I'm building a hybrid car for my kids. I'm up to speed control and hitting a few hurdles. The set up is 4 x 12VDC motors, one to each wheel through a reduction gearbox. I've wired them to a single bus, and have used 4 standard relays to deliver forward/reverse. I have tried varying the speed with a 200w 10ohm pot, (otherwise it wheel-stands!), but there isn't enough current to get the car moving at anything but almost 0 ohms. The power supply is from an alternator run by a lawn mower engine, producing around 14.5 volts. Individual motors were fused at 4 amp (I figure to be safe, assume 5 amp), so around 300 watts in total. It seems I could do away with the relays and use a high power IC? Would the pot still be useful put across the motor bus?