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From: pmk@prometheus.UUCP (Paul M Koloc)
Newsgroups: net.physics
Subject: Re: Re: Question... [On tilt-meters in off-road vehicles]
Message-ID: <172@prometheus.UUCP>
Date: Sun, 25-Aug-85 10:08:43 EDT
Article-I.D.: promethe.172
Posted: Sun Aug 25 10:08:43 1985
Date-Received: Wed, 28-Aug-85 02:11:32 EDT
References: <10041@ucbvax.ARPA> <627@mtuxn.UUCP>
Organization: Prometheus II Ltd., College Park, MD
Lines: 38

> Psychologically, when taking a corner you can still *see* that you're
> on flat ground regardless of what your inner ear (or tiltmeter) says.
> The brain probably averages these readings somehow.
> 
> Jeeps *are* infamous for capsizing in turns on the highway, because of the
> above illusion and because (unlike cars) they will roll before they will slip
> sideways appreciably.  Wider modern 4WD's aren't as bad.

In to these considerations is the almost instantaneous response of the
brain to gauge the "rate of increase in force".  If you are in a train
entering a constant radius turn on a flat bed track so that no slipping
will take place, the passenger car will "lurch" just as it enters the
turn.  The same effect would occur if you simulated a "slope" by putting
your vehicle on a rigid deck and then tilting the deck about an axis 
under the mid-line of the vehicle.  This effect is worse for high center
of gravity machines.  If the deck were tilted very slowly to a fixed roll,
 not much would happen, but if it were abrupt the vehicle would tend to 
continue tilting beyond the equilibrium point for the fixed roll 
inclination.  

Unless you have "taken" a hell of a lot of curves, the brain will sense 
the "jerk" or "roll" acceleration and then extrapolate it to the point in
time where the vehicle should flip over. It takes the brain about a second
to recalculate new information that the "roll jerk" has zeroed out.  
Experience teaches the brain to make "better estimates, and that's what
gives racing drivers that extra edge.

Be careful not to use your static hill side settings as safe values for
similar settings in high speed turns because, like your kinetic senses
and brain, that instrument has delayed response.  In addition, the 
instrument can have inertial errors.

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