For anyone interested in DIY speed controllers, here is one of the best guides to a useful robot wars capable speed controller I've seen on the net so far.
and the 2nd version with more details
also, for those considering which fets to use, and wanting to know "which fet will do X amps ?", heres another page by the same guy that explaines quite well why "it isnt quite that simple"..
If the math scares you at first, perservere, read it all and try not to get confused by all the Rtheta(ja)'s until you have thought about his explanations a bit, its worth it..
If its really above your head, then ask yourself why you want to build your own speed controller.. if its because you want to save money, forget it, I guarrantee you wont, just buy one.. otherwise, strain that brain a bit and eventually it will all start to make sense, you need to know this stuff if you want to avoid making magic smoke..
Some more interesting links for those working on DIY Speed Controllers