Here are the best drawings I could find for you. http://www.instructables.com/answers/how-to-reverse-the-polarity-of-a-DC-motor-using-a-/ You may need to add a pulse width modulator to slow down the movement of the actuator. If you do need one make sure to size it to your motor.
Good Luck
I just joined so that I can let you know that this is amazing. What you are doing over there incredible. You are teaching your family and workers things they may never have got to see without you. Great work and writing. Hello to everyone!