How Muscle Wire Works Motorless Mechanical Motion

"Muscle Wire" is the perfect name for this product because it can be described exactly as it sounds: It is a unique type of wire that acts like the muscles in our bodies. Muscle Wire is an extremely thin wire made from Nitinol (a nickel-titanium alloy) known for its ability to contract when an electric current is applied.

From a historical perspective, Nitinol was used to create the first solid-state heat engine. Although thin and lightweight, one of the most amazing things about Nitinol shape memory wires is that they can lift many times their weight and are able to do 100 times more work per cycle than human muscle. This material is easy to use, small in size, operates silently, has a high strength-to-weight ratio, and is easily activated using AC or DC power. This technology behind Nitinol wire is ideal where mechanics require minimization, such as electronic textile projects, robotics, or nano-applications.

How Muscle Wire Works

You can run current through or place these wires in hot water, and they can contract by 5% and then expand to their full length again once cooled down or when disconnected from the power source.

This type of wire is made up of equal parts nickel and titanium and was developed by the United States Naval Ordnance Lab (where the name Nitinol comes from). Because it is 50% titanium, this wire is much stronger than your average strand of wire. The reason Nitinol is able to expand and contract is because of its combination of crystal structures from the nickel and titanium metals. They react differently in high and low temperatures, making the Nitinol wire soft and flexible when cool yet firm and stiff when heated. This explains its unique mechanical motion.

The explanation for these structural changes lies at the atomic level. The shape changes are the result of the rearrangement of the crystal structures in the solid. When at room temperature, Nitinol can be bent into various shapes. Apply heat or electrical current and the atoms to arrange themselves into the most compact and tight-fitted pattern possible, resulting in shape contraction. The material has been deemed shape-memory because its crystal transformation is fully reversible. Once the temperature is lowered, the Nitinol shape memory wire returns to, or remembers its original shape. This cycle can be repeated millions of times.

Common shape memory effects

Two common shape-memory effects are one-way and two-way shape memory

Nitinol Products

Nitinol Tension Springs: Like Nitinol wire, there are also springs made of the same composition. They can be stretched and deformed, yet once heated, they conform back to their original spiral shape. These springs are even strong enough to lift around 350 grams. You can activate them electrically or with changes in temperature.

This is a demonstration of how applying electric current and quick cooling of a Nitinol spring can be used to lift and lower a large amount of weight. Used similarly in construction or transport, it can do more work using less energy.

Muscle Wire Applications

Nitinol wire has been used in everything from space missions, textile electronics (powered by the Lilypad), arterial stints, robotics, orthodontic braces, eyeglasses, and even magic tricks!

Muscle Wire can be used in a variety of fields, but the most substantial field will have to be the medical field in the case of surgical procedures as well as artificial limbs and hearts. This video shows a medical application of Nitinol.

Although these shape-memory alloys can be used in serious circumstances, they can still be used in a fun and educational setting thanks to their motorless mechanical motion, such as robotics and making a robot butterfly flap its wings. Space Wings uses only five centimeters of Nitinol wire and flaps up to 36 times per minute. It's perfect for annoying cats, amusing babies, or engaging office mates in a fun way. It doesn't really fly, but you'll wish it did!

Learn all kinds of new projects and try out Nitinol with the Muscle Wire Project Book and Sample Kit. The package includes a book full of project ideas and a selection of Nitinol shape memory wire sizes to get you started. It's a quick and economical way to try a wide range of Muscle Wire sizes.

Nitinol Tension Spring

Robert is a graduate of Cal Poly, San Luis Obispo, in Electrical Engineering. He is originally from Lincoln Heights in Los Angeles, CA. His interests include sports, movies, music, and playing with cool, new gadgets.

Mark graduated from Cal Poly, San Luis Obispo, in Electrical Engineering. He is originally from sunny San Diego, CA. His interests include traveling, movies, games, sports, music, playing tennis, and going to the beach.

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