The pneumatic control module pumps air and controls the direction of the airflow using one motor. My previous design used a clutch gear to pump air and control the direction of the airflow using one motor. The clutch gear would slip once the torque exceeded a certain level. This function allows the motor to keep turning once the pneumatic switch changes the airflow direction.

The clutch gear design worked on a pneumatic system for a claw on the robotic arm I built in 2005. I figured the clutch gear design was not suitable for the airsoft sentry because the tension in the clutch gear would slow down the pumps. The air would not flow into the four cylinder fast enough and the airsoft gun would not move up and down fast enough. I had to come up with a completely new design that would pump air and control the direction of the airflow using one motor. I drew out some designs and prototyped them until I came across the best design. The design that worked best used a pneumatic switch mounted on a pivot point. Dual springs were attached to the pneumatic switch to return it to its original position. Above the switch was a rotating gear with grooves. The grooves were designed to catch the switch and change the airflow direction. The pivot point allowed the switch to rock sideways allowing the grooved gear to continue turning and preventing the system from jamming. The springs then returned the pneumatic switch to its original position so the grooved gear could grab it when the direction of the motor was reversed. The grooved gear was symmetrical so it could grab the pneumatic switch when turning in either direction. The motor is controlled by the Lego Mindstorms NXT.  You can see the module working in the video above or in the video of the airsoft sentry.