Page 323 - Robot Builder's Bonanza

292 ROBOT MOVEMENT WITH SHAPE MEMORY ALLOY

Pulley
Deactuate Actuate
SMA wire

Lever

Spring SMA wire

Bias spring
Figure 25- 6 The bell crank changes the
contraction of the SMA wire for sideways
movement. The spring allows the crank to return
Figure 25- 5 Concept of using an SMA wire with a to its original position after current is removed
mechanical pulley. from the SMA wire.

tional motion. A large- diameter pulley will turn very little when the SMA tenses up, but a
small- diameter one will turn an appreciable distance.
Then in Figure 25- 6 there’s a length of SMA wire used in a lever arrangement. Here, the
metal strand is attached to one end of a bell crank. On the opposite end is an ordinary expan-
sion spring, something you can get at most any hardware
store. Applying juice to the wire causes the bell crank to
move. The spot where you attach the drive arm dictates
the amount of movement you will obtain when the SMA
contracts.
SMA wire is tiny stuff, and you will find that the minia-
ture hardware designed for model R/C airplanes is most
useful for constructing mechanisms. Most any well- stocked
hobby store will provide a full variety of bell cranks, levers,
pulleys, wheels, gears, springs, and other odds and ends to
make your work with SMA more enjoyable.

Using Ready- Made SMA
Mechanisms

Several companies have taken up the shape memory alloy
mantra and offer unusual and handy ready- made SMA
mechanisms. Price is reasonable, especially considering
Figure 25- 7 Commercially made SMA that the products are ready for instant use; you don’t need
linear motor. (Photo courtesy Miga Motor to crimp on any connectors or attach any bias springs.
Company.) One such company is Miga Motors (www.migamotors

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