How To Build Your Bot

Combat Robot Building Guide

Choosing a Design
First of all, you need to decide the general weight range of your bot. Currently, there is a very wide range of weight classes, totaling 12.
UK Fleaweight: 75 grams
Fairyweight/UK Antweight: 150 grams
Antweight: 1 pound
Beetleweight: 3 pounds
Mantisweight: 6 pounds
Hobbyweight: 12 pounds
Featherweight: 30 pounds
Lightweight: 60 pounds
Middleweight: 120 pounds
Heavyweight: 220 pounds
Super Heavyweight: 340 pounds
Mechwars-only 390 poundsFor beginners, the antweight and beetleweight divisions are an excellent place to start. 1 and 3 pound bots are much cheaper and much easier to build than heavier bots, and they are just as much fun to fight, if not to watch. Fairyweights and UK ants could also be a good starting point, but it is harder to keep 75-150 gram bots underweight than slightly heavier bots. The heaviest weight class that you should attempt as a beginner, in my opinion, is middleweight. Heavyweight and above get pretty expensive and harder to build.
Now comes the fun part: deciding what kind of weapon your bot is going to have. I've listed some of the most common ones below. Combining multiple weapons into one bot is always a good idea (for example, a wedge and a spinner), and your bot should either be invertible, able to self-right, or really hard to flip just in case you cross paths with a flipper. Also keep in mind the K.I.S.S. principle: Keep It Simple, Stupid! For example, a middleweight with a pneumatic powered weapon is not a good place to start for a beginner (we found this out the hard way). Also stay away from walkers and hydraulics for the time being. Unless, of course, you already know a lot about mechanics and engineering and stuff, then it should be okay to start there.
Pushy bots. By far the most common, simple, and effective type of bot. Pushy bots do just that: push their opponent around the arena, preferably into hazards or into the wall. The front end usually consists of either a wedge for getting under other bots or a plow. You can also put a spike on the front or rear to ram your opponent with and possibly do some damage. In order to be effective, pushy bots should be fast, torquey, durable, and have a good driver. It's a basic, all-around design good for beginners.
Horizontal spinners. The most destructive design out there, yet relatively simple. Horizontal spinners simply rotate a horizontal bar, disc, or full-body shell around at high speeds to store up kinetic energy and then transfer it to the other bot in an often spectacular shower of sparks and debris. But some of that energy will also recoil into the spinner, making spinners somewhat prone to breaking themselves on a big hit. Also, if the object being spun is even slightly unbalanced, it may cause the bot to do a "Mauler dance" and flip over. In order to be effective, horizontal spinners should have a fast-spinning weapon (at least 1500 RPM), a quick spin-up time (no more than 10 seconds), and be able to withstand heavy impacts. In general, they tend to beat vertical spinners and hammers, but lose against good pushy bots and flippers.
Vertical spinners. A vertical spinner is the same concept as a horizontal spinner, except the weapon is spun vertically to store kinetic energy. The weapon is most often a disc, a bar, or a drum. The advantage to this setup is that a large enough impact can flip the opposing robot. A vertical spinner also will not bounce away when it hits a target like a horizontal spinner, and it will not do a Mauler dance if the weapon becomes unbalanced. However, vertical spinners can tip over if they turn too quickly due to gyroscopic effects. They are also beaten by horizontal spinners very easily (except in the insect weight classes, where vertical spinners are at the top of the food chain). They are most effective against pushy bots.
Full-body spinners. Not to be mistaken for shell spinners, which are often called full body spinners although this is technically inaccurate. True FBS's are actually a rare design nowadays, but I've included it because it is so simple and was once quite common. A full-body spinner simply turns around at high speeds to store kinetic energy in the same way as a horizontal spinner. This design requires no additional motor to power the weapon, however, so it is much simpler and easier to make. The disadvantge is that full-body spinners can't move and spin at the same time. Also, due to the weight of the object being spun (the whole bot), they can't store up quite as much kinetic energy as a horizontal spinner. One effective design is to add a long tail to the bot with a heavy weapon on the end so the tip can reach high speeds. This is a basic, all-around design good for beginners.
