The air muscles I built here a sort of a hybrid of cheewee2000's project and Honus'.
They were part of an investigation to see if I could get position feedback from an internal LED and photo-transistor. I learned that is not a very reliable way to get position feedback. At least not in my setup. My purpose in publishing this Instructable is so that you can be more wise than I have been.
Maybe this can be a crowd-sourced problem.
Step 1: Concept of LED Diffusion
I connected the photo-transistor to a Wheatstone bridge to measure the the variation as the muscle contracted. Despite the silicone tubing (but probably because of my translucent fitting) I had lots of interference from ambient light. The readings were all over the place. I suspect that this was due to misalignment of the LED and photo-transistor.
In the future, I want to try position feedback with internal capacitance instead.
What do you think? leave a comment below
Step 2: Building the Air Muscles
What cheewee2000 told me to get:
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
Though I think the mesh is too big, one of my muscles popped after about 50 contractions (see picture below). I also wasn't using a pressure regulator.
Other fittings you might find helpful: (also from mcmaster carr)
44705K36 Low-Pressure Aluminum Threaded Pipe Fitting, 1/8 Pipe Size, Coupling 2.13
2 2808K25 White Polyethylene Single-Barb Tube Fitting, Adapter for 3/8" Tube ID X 1/8" NPT Male Pipe, Packs of 10, 5.53 Per Pack
5116K114 FDA White Nylon Single-Barbed Tube Fitting, Plug for 3/8" Tube ID, Packs of 10, 2.55 Per Pack
And some hose clamps.
I used dental floss for tendons. It's super strong and it makes your air muscles smell minty fresh.
Step 3: Valves and Air
Because they required AC, I chose to trigger them with a solid state relay.
Thanks to pdf below I was able to figure out how to use the valves.
I used two valves one to open pressure and one to open exhaust.;