Pneumatic Muscles

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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.

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    40 Discussions

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    JonathanN67

    1 year ago

    The link for the kit has gone bad, do you have another site link you can post?

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    matthew585

    2 years ago

    i just got all the parts that you have listed and I got 3/8 X 1/2 rubber tubing but then I got the mesh sleeving witch was 1 and a half inch witch was 40mm and it looks pretty big can you help me out like is that the actual size

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    cheewee2000bowmaster

    Reply 8 years ago on Introduction

     It totally depends on how many muscles you have and how fat your pipes are going to be.  If you want fast acting muscles you need fatter pipes and more CFM. I was running it on a 3.8 cfm compressor through 4 muscles and it was pretty slow. definitely not fast enough to run or jump.

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    bowmastercheewee2000

    Reply 8 years ago on Introduction

    I was think around 20-30 muscles and the ability to jog at slow speeds. I guess I'll have to find a better air compressor. ~50CFM.

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    lordl9999bowmaster

    Reply 7 years ago on Introduction

    hello i was thinking about the same, kind of a body suit with pneumatic muscles.
    did you have any thoughts about how to deliver portable power(e.g. batteries) to the air compressor?

    i was thinking about just having a couple of air tanks on the back (kind of like a diver) instead of the compressor, but that might not be enough air if your going for a walk ;) (didn't do any actual calculations yet, so i'm just laying out thaughts/ guessing)

    well, did you have any thoughts about that subject?


    - and to the guy making this instructable; nice work ;)

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    cheewee2000lordl9999

    Reply 7 years ago on Introduction

    I was attempting to go the same route as you. Adding batteries to an air compressor seems like adding bulk to bulk, so I wouldn't go that route.

    I bought a pony tank (mini scuba tank) so that it could be portable, but never got around to getting the proper regulator to get pressure coming out of the tank at the right psi that i needed, but in theory that should work. At one point I was using mini co2 cartridges, but they only last a few actuations, but are super portable.

    good luck!

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    VVVBATMANcheewee2000

    Reply 3 years ago

    Hi, I know it has been a while, but I am interested in the use of Co2 cartridges for air muscle use. I would greatly appreciate it if you could explain how you used the cartridges. Thanks!

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    cheewee2000VVVBATMAN

    Reply 3 years ago

    I was using emergency bike pumps that run off CO2 cartridges as my valve. They were the only valves I could find that drop the super high pressure in the cartridge down to something more manageable.

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    VVVBATMANcheewee2000

    Reply 3 years ago

    Thank you so much for replying,

    Do you have a link to one of these valves anywhere on amazon or anything?

    Thanks again!

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    jo'dell1

    4 years ago

    has anyone tried different materials to see if a more efficient product can result. for instance kevlar mesh with nitrile tubing or how about a nylon mesh as a substrate between for added stability or a tube inside a tube. What about the pneumatic material has anyone tried a nobel gas, helium, nitrogen, what about more efficient compressors Instead or a pony how about a titanium alloy joint and bone under/overlay to take weight stress as one muscle expands and the other contracts. Also why not more smaller muscles instead of less large ones even a grid of muscles to increase the area that mass is being carried on. and a bleeder valve that slowly moves air from one to the other so there is less mechanical jerk.

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    cheewee2000okura

    Reply 10 years ago on Introduction

    umm. OK. i didn't mean to claim that i invented air muscles. i though it was pretty well known that these things existed. You're right. Mckibben is the first to develop the assembly. more on it here http://en.wikipedia.org/wiki/Pneumatic_artificial_muscles.

    My contribution here is a cheap and simple way to make your own. All the parts are available online and you don't need to fabricate any custom hardware.

    Thanks for the positive and constructive comment!

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    tyscofcheewee2000

    Reply 5 years ago on Introduction

    Ok so it looks like I am a few years too late but that reply was probably one of the most mature things I have seen from anyone on the internet.

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    Pooloop

    8 years ago on Introduction

    what kit of vex did you used, and what Microcontroller. grateful peter

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    R3mus

    8 years ago on Introduction

    I bought all the components, and attempted to fit it together as your instructable shows, but some things dont work. First, the mesh sleeve cant possibly fit into the Long nut with the hose. Either one or the other fits, but not both. Second, the End cap is just too big, and it wont fit snug on the end. If the air comes on, its just gonna pop off the end.

    Im going to attempt a mash between this instructable and the other air muscle instructable to get a working device. Now that I know how easy they are to make, I wont spend so much to get one working.

    1 reply
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    cheewee2000R3mus

    Reply 8 years ago on Introduction

    It's tough to get the tube an sleeve in, but i've done it. it's super tight and it takes some practice.