XWonka <XWonka.uequ1@timelimit.unicyclist.com> wrote:
>Has anyone toyed with the idea of making a unicycle like a bike in
>that you can pedal forwards and when you stop pedaling you just
>coast and can’t really ride backwards?
I built a forward only drive unicycle in 1991 that coasts when pedaling
is stopped and backward pedaling has no effect.
The hub consists of a 5/8" axle, a regular bearing and a unidirectional
bearing with a hub shell that fits snuggly over the two bearings. The
axle can move freely in one direction relative to the hub shell and the
axle and hub shell must move as a fixed unit in the other direction due
to the unidirectional bearing. The hub assembly is mounted to any
standard unicycle frame via the two normal bearings in the frame. Thus
such a forward only drive unicycle has a total of four bearings.
The hub assembly bearings have an inside diameter of 5/8" and the
outside diameter was 1". The hub shell is a 1" inside diameter pipe
with flanges welded to each end.
Tom Miller of The Unicycle Factory helped me build the hub assembly.
WARNING: The unidirectional bearings wear out fast and the bearings
must fit quite snug. I used three unidirectional bearings in the course
of a year of moderate use. Should be used only in level areas to reduce
stress to the unidirection bearing. Try to minimize applied torque
while riding to prolong unidirectional bearing life.
In a previous post, Ken Fuchs wrote:
> It used a special needle bearing. The bearing would allow the axel to
> rotate in one direction (free wheel), but not the other direction.
> The needle bearings can move slightly in the direction of axel
> movement in depressions that are normal depth on one side (i.e. the
> clockwise side) and shallow depth on the other side (i.e. the
> counter-clockwise side). Each bearing turns freely on the deep side
> of its depression and binds tightly against the axle on the shallow
> side of its depression. Thus the axle turns freely in the clockwise
> direction (freewheels) and binds to the bearing after a few degrees
> axel movement in the counter-clockwise direction.
> Instead of a normal hub, the unidirectional unicycle has a hub shell,
> axel, a normal bearing on one side and a unidirectional bearing on the
> other side. These two bearings are press fitted into each side of the
> hub shell and the axel is placed inside these bearings. This hub
> assembly is attached to a standard unicycle frame via two normal
> unicycle bearings just like a normal hub would.
> The unidirectional (clutch) bearing failed after at least two
> months of daily use of 1-2 hours each day. I bought some spares and
> later reversed the direction of the seat, making it a backward-only drive
> unicycle. It was originally a forward-only drive unicycle.
> I don’t think the unidirectional bearing was up to the stress of
> human powered crank torque. Also, the press fit seemed to get looser
> after thousands of clutch uses (every time pedaling was engaged), and I
> switched the clutch bearing to the other side of the hub shell.
> (Alternatively, the inside of the hub shell actually may have been
> machined down too much on one end when originally made.) A
> unidirectional bearing on each side might deal with the stress much
> better. Or beefer clutch bearings, if they exist and are reasonably
> priced. The ones I have were a little more than $10 each.
Maybe using two clutch bearings instead of one clutch bearing and one
regular bearing would be sufficient to handle the forces involved.
In another previous post, Ken Fuchs wrote:
> The inside diameter of the hub shell was probably increased after
> months of braking action on that surface. It probably should have
> been a tighter press fit. Switching the clutch bearing to the other
> side helped some.
> Also, it is probably true that the clutch needle bearing used was not
> designed to handle the torque generated by human legs. I tried to
> baby it, but the first one still eventually failed. However, the
> replacement bearing never failed, probably due to my increased
> experience on the cycle and the continued avoidance of over-stressing
> the clutch bearing.
In yet another previous post, Ken Fuchs wrote:
> Tom Miller build a custom coasting hub using a clutch bearing, but it
> had no brake. Tom and I built a second such hub in 1991 which I used
> to learn coasting forward and then backwards and still have today.
> I’d coast on this cycle until I fell and if I ran the velocity down to
> near zero, I’d just start pedaling a bit and coast a few more meters,
> etc. At that time, unicycles didn’t have brakes other than the fixed
> wheel crank set itself and I didn’t need one for my purpose of
> learning to coast on the freewheeling hub, so I never considered ever
> adding one. The rsu archives contain more info on this particular hub
> (and the corresponding coasting machine).
> It would be interesting to hear of any bicycling or tricycling hubs
> that could be readily adapted for a coasting unicycle. Maybe the
> brake can be utilized to learn coasting faster? Maybe the brake can
> be adjusted so it slows down the coasting machine, but doesn’t lock
> the wheel?
> Good luck to any coasting machine builders out there in uni-land!
In a previous post, john_childs wrote:
> Power Cranks <http://www.powercranks.com/> use clutch bearings (one
> clutch bearing on each crank). These are weird cranks that only apply
> power when you pedal forward. The clutch bearings they use are able
> to handle the power output of professional road cyclists without
> slipping. The bearings were rather large which explains the somewhat
> bulky design of the cranks.
> Perhaps you need to use larger clutch bearings. Or the hub body may
> need to be made out of a harder material.
> With the right bearings and the right hub body this is probably the
> easiest way to make a freewheel unicycle hub.
XWonka <XWonka.uequ1@timelimit.unicyclist.com> wrote:
>I mean… obviously you would have to mount a brake on it, but i was
>wondering if the theory has been tested…
The coasting machine works OK without a brake, assuming the goal is to
coast indefinitely (occasionally pedaling to maintain forward movement)
without one’s feet leaving the pedals. Surely a brake could be added to
assist in regaining balance from a backward lean (too great for coasting
reflexes to compensate or if coasting is not even a goal). Such a
coasting machine would be like a unibike without gears and in a standard
unicycle like (pedals and wheel share the same center point) design.
Sincerely,
Ken Fuchs <kfuchs@winternet.com>