Epicyclic geared hub for unicycle

I have finished the design for the epicyclic (planetary) geared unicycle hub. I have photos of the gears and bearings that I’m using posted at

I also have a set of 4 D-size AutoCad release 12 drawings which I would happily send to people or post if there is enough interest. If you have AutoCad release 12 or above you should be able to view these drawings. I will post photos of the parts as I machine them.

The total cost for the bearings for two hub units was $143.62 or $71.81 per unit. The total cost for the gears for two hub units was $193.30 or $96.65 per unit.

I still plan to have both hubs completed and one of them on a 24" unicycle for testing in time for NUC 2002 and Unicon XI.

very nice

Hey Harper,

I’m not the brightest at physics/gears etc. What’s the point of making a set-up like that? Just something different or does it have an explicit purpose?


Great pics- they make a cool background, btw.

RL, Harper’s working on the Bionic Unicyclist thing; you know, the ‘better, faster, stronger’ shtick (emphisis on the FASTER).

Once in place, the wheel will no longer make one revolution per crank revolution- the gears will allow the wheel to move at higher ratio. Looking back at the pic, imagine that the central gear and the outer ring are not both connected to the cranks… oh… that may not have helped… :slight_smile:



I have posted this project before so I apologize for being vague. The idea that motivates this project is converting a 24" wheel to a 36" wheel equivalent. The gear ratio of the hub is 1.5:1. I chose 24" and 36" because it provides a good comparison between a common unicycle wheel size and a Coker 36" wheel with which many people are familiar. As Chris says…speed is the goal.

Backwards Pedaling?


So I’ve been studying your planetary gear set trying to imagine it in action. As I see it, you’d attach the pedal crank to the large gear. The 68(?) teeth engage the 15 teeth in each of the small planetaries, which in turn spin the 30 at the hub which is splined to the wheel. Roughly 2+ to one, by my very crude and quick examination. Only trouble is, I can’t see any way to make the large ring rotate in the same direction as the hub. What am I missing? (Besides a few fries short of a Happy Meal…)

Never Mind


Oh, now I get it! The little gears rotate AROUND the central hub gear, hence the name “Planetary”. Duh!


The sun, or center, gear here is stationary, it is attached to the frame of the unicycle. The ring, or outer, gear is attached directly to the hub. The six planet gears are attached to a planet cage which is part of the axle. I will not repeat in line here what you can find at the Sturmey-Archer site. They have a good description of the operation of the planetary gear system.


Remember that for a unicycle, the planets must be driven from the axle, not from a chain cog.

If it’s any help to anyone here, you could try downloading the free
Voloview Express viewer which always you to view Autocad files without the
full package.

Or you could try using the Crossroads package, which has the added benefit
of letting you veiw most 3d files and convert files between them.

Regards, Noel Holland Sutton, Surrey

I have the detailed, dimensioned drawing set posted as .gif files on my web site:

under the Epicyclic Hub project.

These drawings have almost all of the detail required to make the hub. It’s a prototype so alot of it is cut-and-fit right now. I have the lathe work done on the axles (Part 1 dwg 2) and the sun gear cages (Part 2 dwg 2) and am beginning to modify the gears (Parts 2 and 3, dwg 3) now. When I get the mill work and the welding done on the shafts and sun gear bearing cages I will post photos of them.