[python] Lean disturbances (IGNORE PREVIOUS POST)
- From: ebooth@xxxxxxxx
- To: python@xxxxxxxxxxxxx
- Date: Sat, 26 Feb 2005 16:26:46 -0600
Dear all,
I followed the steering dynamics thread with interest. In that regard, I will
pose a question about the Python's handling, and give some thoughts as to its
answer. Feel free to add to this, or correct me as you see fit.
When one rides a Python-style bike, how does one maintain stability when the
lean angle is perturbed (e.g. by a crosswind pushing you a few degrees to one
side)?
IMO, this is primarily due to the reflexive responses of the Python's rider.
Here is my reasoning:
Clearly, a DF's self-stabilization under these circumstances happens through
lean-steer. Positive trail causes the leading half of the front wheel to "fall"
in the direction one leans the frame, initiating a turn in that direction. Since
the Python has negative trail, it should not lean-steer this way; its front
wheel should, if left to its own devices, slew away from the tilt. If the Python
were rolling along while this happened, its front wheel should promptly buckle
backwards.
While the riderless situation is a contrived one, this still begs the question
of how a Python and its rider can stay upright if the lean angle is perturbed.
Now, there are four Python stability mechanisms:
1) hanging-pendulum
2) pulling of front wheel forward by drive torque
3) pushing of front wheel forward by rider's legs
4) gyroscopic effect of spinning wheels
Of these, the first should be equivalent to negative lean-steer (the slumping of
the seat in the lean direction). The second and third effects center the front
wheel, and thus shouldn't affect lean-steer. The final effect would contribute
to steering the Python into the lean; however, I'm not sure the magnitude of
this force would be enough to stabilize the bike. Therefore, I propose that,
when a Python's lean angle is perturbed, its rider provides the majority of the
force needed to steer it into the lean.
Thanks for reading,
Eric
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