Paul,

I was at Lear Inc. in the late 50's. We had a rotary load that had to be
repositioned
quickly. It was driven by counter-rotating powdered iron clutches which
were geared to
a high angular momentum 400 Hz gyro wheel. The clutches were controlled
by servo
electronics. The load could accelerate at a tremendous rate through one
clutch and then be
brought to a dead beat halt at it's new position by the other clutch.
The gyro wheel
would be back to near sync and the reposition could be done repeatedly
with little
loss of momentum. Not what you would want in a race car but in operation
it was very
impressive to some old jaded servo mechanism engineers.

Fred O.