Pneumatics Control Module (PCM)
The PCM is a small electronic device that regulates the operation of the onboard compressor and solenoids. It is connected to the Power Distribution Panel via its Vin terminals. Each solenoid should be plugged into one of the numbered slots on the right side of the PCM. These numbers can be referenced in code to control each solenoid. If more than 8 individual solenoids are required on the robot, it is possible to connect two PCMs together with CAN wires to provide additional ports. The PCM has red lights on its side, underneath each solenoid port, that light up when said solenoid is actuated.
Pneumatic fittings are used to connect components together, and interface between threaded metal connectors and pneumatic tubing. To prevent air leakage, the threading on all brass connectors must be carefully wrapped with a thin layer of Teflon tape!
Teflon tape is a smooth material that will fit perfectly into the grooves of threaded connectors when wrapped around them. In doing so, the tape corrects any imperfections in the threading and creates an airtight seal, preventing leaking between pneumatic fittings and other components. When wrapping brass connectors, remove any old Teflon tape and add a single, fresh layer. Too much tape can cause leakage as well.
Pneumatic tubing is used to connect various pneumatic components, even when they're not together. Pneumatic tubing is used in conjunction with circular push-to-connect pneumatic fittings. Push-to-connect fittings are not robust and can come lose quite easily if not assembled correctly. Make certain that the ends of the pneumatic tubing are completely flat and "square" by trimming them with the pneumatic cutters, otherwise, the push-to-connect fittings will not seal well. In addition, ensure that all pneumatic tubing has "slack," so that it is not pulled out during robot motion.
The air compressor utilizes a motor to compress air. Atmospheric air is drawn in from the top of the compressor, and compressed air exits from the horizontal pipe connected to its top portion. The air compressor is wired to the COMPRESSOR OUT terminals on the PCM, and should be firmly mounted to the robot frame.
Pressure relief valve
The pressure relief valve is an automatic emergency switch that opens if pressure becomes too high. It should be connected to the air compressor using brass fittings.
When the system reaches maximum pressure, the pressure switch automatically disables the compressor to prevent wasted electricity and overfilling. The pressure switch's terminals should be connected to PRESSURE SW on the PCM, and the bottom of the switch should be connected to the air compressor using brass fittings.
Air tanks store compressed air for later use. On robots that frequently actuate pistons, having 2-3 liters of storage (4-6 Clippard air tanks) is ideal. They should be connected to the compressor using pneumatic tubing.
Pressure gauges indicate the current pressure of the system that they are connected to. It is important to check the robot's pressure gauge (and refill the air tanks) before each match at competition to ensure that the robot has sufficient pressure to start the game. They can be connected to the rest of the system using brass fittings, or they can be connected directly to a regulator.
Regulators control the flow of air in a singular direction, reducing the air pressure on their "output" side. Since regulators have two output holes, a gauge to read output pressure can be affixed directly to each regulator. The maximum pressure they allow can be changed by pulling on the top knob, then twisting it in one direction or another. Typically, when adjusting regulators, the pneumatic system should be pressurized, as the pressure gauges will show the current maximum pressure and respond to the regulator adjustments.
Pistons actuate in/out and can be used to perform tasks on the robot. To extend the piston, pressurized air flows into one side while air is released from the other. The two ends of a piston should be connected to a double solenoid, which controls airflow, using pneumatic tubing.
Solenoids are magnetic valves that open and close in response to electronic impulses, allowing air to pass through. They are used to control the flow of pressurized air to pneumatic cylinders. Because most pistons in FRC are double-acting, powered by air during both the instroke and the outstroke, 4311 largely employs double solenoids, which have two valves. The input to a double solenoid is attached to the rest of the system with pneumatic tubing, and the outputs are connected using tubing to the ends of a piston. Double solenoids come equipped with two red buttons at their top. Pressing a red button results in that side of the solenoid mechanically actuating, which allows for manual control of pistons even when the robot is off (this behavior has been used in past years to do things like load the robot with game pieces). Double solenoids are wired to the PCM, and may be used like two separate solenoids if necessary.
The following is a cross-section diagram of a double solenoid. Double solenoids have three states: neutral, forward, and reverse. The first diagram displays the double solenoid in its neutral (off) state, with inputs and outputs labeled. The other two pictures show the flow of air when the solenoid is placed into forward and reverse (the forward direction depends upon the wiring). If programmed to act like two individual solenoids, the double solenoid can be in a fourth state, where both sides are actuated.