Pneumatics for FIRST RobotsFIRSTFare 2010

Craig BoezwinkleMechanical Engineer – Western Integrated Technologies

Team 2811 Mentor (Skyview HS, Vancouver WA)

Overview

• Intro• Kit of Parts Overview• Cylinder sizing calculations• System sizing calculations• Typical applications on your robot• Pros and Cons

Pneumatics 101“the use of a pressurized gas to create mechanical motion”

• Everyday Uses:– Air compressor to fill your tires– “Shop air” in industrial shops

• Air-operated hand tools• Air-operated paint sprayers

– Pneumatic systems for industry• Packaging lines• Blow molding

– The list goes on, pneumatics are everywhere

Electrical Analogy

• Pressure = Voltage• Volume = Capacitance• Flow rate = Current• Flow Restrictions = Resistance

• HOWEVER: Air is compressible=> Some unique non-linearities when compared to

electrical systems

2010 Kit of Parts

Air Compressor• The only way to add pneumatic energy

• Capable of 120 psi• Lots of vibration• Gets really hot

Air Tanks• Store compressed air

• Use up to four• Can pre-charge and leave the

compressor off the bot

2010 Kit of Parts

Required Equipment• Pressure gauge – indicates pressure in compressor and tanks (not pressure at

cylinders)• Pressure switch – talks to cRIO

•Plug valve – releases all air in the system

2010 Kit of Parts

Norgren Regulator• Primary pressure regulator• Reducing/relieving valve

• Limits all pressure downstream to 60 psi max Monnier Regulator

• Note yellow ring• Secondary pressure regulator• Allows for a reduced pressure

leg, if desired

2010 Kit of Parts

Solenoid Valves• Control cylinder movement

• Come in either single solenoid or dual solenoid

• Control the flow of air to and from an actuator

Cylindersaka NOT PISTONS• Not supplied with KOP

• Custom order up to three FREE• Design first, order second

Rules• Know them. Look in these three places:

• Standalone pneumatics manual• Pneumatics section of rules• Inspection checklist

– 125psi relief attached directly to compressor– Must include easily accessible vent valve– Special label required for pressure release valve– Gauges required on both stored and working pressure

sides of system– Etc, etc, etc. Don’t learn these for the first time during

inspection.

Calculating Force

60 psi

106 lbs

To extend the cylinder, pressurize the cap end port.

Force (lbs) = Pressure (psi) x Area (in2)

• Area = r2 = * (0.75 in) 2 = 1.77 in2

• Force = ( 60 lb / in2 ) * ( 1.77 in2 )• Force = 106.2 lbs

NOTE:• Single acting cylinders are only powered in one direction. They require an external force to move in the other direction (spring retract, load pushing back, etc). • Double acting cylinders are powered in both directions.

1-1/2” bore

Calculating Force

60 psi

To retract the cylinder, pressurize the rod end port.

Force (lbs) = Pressure (psi) x Area (in2)

NOTE: The area on the rod end is always less than the area on the cap end.

• Effective Rod End Area = Cap Area – Area of the Rod• Cap Area = r2 = * (0.75 in) 2 = 1.77 in2

• Rod Area = r2 = * (0.21875 in) 2 = 0.150 in2

• Effective Area = 1.77 in – 0.150 in = 1.62 in2

• Force = ( 60 lb / in2 ) * ( 1.62 in2 )• Force = 97.2 lbs

1-1/2” bore

97 lbs

7/16” rod diameter

This is a good spot to mention, … Safety

• Respect the amount of power that a pneumatic system can generate

• Understand the rules and abide by them even during practice and test (they rules exist for a reason – to keep everyone safe)

• A 2” bore cylinder @ 120psi = 376 lb-force (don’t do this!, it can cause injury or bend the frame of your robot)

Did you notice…

• Amount of force has nothing to do with cylinder length (stroke). Only pressure and cylinder area (bore) matter.

