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Product Review

How Muscle Wire Works

Motorless Mechanical Motion

By Robert Cong & Mark Casilang

"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) that is 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 Muscle Wire is that they can lift many times their weight and are able to do 100 times more work per cycle than the 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 is ideal where mechanics require minimization, such as electronic textiles projects, robotics or nano-applications.

How Muscle Wire Works

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

Made up of equal parts nickel and titanium and 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 wire soft and flexible when cool, yet firm and stiff when heated.

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 the contraction of shape. The material has been deemed shape-memory because its crystal transformation is fully reversible. Once the temperature is lowered, it returns to, or remembers, its original shape. This cycle can be repeated millions of times.

Shape-memory effects
Two common shape-memory effects are one-way and two-way shape memory (above)

Nitinol Products

Nitinol Tension Springs There are also springs made up of the same composition and have the ability to be stretched and deformed, yet conform back to its original spiral shape once heated up. These springs are even strong enough to lift around 350 grams. Activate them electrically or with changes in temperature.

This is a demonstration of how applying electric current and quick cooling 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 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 show 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 such as robotics and making a robot butterfly flap its wings. Space Wings uses only five centimeters of wire and flaps up to 36 times per minute. It's perfect to annoy cats, amuses babies or office mates. 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 wires sizes to get you started. It's a quick and economical way to try a wide range of Muscle Wire sizes.

Nitinol tension  Spring, 3-642
Nitinol Tension Spring, 3-642

Muscle WiresÆ Project Book & Sample Kit, 3-141
Muscle Wires® Project Book & Sample Kit, 3-141

Solar Space Wings Kit, 3-619
Muscle Wire® Super Sample Kit, 3-136

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

If you have an electronics story or project you'd like to share, please email [email protected].