Geared unicycles? Old hat

You'd still need to rig up some sort of gear change linkage from what I
can see on their site. That's the most problematic thing on a unicycle
hub. If it could be made like a self-contained automatic gearbox it
would be interesting - probably bizarre to ride though, and automatic
gearboxes waste energy. Could be a good novelty machine though!

I suppose you could have a sliding bar through the axle, a bit like the
Schlumpf one, but make it variable gearing depending on how far the bar
was pushed through...

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now, I don't know much about how this works, but wouldn't a CVT be
easier to run as a 'freewheel-less' hub? and couldn't you just use the
same thing as a bike shifter, only mounted under the seat?

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flyer said:

couldn't you just use the same thing as a bike shifter, only mounted
under the seat?

The problem is where to have the cable going into the hub. On a bike
hub it's easy because the cable can just come out of the middle of the
axle. On a unicycle hub you can't do that because it would get tangled
up in the cranks. It could be done on a chain-driven giraffe though.
The Schlumpf method of having a sliding rod with buttons for each heel
is a nice solution to the problem, but to make that practical with a
CVT it would need to be made to go in steps like a conventional
sequential gearbox (click one way to change up, the other way to change
down, like on a motorcycle). I'm sure it could be done, but may end up
horribly complicated and expensive (not that a Schlumpf is cheap). For
practical purposes, two gears is probably enough for a slow-moving
thing like a unicycle anyway.

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In that case all you need is a torque dependent system that lowers the
ratio as you put more pressure on. Low gear for powering up steep hills
or accelerating, and high gear for high speed cruising.

Simple. Next? 🙂

Phil

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ah. I see now, after watching the video. The cable comes out of where
the crank bolt would be, and that's most definitely problematic. Even
if it's got to be hand-adjustable, like via an allen key or some built
in mechanism that goes through the axle, it'd be really cool to have
something like a 29'er that could be geared from 24-72 theoretical
inches. I'm a bit obsessed with the idea of a unicycle that is nearly
as good as a bike for transport. Something like this seems like it
would be non-freewheeling by default, and therefore require even _less_
components to be turned into a uni hub. And that'd be just awesome.

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I know what you mean Phil, but I would think an automatic torque-sensing
gearbox would feel very bizarre to ride. Similar things were tried on
bikes in the 1980s but were pretty hopeless. On a unicycle it could
make balancing very interesting... it would be cool to try it though.

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Perhaps they could make it so kicking a lever with your left heel would
up shift, while kicking with your right heel would down shift.

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CVT is continuously variable transmission - that means stepless. They
put CVT on twist and go mopeds and scooters. It is very different from
the automatic gearbox that many cars have, where the car changes gear
with a noticeable shift.

The way CVT works on a moped involves a V belt - a strong rubber/Kevlar
drive belt that goes around two cones (drums) which change size
according to torque and rpm. It's all done with springs and weights.
My gut feeling is that CVT would not be advantageous on a unicycle. It
would be like riding with rubber cranks.

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the site explains that this is not in fact how this CVT works, and it's
actually directly controlled by the user, there's nothing really
automatic about this. Some saturn VUEs have CVTs though, they're
awesome from a pure coolness of machienery point of view.

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There is a Swiss man who has built a Unicycle with a
gear:http://www.schlumpf.ch/uni_engl.htm

I think it's what you mean or isn't it? If I'm wrong tell me, because
my english isn't so good.

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Mikefule said:

My gut feeling is that CVT would not be advantageous on a unicycle. It
would be like riding with rubber cranks.

Awww shucks. Next you'll be saying my idea for 'maglev suspension'
(http://tinyurl.com/ctybc) won't work either... 🙄

Phil

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Mike: I know CVT *can* be stepless, but without a lever/cable this
wouldn't be practical as a manual system. It could however be set up
to change in even steps when a button is pushed, and behave like a
sequential gearbox. Of course it could be a torque-dependent fully
variable automatic like Phil suggested, but I reckon that would be very
freaky on a unicycle, where you need to use torque to balance. The CVT
systems that were tried on bikes (using a sort of variable diameter
chainring) were hopeless - if you tried to pedal harder it just reduced
the gearing. The mechanism Phil linked to is not a belt-drive system
like in DAF cars, it looks like it wouldn't be "rubbery", but I'm
sceptical that an automatic CVT wouldn't feel very odd to ride. If it
was set up as a stepped sequential box though I reckon it might be
possible.

