Visited the powerfile build again, binned the old one and started again with a bigger motor. Frame is 10mm aluminium, motor is sealed, so no chance of particles getting in and siezing the motor. Drive and idler wheels came off the original and switch is just a simple momentary on push button. It'll run on any 12/24volt power source. I generally plug it into an 18volt cordless tool battery. Motor is very slow, but doesn't bog down and surprisingly does a good, quick job of grinding considering it's slow speed.