Pneumatic Muscles

Pneumatic Muscles, or Air Muscles are simple, cheap and extremely powerful. Applications range from machinery, robotics to wearables. Air muscles have no stickction and have a weight to strength ratio like no other linear actuating mechanism. It's weakness is in speed. The speed at which air muscles contract is controlled by how fast air is pumped into the muscle (cfm). So, in order to achieve high actuation speeds, you need large tubes and air controls to get enough air into the muscle quickly.

The assembly I've outlined below is experimental. Pipe fittings weren't meant to be used for this purpose, so please take caution when pumping pressurized air into these assemblies. The muscles I made were used for my Soft Pneumatic Exoskeleton. Air muscles work and are easy to build.

Specifications
max air pressure: 120 psi
suggested lengths: 6"-30"
weight: n/a
strength: n/a

Materials (prices as of 6/29/2008) (materials listed below can be purchased at mcmaster.com)

High-Temperature Silicone Rubber Tubing Soft, 3/8" ID, 1/2" OD, 1/16" Wall
mcmaster.com # 5236K15 | $1.31 per foot

Heavy Duty Polyester Expandable Mesh Sleeving 1-1/2" ID, 3/4" to 2" Bundle Dia, 3'L, Black
mcmaster.com # 9142K34 | $5.83 each

Standard Brass Compression Tube Fitting Adapter for 1/2" Tube OD X 1/4" NPTF Female Pipe
mcmaster.com # 50915K226 | $3.86 each

Standard Brass Compression Tube Fitting Long Nut for 1/2" Tube OD
mcmaster.com # 50915K106 | $2.36 each

Moisture-Resistant Acetal Push-to-Connect Adapter for 5/32" Tube OD X 1/4" NPTF Male Pipe
mcmaster.com # 51055K8 | $1.45each

Standard Brass Compression Tube Fitting Tube Support for 1/2" Tube OD
mcmaster.com # 50915K246 | $7.37 for a pack of 10

Low-Pressure Brass Threaded Pipe Fitting 3/8" Male X 1/4" Female Pipe Sz, Reducing Bushing
mcmaster.com # 4429K522 | $1.78 each

Brass Yor-Lok Tube Fitting Cap for Tubing, 3/4" Tube OD
mcmaster.com # 5272K146 | $8.70 each

Choose-A-Color Flexible Nylon 11 Tubing .106" ID, 5/32" OD, .025" Wall Thickness, Red
mcmaster.com #5635K62 | $0.21 per foot

For each muscle you want to assemble you need:
(1) Silicon tubing cut to length (ex. 12")
(1) Braided sleeving cut to length -1/2" ( ex. 11.5")
(2) Tube Supports (1 pack comes with 10)
(1) Tube Fitting Cap
(1) Tube Fitting Long Nut
(1) Reducing Brushing
(1) Brass Compression Tube Fitting Adapter

Average price per muscle: ~$30

Note: The Tube Fitting Long Nut replaces the Hex nut that the Compression Tube Fitting Adapter comes with.

Pneumatic power and control parts
Valves (mechanical or solenoid)
Pressurized air source ( air reservoir or air compressor)
For pneumatic controls, vexrobotics has a nice starter kit. http://www.vexrobotics.com/vex-robotics-pneumatic-parts.shtml

Step 1: Place Silicon Tube Into Braided Sleeve

Cut the silicon tube to your desired length.
Cut the braided sleeve to the same length minus 1/2 inch.
Burn the ends of the braided sleeve with a lighter to prevent it from fraying and to give it a lip in the compression sleeve assembly.
Shove the silicon tube into the braided sleeve.

Step 2: Place Tube Fitting Cap

Slide the braided sleeve and tube through the hex nut
Place the tube support inside the silicon tube
Screw the hex nut into the fitting tightly

Step 3: The Other End

Place the braided sleeve and silicon tube through the long nut
Place a tube support inside the silicon tube
Screw the tube fitting adapter into the long nut
Screw the reducing brushing into the adapter
Screw the push-to-connect adapter into the reducing brushing

Step 4: Pump Air Into the Muscle

Place the 5/32" tubing into the push-to-connect adapter
Pump air in.