[python] Re: Questions from a total newbie
- From: "gdurbrid@xxxxxxxxxxxxxx" <gdurbrid@xxxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 22 Mar 2006 23:18:10 +1100
---- mchannon <mchannon@xxxxxxxxxxxxx> wrote:
> Hello List
>
> At 09:00 PM 3/21/06 +0100, you wrote:
> >snip<
> >> Well, what I had in mind is a bike where the seat height is constant,
> >> only the angle of the main pivot would change. This would involve
> >> mounting each half of the pivot bracket (front and rear) on a horizontal
> >> pin and controlling their angles together with regard to their
> >> respective halves of the frame with set screws, so that the bike's
> >> overall geometry wouldn't change. Being my first Python, on one hand
> >> you're right, I should keep it simple, but on the other hand, if I
> >> implemented something like that (if it's doable at all), I would have
> >> room to experiment with the pivot angle without having to make another
> >> frame each time.
> >
> >I see. Something like the adjustable rod end bearings solution of
> >Mike and Tim.
> >
>
> I think that an adjustable pivot angle might best be addressed by a virtual
> pivot python. I've been thinking of building one. The front and rear parts
> would be connected with links, each link with a rod end bearing at each end.
> Each pair of links would angle inwards towards the front of the bike. One
> pair would be positioned above the other pair a few centimeters. Each pair
> of links establishes a point on the virtual pivot. Changing the angle of
> the links would change the location of the virtual pivot. I haven't yet
> figured out how to make the mount on the frame adjustible so that the angle
> of the links could be varied. The ultimate would be to incorporate some sort
> of a threaded rod, so that by turning the rod the mounting points would move
> closer together or farther apart. Clearly a drawing is needed...but I don't
> know CAD..
>
> Another benefit of this approach would be the ability to vary both pivot
> angle and trail independantly on the same bike.
>
> Regards,
>
> Mike Channon
> London, Ontario, Canada
Mike and all,
I may have all of this back-to-front, but modelling two-link steering in plan
only (i.e. as seen from above) with matches, I think that you would wind up
with very strange steering, or even none at all. I would build an adjustable
model from wood or Meccano to check the properties, before cutting metal.
If the left and right links are parallel and equal, the front wheel will always
point straight ahead, whether you push it to the right or the left - the bike
will have no steering at all.
If the links converge towards the front, as you push the front wheel left, it
will point right. This action would be difficult to learn. Because it would
displace the front wheel toward the outside of a turn, this linkage might
possibly have a use in delta trikes as a substitute for lean-steer, but I don't
see a use in bikes.
If the links diverge toward the front, as you push the front wheel to the left,
it will steer left, but in a non-linear way, which may not give a satisfactory
degree of steering response.
George
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