The Design Process

A belt - readily available in Kathmandu - struck us as the best way to connect the mill stone to our generator. Pulleys and belts are more available, less expensive, simpler, and safer to operate than gears and chains. The question, then, was how to attach a very large pulley to the grinding stone to drive our system. Ghatta grinding speeds are not terribly fast; to turn a generator, we would need a large ratio between the pulleys.

One idea was to directly use the grinding stone itself as the drive pulley. This seemed problematic for several reasons. For one, as we would learn, the sides of the ghatta stones (being hand-chiseled) are very irregular. The motion of the grinding stone is also fairly elliptical, as the stone is rarely centered on the rotating turbine below. Even more troubling, however, was the nature of the stone itself: since it was meant for grinding, it would quickly tear the belt to shreds.

A better idea seemed to us to be to mount the rim of a bicycle wheel on top of the grinding stone. Light, large, and readily available, a bicycle rim seemed like an ideal pulley for our project, and eventually we did indeed find an effective way to mount it on top of the ghatta.

We have tried to document the design process we went through to help others who may be attempting a similar project. The following few web pages are a narrative of the problems we encountered and decisions we made.