Here's a fun project, an inchworm that walks across the table using a shape memory alloy called nitinol wire as its leg muscle. It's made from very simple parts: balsa wood, staples, copper wire, a spring taken from something else, and of course some nitinol wire.
Briefly, nitinol wire is a wire that will remember a shape that you tell it to. You can deform the wire. Then when you heat it up it goes back to its remembered shape on its own. In the photos below I've made it remember the shape of a compressed coil by putting it in a candle flame. I then stretch it out, and when I heat it by passing electricity through it, it returns to the compressed coil shape.
How the nitinol wire inchworm works
As the illustration below shows, under the legs, connecting the bottom of one to near the top of the other is the nitinol wire coil. It's remembered shape is of a compressed coil, holding the legs close together. That's the closed position.
On top is attached a V-shaped spring, simply a tensioned wire in a V-shape.
As shown below, the nitinol wire is electrically connected to a 0-24 volt DC power supply.
The following is how a single walk step is done:
That ends a single walk step. The electricity is turned back on and the process repeats.
Video - Nitinol Wire/Shape Memory Alloy Inchworm - How it Works
The following video shows my nitinol wire/shape memory alloy inchworm in action.
This video goes step-by-step through the making of this nitinol wire inchworm.