Page 208 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

186 Making Things Move

room temperature. This effect is called shape memory, since the wire “remembers”
what it’s supposed to look like. The metal mix is known as shape memory alloy (SMA).

Dynalloy (www.dynalloy.com) is the main manufacturer of an SMA called Flexinol,
which is designed to be durable enough to create movement in mechanisms.
SparkFun carries some actuators from Miga motors, like the Miga NanoMuscle
(ROB-08782), which can be used to make small linear movements.

The recurring complaint about muscle wire is that it contracts only about 3% to 5%
of the original wire length, which limits its practical applications, but you can probably
make an inchworm robot with a few LEGO pieces and a short SMA wire. For project
ideas, check out the Muscle Wires Project Book by Roger Gilbertson (Mondo-Tronics,
2000).

Electroactive Polymer Actuators
Electroactive polymer actuators (EAPs) are similar to SMA, but based in plastic instead
of metal (although some metal-plastic composites are emerging). They have the ability
to contract up to 380%, which is extreme in comparison to nitinol. Researchers have
tried using it to make arm-wrestling robots and even control a fish-shaped inflatable
blimp, but again, the technology is immature and has not gone mainstream yet,
Figure 6-41 shows a four-fingered gripper actuated by EAPs. See the article at
www.empa.ch/plugin/template/empa/*/74071) for more information about EAPs.

FIGURE 6-41 Gripper actuated by EAPs (courtesy of Yoseph Bar-Cohen,
Jet Propulsion Laboratory/Caltech/NASA)