Flippers/lifters. These bots use either a pneumatic arm to flip bots into the air and onto their back, or an electric or hydraulic arm to slowly lift the opponent and tip it over. The arm can also act as a self-righting device if implemented correctly. They are especially effective when combined with a wedge. Flippers and lifters are most effective against non-invertible bots that can't self-right. They are less effective against invertible bots or ones which can right themselves when upside-down, but can still be dangerous if they are powerful enough.
Hammers. Self-explanatory. Hammer bots have a long rod with a heavy weapon on the end that swings vertically like a hammer. They usually need to be pneumatic powered to be effective, although it is also possible to use a spring under high tension. If it is built right, the hammer can also be a self-righting mechanism. Hammer bots are basic, all-around designs, but not the best place to start for beginners.
Crushers. This type of robot uses a hydraulic or electric jaw to slowly crush the opponent or just to trap them. They can be difficult to build because the jaws need to be able to handle a lot of pressure. Crushers are most effective against slow bots so the jaws can have time to close.
Draw plans of exactly what your robot will look like, how it will work, and how parts will be arranged inside. There's no need for exact measurements yet - it's too early to see what they would be. But you should have a general idea of the size and weight of your bot before you buy the parts. Don't know what parts you need? There's a basic list just a bit further down this page.
Make your design practical! While combining multiple weapon systems is good, don't try to go overboard with it. For example, this is NOT a practical design:
It looks cool, but even a professional bot builder would have major headaches over trying to get it under 390 pounds, if it would even be possible to do. A much more realistic design, if you wanted about the same type of bot as the one above, would have a more boxy chassis, possibly with a wedge in the rear, no flipper, and only one spinner that is much better supported. Titanium armor and expensive motors like E-teks also aren't very realistic for a first bot unless you have a money tree in your backyard. I'll say it again: Keep It Simple, Stupid.
Look for potential flaws or ways you could improve your design. Keep Murphy's Law in mind: "If something can go wrong, it will." Also consider your driving abilities and mechanical skills, and plan your design accordingly.

Finding and Purchasing Parts
First, the basics. Every robot needs the following components:
Power. If you didn't know this one then maybe robot building isn't for you. Batteries don't require much explanation - they need to be rechargeable and they need to meet your motors' voltage and current requirements. They should also be able to last 3 minutes with the motors under load.
Motors. Another obvious one. You need at least 2 motors for drive. Drive motors should be powerful but not spin very fast - if they do you should gear them down for less speed and more torque. Weapon motors for spinners should spin as fast as possible but still have enough torque for a fast spinup time. Weapon motors for electric lifters and crushers should have as much torque as possible but still have enough speed to move the weapon before the opponent escapes.
Transmitter and Reciever. The transmitter is the remote that you hold and push buttons on. The reciever goes in the robot and recieves signals from the transmitter. The reciever is usually light and powered by a separate power source, so about the only thing you need to worry about is frequency (only 75 MHz ground frequency is allowed for robots) and the number of channels. You will need 2 channels for driving and one more for each weapon you have.
Speed Controllers. A speed controller is what turns signals that the reciever gets into commands for the motors. Some can control multiple motors at a time while others can only control one and you must use more than one speed controller. Make sure your speed controller can handle the current and voltage going through it, as they are quite delicate! Many robots have lost matches due to burnt-out speed controllers.
Building Materials. Steel, titanium, aluminum, polycarbonate plastics, and carbon fiber are the most common building materials. For beginners, aluminum is a great material due to its light weight, decent strength, workability, and low cost. Steel is also good if you want more durability, but it is heavier and slightly harder to work with. Carbon fiber is also a good material for beginners for its extreme light weight and rigidity, but is only strong enough for very light classes. At this point, you will probably only be able to estimate how much building material you will need. Get a little more than this estimate just in case you end up needing it.
