This is another solution to the motor control. The bottom potentiometer is used to set the center point, the top would be the action one. This might be used for many things where you want to control the direction of a motor with respect to another value.
I have bread boarded this and it works. The two resistors on either side of the top pot were replaced with CDS cells. When they receive equal light the circuit is balanced, when one is shaded the circuit is unbalanced and polarity is shifted either positive our reversed.
You will not get positive and negative, rather positive and less positive.
