I don’t know if this company’s gears would work for
a uni, but the web site looks interesting: www.hdsi.net
This website is advertising harmonic drive gearsets. They are quite a clever little bit of equipment, but unfortunately I think the reduction ratios are way too large (i.e., over 50:1) to be used for a unicycle. They’re generally used for applications where you have say a DC electric motor with very high RPM, and want to significantly reduce the RPM for use in slow moving robotics or something like that.
Trenton
Re: Gearing
Their HPG Planetary Gearhead (another RAS) looks interesting. A unicycle hub made with that design would be good but I doubt it’ll ever happen, unless someone knows differently (hint: infiltrate the company and teach their head designer to unicycle 
).
Cheers, Gary
They do 1:1 Differential Gearing as well though it’s mainly reduction stuff, but hey a large reduction would be a challenge to ride.
Gary
I am very curious as to what Harper has to say on this subject.
-Mike
I saw this site as well as several others when looking first for a commercially available transmission to incorporate into a hub and later as a source for appropriate gears for my own design. Neither panned out. A unit with an adequate torque rating in the 1:1.4 to 1:2 reduction range doesn’t seem to exist. If it did there is still the issue of retrofitting coaxially if possible but this also is highly unlikely.