variable height unis

A possibility for the “sprung” uni discussed earlier would be to use two chains
and gear assemblies. Each chain and assembly would have its own tensioner, one
on the front side and one on the back side. (So that one chain would always be
tight regardless of the direction being pedaled.)

The problem here would be that until a pedal-reversal, one of the chains would
stop the seat from rising. (This would also be a problem with any tensioner
mechanism. Unfortunately, this would also be felt as a turning force on the
pedal, possibly with bad effects on balance as the wheel and/or pedal turn to
relieve chain tension.)

The suggestion to move an idler wheel outwards as the seat compresses has merit
but would likely be difficult in practice. The idler wheel’s size should’t be
critical, but the total chain length would. A shaped cam of some sort, driven by
the seat’s compression, would probably be required to get the needed precision
of idler extension.

Another possibility would be to use a scissors type extension mechanism, so:

          --- ---
           |                           |
           +                          \ / \ \ / \
              +         or + / \ / / \ /
           +
           |                           |
           O O

[wheel not to scale]

Three chains would be used – one from the pedal/top joint to the middle bend,
one from the middle bend to the bottom joint, and one from the bottom joint to
the wheel. The chains thereby all have constant length and need no tensioner
mechanism. Sprockets would be required at each joint, and the uni joints would
have to use the same axis as the sprockets for the frame’s flex. Additional
guides and support cables would also be necessary to make sure that the upper
and lower frame sections remain colinear (for the model pictured on the left)
and provide for control of the degree of flex.

Some side effects of this construction would be changing rotational inertia
(about the vertical axis) as the uni height is changed, and increased frame bulk
which might impede mount/dismount when not extended.

This mechanism could be used for shock absorption, or just for fun as a variable
height unicycle.

/r

Re: variable height unis

Yes, Sem’s uni was rather impressive, but if I remember right, it took
him several minutes of hard labor to pump up his hydroulic lever,
(actually just an old part from his dads pick-up truck). If someone
could make a uni where the pump action was a result of riding, well,
it would be much cooler. Karl

Re: variable height unis

Sem Abrahams has (had) a unicycle with a folding frame designed exactly as
described except it had four folding sections instead of one. It was adjustable
from about 4 ft. to 10 ft. via a hydraulic hand pump while riding it! It weighed
70-100 lbs. though.

The frame had the following general shape as viewed from the side:

   \___/
     |  / <- hand pump for hydraulic jack / <- hose from hand pump to jack
     |  inside frame
     |
     *          <- sprocket and pedals / \ / |\ <- top of hydraulic jack / |
                \ o | * <- * = sprocket on each side (double chain drive) \
                | | / \ | / <- bottom of hydraulic jack \ /
     * / \ / \ / \
  •           o \ / \ / \ /
      *          <- may not have been sprockets here / \ / \ / \ o * <- 5
                 pairs of chains follow sprockets down to wheel \ / \ / \ / *
                 / \ / \ / \
    
  •           o <- o = no sprocket on either side \ / \ / \ / (*) <- (*) =
              double sprocketed wheel
    

At least this is how I remembered it.

Sorry to say: Some of the krazy unicycling ideas have already been made! Tom
Miller made this one and many others.

Stay on Top,

Ken Fuchs <kfuchs@winternet.com

Re: variable height unis

Ken Fuchs <kfuchs@winternet.com> writes:
> Sem Abrahams has (had) a unicycle with a folding frame designed exactly as
> described except it had four folding sections instead of one. It was
> adjustable from about 4 ft. to 10 ft. via a hydraulic hand pump while riding
> it! It weighed 70-100 lbs. though.
>
> The frame had the following general shape as viewed from the side:

<extendible scissors shape!>

wow, amazing stuff!

]ain