CONNECTING THE PROPORTIONAL VALVE TO THE AIR COMPRESSOR
You will need one of this air compressor tool , that you can open and close the air flow between the air compressor and the proportional valve. Connect this tool to the proportional valve , on the input port of the middle (opposite side of the output ports ) as shown in the pictures bellow
TESTING THE PROPORTIONAL VALVE
Be sure that your code works testing the relation between the proportional valve and your encoders. If you did everything right at the Coding section , when you upload the code into the Arduino and let it run , the system will be steady , and it will move if you move the encoders. To be sure that its working , take the rotational encoder and rotate it and see if the movement of the cart is in the right direction in order to balance the pendulum. In my case , when i rotate the encoder clockwise , the cart should drive backward , to balance it.