This exerciser generates electricity by pedaling. I started with a 20 inch girls Murray bike which I cut in half. I flipped the backend over and bolted it to a wooden frame with a large base for stability. In the video I have a box on top of the base in order to keep it from sliding around while pedaling.

The generator itself is actually a radiator fan permanent magnet motor from a Honda. I cut off the fan blades down to the metal hub. I then JB welded the hub to a 1 inch copper pipe to produce a friction roller. So when you pedal it turns the tire which then turns the radiator fan motor.

NOTE: In order to generator 12 volts for the inverter the motor must spin at 3000 rpm. The bicycle gears have a 3:1 gear ratio and the friction roller has a 20:1 gear ratio with the tire. As a result, pedaling at 50 rpm will cause the motor to spin at 3000 rpm (3 * 20 * 50).