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How to make air muscles!

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I needed to create some actuators for an animatronics project I'm working on. Air muscles are very powerful actuators that work very similar to a human muscle and have a phenomenal strength to weight ratio- they can exert a pulling force up to 400 times their own weight. They will work when twisted or bent and can work under water. They're also easy and cheap to make!

Air muscles (also known as a McKibben artificial muscle or braided pneumatic actuators) were originally developed by J.L. McKibben in the 1950's as an orthotic appliance for polio patients.

Here's how they work:

The muscle consists of a rubber tube (bladder or core) that is surrounded by a tubular braided fiber mesh sleeve. When the bladder is inflated the mesh expands radially and contracts axially (since the mesh fibers are inextensible), shortening the overall length of the muscle and subsequently producing a pulling force.

Air muscles have performance characteristics very similar to human muscles- the force exerted decreases as the muscle contracts. This is due to the change in the interweave angle of the braided mesh as the muscle contracts- as the mesh expands radially in a scissors like motion it exerts less force due to the weave angle becoming increasingly shallow as the muscle contracts (see the diagram below- figure A shows that the muscle will contract to a greater degree than figure C given an equal increase in bladder pressure).The videos show this effect as well. Air muscles can contract up to 40% of their length, depending on the method and materials of their construction.

Gas law states that if you increase pressure you also increase the volume of an expandable cylinder (provided temperature is constant.) The expanding volume of the bladder is ultimately constrained by the physical properties of the braided mesh sleeve so in order to create a greater pulling force you need to be able to increase the effective volume of the bladder- the pulling force of the muscle is a function of the length and diameter of the muscle as well as its ability to contract due to the properties of the mesh sleeve (construction material, number of fibers, interweave angle) and bladder material.

I constructed two different sized muscles using similar materials to demonstrate this principle- they both were operated at the same air pressure (60psi) but had different diameters and lengths. The small muscle really starts to struggle when some weight is put on it while the larger muscle has no problems at all.

Here are a couple of videos showing both of the constructed air muscles in action.


Now let's go make some muscles!
 
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if accurate-yes

Honus (author)  jmacalupu herrera4 months ago

I don not know where to buy materials in Peru. Maybe try a hardware store or a place that sells aquarium supplies?

as it would be for you to bring it to the silicone tube peru because I find

Honus (author)  jmacalupu herrera4 months ago

Sorry I don't understand. Are you looking for silicone tubing in Peru?

Honus thank you tell me where each material conseguistes especially the silicone tube and not the meeting and thanks in advance

could give me the exact link of the materials or detallarmelos nesecito thanks in advance what to draft an exoskeleton

Honus (author)  jmacalupu herrera4 months ago
All of the materials are listed in Step 1.

me podrian dar exactamente el link de los materiales o detallarmelos gracias de antemano lo nesecito para un proyecto de un exoesqueleto

-copper tube-6 months ago

Ich bin ein Dachs

-copper tube-6 months ago

(removed by author or cojacidsaxfhsnk

temmerson7 months ago
what does the strength of the muscle depend on?
Honus (author)  temmerson7 months ago
The pulling force of the muscle is a function of the length and diameter of the muscle as well as its ability to contract due to the properties of the mesh sleeve (construction material, number of fibers, interweave angle) and bladder material.
temmerson8 months ago
Hi i was just wondering how you managed to get the aluminium at the ends of the muscle into the shape they are, did you buy them like that or what?

Thanks in advance
Honus (author)  temmerson8 months ago
I turned them from Aluminum rod using a lathe.
Ghunter102 years ago
i remember seeing this instructable when it was first shown in the email send out as a featured ible and i favorited it, i have now come back and am designing a "gauntlet" that someone puts their arm into and the muscle will hopefully add to the strength of their motion, thank you for the inspiration.
Honus (author)  Ghunter102 years ago
That sounds like a really cool project- make sure to post pics or video when it's done!
Ghunter10 Honus2 years ago
here is what i have so far for a design for a bicep, what do you think?
bicep of suit.gif
I think it needs a rotational joint at the elbow. And the cables should be attached to a disk or something to translate the contraction of the muscle into torque.

