Muscle wire is a shape memory alloy made from a nickel and titanium alloy. At room temperature it can be stretched by a small force. However, when a small current is passed through the wire it returns to a much harder form and to its original length with a reasonable force.
When in use a muscle wire can be stretched up to 8 percent of its length and still recover. However, this can only be done a few times until it breaks or stops returning to its original length. Its life cycle can be extended dramatically if it is stretched to between 3 to 5 percent of its overall length. Within this range it will go through the stretching and return cycle millions of times.
A PIC micro-controller can be programmed so that outputs are switched ON or OFF. When switched ON the muscle wire contracts (shrinks) to its original length. For example, when used within the Dancing Toy project it allows the clowns legs and arms to move.
