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