Date:         Tue, 22 Mar 2005 13:25:27 -0800
Reply-To:     Pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Pensioner <al_knoll@PACBELL.NET>
Subject:      Speedo Odo considerations
In-Reply-To:  <200503221603.j2MG3n0n028060@ylpvm31.prodigy.net>
Content-Type: text/plain; charset="iso-8859-1"

Although driven by the same rotating shaft (the cable) the speedo and odo
are really separate instruments observing  two different characteristics of
the shaft motion.  The odo 'counts' via a set of gears, the number of
rotations of the shaft.  The speedo translates the angular velocity or
rotation rate of the shaft into an angular displacement of the meter needle.
The needle assembly is restrained by a linear spring of known "K" and
includes a magnetic disk or iron plate.  The shaft assembly never actually
comes into contact with the speedo assy, the rotation of the magnet plate
induces rotation of the iron plate (Eddies Magnetic inductance stuff).  The
amount of torque produced is dependent on the rate of rotation or angular
velocity of the shaft assembly.  This torque is balanced by the retaining
spring force producing an angular displacement of the needle.  This angular
displacement is translated into a reading by the calibrated face of the
speedo.  Changing the face calibration does not change the angular
displacement of the needle. but