[python] Re: PX.5 report


So difference between px4 and px5 is you moved COG forward 10 cm and that made it impossible to maintain the same shallow pivot angle on px5 as on px4. On the same time different wheelbase between the models doesn't seem to matter much, allthough this also should have effect on COG.

I feel confused.

olaf


On Mar 9, 2005, at 21:07, Jürgen Mages wrote:

Today I finished PX.5:

  Pivot angle: 63 deg
  Trail: -47 cm
  Seat height: 33 cm
  Wheelbase: 118.5 cm
  Clearance: 11 cm

You might wonder why I fell back to 63 deg?
I would call that experience an eye opener.

As I told you, I adjusted the  bike for my legs by welding another
BB about 10 cm in front of the original one, so the front part became
longer and heavier. Then I mounted gear shifter and rear brake.

The first test ride was surprising because the wheel flop had
reappeared and the bike was not rideable (pivot 55 deg).

As I had to improve the clearance anyway, I cut the 35x35 mm
backbone, bent it and welded it: pivot angle 57 deg.

Test ride : wheel flop!
Cutting and welding: pivot angle 59 deg.
Test ride : wheel flop!
Cutting and welding: pivot angle 61 deg.
Test ride : wheel flop!
Cutting and welding: pivot angle 63 deg.
Test ride : wheel flop was gone, bike rideable and stable!

Absolutely amazing how the behaviour changed from
unrideable to stable within a range of 2 degrees.

This reminded me of a balance where a minimum change of
weight decides on equilibrium or mismatch.

Now, here a formula would be very helpful.

Here the stability program of Ray cannot help because it does not
consider the dynamic perturbation of pedalling legs.

Anyway - tomorrow I will make PX.5 ready for the road and
start the high speed testing this weekend as the snow is melting
away rapidly (finally!).

Picture of PX.5 on the mod page:
http://www.python.tieflieger.net/pics/Python%20PX.5.jpg

Cheers,
Jürgen.
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