I wonder if you could have a uni hub that gradually shifted gears based on
the cadence. It would start out 1:1 (or less) and then gradually reach a
max of, say, 1.8:1, at which point you’d be going really fast. As you
slowed down, it would gradually shift back. It could accomplish all this
via some system of weights and/or cables, like a hub with a miniature,
weighted Bowflex inside it.
Get to it, Harper!
David “Wishful thinker” Stone
they actually make self-shifting epicyclic hubs for cruiser bikes. i’m sure it’s possible, it’d just take new machining to produce all the parts.
instead of weights, it might be better to do it hydraulically, like the first automatic transmissions (new ones are elctronic). you got an oil resevoir, and the oil in it is driven out by centrifrugal force. this oil will then shift the gears. but with such a small space to work with, i guess you’d have to use something a lot heavier’n oil, like maybe mercury
ha ha that’s a point: why should a unicycle hub
be small?
not necessarily … dreaming in my bed right now
I am thinking of a unicycle hub that could be
a cylinder with a fairly BIG radius …
in fact the idea
is to have a crankless hub (pedals fit directly
to the side of the cylinder)
Nick if you are loooking for an engineering project:D …
bear
There is an infomercial that plays quite often in the states with a self shifting bike, it works on what the creators call “centrifugal force” or what i call “inertia”: a masses resistance to an acceleration along the normal line of a point of rotation…
the chain wheel acts as a freewheel, whereas the cassette is mounted to the wheel, therefore spinning with it. as the freewheeling chainwheel gains speed a system of sliding masses apply tension to a cable that shifts a slightly modified deraileur.
i don’t think that could be applied in any way to a unicycle hub that would ideally have zero backlash and no freewheeling.
The problem with mounting pedals to the hub as mr. Bear mentioned is that the pedals would have to move through the frame to complete revolutions, this problem holds true for any cable actuated shifting as well, there is really no way to hook anything to the moving hub beacause of the pedals rotational axis being coinceident with the that of the hubs…
i beleive harpers hub requires a bolt to be moved in some fashion while the uni is not being ridden to accomodate a change in “mechanical advantage”.
i know there has been alot posted on this subject in the past. i have spent alot of time thinking about and composing conceptual sketches of a shifting hub. i have a two speed design that would work through planetary gears and an electronically activated soleniod. i can’t figure out how to get more than two ratios. also can’t figure out how to econamically manufacture such an intricate product.
could someone post a link to any pictures of harpers hub and how it might work?
harper’s hub has a 1:1 gear (ie. hub flanges linked to axle) and a gearing up by a planetary gear, hence the two gearings.
The pedals on the hub is possible if the frame is attached only to the hub outside the pedal circle, but it’d be hard to think of a way to make it strong.
Joe
I’ve got a couple of X-brain yo-yo’s at home and they work of centrifical force as well. I think I’ll get started. ooops, I have a scooter to restore over the winter and I have to work and, well theres just no time.
Wait, I’ve got it. What about crank arms that got longer as you pedaled. Centrifical force could pull them out of sleeves or something like Pinnocio’s nose. That would work.
I’m not trying to make light of the subject, IT MIGHT JUST WORK.
Attaching the frame to the hub outside the radius of the pedals rotaion would in afect creat a hubless wheel…(see wheelman.something(cool little motorized somthing or other that uses really cool hubless wheel)
this would be very interesting an possible. if the pedals connected to a mechanism that drove the wheel by its rim, rather than trough the center connected by spokes… youd have plenty of room to create a shifting mechansim and youd have a way to attach a cable or lever of some sort…
i’m visioning something similar to a “monowheel” where you sit on top rather than inside.
the “frame” would have to attach to the rim at the bottom somehow causing the riders pivot point to be at the bottom of the wheel rather than at the top, i’m thinking the would make a very touchy and fast reacting uni that would quite hard to ride…
(when on a giraffe you’r so high above the wheel that you create a slower pedulum effect giving you more time to react (or so i hear)).
has anyone seen anything like this before? i’m sure a single speed version could be made relatively easily. and a suspension system could easily be integrate since your no longer driving the center of the wheel. (your driving the outside)
This would not make you go faster. It would probably slow you down
Oh crude, your right. So it won’t work after all. Ugh. Back to the drawing board. Oh wait, I’m out of crayons. Dam.
can’t the force u envisaged as sliding the cranks out of their sleeves be harnassed to ‘pull’ pull them into their sleeves?
(asks the technoretard)
oh man, now I have to get a new box and start over. Although I like the idea.
However, in order to speed up or slow down your cranks would have to turn independantly of your wheel to adjust speed. Regardless of how long your cranks are, if their attached to your wheel and its going 300 rpm, so are your cranks. Even if they are 170mm or 125mm. A Coker goes faster because the wheel is bigger. Hence, you cover more ground. What we need is to have the wheel turn once for every half or quarter rev of the cranks.
Winches on sailboats and some socket wrenches perform that task. Maybe we can check into that. 
sorry to contradict you on both grounds
bear
If you had 2 or more sets of planetary gears in a hub and wanted to cable shift, you could do it by running a cable down the torsion arm that is attached to the frame to make the planetary gears work.
You could try looking at http://www.sturmey-archer.com/
There are diagrams on it of the bike 3 speed hubs, so you can see how the shifting mechanism works.
Joe