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Old 2010-01-21, 01:57 PM   #1
MuniOrBust
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How does the Schlumpf hub work?

This is my second Schlumpf thread in as many days. I guess I have Schlumpf on the brain.

I'd like to understand how the Schlumpf hub works. In general, it uses a planetary gear system. Right?

But how does the shifting mechanism work? It would be cool to have an animation of that, but I doubt it exists. But a text explanation might work too, if possible.

I found these images in the forums:
Name:  KHU_schlumpfInternals.jpg
Views: 6981
Size:  60.8 KB I guess the small gears I can see are the "planets" and a "sun" gear goes in the middle, but has been removed in this photo.

Name:  12 KH unit 070420_1.JPG
Views: 7890
Size:  26.1 KB
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Old 2010-01-21, 03:32 PM   #2
juggleaddict
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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.

anyway, the wiki page helps : )
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Old 2010-01-21, 04:37 PM   #3
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Quote:
Originally Posted by juggleaddict View Post
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.

Just kidding.

I do tho think that the hub has any mechanism to smooth out the transfer. When I shift gears, it feels pretty hard.

I like the photos. I want more!
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Last edited by hugo; 2010-01-21 at 04:40 PM.
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Old 2010-01-21, 05:31 PM   #4
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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).

Rob
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Old 2010-01-21, 06:43 PM   #5
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I believe rob has it right. It would be nice to see a few pictures of the dog clutch surfaces, but those are the only two pictures I've seen of the internals before.

Here's a decent explanation, including animations, of how a three speed hub works. The Schlumpf would be using only the 2nd and 3rd gearing options.

http://web.mit.edu/2.972/www/reports...speed_hub.html
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Old 2010-01-21, 06:55 PM   #6
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Cool. Thanks for your summary rob!

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.

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Old 2010-01-21, 07:43 PM   #7
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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.

@rob: your description makes perfect sense
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Last edited by hugo; 2010-01-21 at 07:48 PM.
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Old 2010-01-21, 08:38 PM   #8
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Quote:
Originally Posted by MuniOrBust View Post
Cool. Thanks for your summary rob!

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.

It works on paper! Ship it!
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)

Didier
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Old 2010-01-22, 08:30 AM   #9
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Nice animation of all 3 planetary configurations here.
http://science.howstuffworks.com/gear7.htm

Then scroll down one page.
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Old 2010-01-22, 10:35 AM   #10
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This unicycle was build by some one in germany.
It's not mine.
I have riden it at the unicon 14.
The gear ratio is a lot higher than a schlumpf hub.
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Old 2010-01-22, 01:16 PM   #11
hugo
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Quote:
Originally Posted by rvs View Post
YouTube- Geared

This unicycle was build by some one in germany.
It's not mine.
I have riden it at the unicon 14.
The gear ratio is a lot higher than a schlumpf hub.
That must be jogi's 1:2.5 ratio unicycle. Unfortunately it was broken some months ago, and it was a fixed ratio (no gear shifting)
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