Geared Unicycles

[M.G. Rushton]

Hello, This is my first attempt at writing to this group.

I am an engineering student at Cambridge University and I have been
trying to work out how to make a multi-geared unicycle. From the
research I have done over the last few weeks I have discovered that the
only gear ever made that can do this is a collectors item and less
common than rocking horse shit. This gear was made by Sturmey Archer in
the 1950's and when I asked them about it they denied all knowledge of
its existance. I have discovered however that it was closely related to
their four speed gears and that these can be modified quite simply to
make a three speed fixed wheel just by locking the planet cage to the
outside part of the hub and removing all the ratchets from the annulus.
This loses the top gear and gives you two reductions and a direct drive.
Having done this however you still have to use a giraffe to mount the
hub as you need a chain drive to the hub.

I have designed a hub gear that gives a direct drive and an increase
which fits on a normal unicycle it only gives two gears and these will
be quite far apart. It is however very large, inelegant and a bearing
manufacturers dream, as it uses about 10 roller bearings. This design
only exists on paper and I would be interested to know if anyone else
has made such an item or is interested in doing so.

I hope to have a three speed carbon giraffe built in time for the world
unicycle convention in August, but the two speed crank drive hub would
take too long and cost too much to build and may not work all that well
so is going to stay on paper for the time being.


Mark Rushton

P.S. If anyone knows someone who owns a three speed fixed wheel Sturmey
Archer hub gear and is likely to part with it I would be very
interested.

[Mark Anthony Balzer]

"M.G. Rushton" <93mgr@eng.cam.ac.uk> writes:
> I am an engineering student at Cambridge University and I have been
> trying to work out how to make a multi-geared unicycle. From the
> research I have done over the last few weeks I have discovered that the
> only gear ever made that can do this is a collectors item and less
> common than rocking horse shit. This gear was made by Sturmey Archer in
> the 1950's and when I asked them about it they denied all knowledge of
> its existance. I have discovered however that it was closely related to
> their four speed gears and that these can be modified quite simply to
> make a three speed fixed wheel just by locking the planet cage to the
> outside part of the hub and removing all the ratchets from the annulus.
> This loses the top gear and gives you two reductions and a direct drive.
> Having done this however you still have to use a giraffe to mount the
> hub as you need a chain drive to the hub.

Mark, what about an infinitely variable V-belt transmission design - the kind
with the sliding pulley halves? Smooth shifting and a wide gear range are
possible, plus it's not too complex. It sure would be a unique giraffe!

Mark

[Ken Fuchs]

Mark G. Rushton <93mgr@eng.cam.ac.uk> wrote:

> I have designed a hub gear that gives a direct drive and an increase
> which fits on a normal unicycle it only gives two gears and these will
> be quite far apart. ...

About 12-13 years ago I designed a reverse drive standard unicycle in which the
axle rotated in the opposite direction of the hub shell. The design included
three beveled gears (to reverse the drive), two bearings for the frame, two
bearings for the hub shell and a bearing for the gear in the horizontal plane.

I was a student at the time and couldn't afford to pay the machine shop's
estimate of $500+ to build the unicycle, and it never did get built. A sketch of
the hub design is in an issue of the USA newsletter around 1982-1983.

Mark, think you could add a reverse gear to your design? That would be a really
wild unicycle. Just ride it in a forward gear, pop it into reverse as you give
it to someone to ride, and then watch them try to ride it. :)

On One Wheel, with many gears and one reverse,

Ken Fuchs <kfuchs@winternet.com>

P.S. If anyone has trouble accessing unicycling.org, please email me.

[M.G. Rushton]

Thank you for your reply concerning geared unicycles. Concerning your
question about the suitability of four speed gears for conversion to
three speed fixed wheel, I am sure that you can convert the close and
medium ratio gears but not so sure about the wide ratio version. The
book containing the drawings, which were mainly exploded drawings and
cutaways, was called 'The Sturmey Archer Story'. If you have an old four
speed I am very interested in it if you're not.

Mark Rushton