[python] Re: rws python

Laurent,

Geez I'm WAY TOO excited!!! Looks like you will have the first VRWS* bike in the world! I'm starting on my VFWS* bike this Tuesday! I'm trying to remember that this design may end up having some big problems, like the steering might be too weird, or the forces on the four bar linkage might require heavy bearings and tubes... But it could be so cool! And based on my newer analysis, I think that the steering won't be bad at all.

*I have to stop making up new abbreviations all the time! :-)

I would love to help you with the math if I can!

Let's see... I'm going to convert to my terms to make this easier for me, then I'll change them back to yours, and with any luck we will all be very confused! ;-)

So in my terms, the numbers you are using are:

R = 540 - 600mm (this is your A-pivot)
C =  114mm (this is your A-D)
S = 250 - 254mm (this is your B-A  which should be the same as your C-D)
G = 160mm (this is your B-C)

So let me verify that you have good values for S & C. If we use:

R = 540mm (this is your A-pivot)
G = 160mm (this is your B-C)
Y = 250mm (distance between B-C and A-D, slightly shorter than B-A / C-D)

GIF image



Then:

S = 251.3mm (this is your B-A  which should be the same as your C-D)
C = 109.4mm (this is your A-D)

If you had a larger value of R:

R = 600mm (this is your A-pivot)
G = 160mm (this is your B-C)
Y = 250mm (distance between B-C and A-D, slightly shorter than B-A / C-D)

GIF image



Then:

S = 251.1mm (this is your B-A  which should be the same as your C-D)
C = 112.9mm (this is your A-D)

So those are pretty close to what you are working with already -- would you like me to do some more calculations? I would be more than happy to!

Also, here is my rough sketch of a VRWS bike -- the pivot side links (S, but the distance we see from the side view is actually Y) are probably too short in this picture. Those are 507 mm rims with 50-507 tyres.

JPEG image



Michael

PS: I'm using 4 shortened headsets for the prototype, as Jürgen Mages suggested, but I'm pretty sure that tapered roller bearings would be almost perfect, because:

1) They are just generally better than ball bearings in high-load applications (ball bearings are better in terms of low-friction efficiency)

2) A low-angle roller bearing (that is, one designed to handle big thrust loads and smaller radial loads, i.e. the opposite of the roller bearings in car wheels, something closer to a roller thrust bearing) seems ideal for handling the torque acting on the pivots (the way I imagine it).

3) I think that a tapered roller bearing can be preloaded to reduce play, which I don't think you can do with a ball bearing.

PPS: I sent this link out before, but it's a good basic bearing primer, so here it is again:http://www.howstuffworks.com/bearing.htm

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