However• Amount of air volume required has

EVERYTHING to do with cylinder length (stroke)

System Sizing Notes

• Both system pressure and volume are limited quantities

• Therefore, we have a fixed amount of energy that can be stored and used

• To simplify things, we’ll introduce a unit of measure call the PEU (pneumatic energy unit)

• PEUs = Pressure x Volume

Boyle’s Law SaysPressure * Volume = constant

Energy Usage ExampleStorage Consumption

PEUs P V P V PEUs Total PEUs

2400.0 120.0 20.0 60.0 10.0 600.0 3000.0

1800.0 90.0 20.0 60.0 10.0 600.0 2400.0

1200.0 60.0 20.0 60.0 10.0 600.0 1800.0

800.0 40.0 20.0 40.0 10.0 400.0 1200.0

533.3 26.7 20.0 26.7 10.0 266.7 800.0

355.6 17.8 20.0 17.8 10.0 177.8 533.3

Energy Storage Energy Consumption

Load

Credit: Raul Olivera

Replacing Used Energy

Compressor Power Curve

0

50

100

150

200

250

300

350

400

20 30 40 50 60 70 80 90 100 110 120

Pressure

PE

U/s

• Used energy can be replenished by the compressor, but how fast?• Previous compressor could replace about 110 PEU/s in the cut out range

(90 to 120 psig)• Your mileage may vary – run your own tests!

Pressure(PSI)

PEU/s

20 341.330 259.440 213.550 183.560 162.270 146.280 133.5

90 123.3100 114.8110 107.6120 101.5

Credit: Raul Olivera

Managing the Loss of Energy

• Use only the amount of energy required, not too much more

• Minimize Volume:– tubing length (valve to cylinder)– cylinder stroke– cylinder diameter

• Minimize regulated pressure– But, keep above valve pilot pressure requirement

Typical Applications

• Two-position linear applications– Lifter or gate– Transmission shifter– Linear pneumatic gripper– Braking systems– Lots of 2010 kickers

• Latch release mechanisms

Example: Transmission Shifter

• Toggles between two different gear ratios– Low gear = power– High gear = speed

• Standard add-on for AndyMark Super Shifter

• Or design your own!• ¾” bore x ½” stroke

cylinder – can easily be used without compressor

Example: Linear Pneumatic GripperNOTE: The solenoid valve is

installed close to the cylinder. This minimizes

wasted energy.

Example: Linear Pneumatic Gripper

Example: 1-axis and 2-axis Grippers

Example: Pneumatic Brakes

• Extend cylinder to stop a manipulator, or use on wheels to lock your drivetrain

• Use normally open solenoid if you want the brake applied with no electricity

• Low energy requirements – can easily be used without compressor

Winch-Wound Kicker, Pneumatic Release

Pneumatic KickerNOTE: This is a large bore, long stroke cylinder. Kick frequency is limited by

compressor output.

1-1/2” bore x 12” stroke = 22 in3

@ 60 psi that equates to ~1300 PEUs@110 PEU/s recharge rate, that is

only 1 kick every 12 seconds!

The Good and Bad

• Good At– Fast movement: kickers, shifters, pin pullers, at times equivalent to a

solenoid (solenoids illegal)– Two-position mechanisms: fully extended, fully retracted– Sustained Holding: clamp, grabbers (motors would burn up)– Unpowered mechanisms: for end of match bonus (avoid leaks!)

• Bad At– Rotational movement > 180 deg (cylinders are linear)– Sustained movement (you’ll run out of air)– Accurate position control: middle of stroke = gray area

Less specifically…

• PROs– Doesn’t overheat– Designed to stall– High speed– Accurate end of stroke

position control– Can hold without battery

power

• CONs– Heavy (10 lbs+)– Battery drain– Space– Limited control

General Suggestions

• Order your free cylinders even if you don’t use pneumatics this year

• Because of weight and space requirements, look to pneumatics if you have 2+ uses (unless you can leave off the compressor)

• Do not tolerate leaks• Conserve energy – don’t oversize or over-

pressurize

General Suggestions

• Know the rules• Soapy water (goggles cleaner?) makes for a

good leak detector• Properly apply Teflon tape (more != better)• Cut all tubing at 90 degrees to the tube axis• Tighten + mark all fittings• Have a system schematic / diagram

Questions?Thanks to:Raul Oliverahttp://first.wpi.edu/Images/CMS/First/2007CON_Pneumatic_Power_Olivera.pdf

Andy Bakerhttp://andymark.biz/presentations.html

Ken Staffordhttp://first.wpi.edu/Images/CMS/First/2008FRC_Pneumatics_Stafford.ppt

Chief Delphihttp://www.chiefdelphi.com/

Official FIRST Pneumatics Manualhttp://usfirst.org/uploadedFiles/Community/FRC/Game_and_Season__Info/2010_Assets/

2010%20Pneumatics%20Manual%20Rev%20-.pdf