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.

Comments

[jehan60188]

any more pictures of the air-inlet assembly?
thanks!

[nidobrito]

Any alternative to the expensive solenoid valves?

[bowmaster]

Do you think a 25 CFM compressor is good enough for a full body suit if I want decent speed?

[cheewee2000]

 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.

[bowmaster]

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.

[lordl9999]

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 ;)

[cheewee2000]

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!

[Pooloop]

and thanks for previous answer.

[Pooloop]

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

[R3mus]

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.

[cheewee2000]

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

[Pooloop]

why did you put this : Choose-A-Color Flexible Nylon 11 Tubing .106" ID, 5/32" OD, .025" Wall Thickness, Red and this: High-Temperature Silicone Rubber Tubing Soft, 3/8" ID, 1/2" OD, 1/16" Wall tubes. grateful Peter

[cheewee2000]

the nylon tubing is to connect from the solenoid valves to the muscle. the Silicone Tubing is the tubing that inflates inside the black sleeve.

[007 dragonnel]

I like how you built your air muscles and I intend to build some very much like yours, to help me improve my prosthetic leg. May ask you where did you buy your 3-way valve and 3-way solenoid valve?, what kind of device are you using for pumping air into the muscles?, and finally how much did they cost you?.

[longineus]

Is that electronics board necessary?Can't you just connect the valve to a switch or something like that?

[cheewee2000]

a switch will do. Try just hooking up a 9volt battery and it should fire. Most solenoid valves run on 12 volts or 9 volts. the particular one i used runs on 5.

[longineus]

these valves can retain the pressure on both muscles at the same time?Like, keeping both half full?

[cheewee2000]

not really. the 3 way valve only has 2 states. pressure in for one valve + release one the other and vica versa. you can possibly flip the states very quickly to keep pressure on both.

[shyguy567]

May I ask where you got that one/which model it is?

[benip90]

nice application, despite it being a copy of other Instructables I liked the link to your project and more influence should have been on the system used to make both the muscles operate in synchronisation

[egriff]

I would enjoy an instructable on how you got the muscles to work in unison, where one contracts and the other expands.

[cheewee2000]

it's done by having a 3-way valve. with a 3-way solenoid valve, when the switch is turned on the air flows into one muscle and when it's switched the other way, air goes into the other muscle while the pressure in the first muscle is released.

[egriff]

thank you, you and Honus have been very helpful.

[spry981]

Any idea how much force the muscles exert? I'm thinking of using this idea on a new robot project, but I want to make sure they muscles will actually be able to move the parts. I would want them to be able to move about 40lbs.

[egriff]

they are strong, they can have a lift to weight ratio of 400:1

[bombmaker2]

did you mean very soft silicone tubing

[cheewee2000]

yes. the silicon hardness i used was 50A on the durometer(Very Soft)

[bombmaker2]

thanks

[okura]

This is a copy of another Instructible http://www.instructables.com/id/How-to-make-air-muscles!/?ALLSTEPS
Even that is a copy of various DIY articles on the net. You can Google for it as ' Mckibben air muscle latex silicone '.
You do'nt even have the courtesy to acknowledge the 'copied' original sources!

It is not correct to enter this for any competition.

[cheewee2000]

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!

[MrShifty]

Very slick! I built one of those out of almost exactly the same materials a couple years ago (we used latex surgical tubing instead of silicon). Have you tried letting the tube hang loose inside the mesh? That's what we did, though mostly because we didn't have a good way to terminate the ends... If anything else, it's probably safer that using the compression fittings as described...

[cheewee2000]

Makes sense! Do you have an image of your assembly? did you tie the end of the tube?

[MrShifty]

The assembly is in storage :( I'll post an image when I can get to it, though. But to answer your question, the end of the tube was folded over and tied with zip-ties.