There is plenty of information on building your
own robot on the many websites out there on the net.As this articles develops,
we will provide you with links to some of the better ones rather than reproduce
what they say, A broad general outline will initially be presented, but as
the guides develop, we will also try to present information and sources unique
to the challenge of building a Robot in Australia.
Just a quick note regarding copyright. The articles on this web page have (unless otherwise noted) been written by the Robowars Team for the use of our future competitors and are subject to copyright restrictions. You are entitled to download them and use them for your own personal use, but republishing them in any form, Books, Web Pages, or any Commercial use is not allowed without permission from us in advance. If you have a robotics website and would like permission to use them please email email@example.com with your request.
Where do I Start ?
First, if you are new to Robot Combat, spend
the next few weeks reading everything you can get your hands on. There are
some good books available
[****insert build your own combat robot book details here****]
lots of websites, and hopefully soon, we will be arranging a periodic meeting night in which we can meet, share a pizza, watch some videos and talk about and help each other out with building your machine. More information on this meeting night will appear soon. but for the moment..
The biggest challenge in building a combat robot can be summed up in one word.
WEIGHT - anyone can design a killer machine with 10 weapons, invulnerable armour, supercharged V8 engines, and 10 inch wide armour plated studded tires. But since it's impractical to unleash such machines on each other anywhere near civilzation, all Robot Combat classes are limited by maximum weights. Deciding how to spend these "weight points" is ultimately what decides the nature of your machine.
Will it be like Jim Smentowski's "Nightmare", with 50% of its weight in its weapon system, making it a dangerously offensive robot, but very limited in duration or defensivesness (ie - easily broken), or will you build a heavily armoured invulnerable shell, but which will probably be slow moving, with weaker offensive power ? Most people will naturally aim somewhere in between these extremes, and finding your own perfect mix of speed, power, weapons and defense is the challenge of Robot Wars..
Secondly, most people will naturally start out by aiming for the heaviest weight classes, and design for that. This is not a good move for the beginning robot builder. Yes, the heavyweights are the most spectacular, but they are also the most expensive by a long way. A Bigger bot, means bigger motors, bigger batteries, heavier wiring, bigger speed controllers, heavier weapons, and more destructive opponents which will mean a bigger repair bill after a lost match. (you will lose sometimes). Every extra Kilo will cost you many more $$ in every area of your machine - design to suit your budget.
If you have an unlimited budget, go for it, but first contact me about sponsorship if you have that sort of money to throw around. B-) Another thing to consider is to have a look at even the super-heavyweight bots and you will see many with lightening holes drilled all over them. Do you think they designed them that way ? Not likely - chances are their bot ended up heavier than they thought it would. (They always do) and they had some desperate last minute lightening to do.
If you aim for middleweight and you end up a bit over, you can always bulk up a bit with heavier armour or more battery power and move into heavyweight. If you aim at heavyweight and end up over, you are going to have to lose something which will quite likely end up weakening your machine.. maybe fatally. Cut yourself a little slack and aim a weight class lower than you would like to be in. You will get into the arena with a lot less pain and expense.
Finally, if your Middleweight class machine gets out there and seriously kicks arse, you can build a scaled up version with confidence and the knowledge of experience. . If you build a heavyweight first, and there is some unforseen weakness in the design, you have wasted a lot more money finding that out than if you had tested the design on a smaller scale first.
Before Jim Smentowski built Nightmare, he built Backlash, then used the knowledge he gained to scale up without making too many expensive mistakes
Enough of the sermon, just keep it in mind.. we'd like to see you in the Arena sooner as a lighter-weight contender , rather than on the sidelines because you couldnt afford to finish your super-heavyweight killer in time.
Oh one last thing, you will notice in the following guidelines that I will favour one type of technology over most others - Electric Motors and Batteries. Far more attention will be devoted to these than will be given to other techniques like petrol power or compressed gas for a good reason. 1- This is a beginners guide for people who dont already know how to build a bot. If you are a beginner and are reading this, you should definitely stay away from things like Compressed Gas, and possibly even Petrol Engines until you get some experience under your belt, or else include a team member who does.
