Do you think this idea could be used for a geared hub?
I’m not sure if the wheel not spinning on its own would be a problem or not, it might lead to some spectacular UPDs, but so would a freewheel unicycle. Definently a cool idea, not sure if it is practical, but somebody smarter than me would have to decide that.
That’s not an original idea at all, it’s called a gear rotor and we use it in some pumps and meter systems. “Google image search gear rotor pump”. The only potential advantage I see that it would have over a planetary gear system is fewer moving parts but with all that grinding and vibration that’s not really an improvement.
The real reason we don’t have great geared hubs is because we’re a niche, not because it can’t be done fairly easily.
That’s not an original idea at all, we use that type of gearing in pumps and meter systems. Google image search “gear rotor pump” and you can see this. It’s not really an improvement over a planetary gearing system because of all the vibration, grinding and noise that it introduces. It also requires the inner gear to be off center which is a problem for a unicycle hub unless you want to look like a kangaroo while riding.
I’m convinced that the really reason we don’t have a better hub is that we’re too much of a niche. If there was a large market for them they would exist.
That’s not an original idea at all, we use that type of gearing in pumps and meter systems. Google image search “gear rotor pump” and you can see this. It’s not really an improvement over a planetary gearing system because of all the vibration, grinding and noise that it introduces. It also requires the inner gear to be off center which is a problem for a unicycle hub unless you want to look like a kangaroo while riding.
I’m convinced that the real reason we don’t have a better hub is that we’re too much of a niche. If there was a large market for them they would exist.
I didn’t know that, but now that I think about it, its not really surprising.
a 1:27 reduction… Because unicycles aren’t low-geared enough!
You mean unicycle hub? Maybe, if you want tens of pedal rotations for one wheel revolution. By its very nature, this gear can only gear down. and then again only with quite large ratios.
Edit: why does your thread title say Geared hub improvement?
Not if you just hook it up the opposite way.
To make it spin backwards?
Then it’s self locking. You could not propel the wheel pedaling. But you could roll down a hill and your pedals will move one revolution every 56m (on an 26") 
That’s like freewheel with non constant pedal position … haha
Or thought otherwise … it’s like shortening the cranks by that gearing factor … 125mm cranks will feel like 4.6mm cranks …
What a great improvement … I wonder why Florian hasn’t built up one yet …
This makes me think: you can’t even roll the unicycle without pedalling (in gearing down configuration as the original poster proposed). The wheel will lock if you don’t pedal.
Right.
Just like an automatic locking brake 
A real improvement. Your uni will stop automatically when you upd and not ride away without you
I wonder what happens if you momentarily don’t pedal. Like if you change the direction of the driving force (as happens all the time during riding, to keep balance). Will the wheel lock already? Verrrrry tricky machine!
Isn’t that what happens with normal fixed uni’s…?
I don’t think so. When you stop driving the pedals in a normal fixed uni (or a Schlumpf geared one, for that matter), i.e. you apply zero torque input, the wheel drives the crank set. In this hypothetical downgeared uni, if the pedals are not driven, the wheel locks. That is, it cannot rotate with respect to the frame.
So more like riding with a coaster brake (Or any other sort of brake that automatically activates when you aren’t pedalling forwards) 
Sounds like a surefire way to break a nose.
Well, the good thing is that with downgearing of a factor of 27, the typical riding speed would be 0.5 to 1 mph. So it’s not that dangerous. 
Unfortunately whenever a body is unsupported, as happens when a unicycle fails to progress as expected, gravity still accelerates it downwards regardless of the forward speed of the unicycle.
True but with hardly any forward speed involved, the process is basically the same as dismounting. Usually safe and controlled.