The following tools are not essential to building a bot, but they will make the job much easier:
Metal cutting tool. Usually a band saw, but if you have a lot of money, you can get a waterjet cutter or even a laser cutter. We use a band saw from Grizzly Industrial.
Drill press. You will probably need one of these if you're using rivets or screws to build your bot. A regular power drill just isn't accurate enough for most purposes. We use a drill press from Tool Shop.
Welder. If you don't want to use rivets or screws to build your frame, you will need to weld it, and for that you will need a welder.
Grinder. This is useful for shaving off extra bits of metal that get in the way or for sharpening weapons. Just don't try to grind aluminum or your grinding wheel will get all clogged with dust. We use a grinder from Ryobi.
Soldering iron. Chances are, sometime during the wiring of your bot you will have to solder some wires. We actually use a really old model that we got for free because somebody was going to throw it away, but it still works perfectly fine.
Before buying the parts, make sure everything is compatible, i.o.w. all your parts should have similar voltage and current ratings. The exception is your reciever, which will usually either have a separate battery or have a battery elimination circuit which brings down the power directly from the main battery to manageable levels.
Now it's time to get buying! The first place we always look for parts is The Robot Marketplace. If the part you're looking for isn't there, try one of the other websites on the links page on this site. If you still can't find a part, then try a Google search. Or if you're on a tight budget, with a bit of luck you can find good cheap robot parts at a surplus store. It is also a good idea to look at a few different sites and parts before buying to compare prices and quality. You don't want to get a part, only to see another one later that is better. Also keep in mind that you're probably going to need more parts later in the construction of your bot. It's unlikely that you will be able to buy everything you need all at once.
Building the Bot
Once you have all the major internal parts of your robot, lay them out on a flat surface so you can determine the size of your baseplate. The parts should be close together to minimize the size of the frame, but make sure to leave a little leeway in case something changes later on.
Now measure the amount of space the parts take up and cut out a baseplate. The baseplate should be rigid - you don't want the weight of the stuff on it to make it sag. I recommend mounting the batteries, reciever, and speed controllers to the baseplate via screws for heavy components or those needing a heat sink (such as speed controllers). For light components you can probably get away with duct tape or glue to hold them down. Don't mount the motors on the baseplate (unless you're building a very light bot like a fairyweight or if your baseplate is extra-thick). They should be attached to the frame.
Now you should know exactly how big your frame is going to be. Once you have all the pieces cut to the right length, you need to connect them somehow. This can be done by welding or by screws/rivets. If done correctly, a welded frame is stronger than a bolted one. However, a bolted frame can be easily disassembled for repairs. All our bots are held together with screws because of their simplicity and non-permanentness.
All that's left now is to assemble everything. If your bot ends up overweight, your course of action depends on by how much. If it is over the weight limit by any more than 20% of your alotted weight, I would recommend fighting it in the heavier weight class, possibly adding more stuff to it to make use of extra weight. If your bot is not overweight by much, there are several things you can do to put it on a diet.
Holes. Drill lots of holes in your frame/armor for a trendy Swiss cheese look and a lighter bot. Don't drill them too many or too big, though, or it will severely weaken your bot.
Different parts. There will usually be some parts of your bot that you can replace with lighter ones, or maybe even do away with completely. Sometimes you will get lucky and find a lighter part with equal or better performance than the one you have. If you do, get it, even if it is a bit more expensive. Otherwise, you will need to sacrifice some of your bot's power/durability to be underweight.
New chassis. There may be some way to arrange the parts such that you can shrink your frame and shave off weight. You should probably only do this if you're desparate or if it would greatly increase your bot's effectiveness.
That's all I can teach you for now, as I myself am still somewhat of a rookie. Any more useful information I learn from building bots and competing at events will certainly be added to this tutorial eventually.