Spending your weight Points
Your weight needs to be distributed between the 8 basic components of a Combat Robot, which are...
1. Chassis - The framework that holds everything together, mounts your motors, weapons,wheels, carries your armour, and absorbs impacts from collisions, kickback from weapons (both yours and your opponents). Needs to be light and strong - its tricky to do both without clever design. Steel is the strongest, cheapest , most easily available, and easiest to work with for welding and so on, but it is very heavy. Aim for thin-wall tubing and clever cross-bracing design to give you strength without weighing you down too much. Aluminium is better for strength-vs-weight, but takes an expert with special equipment to weld, and is more expensive and bulky for a given strength.
2. Power Source(s) - Batteries, Compressed Gas, Combustion Fuels (Petrol). The energy storage of your robot. You need enough energy to carry you through up to 5 minutes of intense combat. Much harder than it sounds. Batteries, Air tanks, and so on are all heavy items, and squeezing enough in to last you the distance will require some careful thought. Petrol sounds tempting, as it offers a huge amount of energy per kilo of fuel, but the machinery required to convert that stored energy into useable power is very heavy. Not just the Engine, but the drivetrain as well. Petrol engines cannot easily be reversed or slowed down to a stop, so you need heavy clutches and gearboes in addition to the engine.
Compressed gas is also an excellent high-density energy source, but again, releasing that energy in usable form takes a lot of regulators, high-pressure fittings, cylinders and high-flow solenoids. Not to mention the fact that high pressure gas is extremely dangerous. A high pressure line blowing off can easily whip around with the force of whipper-snipper in your hands, and a punctured tank or reservoir can instantly turn into a shrapnel grenade. Escaping liquified gas will freeze anything it comes in contact with in seconds. Accidental activation on pneumatic systems or weapons can injue or kill you faster than you can blink.
Batteries are by far the safest, most flexible, most easily recharged, and most easily worked with form of energy storage. Unless you have extensive experience with high pressure systems or lightweight petrol engines and drivetrains, you would do well to start out with electric motors. and gradutate to other systems later. Batteries come in many different forms and contents, Sealed-Lead-Acid, Dry-Cell, Ni-Cad, and Ni-Mh just to name a few. all with their own benefits and drawbacks. We will have a further article on this later.
3. Motors - Your robots muscles so to speak. Whatever technology you use, these are the things that take the stored energy and turn it into work and movement. The most common method is Electric Motors, relatively cheap and reliable, and easy to work with they come in all types from tiny Hobby R/C ServoMotors, up to Massive 20 Horsepower monsters drawing hundreds of amps of electricity to run. You can buy them new from motor manufacturers if your name is Rupert Murdoch, the rest of us will be using our ingenuity and scrounging skills to find them already around us and adapt them to our nefarious purposes (hehehe.. ahem).
A very good and cheap source of motors for the medium weight robots is from Battery Drills. These can be bought from Trash'n'Treasures or Flea-Markets for as little as $25, or over the counter from Dick Smith Electronics for $40 brand new (for the cheaper brands). The advantage of electric drills are that 1. You get suitable batteries and a (cheap) battery charger thrown in with it, and 2. they already have a small planetary gearbox build into the motor. Most electric motors spin far too fast and with very little torque (twisting power) for you to be able to hook them directly to your wheels. Some form of gear reduction is essential. Chains, Drive Belts and sprockets, or gear reductions are all popular techniques, but an Battery drill has a compact planetary gearset already built and connected to the motor for you.. How easy can it get ? Another good reason to start with a medium weight bot.. since the Drill motors arent powerful enough to power a heavy weight, if you go for bigger motors you will need to work on a reduction drive system as well.
