It's on my list of things to do, but I'm about 3 hobby projects behind documenting at the moment. :-)
The most interesting bit is probably the gearbox, since it's an 8:1 stage then a 10:1 planetary stage. It's all printed PLA, stainless steel bolts, and bearings from amazon. There's two motors (to make it look cool, since one motor with the 80:1 reduction is probably already excessive), and a 1024 count encoder on the sun gear, giving 40960 counts per wheel revolution. It's all designed around the mounting holes of the steering wheel I used, too, so it's very pretty.
The electronics are "boring" in that I used an Arduino Leonardo, a quadrature decoder IC, and a 13A rated H-bridge. The trickiest bit was adding a "braking resistor" to keep the power supply voltage from shooting up when applying deceleration torque.
