FRC Pneumatics Nate Laverdure FRC Team 122

What is this presentation? Goals: Teach you the words transducer, damper, and venturi Attempt to: – Show that pneumatics have great advantages – if used correctly! – Provide a workable understanding of FRC pneumatics My personal goal: inspire you to build your own pneumatic system!

Alternative configurations Three major categories: 1.On-board compression 2.Off-board compression 3.Serious off-board compression

CMP HP MP LP TANK PS

CMP PS HP MP LP TANK Off-board

Off-board compression Why? Less weight (about 5 lb) Less power draw during the match

Off-board compression Why not? No pressure regeneration during the match No way to replace pressure lost to leaks Adds an additional pre-match check

Off-board compression limitations Off-board compressor must be: Powered by robot Power must come from Spike Relay on robot Controlled by robot Via pressure switch  Digital Sidecar  cRIO Protected by relief valve Ventable Requires additional vent valve

CMP PS HP MP LP TANK Off-board

CMP PS HP MP LP TANK Seriously off-board

Serious off-board compression All the limitations of standard off-board compression, PLUS: On-board storage is limited to only 60 psig

Building a pneumatic system General guidelines: Read, know, and understand all the FRC pneumatics rules Be able to explain your system to the inspectors

Building a pneumatic system General guidelines: Read, know, and understand all the FRC pneumatics rules Be able to explain your system to the inspectors Here’s a $6,000 hint: Refer to a printed flow diagram during inspection!

Building a pneumatic system Tips for tube fittings: Use plastic push-to-connect fittings where possible (Less weight compared to brass fittings)

Building a pneumatic system Tips for tube fittings: To connect: push tube in until firmly seated To remove: press rim down, then pull tube out Tubes cut at an angle will leak

Building a pneumatic system Tips for teflon tape: Use 4 to 6 wraps of tape Don’t use tape more than once Wrap tape in the right direction Don’t allow loose pieces of tape to get into the tubing

Building a pneumatic system Tips for brass fittings: Brass is very soft Do not over-torque Do not use adjustable wrenches Use box-end wrenches where possible

Caring for your pneumatics Problems maintaining pressure: Chronicleak Acute catastrophic pressure loss

Caring for your pneumatics Problems maintaining pressure: Chronicleak Acute catastrophic pressure loss Catastrophic pressure loss may be caused by: Tube disconnection or breakage Component failure

Caring for your pneumatics Tips for avoiding leaks: Use as few fittings as possible Perform leak test as each component is added Use leak test fluid

Leak test fluid Recipe: Add 2 tbsp dish soap to empty spray bottle Fill spray bottle with water Directions: Shake well Cover all exposed electrical parts! Spray directly on pressurized pneumatics

Caring for your pneumatics Protect your cylinders— Thin wall tube can be crushed by side impacts Internal seals will not handle side loads Not repairable!

Design sequence 1.Find the required stroke length 2.Find the force & set the operating pressure 3.Guess how many times you will actuate the cylinder during a typical match 4.Find the required storage capacity

Determining the actuation force A

P1P1 P2P2 A

F 1 = P 1 AF 2 = P 2 A

Determining the actuation force F = F 1 – F 2 = A(P 1 – P 2 )

Determining the actuation force F = F 1 – F 2 = A(P 1 – P 2 ) Warning: simplification! Because of piston rod, A 1 ≠ A 2

Determining the actuation force F = F 1 – F 2 = A(P 1 – P 2 ) 0 F = PA P

Example 1.Find the required stroke length 2.Find the force & set the operating pressure 3.Guess how many times you will actuate the cylinder during a typical match 4.Find the required storage capacity

Example Cylinder Stroke lengthL = 3 in L

Example 1.Find the required stroke length 2.Find the force & set the operating pressure 3.Guess how many times you will actuate the cylinder during a typical match 4.Find the required storage capacity

Example Cylinder Stroke lengthL = 3 in Diameterd = 1 in AreaA = (d 2 )(π/4) =.785 in 2 P d L

Example Cylinder Stroke lengthL = 3 in Diameterd = 1 in AreaA = (d 2 )(π/4) =.785 in 2 PressureP use = 60 psig = 60 lbf/in 2 P d L

Example Cylinder Stroke lengthL = 3 in Diameterd = 1 in AreaA = (d 2 )(π/4) =.785 in 2 PressureP use = 60 psig = 60 lbf/in 2 ForceF = (P use )(A) = 47 lbf P d L

Example 1.Find the required stroke length 2.Find the force & set the operating pressure 3.Guess how many times you will actuate the cylinder during a typical match 4.Find the required storage capacity

Example Cylinder # ActuationsN actuations = = 20

Example Cylinder # ActuationsN actuations = = 20 Warning: Remember to count both the forward and reverse strokes!

Example Cylinder # ActuationsN actuations = = 20 Gas use= ~(N actuations )(P use )(V cyl ) = (20)(60 psig)(2.36 in 3 ) = 2832 in*lbf

Example Cylinder # ActuationsN actuations = = 20 Gas use= ~(N actuations )(P use )(V cyl ) = (20)(60 psig)(2.36 in 3 ) = 2832 in*lbf This is in units of energy!

Example 1.Find the required stroke length 2.Find the force & set the operating pressure 3.Guess how many times you will actuate the cylinder during a typical match 4.Find the required storage capacity

Example Storage VolumeV tank = (L)(A) = 16 in 3 PressureP store = 120 psig # TanksN tanks = 2

Example Storage VolumeV tank = (L)(A) = 16 in 3 PressureP store = 120 psig # TanksN tanks = 2 Gas storage= ~(N tanks )(P store )(V tank ) = (2)(120 psig)(16 in 3 ) = 3840 in*lbf

Is the example design OK? Safety factorη = Gas storage 3840 in*lbf Gas use2832 in*lbf = = = 1.36

Is the example design OK? Safety factorη = Gas storage 3840 in*lbf Gas use2832 in*lbf = = = 1.36 Result: The design is marginal. Add another tank, then test to make sure it works!

Gotchas Inspection checklist: Relief valve is set at 125 psig Off-board compressor must be controlled by cRIO Vent valve must release all system pressure

Gotchas Inspection checklist: Relief valve is set at 125 psig Off-board compressor must be controlled by cRIO Vent valve must release all system pressure Mitigations: The KOP relief valve is not pre-calibrated! Set the relief valve per instructions.

Gotchas Inspection checklist: Relief valve is set at 125 psig Off-board compressor must be controlled by cRIO Vent valve must release all system pressure Mitigations: Build an off-board compression rig, complete with: – Compressor – Relief valve – Vent valve – Pressure gauge Do not use shop air!

Gotchas Inspection checklist: Relief valve is set at 125 psig Off-board compressor must be controlled by cRIO Vent valve must release all system pressure Mitigations: Test all configurations Can be caused by: – Solenoids with closed center positions – Systems that switch between pressures – Systems that stop cylinders partway through their stroke

FRC Pneumatics Nate Laverdure FRC Team 122