I think the problem with this is that the intermediate gear would need
to move away from the seatpost, the base of the triangle if you will,
in response to changes in the length of the seatpost. So you would
need some kind of linkage between seat height and WWW arm length. Not
insoluble, just a complication.
> The way to make this work is to drop the "WWW" arm. The idler wheel axis is
> supported by two arms. One arms pivots about the crank axis & the idler wheel
> axis; the other about the wheel axle axis and the idler wheel axis. That is
> each arm follows the "chain lines"; as the seat tube compresses,the arms force
> the idler wheel out, keeping the chain at the same tension. Note that you
> really need two idler wheels, so that the "inside" chain doesn't simply ignore
> the idler wheel. I suspect that to keep the geometry right, all of the gears
> and idlers need to be the same diameter.
> -- Charles Clinton
I think this mod solves the problem of the chain length. But, similar to
my comment on a parallelogram idea in another post, I think you may
have a problem of vulnerability of the mechanism in a "gravity-driven
event" (wink-wink). OTOH, simply making the two arms of unequal
length, and positioning the joint within the circumference of the
wheel might solve that. Hmm... Yet another idea deserving of more deep
thought than I seem to have had time for lately!
I just want to say to everyone who has been in on this thread: It's
been VERY stimulating! Everyone has obviously been exercising their
thinking caps. I, for one, hope to be able to massage some of these
ideas into something rideable, the manifestation of cyber-thought in
the cycle-flesh, so to speak, and I hope others are similarly motivated.
Stay on top!
* ------------------------ * ----------------------------------- *
| Mark Schecter | "Please identify yourself." |
| schecter@tfs.com | (Self checks pocket mirror) |
| | "Yes, that's me." |
* ------------------------ * ----------------------------------- *