>My thought, although I hadn't written it "out loud", was to use very
>light metals, such as aluminum for the shaft, and rather small gears,
>for exactly that reason
Small, light aluminum gears would be nice, but would they stand up to the load
placed on them? Your legs can put out a pretty decent amount of torque and a
unicycle wouldn't be much good if you had to worry about stressing the gears
all the time. Even if the gears did stand up initially, the aluminum would
probably wear fairly quickly and there go the tight tolerances somebody
mentioned you would need. There's also the occasional collision with the
ground.
Alec