Has anyone ever made a guni with a worm gear on the axle and offset cranks running straight-cut gears against the worm gear?
You’d need to concentrate on what worm gear you ended up with otherwise you’d end up reversing…
Given worm gears tend to be used to achieve speed reduction and introduce a 90 degree change of direction in a situation where you want drive in the same direction as the driving force, they don’t seem that useful an idea.
I think “offset cranks” meant the cranks some distance from the hub - in the same way as on a giraffe or penguin unicycle. There are also “jackshaft” unicycles where the two cranks are not on a common spindle (although they have a common axis), but they are each connected to the hub by a chain and a pair of cogs.
If so, then the worm gear idea would work “in theory” in that it would allow a 90 degree change of rotation at the crank and a second 90 degree change of rotation at the hub. In effect, the unicycle would be a sort of shaft drive giraffe/penguin.
However, if you’re going to build a shaft drive, I think bevel gears rather than worm gears are the way to go. Worm gears are not good for friction. Shaft drive motorbikes and cars use bevel gears. There is some loss of power transmission compared to a chain, but the benefits of cleanliness and low maintenance outweigh this. (I have a shaft drive Moto Guzzi and come rain, shine, snow, salty roads, mud, grit or sand, I never have to clean, tension or lubricate the chain, because there isn’t one.)
I have seen shaft drive bicycles but never yet ridden one. All the ones I have seen have been municipal “city bikes” clearly designed for durability and low maintenance rather than speed and efficiency. I see no advantage to a shaft drive unicycle, and various disadvantages in terms of weight and cost.
If I have completely misunderstood the original post and “answered the wrong question” perhaps Kitibob can clarify?
Worm gears always work with the worm gear as the drive gear. If you find a physical example and try to move the straight cut gear, you’ll immediately see that it’s not feasible. Having the worm gear on the axle isn’t going to work without an extremely high helix angle.
Yeah the thought was that you’d have a shaft coming several inches above the hub axis, from the frame. On this shaft is the crank, and on the inside of the frame is a straight cut gear.
On the axle itself, there is a worm gear which binds to the gear referred to above. It wouldn’t be like a jackshaft system, as the crank would come out offset from the axis of the hub.
It was just a theory, really. I don’t really intend on doing it as it seems impractical, and yes, it would require both a very strong pair of gears to deal with the torque and a very acute helix angle. It would also need to be symmetrical so that both of the cranks worked…
Yeah, I’ve seen one but haven’t had the chance to ride one either:
I personally found this much more interesting than the E-Type Jag in the background.
Worm gear drive is great for reducing speed. It doesn’t get used for increasing speed because any friction between the two gears is amplified by the mechanical advantage–well, disadvantage in this case–if you try to drive it from the worm side. Most configurations are non-reversing as juggleaddict points out, where any effort on the worm gear increases the locking force and just locks it tighter. This is usually a feature, since it keeps what you’re driving with the speed reducer from kicking back and hurting you. Even for a worm drive that isn’t fully non-reversing, the loss of power due to friction when driving it backwards is immense.
Shaft-drive bicycles like the one in the picture typically have a pair of bevel gears at each end of the shaft to realize the 90° turn. Also, some car and motorcycle engines have used a shaft with bevel gears to drive overhead camshafts. Maybe that’s more like what you had in mind. It’s a lot more efficient for transmitting power, and the modest step-up ratios we’d use are far easier to get than with a worm drive.
Don’t get me wrong, I like the bike. But please excuse me if I don’t. 
Aha, so the thought was flawed from the start. A great example of my shallow depth of knowledge in the field
Cheers for all the contribution, everyone.
What about the antique low gravity delivery bike next to it? That’s pretty cool too.
https://bicycles.stackexchange.com/questions/20591/any-experience-with-shaft-driven-bikes for those a little more interested in a detailed pic of that transmission : )
The Jag contains every bit of technology in that bicycle, and much much more, so I find the E-type 10x more interesting. The only thing that’s more complex (and therefore interesting to me) on the bicycle, is how it manages to keep stable, even without rider input.
It’s not that I think the shaft-drive bike is particularly amazing, it’s just that I think E-Type Jag’s are a bit overly celebrated and, if I’m honest, that’s sort of spoiled it for me.
Plus, being a unicyclist, i’m not necessarily impressed with overly complicated mechanisms: one wheel will do
Well sure, and it was my generation that did a lot of the celebrating. I had a couple of chances to buy one or another E-Type when I was around your age, more than a little bit rough and trying to keep it out of the junkyard would have broken me for sure even I could have found the little bit more money than had at the time to buy it. But that didn’t figure into my thoughts at the time and it doesn’t tarnish the feeling of, “I almost could’ve had one.” Overrated perhaps but there’s a lot to rate about it.
So says the man proposing a worm-drive geared unicycle.
What about the back half of this? I don’t see what holds wheel to the frame, and maybe nothing does since it’s just a concept, but that’s pretty simple.
