Tutorial: Build air muscles

  1. sam's Avatar
    sam sam is offline Positronic Brain
    How To, DIY

    Build air muscles

    Estimated Time
    30 minutes
    Skills Required
    No special skills required
    Parts Required
    *Latex or Silicone tube
    *Braided mesh
    *Wrom-drive clamp
    *Coupling adapter
    *PVC clear tube
    ---More specifications lower in the tutorial
    Tools Required
    Tutorial Navigation
    Hello everyone.

    Important note :

    Please wear protective eye glasses when using air muscles and other pneumatic devices. It happen to me once that fittings poped and went into my protective glasses. A good thing I was wearing them!

    ---------------------------Brief information on the air muscles-----------------------

    The air muscles were invented by McKibben in the 1950's. They are very strong actuators and can lift up to 400 times their own weight. They are soft actuators so they don't have to be precicly placed for them to work (unlike some pneumatic rams). The basic principle of the air muscles is a latex or silicone bladder that is surrounded by a mesh sleeving. When filled with air the latex will expand and push on the mesh sleeving, but the mesh sleeving isn't elastic, so it will expand horizontaly and shorten verticaly. This is the basic principle of the muscles.

    ---------------------Terms to know and understand : -----------------------

    *PSI : Pounds per square inch. This is a mesurement of the pressure of gasses.

    *Durometer : A scale on wich rubbers are tested to find out there hardess. A lower number means it's more flexible and a higher numbers means it's harder (like on squateboard wheels).

    *OD X ID X Wall : These are mesurements used to calculate tubes. OD is outside diameter of the tube. ID is the Inside diameter. Wall is the thickness of the rubber.

    *Relationship between compressed air : V1 X C1 = V2 X C2 Where the v's are the volume and the C's the compression of the air. So Let's say you want to calculate an air tank wit a 125 max PSI rating. How much air will you get? 1.0889 (the volume of my tank in cubic feet) X 125 / 60 (the pressure at wich I will let ou the air) = 2.27 cubic feet of air @ 60 PSI).

    ---------------------------Materials :------------------------

    -Bladders :

    *Material : Silicone or Latex

    You have a lot of choice in the section. You can use latex or silicone. Latex is a bit softer (35A on the durometer scale) and silicone is around 50A (so a bit harder). I have read in a couple places that silicone is more resistant to higher pressures than the latex. On the other hand, the latex's fatigues much slower. So it will last longer. We usualy don't use pressures over 60 PSI so resistance to higher pressure is a waste of air power in my opinion. I would use latex, but it's up to you

    *Size :

    The diameter of the rubber tube is also important. I have found that 3/8" smaller tube than the sleeving works well. Even a bit more. Over 1/2 inch would work nicely. (I haven't tested too many different combinations).

    -Sleeving :

    The important part here is the maximum and minimum diameter of the sleeving. The maximum should be around 3/8" to 1/2" more than the OD of the bladder. That works usualy well. You can also modify how the muscles will work by changing the lengh of the sleeving. More sleeving means that the bladder will expand more thus giving the muscle more power.

    -Caps :

    Where the muscle is connected to the air tank, I used a coupling to hold the PVC clear tubing (that goes to the air tank) to the bladder. On the other end of the muscle, I used a bol just to block the entry. Using caps about 1/8" more than the ID of the bladder gives usualy better results. To hold the bladder secure I used some worm-drive clamps (with the little screw to tighten the clamp).

    -------------------------------Source list : ------------------------------

    Ok, so here are the parts and where you can find them.
    My images are taken from google and not the actual specs of the ones mcmaster sells

    -6 inches Super Soft Latex Rubber Tubing 1/4" ID, 3/8" OD, 1/16" Wall, Semi-Clear Amber-------- For 1.06$ per foot = 0.53$ for one muscle (Part number : 5234K33)

    -1 foot of Easy-Cut Polyester Expandable Mesh Sleeving 1/2" ID, 1/4" to 3/4" Bundle Dia, 10'L, Black------ For $6.72 per 10 feet = 0.67$ per muscle (Part number : 2837K14)
    -Less than a foot of Easy-Cut Polyester Expandable Mesh Sleeving 3/4" ID, 5/8" to 1" Bundle Dia, 10' Length, Black----- For $8.45 per 10 feet = .85$ per muscle (Part number : 2837K15 )

    -4 of Worm-Drive Hose Clamp W/Zinc Pltd Steel Screw 7/16" to 25/32" Clamp Dia Range, 5/16" Band Width----- For $5.28 for 10 = 2.11$. You can probably buy this item at a store near you where you can make sure that it fits all right with your tubing. Looking at numbers like this is difficult. (Part number : 5388K16)