Bigger Electric motors can be found in Windscreen-wiper motors from cars, Car Heater-Fan motors, Car Electric Thermo-Fans (the ones that cool the radiator), in some cases even Car Starter Motors (although they take a fair bit of work to adapt since they are often designed to only spin in one direction and you should also make sure they are "Permanent Magnet" motors, since these are the easiest to control), DC -Battery powered (not AC-Electric-cord) lawn mowers and so on. Motors from AC powered devices like washing machines and dryers or house fans, fridges and so on are generally not suitable, since they require 240v AC (Alternating Current) to power them, and you wont be getting that from your 12-48v DC (Direct Current) Batteries.
Wheelchairs and golf-buggies or Carts are an excellent source of powerful motors with gearboxes already built in, some wheelchair motors run fairly slowly for a combat robot, but you can sometimes alleviate this by running them on a higher voltage than they normally do, although you run the risk of frying them if you do it for too long, or stall them in a pushing match when operating at higher than normal voltages). NPC (***link***) in America sells remanufactured wheel chair motors suitable for Robot use, and as soon as we find a similair supplier here in Australia we will let you know. Anyone already know of one ?
Finally, and briefly, other forms that Motors take other than Electric are Cylinders or Turbines for converting Compressed Gas into motion, These can be found at Flea Markets on occasion, or in air-powered hand tools like "Rattle Guns" or Riveters, and of course the Petrol Engine which can be found everywhere from lawn mowers to chainsaws, or whipper snippers. more detail may be forthcoming on these later.
4. Locomotion - This is how your Robot gets the energy from its Motors down to ground to make it move. By far, the most popular method of this is through one of humans greatest inventions.. the Wheel. Of course choosing a wheel is not so simple when you need to take into account things like another machine with malevolent intent doing its best to turn your wheels into scrap to disable you. Also keep in mind, that unlike the English Robot Wars and American Battlebots arena's we are NOT going to guarrantee you a perfectly smooth flat floor. This is to prevent the domination of the sport by the relatively boring wedge-style of robots that literally scrape the floor. Our arenas will be highly variable in shape and texture, they may include ramps, pot-holes, obstacles and possibly even sand, dirt or wet areas.
Thus wheel choice is important for your bots survivability. Traction, weight, damage-resistance and all-terrain capability are considerations. If your Robot is a ram-style machine likely to get into pushing wars, then wide sticky slick go-kart tyres are worth considering, but they are expensive with their custom aluminiun hubs. Cheap wheels can be bought in all sizes at most Flea Markets for a bargain. Pneumatic (air-filled) tyres are good for traction, but can be punctured leaving your mobility severely impaired. You can look into Foam Filling them for improved "flat resistance", or consider rubber-wrapped solid tyres, although these tend to be limited in traction. Beware of plastic wheel hubs, since they often easily break, although some forms of Nylon (not normal plastic) hubs are very tough and lightweight. If you have access to a Lathe, you can custom machine your own hubs and glue rubber belts to them, or else check out the wide array of wheels and tyres available from most hardware stores or online robot part sources (***link***)
Keep in mind how you intend to transfer the power to your wheels.. some form of hub will be required. a Metal plate bolted to the wheel hub, a driven axle with the wheel secured to the axle, or a floating wheel with sprockets attached.
(notes on Skid/Tank Steer vs Ackerman steering to go here)
A variation on wheels is a tracked-robot. Similair to caterpillar tractors, this uses a wide, usually rubber belt wrapped around a number of drive and idler wheels which keep it on the floor. It would seem to offer some big advantages in traction, but is significantly harder to build, since tensioners, and guides must be used to keep the belt where you want it. Also, when turning, Some of the belt will be sliding against the floor, which can eat up your battery power quickly since the motors will be straining to overcome the belts own traction to turn. I have heard that tracks are not worth the trouble for their increased traction, but I havent tried them so I dont know. Again, they're probably something you should avoid on your first bot, unless you happen to have most of the parts for a track system lying around in your back yard.
