Non-electronic speedometers such as for older cars as well as
GM cruise control units before the advent of electronic control
systems use this principle at their very heart.  The speedometers spin
a cylinder of aluminum embraced by the poles of a horse shoe magnet.
As the cylinder spins faster, the eddy currents tug on the magnet and
try to get it to spin, also.  There is a spring balance that moves the
needle over the dial proportional to the amount of force and that's
how one gets the speed reading.

        Cruise controls have a disk like a little hard disk platter
that tries to pull a magnet along with it.  That magnet is connected
to a spring balance that modulates an air valve on the vacuum line to
work the throttle.  You set a little clutch at the right speed which
determines the set point for the valve.

        So, one might find information about this topic in the oddest
places.

        I hope this helps a bit.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Division Network Operations Group

Lyle Killough writes:
>As in motor drive couplings like the one made by MagnaDrive?
>http://www.magnadrive.com/
>
>I too am interested in some theory behind these devices.  I'd also
>appreciate any reference links which might be available.
>
>Lyle Killough
>
>
>> -----Original Message-----
>>
>> Has anymore got any good web references to anything related to eddy
>currents
>> and rotating disks. Google has many strikes but there may be some gems
>it
>> doesn't know about.
>>
>>         Russell McMahon
>
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