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.

Inchworm walking one step.

The setup

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.

Making it remember a coil shape.

Stretching the wire.

Electricaly heating the wire.

For more details you might want to see my page that explains the nitinol wire as well as shows a few ways to shape it.

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.

Legs close together.

Legs spread apart.

The V-shaped spring.

0-24 volt DC power supply.

The following is how a single walk step is done:

• 1a. When the electricity is turned on, around 1 amp of electrical current flows through the nitinol wire causing it to heat up.
  As explained above, that heating causes it to go back to its remembered shape, which is a compressed coil. Because of different positions at which the nitinol wire is connected to the respective legs, that compressing of the coil brings the back leg forward while the front leg stays put.
  Basically the legs come together.
• 1b. At the same time that the coil is pulling the legs together it is also compressing the V-shaped spring.
• 2. The electricity is then turned off. The nitinol wire cools and weakens. As it weakens, the V-shaped spring expands ot its normal position, pulling the legs back apart.

That ends a single walk step. The electricity is turned back on and the process repeats.

Inchworm walking one step.

Video - Nitinol Wire/Shape Memory Alloy Inchworm - How it Works

The following video shows my nitinol wire/shape memory alloy inchworm in action.

Video - How to Make Inchworm using Nitinol Wire/Shape Memory Alloy

This video goes step-by-step through the making of this nitinol wire inchworm.

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