Stopping the motor can be done by dropping a short circuit (or, more kindly, a 5
to 10 ohm resistor) across it when the power is removed. This is the technique I
use on my motor driven VVC's: however, I don't drive them as fast as Verner
does. One problem that has to be faced with a full servo system is backlash:
I've used 'bang-bang' systems quite successfully to get over the problems
inherent in fixing this - in fact, that's what I have in my home brew auto tune
antenna tuner.
In the final analysis, there's always the mechanical approach of putting extra
step down gearing in between the motor and the capacitor itself, but that could
be as big a project as building the whole amp! I feel that the suggestion of the
'H' arrangement of MOSFET's and arrange them to short circuit the motor when you
want to stop it may offer the best chance of success.
73
Peter G3RZP
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