DBC writes -
The USB Bike Generator is a small bike mounted electricity producing device optimized to provide power for two USB ports. There are so many small electronics that can be powered or charged from a USB connection it only makes since that people might want to do this while riding a bike. The basic idea for the USB Bike Generator is to use a suitable stepper motor as a generator and a voltage regulator circuit to maintain the 5 volts needed for the USB ports. In this instructable I will show you how to build this generator and through testing show that it is 70% efficient at converting the power from the generator to the power needed for the USB port.