uni design from vintage "kangaroo bicycle"

General
1

I got this idea after seeing an old bicycle video. It seems there was an intermediate step between the high wheeler and the early safety bicycle. It was the kangaroo bicycle. The best illustration I could find on the net is: http://www.quido.cz/objevy/kolo.a.htm

I have seen a picture of a unicycle designed like this, but with the pedals on top so a child could ride a large big wheel.

What I would like to do is build a Coker like a kangaroo bicycle and gear it up slightly. I’m thinking a flat blade design like that of a Schwinn/Semcycle “deluxe” with the frame extending through the center of the wheel to the pedals below.

I have long legs, so I think there should be enough room to build two short chains and small enough sprockets to still have some seatpost on top.

I want to use as much existing cycling parts as possible. It seems to me the main challenge in the design would be how to fit the cranks to the frame in a secure way and to keep both of the short chains tight enough so there isn’t a lot of slop or independence of the left and right side. And a way to put the chains on and slide them up to tighten?

I would also have to figure out how aggressively to gear it. I think the size and mass of the Coker wheel would be fine at a greater speed. This would also reduce my profile by bringing me closer to the wheel. The flip side of that would be that I would have less time to get my feet under me in an UPD.

I’m sure this has already been done with smaller wheels and perhaps part of the problem was with the bumps in the road at high speeds. I would like to get feedback from anyone, esp. someone who has tried anything close to this.

-Mark

2

Here’s a 6 foot shoe uni made by Sem that has a short double chain drive. But the drive system is upside down from what you want.

6footshoeuni1.jpg
6footshoeuni1.jpg210×375 63 KB

3

And here is the big wheel version with a short double chain drive. But again, the drive system is upside down from what you want.

bigwheelwithchain.jpg
bigwheelwithchain.jpg273×288 16.8 KB

4

Re: uni design from vintage “kangaroo bicycle”

I think a flat blade frame design is going to be too flexy. With the cranks down on a cantilever arm with a flat blade frame it’s going to get very flexy down where the cranks are. There can be a lot of force put on the cranks that the cantilever arm is going to have to support. I think ovalised or round tubing will be much better than a flat blade design for handling the pedaling forces with a minimal amount of flex.

You should contact Sem or Tom Miller (The Unicycle Factory) and see if they have any experience with that kangaroo bike style chain system.