In a bot, motors are the components which actually provide the force to the wheels. Outside of a bot, all you have to do to get a motor to turn is apply voltage to the leads, and to reverse, just switch the polarity of the leads. Unfortunately, though, you can't just stick the leads of a (non-servo) motor into the receiver and have it work. The electronic speed controller (ESC) is usually the component which fixes this problem. Many small electronic switches (transistors, see Electronics section) make up the innards of the ESC, allowing the battery power to go through to the motor to get the motor juice when it needs it, but not otherwise. Most ESCs also provide more accurate control: rather than all-on or all-off, they allow lots of in-between power outputs, so you can turn one motor slower than the other for efficient turns, and have incredible control over the speed of each motor.

But, seeing as the ESC is made of lots of those small switches (and a special kind of transistor, the MOSFET, a really delicate and expensive switch, albeit one that can handle a lot of current, so it is suitable for running motors), it tends to be an expensive component compared to others found in a bot. The often-used Victor 883, for example, costs $150 each (unless you get 5 or so directly from its makers: they have a minimum order number at their lower price). Smaller-bot builders sometimes opt for less-expensive race-car or boat ESCs, which can range from $30-70 each on average, depending on the model. But while some of these ESCs are usable, others aren't, especially in the extremes one may face in a bot-fighting arena. See below for tips on evaluating these types of ESCs.

ESCs also tend to be fragile physically and electrically. Be smart, first of all. Motors can be overvolted, usually, for more power, but motors don't have microcontrollers or sensitive microswitches in them. Don't use an ESC outside of its recommended voltage range, and pick one which can handle the typical currents your motor(s) will draw from it. Otherwise, you will probably encounter what is called "magic smoke". It might sound attractive, but once the magic smoke leaves an ESC, it doesn't go back in. And to watch a $150 investment turn to flame just because of poor design wouldn't be fun. And protect your ESC physically with shock protection of some sort, as they can be fragile, and frustrating to break. It's harder to repair a damaged ESC than a damaged wedge, usually, for example.

So, there are some terms which you should know and use to evaluate how an ESC will do in your situation:

Operating Voltage: What the ESC needs to function. Undervolt it, and it won't turn on. Overvolt it, and it may destroy itself.

Continuous Amperage/Current: The maximum amount of current in amps that the ESC can handle indefinitely going through it. This should be at least equal to, if not greater, than, the current your motor usually draws when pulling your bot.

Peak Amperage/Current: The maximum amount of current in amps that the ESC can handle, period. If a time is mentioned as well, the time is the amount of time the ESC can be expected to survive the peak amount of current. Ideally, this would be equal to your motor stall current, but if not, make sure that your motor almost never reaches this point. For example, Ni last year had a stall current of 106.25 amps. We used an ESC which easily handled that, and therefore probably overspent. We should have gotten an ESC where the peak was just that, especially since the bot could push 6 times its weight before stalling, and therefore it was almost impossible for it to reach stall normally. Oh well: learn from our mistakes! If you can't fit your stall current in here, make sure it's incredibly unlikely for your motors to stall!

Resistance: This is just the resistance of the ESC. The larger the resistance, the less battery power makes it through to the motors, but usually this is so miniscule you can ignore it.

Reverse Delay: This is a feature on some ESCs, usually for racing, I think. It reduces wear on the motors by avoiding immediate reverse: if you go from complete forward to complete reverse, it takes a second to kick in, whereas otherwise there would be a sharp force in the motor itself, lowering its life. You may like this feature, but most don't, I don't think. In my opinion, it reduces controllability and motors' lives don't tend to be long in bot fighting anyway. If your ESC comes with this, either look for a way to disable it, or look for another ESC, unless you are very concerned with your motors' well-being.

Forward-Reverse/Forward Only/Reversible: With racing ESCs, most consumers are race-car drivers, who rarely have to go in reverse during a race (another reason for the aforementioned reverse delay). So, some ESCs only control motors in one direction (forward), and others have both directions but forward has a higher continuous and/or peak current than reverse. I don't know if there is a way to tell just by the description, but look closely at any ESC to make sure it controls both directions, and both equally (or at least both within your desired specs).

Brake: Similar to reverse delay, and sometimes in place of reverse, brake just brakes the motor (brake, not break!), which may or may not be to your liking. Be careful as always that the ESC is really what you want..

