[python] Re: New Drawing: Drive system

Sometimes, using Outlook (to read my mail from everywhere in the world, was my employers choice, not mine...) is a pain. This is a replica of an answer I sent the 18th June.....It got stuck somewehre.

Hello Paul,

in principle it would work, but...

-it requires a stronger front frame because of the momentum each half crank induces in only one of the tubes separated by the wheel

-you will have to come up with some really clever bearing design for your half crank, as the force is at least equal to a normal bottom bracket system, probably a lot worse (you push forward with your foot and the short chain excerts a pull to the front as well) and the maximum possible distance between two bearings is much, much shorter than in a standard pedal bearing.

I experienced at my Speedbike that the whole frame deforms in an elastic manner (really hope it stays like this and does not go to plastic deformation) when I use the 26 chainring I fitted this year, while riding uphill. First I thought the rear shock absorber blocking was faulty, but no, the chain makes the frame bending slightly... In fact the bike is most efficient using the 53 chainring, the 38 is almost the same unless I go uphill, but the 26 is an emergency exit only. Just calculate: if you push with, let's say 500N, this force is multiplied by ~3 with small chainrings, so 1500 N pull at the chain.

Best whishes for your design

Ralf


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At 10:46 18.06.2004 -0400, you wrote:
Hi all,

and welcome to Ralf.

I am pretty busy until after my wedding day on July 10th. I have been
working on a design until I can start building in at the end of July.

One of my problems is my short 5'4" frame and legs. I have been trying to
figure out how I can fit 26 inch wheels(559's I think in metric)

I drew up a design for the pedal system which has half a crank on each
beam of the front frame, ahead of the front axle.  I'll not try explain
further but give you the link to my drawing. The drawing is not to any
real scale as I just use Illustrator to do the sketch, and not a CAD
program.

http://www3.sympatico.ca/jebelisle/pythonpedals.gif

Any comments on this design concept???

I think this might help stability as power transmission from the legs will
be closer to the front wheel axle, but its just a guess.

Cheers,

Paul Bell

p.s. Have one other drawing on my basic web page...
http://www3.sympatico.ca/jebelisle/




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