Introduction to Pneumatics

MN SplashDec 7, 2013

Presented by: Logan MildenbergerFRC Team 2052 – KnightKrawler

www.team2052.com

Acknowledgements Slides by Raul Olivera from FRC 111 –

WildStang› Presentation from the FIRST Championships

in 2008› http://

first.wpi.edu/Images/CMS/First/2008CON_Pneumatic_Power_Olivera.ppt

FRC 358› Lots of great resources!› http://team358.org/files/pneumatic/

FIRST Pneumatics Manual› http://www.usfirst.org/roboticsprograms/frc/

2012-kit-of-parts-pneumatics

What is Pneumatics? Pneumatics:

› “The study of the mechanical properties of air and other gases”

› The system on an FRC robot which uses pressurized air to transfer force

Pressure = matter pushing against matter› Object pushing against another object

Absolute (psia): true matter-based pressure› 0 psia - no matter present to press against objects› Not too important in our designs

Gauge (psig): Relative to Atmosphere› 0 psig - pressure in equilibrium with atmosphere› All regulators and gauges based on this› At sea level: 0 psig = ~14.7 psia

Calculating Applied Force Pressure = Force / Area Force = Pressure X Area Example: 30 psig in 2” diameter

cylinder

30 psig

Force = 30 psi X 3.14 in2 = 94.2 lbs

Area = pr2 = p(1”)2 = 3.14 in2

94.2 lbs

Using Pneumatics in FRC Low to high force applications

› Up to 188 lbs (plus any mechanical advantage in design)

› Can vary force by changing pressure Linear and rotational motion

› Linear is much more common Two positions

› Great for applications where a motor would stall› Open/close or on/off applications

Claws, lifters, pushers, pokers, levers Shifters and clutches

Flexible design options› Excess cylinder length can be accommodated in

design Move mounting point Push against rigid object

› Can start match with force applied, and keep it applied at end of match

Using Pneumatics in FRC Relatively straightforward rules and

implementation› Mounting hardware included› Easy interface to robot› Can test manually without code› FIRST provides instructions!

Economy of scale – easy to add more later Easy to transfer energy from robot “base” to

manipulator› Flexible tubes› Don’t need chain, belt, or perfectly aligned shafts› All components except for cylinder can be

mounted anywhere

Pneumatic System Components

High Pressure (120 psi)

Working Pressure (60

psi)Optional

Lower Working Pressure (30

psi)

Pneumatic System Components

Compressor› Mount with rubber vibration isolation

mounts› Must power with Spike relay with 20

amp breaker (not fuse)› Gets hot!

Pressure Relief Valve (Norgren)› Must be installed on output of

compressor› Vents at 120 psi for safety (in case

your code to shut off compressor doesn’t work right …)

› Must check that this is calibrated properly

Pneumatic System Components

Pressure switch (Nason)› Normally closed (compressor runs)› Opens at ~115 psi (code to turn

compressor off when switch is open) › Wire to digital input and ground on

digital sidecar Accumulator (Air Tank)

› Check rules regarding # allowed› Make sure to mount on high

pressure side to take advantage of higher pressure storage!

Pneumatic System Components

Primary Regulator (Norgren)› Restricts working pressure to 60 psi

max on output side of regulator› Can adjust to less than 60 psi if

desired› Make sure arrow points in direction

of air flow! Secondary Regulator (Monnier)

› Yellow ring› Allows additional lower pressure

circuit if desired

Pneumatic System Components

Gauges› Provide readout of pressure in line› Place one on high pressure side and

one on working pressure side (can attach directly to regulator)

Plug Valve (manual release valve)› Install on high pressure side› Must be able to release all pressure

in system› Must be easily accessed and labeled

on your robot

Pneumatic System Components

Cylinders (aka “Pistons”)› Donated by Bimba› Order to team specifications from FIRST-

specific options› Single or double acting

Single = spring-based return when vented Double = air pressure drives both

directions

› Magnetic position sensing option Solenoid valves (Festo/SMC)

› Switches direction of air flow to drive cylinder motion

› Connect to solenoid breakout on CRIO› Need a double solenoid to drive double

acting cylinder› Can activate manually with blue buttons

Solenoid – Cylinder Action

Solenoid – Cylinder Action

Things to watch out for Safety

› Pressurized air has a lot of potential energy

› Follow rules EXACTLY and be careful Rotation

› Difficult to control orientation of the end of a round shaft

Leaks› Can be hard to find – so prevent them

with good assembly technique! Cut tubing straight and clean Tighten fittings with proper tools

› Use methodical approach to narrow in on one area

Things to watch out for Pipe thread wrap

› Too much is not a good thing› Leave last 2 threads clear› Avoid getting into valves and hoses

Extra components› Bring spec sheets for non-KOP items to

inspection Cylinders are sensitive to side loads “Pulling” force is slightly reduced due to area

of rod Large cylinders use a lot of air – make sure

your compressor and storage can keep up with expected use

Plug valve must be closed before you start the match!

Common Myths MYTH: Using pneumatics is complicated FACT:

› Simple system with detailed instructions, and it’s the same every time!

› Robust system with fewer parts to fail

MYTH: Pneumatics is heavy FACT:

› 2013 compressor is only 2.5 lbs Could be left off robot to save weight (check rules in 2014!)

› Cylinders have high force/weight ratio (compare to CIM+gearbox+chain+speed controller…)

› Adding a second, third, etc. cylinder is trivial› Plastic air tanks are available› Solenoid and tubing weights are negligible

Common Myths MYTH: Pneumatic cylinders are uncontrollable FACT:

› Flow control valves can slow down motion› Can choose piston length based on geometry› Magnetic reed switches can be used to sense

piston position

MYTH: Pneumatics is difficult to program FACT:

› Program compressor to run when pressure switch is closed – connected directly to digital sidecar

› Double solenoid consists of two on/off switches – when one is on, other is off!

Tips Use all 24v or 12v solenoids – don’t mix! Even if you aren’t using pneumatics on your

robot, take advantage of the Bimba donation – play with them in the off-season or have on hand for next year!

Solenoids need a minimum pressure (~30 psi) to work. Test your code with pressure in the system!

Clevis pins can be replaced with bolts for more mounting options