I made this friction drive bike generator to power my head light and tail light. I got the idea and a lot of the info for this project from another great instructable personal powerPlant
I recently bought a bike to commute to work and around town and figured for safety's sake I'd get a light set. This is the light I got, Planet Bike 1200, but there are many options for bike lights. There are many instructables on bike lights too. My lights are both 3V, two AA's in the head light and 2 AAA's in the tail light, and the box said the head light will work for 4 hours and the tail light for 20 hours in blinking mode. While this is respectable it still requires some attention. I got this bike for its simplicity, single speed means I can just hop on and go, but replacing batteries gets expensive and complicates things to much. By adding the generator I can power the lights while riding.
Thanks to instrutables member aaronscottaugustinhotmail.com a schematic of the circuit is also available.