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'[OT][WOT] Speed wobble cure'
2006\09\25@005643 by Russell McMahon

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I recently discovered in a very niche situation (stupidly overloaded
vehicle with largish rear bias)(at 2am fwiw) that speed wobbles in a
car could be instantly corrected by applying a ~ 2 Hz oscillation to
the steering wheel, approx 30mm movement range on a reasonably low
geared steering system.

As I don't have vehicles / situations which have speed wobble
available every day I can't retry this in a hurry. I was wondering if
anyone else had heard of this "cure" or of how universally applicable
it was.

Results were "like magic" - at one moment a slowly building (slow in
this case) oscillation that required intelligent ongoing correction
and the next moment instant stability. No head shaking or slowly
coming right but an instant transition to stability.

The friends who I have asked about this all lecture me about
overloading, which is fine, but fail to comment on the "wobble cure".



       Russell





2006\09\25@065004 by Howard Winter

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Russell,

On Mon, 25 Sep 2006 16:56:42 +1200, Russell McMahon wrote:

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I think you may have been experiencing "Pilot Induced Oscillation", somewhat familiar to flyers!  :-)  Once it started your attempted correction input
was just at the right phase to add to the problem, and doing something to distract you from that (the deliberate steering-wheel wiggling) stopped
that, and it sorted itself out.  Did you try letting go of the wheel?  That may have worked too!  (Or you may have ended up in a ditch...)

Overleading the rear is a very Bad Thing because it reduces steering authority.  I was once in a seriously overloaded van (I and two other mechanics
at the garage where I was working had just loaded up a large stack of wet asbestos-cement sheets - it was a long time ago!) and it was possible to
turn the steering-wheel half a turn each way with no change of course at all.  The only way to get round corners was to brake, so transferring some
weight to the front wheels.  Looking back, I sometimes wonder how I made it out of my teens...  :-)

Cheers,


Howard Winter
St.Albans, England


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