Blue shaft receives motion from two sources: electric motor (not shown) at the left end and human force at the right end.
Red spring tends to disengage the yellow crank and the blue shaft.
When the motor makes the shaft rotate, the crank is idled on the shaft.
Push and turn the crank to make the shaft rotate when the motor is not in action.
Disadvantage: the operator has to push slightly the crank when turning.