One final alternative, although again probably not one a new builder should consider too hard, is a walking robot. also known as a "Stomp-Bot" in some classes. Generally, they have at least 4 legs, although 6 or 8 is easier to work with for balance reasons. The rules allow a 20% weight bonus for walking robots, taking into account how much harder it is to build a walker, but wanting to encourage people to give it a go. Walker bots have to meet strict criteria on what constitutes "Walking". Making rotating wheels with little legs stuck to them doesnt count. Generally, no Rotating parts are allowed in the locomotion system. All movement must be of the reciprocating (back and forth) kind. If you are interested in this area, I suggest you consult the battlebots tech regs for advice on what is required for a walking robot.
5. Electronics and Wiring - There is not as much of this is a combat robot as you might first think. Because these are primarily remote-controlled machines - they generally do not require Microprocessors, Sensors or other forms of onboard electronics that Autonomous robots need. This makes them much easier to build for those who do not wish to learn advanced electronics or Micro-Programming, and also makes the fights more interesting since Humans are at the controls making it a much more "Personal" form of combat than watching two "Intelligent" machines blunder about the arena trying to work out where the other machine is.
Most of the Electronics in a combat robot are the Radio Control System,which we will examine in a moment (below), and the electronics necessary to translate the radio control signals into commands to the motors, relays, solenoids and switches that activate the robots movement and weapons systems
a simple technique for those experienced with Radio Control is to use the normal servomotors that the Radio Control receiver can "talk" to, to activate switches or relays directly. There are two problems with this method. One, is there is no "proportional" control. The switch is either full-on or full-off. OK for a weapons motor maybe, but not much use for precise control over the steering or drive of your robot.. Secondly, this technique requires an additional "Fail-Safe" unit to be installed between the radio receiver and the servo'motors so that if the control signal from the transmitter is lost (due to interference, a flat battery, or the end of the match so you have turned your transmitter off), all servomotors must return to the neutral position to deactivate the robots weapons and drive. Without a failsafe unit, the servos position will randomly jitter about when the transmitter signal is lost, which will certainly cause your robot to fail technical safety inspection, and be barred from competing. No-one wants an out-of-control robot equipped with a Chainsaw in the Arena !. If you do use either servo-actuated switches or relays, ensure you have a failsafe module in the line. These can be purchased from most radio control hobby shops. You will need one for each channel you use wish to use a servomotor on.
A better solution (and much more expensive - but highly reccomended nonetheless) is to use a "Speed Controller" to control your weapons and drive motors. Sometimes called a PWM (Pulse Width Modulation) controller, these clever little boxes take the (PPM) signal from the Radio Control Receiver that is intended to drive a servo motor, and convert it into a PWM signal that is suitable for controlling both the speed and direction of a normal (non-servo) electric motor with great acuracy and fine control over the speed, making it much easier to precisely drive your creation where you want it to go.
Speed Controllers are available from a number of sources. The most straightforward way for those with some money to spend is to just buy a commercially available unit like the Vantec, IFI Robotics, or 4QD Speed Controllers (***links***). These units will just plug into your Radio Control Receiver and you connect them to your motors and batteries and the job is done. Most have a built-in failsafe system, so they will shut your robot down if the control signal is lost, making it easy to pass tech inspection. Unfortunately, The job of the speed controllers is to feed the amount of power dictated by your radio control singal to the motors. and usually this amount of power is not small. Quite often we are talking about hundreds of amps for the bigger motors and 50 amps or more even for smaller motors. This means the speed controllers need to use very high-power switching transistors called MOSFETS (Metal Oxide Semiconducting Field Effect Transistors if you must know. B-) and these little beasties arent cheap.
Commercial Speed Controllers are worth quite a few hundred dollars each (sometimes you will need more than one if you have more than two motors to control) , and there is no easy way around this expense unless you are an Electronics Guru and can build your own. Even then, there are many pitfalls for the unwary, since controlling something as electrically 'Ornery as a high power motor is an art form in itself, so unless you are willing to spend lots of time fixing blown up or melted-down home-made controllers that have failed under the high stresses of combat, I reccomend you just stump up the cash and buy them. It will save you a lot of trouble.
