Battery module interface

We found these pins to be connected to the motor directly, where green dots indicate ground and red ones positive voltage.

Drivetrain

Left side of bicycle

Right side

Motor

Motor runs at 24 volts. Assuming a maximum wattage of 500 watts, 500 divided by 24 is 20.8333333333... or about 21 amps. Accounting for peaks and such, the motor controller better be able to comfortably handle 30 amps.

"Actually it's a 350 watt motor."
- Dan

We found 30 Amp fuses on the original supply, so we reused some original parts.

Motor controller

A 30A Pulse-Width Modulation motor controller capable of 8-30v. The two knobs adjust the frequency and duty cycle (throttle) of the PWM.

Throttle and New Freewheel

A Magura 5K twist grip throttle replaced the original 10K potentiometer on the motor controller board with only minor modification, adding a couple resistors to get the right impedances. Also worth mentioning in this picture, we added a freewheel on the crankset so the pedals and motor can drive more or less independently.

Batteries

Ping Battery from China allows us to live the Green American Dream. Shown below is the module with its new innards, prepared and ready for its maiden voyage.

Maiden Voyage

On the first twist of the throttle, a fuse blew. This motor was always meant as a power assist, so at the moment the throttle configuration is a bit silly. The motor can really only be engaged if the bike is already moving. A planned addition to overcome this problem is to add current-limiting to the throttle, probably with an MCU that can also take speed readings and drive a display.