Hi Ray,
Thanks for sharing the program. Is there a way to automatically grind through
the 18 parameter space, and save the output? I think we need to find stable
speed between 4-8mph to run along with the experimental bike. The console
output
velo A B C D E #6 #7
m/k 10**8 10**9 10**9 10**9 10**10 10**20 10**26
suggests that when colunm #6 and #7 both go positive then we have stability, and
can be used to search the parameter space.
Vi
________________________________
From: RayS <rays@xxxxxxxxxxxxx>
To: python@xxxxxxxxxxxxx
Sent: Sun, April 17, 2011 8:01:36 AM
Subject: [python] Re: A Bicycle Can Be Self-Stable Without Gyroscopic or Caster
Effects
Interesting thread - the self-stability program I wrote
http://rjs.org/Python/FrameGeometry.zip
shows the effect the researchers wrote of pretty clearly. It does also have
input for rim/tire mass (mouse over the boxes for explanation).
If a python's:
- front mass is at least 45cm in front of the pivot line
- rear mass is <24cm to rear axle
- trail <11cm
-wheel mass is low
it is nearly neutral.
All these things have been covered on the list one way or another, except wheel
mass.
Panniers off the back, shifting weight backward, reduces self-centering force on
the pivot.
Weight in the very front can increase some desired flop, but is a sensitive
factor and makes slow riding more tiresome.
Trail should generally be minimized.
Importantly, the dynamics are very sensitive to wheel mass; heavy wheels,
especially the front, eliminate any chance of stability! If you think about it,
gyroscopic effect prevents the front wheel from responding to lean, which is
what gives bikes stability; it actually turns the forks the opposite way when
leaned.
Remember all this has to do with self-stability, and not necessarily how a
python "feels" to ride using leg steer. Note that in the attached I set the
pivot torsional K to -7; a small opposite force like your hips make when riding
the python which counters the self-center effect. It then has a wide range of
stable speed. The further mass is from the rear axle the more -K is required,
and the lower it is the less stable.
It would also be interesting to let the code grind through all reasonable
combinations of the 18 variables used and see where the islands of stability
are.
Ray
