Introduction to Pneumatics

What are Pneumatics?

• Pneumatics is the use of pressurized gas (we use compressed air) to create motion.
• Similar to Hydraulics, which uses fluids instead of gases.

Why use Pneumatics?

• Pneumatic Cylinders are much lighter than motors. Although there is a large base weight (compressor, accumulators, etc), as long as several cylinders are used, it usually balances out to be lighter than motors overall.
• Pneumatics are strong. Anywhere from 0 to 188 lbs of force per cylinder, depending on bore size and pressure.  Strength is easily adjustable with flow control fittings.
• Pneumatics are simpler than motors. Once the base system is setup, it is easier to mount a cylinder than a motor.  Furthermore, pneumatics do not require complex chain, cable or rack-and-pinion systems to achieve linear motion.
• Pneumatics are more durable than motors. When motors burn up, pneumatic cylinders simply stall if they do not have enough force to complete the task.  Stalling a pneumatic cylinder causes no damage to the cylinder.

Disadvantages of Pneumatics

• High initial weight cost.
• No intermediate positioning. The cylinder is either all the way in or all the way out.  It is hard and typically impractical to construct a pneumatic system that allows the cylinder to stop mid-stroke.

Applications of Pneumatics

• Pneumatics are great for straight movement.
• Linkages can be created if rotation is needed.
• Great for grabbers, as shown in 254's 2004 robot.

Pneumatic Components

Compressor

• Converts electricity to compressed air.
• Has attached relief valve to protect system from too much pressure.  Relief valve bleeds air at 120psi
• Controlled by a Relay Module using a 20amp breaker, not a fuse.  Always run in forward.  Do not attempt to create a vacuum by running it in reverse.
• Can produce significant vibration.  Rubber vibration isolation mounts are provided in the kit and are recommended.

Accumulator(s)

• Store compressed air at 120psi
• Up to four can be used on the robot.

Pressure Switch

• Digital switch detects pressure.  Switches to "on" if pressure drops below 95psi.  Switches "off" after pressure reaches 115psi
• Connects to digital input on digital sidecar.

Regulator

• 2 Regulators are provided in the kit.
• Primary regulator regulates pressure to an adjustable value (maximum of 60psi).  It must be used with a pneumatic system on the robot.
• Secondary regulator allows presence of a reduced pressure leg.  Can be optionally used after the primary regulator on a robot.

Solenoid Valves

• Used to control pneumatic cylinders and actuators.
• Single solenoids always default to one position if power is cut.
• Double solenoids remain in active position when power is cut.

Dump Valve

• Used to release all air in the pneumatic system.

Fittings

• Pipe threads require teflon tape.  Do not wrap on first two threads, as threads are tapered and tape tends to loosen, clogging airflow.
• On quick-release connectors, tubing is attached by pushing into connector.  End of tubing must be clean to ensure proper seal.

Flow Control Fittings

• Regulate flow of air into and out of a cylinder.  Used to control cylinder extension and retraction rate.
• If used to regulate flow, attach directly on only one end of the cylinder.

Cylinders

• Linear actuators.
• Force = Pressure x Area
• Maximum force of 188lbs with 2" diameter cylinder (largest available in FIRST) at 60psi
• Due to rod, area of face when retracting is smaller than area of face when extending.  Therefore force is greatest when extending.

Additional Resources

• 2009 FIRST Pneumatics Manual