[python] Re: front-end - "my zero is twice the size of your zero"

  • From: "daryl bender" <darylbender@xxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Wed, 16 Nov 2005 21:53:49 -0500

You know I think it's suddenly dawned on me in a new way. All this talk about pivot angles and trails may be of little consequence at speed. If you look at the last graph;

http://www.python-lowracer.de/pics/height_vs_ab.gif

You can see that for small steering changes the restoring force at *any* (neg) trail or pivot angle is 1) very small (approaching negligible) and 2) almost the same for each case. They only diverge noticeably beyond 10deg turn!I At a 10deg turn the road force trying to turn the front sidways would be incredible! Way way beyond the restoring force. I suspect they are proportionately larger right down to 0deg (the asymptote). Hence the instability. The limiting factor is at what speed (reduction) the restoring force wins out again.

And here I was sketching a variable pivot angle design this morning. Hmmmmmm........ I'm thinking now this won't change too much in the overall scheme of things as the road force (curve) will rise exponentially but the restoring force (curve) is essentially constant. My variable pivot idea may slightly defer the instability but it will always arrive.

I'm thinking now that if you were to have enough force to prevent this the python might not be a good handling bike. Hmmmmm.... This is like battle of the limits in calculus. A "my zero is twice the size of your zero" kind of thing as you are working at the asymptote for both forces.

Cheers
Daryl


From: Jürgen Mages <jmages@xxxxxx>
Reply-To: python@xxxxxxxxxxxxx
To: <python@xxxxxxxxxxxxx>
Subject: [python] Re: frontend
Date: Wed, 16 Nov 2005 13:41:15 +0100

The curse of NT is the decreasing stability when coasting high
speed downhill. 60 kph is kind of a limit for this.

But the way I understand it, that is the curse of NT in general. When
you have more NT, you get more stability and I would expect downhill
speed to improve as well. Or am I wrong?


Unfortunately I am not good ad technical mechanics, but I assume
the following:

As Dirk's calculation shows:

http://www.python-lowracer.de/pics/height_vs_trail.gif

the seat rising increases almost linearly with the NT, thus is the self
centering force.
With increasing NT, the coasting force that wants to turn the front part
backward will increase as well - most probably much more than
the centering force, thus easily zeroing this force out.

I wish some ingenious physicist will join this list and help us calculating
these effects ;-)

Jürgen.

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