[python] Rear Wheel Steer / Virtual Pivot

Hello All,

Rear Wheel Steer, or in other words, having the seat mounted to the front instead of the rear: I finally realized that that is what Laurent was talking about in this email:

        http://www.freelists.org/archives/python/08-2004/msg00050.html

My math friend had the same idea, although I was thinking that you might have an issue with balancing the weight so that the rear wheel would stay still while the front of the bike would rotate around the front wheel (i.e. the rear wheel steers the rest of the bike) while still maintaining good front drive wheel traction when going uphill on gravel or loose dirt.

Still, this is a very interesting idea, since everything that is rigid on an upright bike will be rigid -- the entire drivechain plus the seat -- which should result in great efficiency. Of course since your weight swings out to the side as you steer, it could be a bit tricky to get used to! Still, fascinating!

To design this bike, the virtual pivot remains the same (on or near the center of the front wheel), but since the four bar linkage will now be behind the seat (between the seat and the rear wheel), the value of R (distance from the C to the center of the front wheel) will be much greater, so the four bar linkage will have less "toe-in", i.e. the value of C will be closer to G, and the value of S will be closer to Y. My brain is a bit tired to figure out or remember (if I once knew) what this means... If anyone wants to pick some values for R, G and Y, then use the equations I gave above to calculate S and C, they can make a model and see how it looks.

Michael

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