[python] Traction / stability - sliding / falling on gravel
- From: Vi Vuong <vi_vuong@xxxxxxxxx>
- To: Python <python@xxxxxxxxxxxxx>
- Date: Sun, 13 Nov 2011 22:22:01 -0800 (PST)
Hi All,
As preparation for a FWD tadpole, we did some traction/stability study on
gravel, comparing FWD bike, FWD delta trike, and FWD quad. YouTube videos are
up for group observations.
Guinea Pig bike:
http://www.youtube.com/watch?v=DEsGiGk6Yhg
The longer wheelbase giving more traction (~60%) to front wheel seems to help
with slipper surface (gravel), compared to short wheelbase. Lower seat height
also eases the fall. The low pivot angle (46deg) is suspect for sudden lost of
control that also seems to depend on the pedal position at the moment of
traction loss. Rear wheel slide seems to trigger front wheel flop also...
Flintstones trike:
http://www.youtube.com/watch?v=TyrIZR9qZ-w
This turns out to be blast to ride on slippery surface. There is some swirling
at the front but Low COG and wide track feel somewhat stable/reassuring, and
fun... Forgot to do high speed test :)
Bango quad:
http://www.youtube.com/watch?v=8vlVgoLueb0
Very stable during traction loss, almost boring compared to the trike. Will
try higher speed next time...
Some more observations on steering dynamics, as we found early on that the
vehicle can be turned mostly by the outer wheel. The inner wheel only requires
a smaller angle to minimize tire scrub, versus a larger turning angle suggested
by the Ackerman geometry. This behavior may be explained by the pivot rise
effect counteracting the weight shifting outward (outer pivot needs to be
higher). Tire scrub is pleasant lessened on slippery surface...
Cheers,
Vi
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