Artificial Muscles

Padu,

There are several types of EAP artificial muscles. Most of them fall into two categories: Ionic which must stay wet and require low voltages, and dielectric which work dry but need very high voltages (10 KV range) to operate.

I work with dielectric EAP's. They can be very dangerous. A dielectric artificial muscle is basically a very large mushy capacitor. There is very little current while they are being used, but there is a huge amount of stored energy. Any shorting in the system will release a huge (i.e. deadly) amount of current. In addition, electricity starts acting a little different in the multi-kilovolt range. Insulators become just poor conductors. Edge effects cause seams where insulators are joined to act like wires. We often see "thermal events" (fires) during our tests. Dielectric EAP is not something to experiment with at home.

With their lower voltages, ionic EAP is not so bad, but then you have electricity and water so you still need to know what you are doing. There are one or two commercial products out now that use this technology.

If you are really interested, see if you can get the book: "Electroactive Polymer (EAP) Actuators as Artificial Muscles - Reality, Potential and Challenges" through inter-library loan (its $75 online). The second edition is now out. It would be a safe guess to say that about 75-80% of what is known about the subject is covered in this book.

For the time being, you are better off working with muscle wire unless you have a really well equipped lab.

Paul Pawelski

Padu wrote:

EAP's seem to have been "useful Real Soon Now" for a long time :->

Catman writes: [snip]

have a really well

Or Air Muscles, of course :->

cheers, Rich.

There's been an earlier kind of "artificial muscles" called Flexinol, which are made of Nickel-Titanium wires, for over 10 years.

They draw a significant amount of current and are kind of slow, but easily available. That might be a starting point for such a project.

Polymer-based muscles are too difficult to get ahold of and use for the time being.

Correct me if I'm wrong, but isn't most EAP actuation inherently non-linear? They tend to bend instead of retract, which can be an awkward motion to make use of.

Muscle wire is certainly a much safer element, although they're far too slow, weak, and hot to be of much use in the long run.

Air muscles are interesting, except for the noise and inaccuracy due to compressibility of air.

EAP actuation depends on how the "muscle" is formed. For dielectric EAP, the material compresses along one axis (perpendicular to the compliant electrodes) and expands on the other two axis to keep a constant volume. If you have one big sheet of EAP material with continuous compliant electrodes on the major faces, you can roll it up and make a device that will extend along the axis of the roll. If you do the same thing, but instead of having one compliant electrode on each major face you have electrode strips that can be independently activated, you can make the tube bend by only activating the electrode pairs that are on one side of the roll.

Air or McKibben (SP) muscles are cool, and a lot safer than EAP for the experimenting at home. The only big problem with them is how fast they wear out. They are usually made of a rubber bladder with a crosshatched nylon shell around them (like a fat Chinese finger torture toy - woven nylon cable protectors work good). The nylon rubs on the rubber each time the muscle is moved. Eventually it weakens a spot on the bladder until it pops. You could improve their accuracy by using a liquid instead of air, but the weight goes way up and it is a much bigger mess when they pop.

Paul Pawelski