give me a month and I could model it in autocad and then run a dynamic simulation on it . . . . ok, a few months . . . I’ve got other work too ; P
though this would have been a really cool group project for that class now that I think about it. . . too bad though, I’d have to kill a shlumpf to do it. Anyway, check out the wiki on planetary gearing. http://en.wikipedia.org/wiki/Epicyclic_gearing
I’m not sure how it shifts precisely, my guess is that you physically move the whole gear over to another set of planetary gears, toootal guess here. Though you would need some sort of system to smooth out the transfer of gears there, it’s not like you’ve got a clutch.
That’s an interesting thought. I can’t imagine how to engage a clutch, but if the hub had one, and the rider was a “professional” in coasting, shifting could be quite nice: Push or pull or whatever the clutch, coast, shift the gear while coasting, and then smoothly pick up the rotation again.
I do tho think that the hub has any mechanism to smooth out the transfer. When I shift gears, it feels pretty hard.
The way I think it works is like this:
In the second photo in the first post, the middle “ring” is driven round by the pedals and can be moved side to side by the shift buttons. It engages a toothed dog clutch on either side (sudden engagement, no slip) depending on which way the buttons are pushed. On the left in that picture, it would be directly connected to the hub flange, so making the direct drive 1:1 gear. On the right, it is connected to the hub via the planetary gears, giving the geared-up mode. If you could get it to balance in the middle it would freewheel, but the shift mechanism is presumably spring-loaded towards the sides to avoid this (it would only rotate far enough for the teeth of the dog clutch to engage, then spring home). The reaction “arm” required by the planetary gear mechanism is provided by the knurled part that is gripped by the bearing holder on the frame (this hold the sun gear still, visible in the second photo). Earlier Schlumpf hubs (and Greg Harper’s ones) had a separate arm that needed attaching to the fork leg.
And of course all very accurately made to minimise the gear slop, which is presumably a lot of the reason for them being so pricey (as well as the limited production volume).
So the middle ring is pushed to the left or right to engage it into either “gear”.
With those two options of “left” or “right”, is makes sense that you could only have two gears.
How could it be changed in the future to have 3 gears?
Maybe if the 1:1 gear was in the middle and to to the sides were different planetary gear sets. For the 1:1 gear, the middle ring would have to engage in a completely different way than it does now. Instead of engaging with the hub flange, maybe it could engage with the hub body. Then a push to either side would engage it with a planetary gear.
But having a left, middle, and right position would probably require a bit more dexterity than the average foot possesses. Maybe if the push buttons behaved more like a clickable pen. Each button engages or disengages the planetary gear it is associated with. If neither is engaged, it’s 1:1. If both are engaged it explodes.
I would prefer that one of the buttons shifts up, and the other shifts down, independent of the number of gears.
Multiple gears are possible in bicycle hubs, so it must also be possible in a uni hub. Of course, bicycle hubs rotate in only one direction and there are more differences, so I do not know if it is possible at all to design a multi-gear hub for a unicycle, I would just assume it is.
You want pictures? Here are all of the pictures that I’ve been able to collect over the last couple of years: I don’t pretend to really understand how this works. I’m happy just treating it like a black box that performs miracles. Although these pics sure are cool looking. Hope they help your understanding.
For information the exact Schlumpf ratio is not 1.5 but 1.5625 . Difference between the 2 Schlumpf ratios is very important, much more important than a change of front gear on a MTB !
An other photo of the Schlumpf hub :
Last summer, I made a design with exactly such concept with 2 planetary gear sets on both sides and a direct drive in the middle but this has a major concern regarding buttons has their travel will be twice as Schlumpf and will make them very fragile in case of UPD
My current design is cable control and with just one sliding planetary gear sets and with 3 sliding claws to get all the 3 gears (0.72 / 1 / 1.38)
I also remember seeing a video that showed Florian spinning a Schlumpf hub that was mounted on a board. The hub was a special demonstration model that had a cutaway that allowed you to see inside the hub as the gears spun. I remember this video being on the Schlumpf Innovations website, but I couldn’t find it there when I just checked. Maybe you could email Florian and he’d put it back up on the website.
Super G- To change gears on the Schlumpf hub the rider hits the shifting button with his/her ankle on the down-stroke of their pedal revolution. This engages the second gear- to shift back, the rider simply does the same but with their other ankle.
Yes, in fact most three speed hubs have a reduction gear as it is simply the inverse of the higher gear. In high gear, the sun gear is the input (cranks) and the ring gear is the output (hub) if you switched the bindings around so that the cranks turned the ring gear and the hub was turned by the sun gear than you would have a lower than 1:1 gearing.
If I understand the description correctly this is an specific variation on the planetary gearing system which while ingenious probably only works for very low gear ratios and has an inherent backlash which would only get worse as one increased the ratios.
I do not want to get into a “heels or ankles” discussion, but I started with using the heels, until I recently found out that it is easier to shift with the padding of the shoe which is just below the ankle.
That’s way more complicated than it needs to be, you really just need to make the gears on surrounding the main gear larger, and make the main gear smaller. that way all you’re changing is the diameter, not the construction of the entire hub assembly.
darkoman drive system solves all problems, put it on an 09 torker and you have what you all are looking for!!
a unicycle hub has to be simpler than a bicycle hub w/ the same amount of gears considering that neither can really slip either direction w/ the exception of a ratchet system for the chain cog on a bicycle.