Step 3: Rotor and Stator
One of the more technically challenging and labor intensive parts of building a wind turbine is winding and casting a stator coil. A very thorough knowledge of permanent magnet generators is needed to calculate how to wind an optimal stator. If you are determined to do it, you can simply follow the example of someone else's successful generator. Again, this being my first shot at windpower, I didn't want to risk winding the wrong thing, messing up the wiring, or ruining the casting, so I bought one from Otherpower.com. They make lots of different stators for a variety of magnets (rectangular and round) and voltages. Most axial flux wind turbines use a three phase stator for more efficient generation.
Since this is a single rotor design (stators on Otherpower are usually made for dual rotors) we will only be generating half the stated voltage. So, for this project I wanted 12 volts and had to buy a 24 volt stator. Otherpower actually is now offering a kit for a single rotor wind turbine that is pretty much the same as this one. It's still cheaper to fabricate your own, though.
The stator is made for a 12 inch rotor, but the Volvo brake rotor is only 10 inches. So, we were forced to add on to the outside edge. This was probably not the best solution, but it should work fine. I would recommend getting a 12 inch steel disk from a CNC water jet if possible, which would be a lot cleaner and provide a better surface to mount blades.
We used a piece of 1/2 inch plywood mounted to the strut and then mounted the stator to the plywood. Make sure there is clearance for the stator coil to clear the wheel bearing.