[python] Re: airbike - programm results
- From: Ray Schümacher <mtb@xxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Sun, 06 Mar 2005 11:18:55 -0800
Hi Peter,
At 05:45 PM 3/6/2005 +0100, you wrote:
>I am not sure now how to interpret the results of the program run with Airbike
>data, and to which extend I can trust the results. You should know that with
>some practice one can drive the Airbike at something above walking speed.
As Jürgen said, it is mainly about self-stability; a bike with no rider inputs.
The green on the graph is the calculation for complete self-stability and is
the same as the text output. In the text, the stable region is where all of the
5 main criteria are positive. The meaning of A-E has to do with the sum of the
eigenvalues and eigenvectors of the basic equations. The Laplace stuff is a bit
above my math, I just use the shortcut code.
The yellow is where the value of E, the fifth, is not too negative. It also
then includes, from a separate calculation, the speed range where all are
positive when the main variables are held constant and the k factor for pivot
spring is varied slightly, hopefully an analog of the normal small inputs of
the rider.
None of this is precisely true as the method makes certain assumptions like
zero damping and resistance and knife-blade wheels. I did some more reading to
hopefully add damping to the pivot.
>Living at near the Black Forest speeding savely downhill (and climbing up
>steep hills) would be an important ability of the Python for me. So far no
>design performed too well on this, right?
After reading more, I would like to see someone test adding significant weight
in front of and low, below the cranks, >10kg. For some aspects of stability,
positive trail and having the front mass in front of the pivot axis are
similar, and so an upright with negative trail can be stable only with mass
well forward to make the front wheel fall in the direction of the turn. This is
why it shows shorter pythons being more stable; more of the rear mass is on the
rear wheel, rather than at the pivot and counteracting the front mass falling
into the turn. I included a python design .cfg that was stable and had -8cm
trail. Panniers well behind the rear axle would be similar.
This is also why an upright with 90 pivot angle and zero trail can be stable as
long as the front mass is far enough forward. Similarly, very old bikes had
straight bars and forks and so zero mass forward, but good trail, and so were
stable no-hands.
Front mass would also increase the turning moment and help resist high speed
wobble.
Cheers,
Ray
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