A bicycle wind dynamo is a three-component apparatus that uses wind to power your bicycle lights, eliminating the need to charge batteries. Propeller blades, curved to catch as much energy from the wind as possible, turn slowly when they catch wind. The rotor, the rotating hub to which the blades are attached, converts the slow speed of the propeller blades into faster rotary motion. This motion, in turn, powers the motor, creating enough energy to power your bicycle lights.
Choose a motor that will generate about three watts of power, the typical amount required from a wheel-powered bicycle dynamo.
Choose the proper blades and rotor for your wind dynamo. You can build your own three-blade set-up using PVC piping, which is both lightweight and inexpensive, to go with a desired rotor. You can purchase the blades pre-made and engineer your own rotor hub to go with them -- perhaps from a piece of PVC piping. Or you can buy a pre-made set of blades and rotor, which is slightly more expensive but saves time and will potentially lead to better results.
Obtain a lightweight platform (such as a two inch by four inch rectangular piece of wood) that you can easily attach to your bicycle wheels or handle bars (depending on where you wish to mount your dynamo).
Mount the blades and rotor to the platform. Connect the shaft from the rotor to the shaft on the motor.
Mount a tail to the opposite end of your dynamo from your blades and rotor. The tail keeps your dynamo turned into the wind. Mount your completed dynamo to your bicycle.
Ideally, choose a motor that produces substantial power at relatively low RPM, so that you can connect the blades and rotor directly to the motor without needing a gearbox.