Experiments in textile pneumatics


An ongoing project with the ever-marvellous Rusty Squid.

I came across the aeroMorph project (and their published paper, full of delicious constructional details) and was inspired. Seems like it ought to be possible to make light, cheap, safe robot structures that use this kind of fabric-based pneumatics for actuation and easy sewing, pleating and folding techniques for fabrication.

One challenge with pneumatics is always the cost of the parts. Most projects use a bank of solenoid valves,which are big, power-hungry, and relatively expensive. AeroMorph uses the Pneuduino, which is small and convenient but still expensive.

Russ pointed out that cheap blood-pressure meters are now a thing, and the pumps and valves they use are readily available for cheap. Ebay reveals a whole array of little pumps and valves, all for a couple of pounds, all operating around half a bar. So I got this lot:
"DC 6V small air pump Micro Pressure Pumps Oxygen pump sphygmomanometer UK"
"DC 6V NO Micro Straight-through Air Pressure Relief Solenoid Valve FA0520F"
"Pressure Gauge 50mm 63mm 100mm Dial Bottom & Back Connection Pneumatic Air Range" (0-1 bar, 1/8BSP)
"TEFEN Nylon Pipe Fitting Plastic Barbed Hosetail Joiner Tubing Connector Blue" (Female swivel nut, 1/8 BSPT by 5mm)
"T Piece Hose Mender Pipe Repair Pond Fuel Diesel Joiner Connector Air Water" (3mm)
I used 2mm ID silicone hose, which is a push-fit over all those, for most of the plumbing, plus a 2.5mm OD PVC hose from the Scrapstore for the glued-in connection to the actuators.

Then we need fabric and glue film. I started with a 4oz PU coated nylon (which is very lightly coated, but basically airproof on its own) and a thermoplastic polyurethane glue film sold for use in marquetry. I think this is actually Bemis 3218. The data sheet suggests it should be glued at 120 to 130C

Here's one aeroMorph-style actuator at work:

And a different style of bending actuator, sewn to a simple cylinder to provide a restoring force:

Construction sequence:

Glue film

A medium iron (this is a 4 iron from Wilko for glue-based experiments)

After peeling the backing paper:

The glue film will also help secure the filler tube

I tried a couple of other fabrics in this session - a stretchy lycra knit and a very mobile woven nylon, used on the bias - but both of them came out so leaky that the little pump couldn't get them up to pressure. A water immersion test showed that they were pinholed all over. Which suggests (unsuprisingly) that this glue film isn't sturdy enough to make these assemblies airtight, they need an air-proof fabric backing up the film.

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