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There've been various CVTs designed for bikes previously. All of them
failed because they weren't as efficient as a derailleur or a standard
epicyclic gearbox.

I'd guess this isn't that efficient because they seem to be only aiming
it at casual cyclists. If it was efficient, they'd be trying to get it
onto racing bikes.

Joe

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You Know thoes bikes that shift grear automaticaly image that on like
mini graff coker.😕 :eek: ???? WOW

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flyer said:

ah. I see now, after watching the video. The cable comes out of where
the crank bolt would be, and that's most definitely problematic. Even
if it's got to be hand-adjustable, like via an allen key or some built
in mechanism that goes through the axle, it'd be really cool to have
something like a 29'er that could be geared from 24-72 theoretical
inches. I'm a bit obsessed with the idea of a unicycle that is nearly
as good as a bike for transport. Something like this seems like it
would be non-freewheeling by default, and therefore require even _less_
components to be turned into a uni hub. And that'd be just awesome.

You could have the gear (ratio) changing done electrically and
wirelessly. There was a high end road bike component company that made
a wireless shifter for the rear derailleur. I can't recall the name of
the company right now, but it might have been Mavic. A battery, motor,
actuator, and a wireless connection and you've got it.

The same kind of wireless shifting for the Schlumpf hub would be cool
too. No need to try to tap that button with your heel. Just push a
button under the seat and it shifts.

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While that sounds possible, it also sounds complicated, and therefore
expensive and unreliable. I don't think I'd want any part of my
unicycle that I use at all often to be electronic, I have enough
problems with airseats.

It would be cool to hold a button under the seat and feel your legs
have to push harder slowly to keep going. If these ever become
available in unicycles, I'm going to buy one, if I haven't made an
excuse for buying an outta phaze yet. 😄

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The new MINI will eventually have a CVT gearbox, i know 'cause my
brother worked on it at one point, the idea being that the engine is
always held at the rpm at which it generates most power and thus better
acceleration etc. and no jerk like an auto box 'changing gear'.
However, this means that whatever the position of the throttle, the
speed or the gradient of the road the engine retains the same rpm and
thus the same noise, which freaks people so much that they've had to
make it only moderately effective, i.e. it only holds it withtin a
certain range. Imagine flooring it to overtake, and the revs not
picking up atall even though you're suddenly going much faster i can
see where they're coming from. Back to the real topic at hand, i once
saw a bike which used sliding weights in the wheel to change gear of a
presumbly epicyclic hub, if you go fast the weights fly out and it
shifts up, only problem, if you go fast up a hill and then slow
dramatically it can't keep up and you get stuck in a high gear. Might
be applicable to a unicycle.

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phil said:

I can't quite get my head round how the system uses enough friction to
transfer the torque without either making it hideously inefficient or
grinding away the disks or balls

While they have various lists with advantages etc on the NuVinci site,
they don't mention anywhere that the power transmission is efficient,
so that must be the answer to your issue: the thing is hideously
inefficient.

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Klaas Bil said:

While they have various lists with advantages etc on the NuVinci site,
they don't mention anywhere that the power transmission is efficient,
so that must be the answer to your issue: the thing is hideously
inefficient.

In the 'FAQ' (http://www.fallbrooktech.com/02_FAQ.asp) they do mention
efficiency.

Quoted message said:

How is the NuVinci CVP different from conventional transmissions?

The NuVinci CVP offers a wide range of advantages over conventional
transmissions. These advantages include:

Quoted message said:

Quoted message said:

- Less complexity
- *Greater powertrain system efficiency*
- Greater acceleration and optimum performance
- Easier shifting
- Ability to accept multiple inputs while varying speed and

Quoted message said:

managing torque

- Multiple power outlets such as for a power take off (PTO)

Quoted message said:

application

- Easier to package and potentially lighter
- Easier and less costly to manufacture
- Greater scalability and potential to reuse tooling

Quoted message said:

I don't know what they're comparing the efficiency to. They may be
comparing it to an automatic automobile transmission or maybe what they
consider conventional CVTs. I'd be interested in finding out what the
efficiency is for their bike hub in various ratios.

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