is a lot to pay for something you are going to pull apart. A few other sources for cheap drills have been found but you can always just go down to bunnings and grad the two cheapest standard drills they have. (Hammer drills aren't suitable)

If you want new drill buying just the gearboxes from e-replacement parts is probably the cheapest option or you can always have a look at your local dump shop or recycling station as your normal drill will just be thrown out once the batteries die. Drills here can be picked up for as little as $2.

Once you have your drills time to convert them into a drive system see drill hacking 101 for a simple guide.


In general the two favorite types of batteries are LiFe or LiPo batteries.

LiFe batteries

LiFe batteries are probably the most commonly used battery in combat robots. They are robust, can be charged fast, don't fail violently and can be abused and generally survive. The most common form of cell used is the A123 cell which is used in dewalt cordless drills. Unfortunately no convenient source for these batteries is known at this time. eBay has them but sellers often rip you off with fake or used cells so be very very wary.

LiPo batteries

Lipoly batteries are the other main type of batteries now used. They are similar slightly light in power to weight than LiFe but have lower rated charge and discharge rates and are more unstable. Fortunately lots of progress has been made in the last few years which make these batteries suitable for use in robots. Our friend HobbyKing has us covered here with a huge selection of batteries. For just a drive system I would grab a 4 cell (4S) battery with 2 amp hour (Ah) capacity or bigger with a rated discharge rate of at least 40C.

For more information see the Batteries & Power section.

Speed Controller

Speed controllers are another item which you will require and are usually the most expensive part of your robot.

My recommendation would be to go to Robot Power and buy an XXL controller. This is probably the most proven controller out there. (Check forums for more up to date info)

There is other options, personally I use my own custom Hacked ESCs, based on Hobby King controllers but be prepared to do lots of research if you want to save some money. And the resulting solution may not be as reliable as a commercial solution.

Servo Switching

For those really short on cash you can go back to the good old servo switching techniques. What this means is that you get an RC servo with a horn on it and it pushes on two sets of micro switches to change the direction of the motors. This is probably the cheapest, easiest system for those who don't want to spend $150 on an ESC. Downside is your control is limited and it is not as reliable (well this really depends on how well you make it).
For a more detailed description see MicroSwitching


Armour is a key part of your robot. Not only does it protect your internal structure but these days it usually doubles as a frame. The minimum which is really acceptable in a robot is 3mm steel but this may still not be enough against some of the high powered spinners.

There are some tricks however which you can use in order to get the most out of your armor. First is angle the armour. This requires slightly more surface area but deflects impacts. The other option is to use hardened material such as hardox or bisalloy. Which will work much better in combat.


So what will it cost?

You can spend a lot of money on combat robots but if your reading this then you are probably interested in doing it on the cheap. So here is a quick break down of your typical budget if you are willing to shop around or try and recycle parts it can probably done quite a lot cheaper.

Radio - HK Radio $50
Batteries - 3Ah 4S Lipoly $50
Drive - 2xDrills $60
ESC - Servo switching $20 - proper ESC $150-200
Armour - Mild 3-6mm steek $50

Just really a guess but a good place to start. If you want to save cash, harvest a radio from an old RC model, use drill batteries or RC car batteries if you have them, go to your recycle shop and buy drills for $2, use some simple servo switching to get you started, use scrap steel and whatever you can find for armour. In this case you can probably be battling for <$100 but be prepared to do the leg work and deal with plenty of issues.


And have fun building


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