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flag Honus
Posted: Mar 4, 2010 at 11:40 Quote
I know exactly what you mean. Every time I read these threads I start chomping at the bit to get out in the garage. I was in an electronics surplus store the other day and saw some linear slide components (I'm currently building a 3D printer) that I thought would be perfect for building a transmission. If you used a fast pitch lead screw to shift the chain across the gears you could get rid of all the pulleys that are shown in the phaser transmission. It would greatly simplify it and make it more compact. Packaging is always going to be tough on a bike of this type.

I sketched up a couple of bike designs some time ago. The first one would use a derailleur type transmission and the second would use a gear hub (Alfine) that sits in front of a large backbone type frame. The problem that I have with gear hub bikes is that I don't like the width of the overall bike. I'd also like to make it as light as possible. I used a pull shock just because I have one and I thought it would be neat. You can get adjustable ride height and variable compression curve and no linkage is necessary. Simple and light. Of course it could be built with a standard compression shock and linkage assembly.
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flag PerryDH
Posted: Mar 4, 2010 at 11:51 Quote
The DC special is worth a look at for 'derailleur in a box', Though his welding the cog to the axel is a little...messy!

DC Special
flag jacobharrel
Posted: Mar 4, 2010 at 16:46 Quote
Honus wrote:
photo

Where are you getting the pull shock from? Or did you grab it off an older bike? Aside from the occasional scott you really don't see any around anymore, especially pull-coils.
flag Jose-David-DH
Posted: Mar 4, 2010 at 17:33 Quote
how much clearance do you have with a 83mm BB?... cause the alfine rear hub is 185mm (with the lock nut) or, can you change the lock nuts and maybe mod the axle? to make a "gearbox" bike

my FSA gravity moto x have only 140mm of clearance (73mm BB + chain line spacer + chainguide)
flag 3lfd3wd
Posted: Mar 4, 2010 at 17:43 Quote
Jose-David-DH wrote:
how much clearance do you have with a 83mm BB?... cause the alfine rear hub is 185mm (with the lock nut) or, can you change the lock nuts and maybe mod the axle? to make a "gearbox" bike

my FSA gravity moto x have only 140mm of clearance (73mm BB + chain line spacer + chainguide)

185mm?! How on earth does anyone expect that to fit in a frame then?
flag Jose-David-DH
Posted: Mar 4, 2010 at 17:45 Quote
without the lock nut, the hub is 135mm
25mm each lock nut
135mm+(25mm*2)=185mm
flag 3lfd3wd
Posted: Mar 4, 2010 at 17:53 Quote
Jose-David-DH wrote:
with the lock nut, the hub is 135mm
25mm each lock nut
135mm+(25mm*2)=185mm

Er...with the locknut, it's small number, added locknuts, it's a bigger number? I'm really not following here
flag rokor
Posted: Mar 4, 2010 at 17:54 Quote
Probaly a typo. Could you really not get that? It's not that hard to figure out...
flag Infiltrator
Posted: Mar 4, 2010 at 17:55 Quote
read back a few posts... typo is a bit of a stretch
flag rokor
Posted: Mar 4, 2010 at 17:56 Quote
He said "with", and I assume he meant to say "without"...
flag 3lfd3wd
Posted: Mar 4, 2010 at 18:01 Quote
A standard hub is 135mm wide between the dropouts, right? Why would you include locknuts on top of that standard width, you're not forced to use the same locknuts if you're mounting it as a gearbox in a frame?
flag Infiltrator
Posted: Mar 4, 2010 at 18:03 Quote
the alfine has a 135mm axle width... but the "over locknut" measurement is 185... Very confused
flag Jose-David-DH
Posted: Mar 4, 2010 at 18:04 Quote
rokor wrote:
He said "with", and I assume he meant to say "without"...
sorry
flag bennett12luke
Posted: Mar 4, 2010 at 19:59 Quote
that JKFAB pullshock design looks AWESOMEtup
flag Honus
Posted: Mar 4, 2010 at 20:14 Quote
Trocadero wrote:
Honus wrote:
photo

Where are you getting the pull shock from? Or did you grab it off an older bike? Aside from the occasional scott you really don't see any around anymore, especially pull-coils.

It's the same pull shock that Yeti used on the Lawwill bikes. When I worked in the bike industry as a designer I was friends with a guy that was an engineer at RockShox- he custom built it for me.

The biggest issue with pull shocks is that they require a lot of space. There are some advantages to through shaft damper construction as they don't require a floating piston since the internal volume doesn't change as the shaft moves through the damper body. Both Ohlins and Sachs use through shaft dampers on their high end motorsport dampers. It would be neat to build a high end pull shock using the latest technology. Ideally I'd like to build a longer travel shock so I could lower the leverage ratio- right now it starts at 3.26:1 and ends at 3.04:1 which is as high as I'd ever want it. A 2.7:1 to 2.5:1 range would be much more ideal.

 


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