[python] Re: px5 stability
- From: Dirk Bonne <dirk_bonne@xxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 30 Mar 2005 11:08:09 +0200
Laurent Dechenne wrote:
Le 29-mars-05, à 19:02, Dirk Bonne a écrit :
Olaf Johansson wrote:
The impact from pedalling upon steering has been no problem for me
on my flevo bike.
Entirely agreed! Its a technique thing.
Yes, but not only. I think there is 2 iportent mesures influe on the
pedaling impact on steering:
- the angle between the pivo and forces of the legs; more sharp,
better it is , it's flevo solution
-the position of the pivo : more far off BB better it is ; it's python
solution
- TT bike or my bikes have a part of each of these solutions... well
... flevo too, but it's too much and at high speed i think steering
is havy , too reactive
hmm, on both the python and the flevo the pivot is about the same
position to the seat, and thus also from the BB. So that is not very
different. It is only the TT that moves the pivot very much forward. It
is only too bad that it reacts so much on pedalling, because it seems
like an easy bike to build (and may be to learn?).
When I started cycling on the python the nodding of the BB at speed
reappeared, even though, on the fleov, I had learned to compensate that
effect completely. So it seems that the straigther angle has this
negative influence. But this is gone now again ---even though I am not
highly experienced in python cycling (its still freaking cold here :-(
). One thing to note is that I ride with 145mm cranks on the python, and
my cadence is much higher.
Anyway, it is probably going to be more difficult the bigger the angle
gets. Looking at the project survey the other pythons all have a
straigther angle then I have on mine (with a max of 70degrees: 25hz and
MD). They should be able to say if it gets really difficult to
compensate the nodding of the BB at high cadence and lots of power output.
On the flevo the pivot angle is 45 on my python it is 60. I agree only
partly that the sharpness of the flevo is so much better. Together with
the positive trail you have a large wheel flop. This does not influence
this small swaying of the BB during cycling, but does influence steering
as a whole. The more straigther pivot angle was by the way the most
important reason for me to make a python. I hoped that the python would
be a better climber. The front part of the python is lighter, has less
wheel flop, the center of gravity is lower (so less displacement of the
cg when its hill up, and thus more weight on the front wheel) all should
make the python better at climbing.
There are lots of factors to choose an angle, and these factors collide
with each other.
Dirk
Laurent
In the beginning I could see that the bicycle was slightly shaking
its head over my pedalling.
But after a while the legs (somehow) learned to compensate pedalling
disturbances. This I experienced both on the flevo, and now on the
python.
Dirk
On Mar 29, 2005, at 18:04, ebooth@xxxxxxxx wrote:
What if, instead of rigidly fixing the seat bottom to the front
steering
assembly, one attached it to the rear assembly on a swivelling
mount, with the
seat back separately and firmly connected to that aft part of the
frame? Perhaps
this would accomplish what Frank has in mind.
Eric
Quoting Olaf Johansson <noll@xxxxxxxxx>:
In the original set up with the seat attached to rear part you use a
mixture of leaning the legs and swivelling the hip in order to steer.
If you sit on the front part of the frame – the part that is to be
steered – it will be impossible to manoeuvre the bike unless your
shoulders were tightly strapped to the back rest. Even then steering
would be a real stunt ;o)
Olaf
On Mar 28, 2005, at 21:18, Frank Parmir wrote:
Hi Jurgen, I've been reading the list for several monts. A while
back
you reported the px2 was not as stable at high speeds as the p1 and
p3. Is the px5, which has the pivot moved to the rear any more or
less
stable? I hope to begin building the first python in Columbus, Ohio
(USA) very soon and am anxious to hear. Also, I am thinking of
attaching the butt bucket part of the seat to the front half to
eliminate pedaling perturbance. I will still attach the back
support
with arm rests for shifters and brakes to the back half. That means
steering by swiveling the hips, not just the legs. Do you have any
predictions about how sucessful that might be.
Also, I'm a little woried. You haven't posted since your speed
record.
Are you OK?
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