Saw on Thinkiverse E-Bike conversion (thing:1701528). So I laser cut the big pulley and added an extra outside ring part to help center the belt on the bike wheel. Ordered the belt and 20 tooth pulley, 5mm pitch, 10mm wide belt from MacMaster Carr for around $25. Gear ratio is 100 big pulley and 20 small pulley. I had several 32 volt DC 1 amp motors. Ordered from Banggood 36V 800 watt speed controller and throttle grip for E-bike for $28 plus shipping. Drew up in CAD a housing for the motor and a case for the controller which I 3D printed out of ABS, 50% fill. For batteries I used 5 cells from a Prius battery I got from a salvage yard. The cells are like 7.2 volts each. Assembled all on my old mountain bike & tested. The motor did not have enough power to really make pedaling much easier. So I changed the motor to 24 volt 10 amp that I had from an old elec. scooter and reprinted a new motor housing. Now I wish I had bought a different motor controller. Tested! This works, pulls me around without pedaling on the flats. But the batteries only lasted 15 min.

Next I need to add a servo for the brakes, a servo for steering, a camera for optical object resolution, a raspi for cpu, some lidar detectors, and MRL (brains)  for an antonymous bike

WHAT COULD GO WRONG?

YouTube   https://youtu.be/UAKaVsPvw2o

I just enjoy building stuff...