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Old 12-17-07, 09:42 PM   #1
dcb
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converting 3 speed hub to direct crank?

Has anyone ever seen a direct crank (like on a kids trike) internally geared setup? Might it be possible to convert an old three speed hub to such a setup with a bit of fabrication?


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Old 12-17-07, 10:12 PM   #2
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Has anyone ever seen a direct crank (like on a kids trike) internally geared setup? Might it be possible to convert an old three speed hub to such a setup with a bit of fabrication?
What you call "direct crank" is more commonly known as "fixed gear."

See: http://sheldonbrown.com/asc

and: http://sheldonbrown.com/gunnar

Sheldon " http://sheldonbrown.com/fixed " Brown
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Old 12-17-07, 10:28 PM   #3
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Specifically I was thinking of the situation where the crank axle and the wheel axle are the same.

Edit, like for a 3 speed pennyfarthing, or a funky FWD recumbent or something.
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Old 12-17-07, 10:49 PM   #4
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So you want a 3-speed rear hub put on the front wheel? Most fork dropouts are 100 mm and narrower than rear dropouts, though. I wonder if a steel fork could be spread. Old 3-speed hubs are 110 mm, maybe a steel fork could be spread the extra cm?

Edit: Now that I think about it some more, forget about dropout width, how do you expect to attach the crank?

Last edited by JiveTurkey; 12-17-07 at 11:01 PM.
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Old 12-17-07, 11:04 PM   #5
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Now you get it cold setting 10mm is nothing, setting in some bearings and figuring out what to spin where is the fun part.
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Old 12-18-07, 04:51 AM   #6
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Schlumpf makes a 2-speed internally geared unicycle hub.

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Old 12-18-07, 11:15 AM   #7
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It looks like Schlumpf has your answer! Then all you have to do is fabricate your fork to fit.

The real challenge would be fixing the cranks as JiveTurkey mentions. Only one side of a 3-speed hub would turn at crank speed. The other side would turn not at all, since it's just axle over there; there's no spindle on a hub. You couldn't attach to the hub because, on the left, it would be turning at a different speed than the right.

Edit: Oo! You could attach a chain to the right crank that went up to the top of the wheel, turned a shaft, which turned a chain on the left, which went back down to the axle, which turned the left crank! The challenge *then* would be attaching the crank in such a way that you could apply real pressure to it. Like, maybe you'd have a superlong axle fabricated for the hub, and the crank would spin around the axle. But it would be a really kooky solution, probably of very low durability, and extremely complicated.
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Old 12-18-07, 01:06 PM   #8
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Schlumpf costs more than all my bikes put together

I recon I'll have to do an experiment, see what happens when you spin the axle and hold the sprocket steady and shift through the gears. It might turn the wrong way

Shifting becomes an interesting problem too. The Schlumpf approach looks manageable for two gears.
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Old 12-18-07, 03:26 PM   #9
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Maybe you could substitute a gear for the sprocket and turn it by a second gear on the cranks? It would still be pretty close in proximity though not direct. And you could even tailor the bike's gearing by changing the tooth count of the gears. Without an idler gear you'd have to pedal backward, though...
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Old 12-19-07, 10:39 AM   #10
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Some newer info: A new BF member builds penny-farthing bikes, and has built one with a Sturmey Archer three speed hub. See http://www.pennyfarthingworldtour.com/penpics.htm
It looks complex but it works.
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Old 12-19-07, 11:02 AM   #11
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Florian Schlumpf showed me a cutaway of his unicycle hub. Sturdy doesn't begin to describe it. Makes Sturmey Archer guts look like ladies watch works.

He came up with the idea while touring Europe on a unicycle as a young man. Originally trained as an artist, he went back to school to become an engineer and a machinist. The 2 speed mountain and speed drives were easy by comparison, so he brought them to market 1st.

If I could afford one I'd build a 2 speed Geared Dwarf Safety around a 36" Coker wheel.

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Old 12-19-07, 11:54 AM   #12
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Why do they call that a "dwarf safety"? It seems more like a "dwarf ordinary". And a sporty thing it is, too. In India there's a bike patterned after that, but smaller and with no gearing, meant for children.
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Old 12-19-07, 07:37 PM   #13
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In the vernacular of the day, any deviation from the standard "Ordinary" design that lowered the riders CoG or moved it rearward was considered a "Safety". Consider the passage about the "Xtraordinary" safety on Page 150 and the illustration on the next page, of Archibald Sharp's "Bicycles & Tricycles: A Classic Treatise on Their Design and Construction"

To our eyes, the machine is only slightly different from an Ordinary. To a 19th century cyclist, who was attuned to the subtle differences between ordinaries, it would have looked radical.
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Old 12-19-07, 10:02 PM   #14
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So is there a proper name for a crank that has a common axis of rotation with the wheel?
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Old 12-20-07, 08:15 AM   #15
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So is there a proper name for a crank that has a common axis of rotation with the wheel?
Maybe coaxial?

And MnHPVA Guy: Thanks for the explanation and link; very helpful!
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Old 12-20-07, 08:50 AM   #16
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Originally Posted by cyqlist View Post
Schlumpf makes a 2-speed internally geared unicycle hub.

A unicycle with a geared hub. Have I seen everything in my lifetime, now?
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Old 12-20-07, 08:57 AM   #17
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Originally Posted by MnHPVA Guy View Post
In the vernacular of the day, any deviation from the standard "Ordinary" design that lowered the riders CoG or moved it rearward was considered a "Safety". Consider the passage about the "Xtraordinary" safety on Page 150 and the illustration on the next page, of Archibald Sharp's "Bicycles & Tricycles: A Classic Treatise on Their Design and Construction"

To our eyes, the machine is only slightly different from an Ordinary. To a 19th century cyclist, who was attuned to the subtle differences between ordinaries, it would have looked radical.
By the way: the original print of that book (1896) will set you back some US$560. I am a collector of antique scientific books, and I'd love to have this in my collection - but it's not going to happen. Not in the following 2 years.
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