I never cease to be amazed at how a thread that started a year and a half ago can be revived. Anyway, being a motorcycle enthusiast, I’m with Ileberg on the unibike thing.
Re: Geared hub unicycle
On Wed, 3 Nov 2004 05:51:41 -0600, “rob.northcott” wrote:
>I’m sure somebody has already considered this
Haven’t heard of it yet.
>Make the hub with the epicyclic gears permanently engaged (with the arm
>permanently attached to the frame), then have two clutches (actually
>would be more like two drum brakes) that would lock the axle to the hub
>body in one position (1:1) and the outside of the epicyclic mechanism to
>the hub in the other position (1:1.5 or whatever).
It’s a nice idea, and as Mike Roberts pointed out, the option to coast
is a nice extra. Another extra is that you have a brake, if the two
drum brakes can be operated independently. And if they are, you can
also determine yourself how much ‘coasting time’ there is while
switching gears. I don’t know how technically feasable this whole
thing is though.
Klaas Bil - Newsgroup Addict
I figure it’s pretty clear that offroad unicycling is a stupid thing to do - joemarshall
Re: Geared hub unicycle
On Wed, 3 Nov 2004 14:01:35 -0600, “lleberg” wrote:
>I’m still waiting for the unibike, the motorbike with one wheel only.
Look at the Bombardier Embrio, e.g. at
<http://www.gizmohighway.com/transport/bombardier-embrio.htm>. But
indeed you’ll have to wait…
Klaas Bil - Newsgroup Addict
I figure it’s pretty clear that offroad unicycling is a stupid thing to do - joemarshall
Re: Re: Geared hub unicycle
That’s a good point - I hadn’t thought of that… if the two brakes/clutches are both partially engaged it would act like a brake. I would imagine the control linkage would get a bit complicated though - could have two cables, one for each brake, then the brake lever would have to operate them both in the same direction while the gear shift lever needs to operate them in opposite directions. Could possibly work if the gear lever was mounted on the end of brake lever. Hmmm… Could get horrendously complicated - both to build and to ride 
Rob
Re: Re: Re: Geared hub unicycle
I think it’s easier than that. During normal riding one of the brakes is already fully engaged (blocked) - which one depends on the chosen gear. I imagine that the lever is somehow (for the time being) fixed in the fully engaged position. Now when you want to brake, keep that one fully engaged, and operate the other lever to the degree that you want to brake.
Klaas Bil
Ahh, so you see it as having two separate gear levers, one for each of the brakes, so when one gear was engaged the other lever could be used as a brake? Sounds good in theory… but would manipulating two levers to change gear be too taxing (of course, at the same time having to cope with the change of gearing without falling off!)?
I suppose you could have the two levers next to each other so that one is engaged when back and the other is engaged while forward. Then to change gear the rider would just grab both levers and move them together, then braking would be done by fiddling one lever only (but it would have to be the correct one depending on which gear is selected - the other one would introduce slip rather than braking).
Sounds interesting, but unfortunately I don’t have the equipment or skills to build one and see what happens, so it’ll probably stay as theory (unless one of you engineer types wants to make me one ;)) Could get expensive as a one-off I imagine.
Rob
Not more than (in a manual-shift car) operating the accelerator, clutch and gearstick in a coordinated fashion (of course, at the same time having to cope with traffic around you).
I think the idea has potential but I’m far too un-techie to give it a go.
Klaas Bil
I’ll start and stop with the most obvious problem. Where do these cables run? Do they come out the axle? They would have to in order to keep them from tangling in the spokes or frame. Where do they go from there, do you just hold them or do they loop around your legs and back onto the frame? Remember, on a unicycle there’s a pedal and a crank that has to go around on both sides of the axle. On a bicycle that’s not the case because it’s chain driven and the axle is stationary. Does the cable rotate with the axle? There has to be some running surface inside the hub and outside the axle so the cable doesn’t twist constantly. Where do you put all this stuff? Then you have these two cable loops, one on each side, trying to snag anything they can find on either side of you.
I’ve been thinking about this and realised that the problem is how to connect the levers/cables - I knew there ought to be a catch 
I see Harper has already beaten me to it by posting this fact - I’m glad it was you who noticed this - I imagine you must have done plenty of research into this type of thing before coming up with your design, that’s why I expected my ideas to be shot down straight away!
I think it COULD be done in theory by having some sort of sliding collar/trunnion arrangement so the cable wouldn’t have to come out in the middle of the axle, but that would necessitate some sort of ridiculously complicated concentric bearing-inside-bearing that would be pretty much utterly impractical.