If this works out, do you plan to extend the exoskeleton to more body parts? I just read Wearable Robots: Biomechatronic Exoskeletons and I suppose I'm interested in working on the same sort of thing. Also, I just found this website, are other people here working on exoskeletons?
I would love to turn this into an exoskeleton (and hope to), the problem I' ve had is cost so far, so a decent amount of time is taken saving up for the different parts.
You should enter the Jack Daniel's contest. $25,000 would buy a lot of parts.
dratman pharseid8 months ago
You might think so.
Hey just spotted this and thought it would be really cool if you could do this, but if you use this for an exoskeleton then note that the air muscles can fail and cause a lot of pain, trust me if done something like this and couldnt bear the pain it gave me, when it collapsed it had caused a metal 'pinch' and fractured my arm. Just watch out for that but good luck with the attempts. :)
Honus (author)  Ghunter102 years ago
That looks pretty interesting- how exactly will it work?
Ghunter10 Honus2 years ago
i intend to have the system set up where a button operated valve will be on the ring in the bottom left of the picture set up where it faces downward towards the arm inside. when the arm flexes the valve will open and provide air for the air muscles (depicted as black cylinders) which would contract, as they contract cables attached to the muscles and the ring with the valves would hopefully pull the arm up into a flexed position, i then need to design another system on this that would involve more muscles that will create the opposite motion to bring the arm and frame back down.
ExoFOX1 year ago
im building the iron man suit obvsly minus anything power by the fictional arc reactor , any tips or comment are welcome , just looking to talk and make sum friends in the process of this exp,......thank you all
Honus (author)  ExoFOX1 year ago
I'm currently working on a full animatronic Iron Man suit for a friend so I'll have a complete instructable up when it's finished. Everything is powered by servos though- no air muscles.
ExoFOX Honus1 year ago
thats whats up i would like to see the process of your exp' i myself am using linear force and gravity to make mines work sum hydrolics or shock obsobvers but not batteries,
ExoFOX1 year ago
im using old technology like the pharros back in egypt days meaning i wount be using battery i am using motors but not run on batteries or liquids just motion and pure physics
strongbino2 years ago
In order to decrease the weight of the system, can the air compressor only be used in the initial filling of a muscle and then removed and then have the air flow into the adjacent muscle or another container and then the adjacent muscle?
I would think that would complicate the valve system, one set of valves to prefill the muscle and the other set to take it to full pressure. Plus there's no guarantee that a muscle will need to deflate at the time another muscle needs to inflate. But if the muscles all deflated by releasing into a common line, you could put a compressor on that line which exhausts into the system's holding tank. The compressor would have to do less work when the air at the inlet was at higher than atmospheric pressure.
Honus (author)  strongbino2 years ago
I don't know about that- I guess you would just have to try it and see.
I just feel like its a waste to expel the air from the muscle into the atmosphere. It would be more efficient to have it circulate through the system to another muscle so that the pressure remains constant.
jibblesmgee2 years ago
I want to scale this up a little. I had the idea of using sections of bicycle innertube, and finding a substitute for the nylon mesh (or just some heavy duty wide diameter nylon mesh) and seeing what I could do with it. Has anybody tried this? I'll let everyone know how it goes when I get around to it.
Graceria5 years ago
I'm working on a set of animatronic angel wings and I need it to be entirely free of any showing tubes or wires and I need to be able to move freely without being attched to anything. These air muscles look like they could be the solution to a problem I've been having with the wings not looking natural enough. Could these be made using a small air canister with a limited supply of air and is there a way I could set it up so that the air would return to the canister when the muscles relax? I'm not quite sure how I could get the air moving the way I need it to.
Honus (author)  Graceria5 years ago
Sorry for the late reply- been super busy! I think they would work really well for your application. You could make a small air tank from a plastic soda bottle (I think they're good to at least 60psi.) I'm not sure about the air return as I haven't yet done anything like that. The smaller muscles don't consume that much air so it might not be that big a problem unless you need it to go for several hours or over say fifty cycles. A lot of it is going to depend on your design.
Tolderian Honus2 years ago
Only a few years behind the times but... check out EARS... stands for (E)something (A)ir (R)eturn (S)ystem. Not sure how to incorporate it... but, that's why I'm telling you. Surely you, or someone on these sortsa pages, can come up with something for the common man. w00t!
Thanks! I'll check that out!
Honus (author)  Tolderian2 years ago
Exhausted Air Return System is a really great idea- I'll have to do some research on that to see if it would work.
Tolderian Honus2 years ago
Well if you figure out a way to Macgyver it, that'd be pretty sweet.

I made a couple of the muscles that chewee threw up here that worked well but it just seems like an awful lot of wasted air that could be recycled and make any reserve tank last longer.

Just throwing that out there.

I come back along from year to year to see if anyone else has pooped another gem of amazing. First time I've ever posted. Good luck!
kikiclint Honus4 years ago
 as long as you have some kind of quiet pump, capable of the necessary psi, you could just have it continually fill the bladder, and just let a solenoid valve release the air.  Either that, or you will have to pump the air back from the muscle.  It wont be that important to recycle the air, unless you are in space. 
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