Le 16-févr.-05, à 22:35, Laurent Dechenne a écrit :
i'm not sure to understand evrything... and not sure to be included...not because the legs, but because the wieght of the bike on this angle (Laurent)
but... if look difference between python and TT we understand why (if we imagine same angle between pivot axle and puch of the legs) on a python we have a better proportion between the puch of the legs and the influence on the direction
<jambe-direction.gif>
on a tt thath was improve by the angle between the pivo and the "puch of the legs", if this angle was 90° there is no resistance and the bike turn evry time you puch on pedals ,(i thing on TT this angle is too close of 90° you have too correct this with you arms... Tom traylors said Another advantage in having the BB mounted on the steering unit is that the forces between the arms and legs are balanced out. ( i think this is not an adventage) (and i have test this)
if that angle is too sharp, you have a trail angle too sharp like on the flevo (this is my point of view and my experience) and you bike turn too strongly
(i feel thath on down hill)
the best compromise i find is 60° for pusch legs/pivot, and 60° too for trail angle thath mean seet and pedals at the same high
<Laurent.gif>
And i thing these angles moore important than the number of cetimetres of the positive trail, i d'ont feel difference between 5 or 15 cm.
Now there is no comparaison with python... i want make a new one, but d'ont now wath change to experiment and find wath is importent on a python to go down hill...
Ciao
Laurent
Le 16-févr.-05, à 16:10, Dirk Bonne a écrit :
Jürgen Mages wrote:
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.
The legs do not start from the spine. The legs are connected to the hip. The point around which the legs rotate --at the moment the legs are straight- lie very far behind (this point changes of course as the legs rotate sideways in the hip, so it is a momentary roation point only).
If the legs were totally parallel, then this rotation point lies in inifinity behind the spine even. If you do not want any effect, then you should have the pivot far behind you (but turning will not more work).
From this point of view, the pivot position of a flevo/python is also only a compromise. The farther behind the pivot the less the influence of the legs is on the stearing. But the less the legs can actually steer. The TT is only more a compromise, I would guess. I would also very much like to test a TT!
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.
In the next time I will build a scrap python which will
undergo a lot of geometry and steering experiments.
Some of them are: rubber pivot, four bar linkage pivot,
shallow steering angles around 50 degrees and lesser
negative trail. Will let you know.
Really cool! I am especially interested in the influence of the trail!
Dirk
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