One possible alternative is the O.S.M.C. The Open-Source Motor Controller Project. A bunch of Robot War enthusiasts decided to get together and apply the "Open-Source" model of development that has made the Linux operating system for computers so popular. Basically, all the development (source) is OPEN, meaning free for all to share. The people who have contributed to the development of the OSMC have put all their collective hard work on the Internet for the benefit of any who wish to use it. This means anyone can download the circuit diagrams, PCB layouts, source code, and anything else you need to construct the OSMC yourself, saving you a huge amount of money. You still need a significant amount of electronics skill to find all the parts (you wont find them in Dick Smith Electronics stores) and assemble the circuits if you want to do it all yourself, but if you dont think your skills are up to that, the Team here at RoboWars Australia are presently building a batch of OSMC's (since we need them too) that we should be able to offer to Australian Roboteers at very competitive prices. More information on these soon, or else go to www.robot-power.com to check out the information on these clever controllers. Note that the OSMC is new, and has limited battle experience so far, although with the BattleBots series 5 tournaments presently underway in America, more experience of how they fare under combat conditions should be shortly available. Contacts us via firstname.lastname@example.org for more information on the OSMC Australia Project.
6. Radio Control System - This is a contentious area. There are quite a few different optinions on what is the "best" radio control system for your Robot. Most Robot Combat organisations place from mild to extreme restrictions on what Radio system you can use. For example, BattleBots in America have recently forced every robot heavier than lightweight classes to use the extremely expensive PCM style hobby radios, or the even more expensive IFI Robotics Radio Modem based system. Many competitors believe this is due to an erroneous perception that the most expensive system will be the best, combined with the lawyers telling them to CYA (Cover Your Arse) by insisting on the top-gear. Prior to this recent upgrade to requiring PCM radios, they required FM radios, with all AM sets banned for all classes.
After advice from BobYoung of Silvertone Electronics, who writes the Radio Control column in the Silcon Chip Magazine and has been designing Radio Control systems for the Military for over 30 years, it seems to us that the perception the FM is better than AM and PCM is better than both is a common, but nonetheless wrong view. Apparently it has its roots in the fact that FM Radio (the sort you listen to Triple-M on) sounds heaps better than 3KZ on the AM band. In actual fact, this analogy comparing the transmission of Hi-Fi Audio and Digital Radio Control Signals is completely invalid.
With this in mind, we have initially decided not to place the same tight limits on what radio can be used as exists overseas. We stress that the quality of the system is of more importance than Modulation Technique (FM/AM/PCM) used. Any radio system you use will have to pass tech-inspection safety requirements (see radio rules). You will be required to demonstrate control at a distance, the ablity to operate on more than 1 frequency to avoid clashes with competitors, and that the robot is imobile and deactivated when the transmitter is shut off. No twitching or jerking will be allowed.
We suggest using a quality Hobby RC set from a reputable brand such as JR, Hitec, Futaba etc. Failsafes must be incoporated into the system either through the motor controllers or as seperate modules if servo-style controls are used. The frequencies must be legal for ground use in Australia (presently 29Mhz and 40Mhz as far as we know). Using standard hobby gear also has the advantage that if you end up wishing to compete overseas, it will be easier to adapt your robots control system to suit their regulations as most hobby RC gear has standard connections. The hobby gear is very reasonably priced for 4 channel units, which should be enough to control most robots. The JR 421ex (4 channels, plus 1 switched channel) can be had for around the $400 new. including batteries, chargers, transmitter,reciever and servo's.. an excellent starting point
If more channels are needed, but the budget doesnt allow the $800+ 7 or 8 channel hobby units, then the Robowars Team may have an answer for you. We are presently investigating the Silvertone Mark 22 control system designed by the aforementioned Bob Young. This is an 8 Channel radio with a host of features and seems like it may be a good choice. In its standard form, it is quite expensive ($800+), but a large part of this cost is the special folded metal case and aircraft style joysticks used in the standard system.