Thanks Alain for the comments.  The model here is a double steering bike, with
steering axis both for the front part and  for the rear part. I already built
one. It was rideable (and fun :-) see this video :
https://www.youtube.com/watch?v=kP08CeD9aV8 ) but there were several points to
ameliorate.

The projection of the pivot may be behind the wheel ( google for python bikes to
see some models and for the explaination of stability - minimum of potential
energy with a centered wheel). And for double steering, it is probably
inevitable because positive trail yields to "wheel flop" difficult to control.


Alain <kua### [at] videotronca> wrote:

> > Here an image of the bike I plan to build. Mostly parametric description.
> > Modelisation done with Pycao, using between 200 and 300 lines of code ( not
> > including the many parameters at the beginning of the file)
> >
> > Thank you Povray and the povray team  :-)
> >
> >
>
> Nice... but, I see some problems on the mechanical and functional point:
> 1) The handles are in an awkward location. Located like that, you lack
> leverage in your steering.
>
> 2) Normally, the chain goes to the rear wheel. How do you plan on
> routing it? As it is now, it can hardly go there without interfering
> with the front wheel and it can't bend laterally. Maybe it's a front
> wheel drive? You really don't want the pedals to turn with the front wheel.
>
> 3) How does the front wheel can ever turn in order to steer? If the
> pivot is under the pilot, it will be insanely difficult to go straight
> if there are any irregularity on the road, and any curve will be
> uncontrollable. Then, here is the problem of the chain that can't bend.
>
> 4) If the pedals turn with the front wheel, pedalling will make you turn
> to the right and left. As they will have a MUCH longer lever than the
> hands, you'll be powerless to control that.
>
> 5) The front wheel's pivot axis projection reach the ground behind the
> wheel's contact point, it must be in front of that point.
>
>
> My propositions:
> Have a smaller front wheel, about half the size of the rear wheel.
> Place the pivot for the front wheel further in front, over the wheel.
> The projection of the pivot must reach the ground in front of the wheel
> to insure driving stability.
> Make it a rear drive bike.
> If you want the handles to be under the seat, you need to make them
> wider. Typically, they are placed slightly more forward and have an U shape.

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