Number of channels, or mixing: "Mixing" means that two different motors are controlled on the same joystick (works best with joysticks that can move in all 4 directions on the same stick). Some like this, some don't. I personally think it's more controllable without mixing, but at times it can probably be too controllable. It's up to you. As for number of channels, a single-channel only controls one motor (or side, if you have two motors rigged up to each ESC), two channels controls both motors, although not necessarily with mixing (often this is an option, though). With two-channels, you only have to buy one to control both sides. With single-channels, if one breaks, you only have to replace one ESCs. So each has its advantages, and each has its examples (single-channel: Victor 883, most hobby ESCs, double-channel: ant ESCs, Vantecs).

There are other ways to control motors, though, for the stubborn and strong-of-heart. Relays are electromechanical devices. When activated, they physically switch, connecting different contact points. They can handle small to moderate currents and are fairly cheap compared to ESCs, usually. However, they only have an all-on and an all-off, and to get a forward/reverse system, it is more complicated than setting up an ESC. They are useful for activating weapons, though. Also, some people (used to) try to use servos to physically flip switches to activate motors. These aren't very reliable, though. Especially since, for some radios at least, servos are known to twitch when there is no signal, increasing chances of the bot losing control when it shouldn't.

Other general tips? Be careful with your ESCs! Don't drop them, and be careful not to shock them with static: the MOSFET transistors are really susceptible to that and will die given the right conditions. Just be careful. Always connect the battery to the ESC respecting proper polarity.. Bad things may happen otherwise. And if you've tried everything to get your ESCs to work, but nothing works... Try carefully checking that you plugged the receiver-ESC connection properly. I stupidly reversed it, and it took me 3 weeks to figure out what was wrong (luckily, there was no damage, as it was just the receiver connection, not to the battery). And pick the right ESC for your job: if you buy an ESC that is too powerful, it will hurt your budget and you won't be able to afford spares. If you buy an ESC that is too weak, it very will may burst into flames under pressure.

Having said all of that, time to let you loose! Here's some good sources for ESCs or that I otherwise thought would be useful for you:

Innovation First (http://www.innovationfirst.com/)
Makers of the Victor 883 and Thor ESCs, both long-used by bot builders.

Tower Hobbies (http://www.towerhobbies.com/)
In my opinion, the best place to go for radios and radio accessories. They also have hobby ESCs.

Team Delta (http://www.teamdelta.com/)
A small but high-quality store run by bot-builders. They are also distributors of the Victor 883, and sell several relays.

Barello Robot Products (http://www.barello.net/Commerce/index.htm)
Makers of various antweight (1-lb) ESCs, equipped with all sorts of neat stuff (a sensor to tell if you're flipped, a third weapon channel, etc.).

Servo City (http://www.servocity.com/)
In my opinion, one of the best places to go for your servo needs. And free shipping!

Sonik3 Marine Eco (F/R) ESC (http://www.hobbypeople.net/gallery/159100.asp)
A hobby ESC recently discovered by the robot community which reaches the coveted 12V operating voltage mark, rare for a hobby ESC. And relatively cheap.

Vantec (http://www.vantec.com/)
Home of the once-incredibly-popular Vantec ESC. Tend to be two-channels. Expensive but high-quality.

RelayCenter.Com (http://www.relaycenter.com/)
I just found this in my bookmarks and it seems to fit. Relays, and even surplus.

4QD (http://www.4qd.co.uk/)
British makers of an ESC which I have rarely seen used, but hear it is pretty good, just requires some work to get set up originally. At this time, they seem swamped, but they may be doing better by the time you check.

SozBots (http://www.sozbots.com/)
Home of one of the fiercest one-pound competitions in the country (SozBots=Sixteen OZ. BOTS), and they have plenty of antweight products, including an ESC.

Robot Marketplace (http://www.robotmarketplace.com/)
Run by a botbuilder, this site is essentially a directory of bot parts, but I have had no problems with it, and he has almost anything you could want! Including ESCs.

Mechanical Speed Controller and RFI Control (from Team Rotraktor) (http://www.psi-design.co.uk/ideas/Rotraktor/Electronics.htm)
I wouldn't recommend you try this for yourself, but it is an interesting read.

Robot Combat (http://robotcombat.com/faq1.html#steer)
Jim Smentowski, builder of Nightmare and Backlash (and owner of the Robot Marketplace) only has one bit about ESCs, but it may help you some. Take a look.


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