[python] Re: A Bicycle Can Be Self-Stable Without Gyroscopic or Caster Effects
- From: pybuen@xxxxxxxxx
- To: python@xxxxxxxxxxxxx
- Date: Sun, 17 Apr 2011 22:24:34 +0800 (WST)
Hi DirkS,
On Sat, 16 Apr 2011, dirk@xxxxxxxxxx wrote:
what do you mean by weights? a gentle leaning and a harsh leaning into a curve?
still, this experiment would be a good starting point.
I mean putting some more-or-less heavy material on the seat (experimenting
both might be instructive), as in the video from B100Saa on youtube (although
I would fix them in some way, eg. sand bags):
http://www.youtube.com/user/B100Saa#p/a/u/1/khpO2n0szFs
then managing to launch the python and letting it go with a certain speed, as
straight as possible, or as you suggest, with a lean into a curve (this might
be tricky to achieve). And see what happens to the foam protection you would
have dressed your python with... :)
i was trying to derive from the experiment. if the clue is to have more mass
towards the front which is still attached to the rear part in order to improve a
bike with negative trail,then:
ok, I see.
A bike with a loaded front wheel only changes the relation of the mass between
front and rear part. i does not alter the CoM of the rear part alone.
Indeed, it does not alter the CoM of the rear part alone. However, the CoM of
the front and of the rear parts are influencing each other in a lean-and-turn
via the pivot axis, and it is this combination which ultimately determines the
steering and leaning behaviour of the bike. Perhaps you could replace the
long-reaching pole attached to the rear frame of the article experiment
equally as well by a weight attached on the front frame, either between the
pivot and the front wheel contact point or ahead of that contact point (not
sure which)? Sure, the bike's behaviour might never be exactly the same, but
you might still retrieve self-stability with negative trail in this way.
i think its a good start adding weight here and there and let the bike go to see
what happens. It should be better than the pushing test we discussed the other
day, since there aren't any external, varying forces involved :-)
That opens up new, trickier issues in the design of the bikes: not only
geometric variables (e.g. pivot angle) are affecting behaviour, but also
weight distribution. The good thing is that one may be able to play these
features against each other, although they are actually interdependent. I mean
by that: if you have to have certain restrictions as to the geometric design
of the bike, you may be able to compensate poor rideability by a
redistribution of the weight (hopefully not by adding sand bags and other
dumbells everywhere...).
Now how is the resulting influence on the steering behaviour? What geometry
makes the bike wanting to steer to the right side?
That is all the question, indeed. The physics of bikes looks simple at first
sight, but it raises tricky geometrical and dynamic issues.
Regards,
Pascal
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