    -1 of FDA White Nylon Single-Barbed Tube Fitting Coupling for 3/8" Tube ID-----$2.88 for 10 = 0.29$ for one muscle. (Part number : 5116K45)

    -1 of Durable Nylon Multi-Barbed Tube Fitting Adapter for 3/8" Tube ID X 1/2" NPT Male Pipe----- $4.34 for 10= 0.43$ for one muscle (Part number : 5372K119)

    -5 feet of Abrasion-Resistant PVC/Polyurethane Tubing Clear, 3/8" ID, 1/2" OD, 1/16" Wall Thickness-------$0.88 Per feet = 4.40$ per muscle (Part number : 53955K23)

    So the grand total to build 1 muscle will come to : $8.43. So These are cheap to make. But then again, you have to have an air tank, wich I didn't count. You could also use a hand pump and pump it direcly, but you would need an adapter for that.

    -----------------------------Putting it together : ----------------------------

    Step 1 :

    You will start by putting you're tube taht connects to your muscle from one end to the air tank together. You can use a PVC tube and insert a coupling for the connection to the muscle and an adapter to fit the air tank.

    Step 2 :

    Then you will Insert the bolt on one side of the rubber. I read that most silicone tubes can elongate 2 times and get back to their normal position. Latex on the other hand can elongate 3 times it's lengh and come back to it's original lengh with no problems. So think about that when you decide the lengh of your muscle.

    Step 3 :

    Then you will connect the rubber tube to the couling.

    Step 4 :

    Now, you will insert the sleeving over your rubber. You can use a spare lengh of sleeving to create a holding device on your muscle. Usualy on worm drive's, just beneeth the screw is a rough patch. If you tighten to much it could pock a hole in your rubber cousing your muscle to leak. To avoid this I put the mesh sleeving to hang the muscle under that part of the clamp. Note : In the picture below, I didn't put the mesh sleeving beneeth the screw, but you can see that I fixed taht in the next picture after this one.

    Step 5 :

    Now it's time to instal the second worm drive. With 3/8 inches more sleeving than rubber (in diameter) I have to push the sleeving so that it's at it's maximum diameter when putting the second clamp. you can also calculate the lengh required by roughly calculating the rubber (excluding the part with the coupling and the bolt). Then you do 3 times longer mesh for latex and 2 times more for silicone. the Sleeving has to be the same diameter as the rubber when you are doing this! When putting in the second worm drive, you have to do a loop with the mesh to creat a second hanging point.

    Voila your finished muscles.

    (Page 1 of 2)

Replies to Tutorial: Build air muscles
  1. Join Date
    May 2008

    Re: Build air muscles

    Great work!
    Do you have a source list - particularly the braid?

  2. Re: Build air muscles


  3. Join Date
    Jan 2008
    Montreal, Canada

    Re: Build air muscles

    Quote Originally Posted by ooops View Post
    Great work!
    Do you have a source list - particularly the braid?
    Is the source list Ok? You can also find some mesh sleeving on amazon, but you have MUCH less choice for evrything

  4. robot maker Guest

    Re: Build air muscles

    very nice info on air muscles,always wanted to make my own since the cost to buy them is very high and i need many for another hand design i am building

  5. Re: Build air muscles

    I really like concept of artificial muscles,
    good stuff.
    Greatness is achieved through one vision.

  6. Join Date
    Sep 2006
    Carol Stream, Illinois

    Re: Build air muscles

    nice work Sam! +rep

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  7. Join Date
    Nov 2008
    Gainesville, Florida

    Re: Build air muscles

    Quote Originally Posted by ooops View Post
    Great work!
    Do you have a source list - particularly the braid?
    This is where I have bought braided mesh before, they have a good selection and also sell them in different colors which is great if your muscles will be visible:


    Sam's tutorial is perfect, but I am going to put up some images just to show another alternative with simple balloons. Of course the latex tubing he suggests is much more resistant, but the bigger thicker balloons have yet to burst in many times I have used them in class. Also, since the balloon is already closed on one side you only have to deal with one opening. There are pros and cons to this, like the air release time.

    One test that surprised me (since it is not obvious visually and of course I did not do any calculations), is that the smaller diameter tubing actually contracted more with the same balloon/air pressure. I thought the wider braid would contract a lor more.

    Take a look...

    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  8. Join Date
    May 2008

    Re: Build air muscles

    Thank you for the source info.
    I need to move the air muscles up on my "projects to-do list".
    Great job Sam, and thank you Sunithaya!
    I am sure when I do get around to it, this info will be invaluable!

  9. Re: Build air muscles

    What sort of relay or solenoids are common to use when interfacing with an MCU?

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