I am not sure if this is what you are asking.
I have seen selsyns (Self Synchronous Motors) installed on two DC motors. Normally one selsyn drives the second as a position indicator but in this instance the control computer looked at the error between the selsyns and controlled the motor speeds to minimize the error. This was to match the speed and relative position of two drives that must be synchronized but had no mechanical connection between them.
Bill
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"Why not the best?"
Jimmy Carter
