Ebike Chain motion sensor with a broken inductor (opens in new tab)

Making an ebike is easy enough, but controlling the motor speed is tricky. You want a bit of regen for braking (so a sensor on the brake lever?), and power when pedalling (A crank rotation sensor?), and it would be nice if the bike was only putting a lot of effort in when you were, which is really the product of the speed the pedals are turning times the force on them (A force sensor on the pedals?).