For my new book I'm testing out different VAWT (Vertical Axis Wind Turbine) designs. One thing about a typical VAWT, especially savonious is that they spin with more torque but much lower rpms. So a pulley is required to step up the speed. The motor I was testing with is a 3200 rpm motor, 17 amps and 130 volts DC. And it has a 3 inch pulley on it. As you can see from my VAWT windmill calculator, it needed a 7 to 1 gearing. In this case that is a 21 inch pulley.
Well, good luck finding a 21 inch pulley that fits an "A" belt and attaches easily to the bottom wooden plate of a savonius windmill. Basically, the situation required a plywood pulley. You can make them almost any size. They are a lot easier than most people think to make and they work fantastic. Here is a pic of my 21 inch plywood pulley on the 48 inch diameter bottom plate.
Here is the jig for the router and the next picture is the VAWT bottom plate
If you go to this page http://www.gizmology.net/pulleysbelts.htm then you will see a pulley calculator. It is good to play around with those numbers to estimate the load on the bearings due to belt tension. The bigger the pulley, the less belt tension you need.