Harper - I hope you don’t think I was trying to suggest I could do better than your design… it’s just that the discussion about it got me thinking about things. The tone of my post was intended to be “why is this a stupid idea?” rather than “this is how it should be done”. I’m always a pessimist - there’s (nearly) always a catch, and Sod’s Law always prevails
Rob
Sorry about the double post, but I couldn’t resist this… please take it as pretty much tongue-in-cheek 
Firstly, the “cranks in the way” problem could be got round by making it a giraffe - a 20" wheel giraffe with the bottom bracket only just above the top of the wheel wouldn’t be that much higher than a coker.
Another way round the linkage problem would be to operate the clutches with solonoids inside the hub, then there is no need for a mechanical link from the outside to inside of the hub, and the electrical connections would be easily done using brushes. Of course you would need to carry a battery to operate all this, and using solonoids would make it all less controllable (each clutch would be either engaged or disengaged, ruling out the braking/slipping features)…
Sorry, I’ll shut up now.
Rob
Why use the brushes? The magnetic fields will easily penetrate an aluminum hub that’s not rotating too fast. That way you can keep the coils on the outside.
On the contrary, I like seeing ideas like this develop, not shoot them down right away. Just because I don’t see how it would work doesn’t mean it can’t be done somehow. Bendix used to make a shiftable, two-speed coaster brake hub that you shifted by back pedaling slightly. It’s inappropriate for use on a unicycle but the clutch, gear, and brake mechanism is all contained in the hub with no cables coming out of it at all.
Klaas will figure out how to do it with petroleum eventually. Ow. My tongue is buried so deeply in my cheek it hurts.
F&S had a fully automatic hub that worked with flyweights.
<http://www.3gang.de/3-gang/2-gang_naben_automatic_seite3.htm>
The flyweights moved a metal disc that engaged a different pawl and ratchet system for slow and for high speeds.
I also own an old Shimano hub that has automatic shifting with flyweights.
Still not usable for unicycling because of the pawl/ratchet mechanism (=freewheel), but a very interesting design.
Regards,
Juergen
If you were to run cables down the frame, would it be possible to connect them to the hub using a mechanism similar to a gyro on a bmx? Basically it’s a thing that lets you do bar-spins all the way round and never get tangled cables. I’m not sure how it works though. It doesn’t seem to add massive drag to the bars, but I assume adds some.
Joe
Yes I think you probably could use that type of linkage. In a unicycle hub application the mechanism would have to have proper bearings because it is constantly moving and we don’t want it to wear quickly or add too much friction to the wheel, but it sounds like it should work. Might be a bit fragile though - there would have to be at least two (preferably three for stability) sliding pins poking out of the hub and attached to the inner disc of the “gyro” as Joe called it (I’m not sure of the terminology but I know the BMX brake linkages he means), which could be quite prone to damage, although they could be protected by some sort of guard.
Rob
ok, i know for a fact there are one or two of these things in existence, but there has been a lot of talk and not much action..
instead of trying to develop clever gear change systems, wouldnt it be more sensible to start at the beginning and produce a simple one gear unicycle hub? no changing needed or existing.. then develop from there?
it would improve street riding if nothing else…
As far as I understand, Harper is having a batch of hubs made to his design and has already had the test one(s) back.
That’s what Harper’s design is if left locked in the “geared” position - it already exists, although not in mass-production (yet) and probably quite costly at the moment.
What I’ve been posting about was just inspired by people’s comments that it would be good to be able to change gear on the fly, like on a bike, and the problems of doing that with a unicycle hub. I don’t expect anybody ever to build something using these ideas, because although I believe it to be possible in theory it would be horrendously complicated (thinking about it more, the solution mentioned above using BMX gyro linkages would involve slipping rings both inside and outside the hub at least for one of the two clutches) and therefore probably unreliable, very expensive or both. It’s just fun to think about the possibilities
Rob
it cant be impossible tho.. cos there are internally geared mountain bike hubs which it can be done one… the only difference is that drive comes from a rotating axle rather than a sproket on a fixed axle…is there any information on harpers hubs? and i recently heard there was a swiss (i think theyre swiss) company whod developed one and were ready to mass produce… any one no anything about that?
check this thread
Re: Geared hub unicycle
On Thu, 11 Nov 2004 07:37:04 -0600, “GILD” wrote:
>check ‘this thread’ (http://tinyurl.com/5r9b6)
And when you’re done with that, this one:
<http://www.unicyclist.com/forums/showthread.php?s=&threadid=36100>
Klaas Bil - Newsgroup Addict
“Deflating pi does not reduce calories, it just concentrates them. - billham”