[python] Re: Python stability

At 01:33 PM 2/16/2005 +0100, Jürgen Mages wrote:
>Great to have some more mathematical brain power
>here. 

I cheat and use computers whenever possible ;-)
I was actually searching for a Python logo on Google when I saw the image of 
your P1 (I program in Python). I have done some longer rides again recently and 
found my back and wrists not enjoying it anymore, so a bent is what I need.

>Dirk already made some nice calculation works.

Yes, his charts got me interested in the math. I still haven't done the method 
I originally planned, delta-t integration of the "simple" forces on a moving 
bike. I'm hoping my brother-in-law (a physicist, cyclist and recreational math 
guy) will help out.

>>The most important is smallish negative trail, no more than
>>-4cm. A longer wheelbase, with rear mass CG more forward,
>>a more horizontal pivot angle and several others can add stability.
>
>I have heard that NT bikes could be stable, if the trail
>is not too big and if there is enough weight on the
>front wheel. Maybe that corresponds to your idea.

Yes, from test results, additional mass attached to the front is a stabilizer, 
and position relative to the pivot axis seems very important.

>So far we have the practical affirmation that a python
>with the usual dimensions is fairly rideable with
>45 km/h on flat terrain and 50 km/h (14 m/s) coasting
>downhills.
>The latter requires more skill because the front wheel
>is not pulled but pushed.
>At low speed (< 10 km/h), the python is more stable than the
>flevo.

The front mass damps high-speed oscillations, at low speed the mass accentuates 
wheel flop, the flevo's apparent problem. It would also be with Traylor's 
without handlebars.

>>I noted that the "height" of the pivot is not the real factor,
>>it is the angle and trail it creates.
>Right.

The low pivot does allow the low rear mass; I hope to have time soon to 
characterize the theoretical effects of some of these better.

>>It appears that if the pivot was directly in front of one's
>>crotch (!) it would add self-stability, but as it got higher
>>up it would seem to make leg-steering awkward.
>
>According to most people, the steering axis has to go
>through the middle between the two hip joints to minimize
>the pedalling/steering interferences.
>I wonder how the Tom Traylor like bikes are rideable.

Does anyone here have direct experience with both? It seems like the bikes on
http://traylorfwd.home.mindspring.com/monocoque.html
would be nice and stable, the odd thing being how much the hip-to-pedal 
distance changes with turning. I rode Big Wheel trikes madly as a kid, which 
have that feel and identical pedaling issues - you don't pedal on tight corners.
The Traylors need the seat positioned high up so the tire doesn't rub the 
thighs, which is a point against, to me. They seem to have geometry of a short 
penny farthing, sitting over and pedaling the front wheel with little weight on 
the rear.

>>I'm still working on the script and understanding the meanings
>>of the stability matrix equations, hopefully I'll be able to
>>contribute something more concrete soon.
>
>We are looking forward to your work.

I did made a neat script which shows a simple stick-bike drawing and allows you 
to change the geometry factors with sliders and watch the shape and stability 
results change.

>In the next time I will build a scrap python which will
>undergo a lot of geometry and steering experiments.

Maybe try some moveable, clamped joints. I made a rear-steer recumbent trike 
years ago with an adjustable head angle (two bolts, one as a pivot, one a 
clamp). I didn't like the steering very much.

>Some of them are: rubber pivot, four bar linkage pivot,
>shallow steering angles around 50 degrees and lesser
>negative trail. Will let you know.

Should be interesting!

Ray

============================================================

This is the Python Mailinglist at freelists.org

Listmaster: Juergen Mages jmages@xxxxxx

============================================================

Other related posts: