Muscle Wire: Motor-less Mechanical Motion

How muscle wire works

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By 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.

Nitinol was used to create the first solid state heat engine:
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Nitinol Tension Springs are 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.


Although thin and lightweight, one of the most amazing things about Muscle Wire is that it can lift many times its weight and is 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 It Works

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

The wire is made up of equal parts nickel and titanium and developed by the United States Naval Ordnance Lab, (where the name Nitinol comes from). Since 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 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 effectsTwo common shape-memory effects are one-way and two-way shape memory (above)

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. 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.

Project

If Muscle Wire has piqued your curiosity and you're looking for a project so you can try it out, we found this quick, easy and impressive project from highlowtech.org. The project combines craft skills with electronics. It will introduce you to Muscle Wire and hopefully inspire you to create more motor-less mechanical projects.



Assembly Time: 2 hours
Skill Level: Beginner

Tools Required:
Scissors
Wire strippers or pliers
Soldering iron
Solder
Sewing Needle
Crimper

Materials Required:
1 sheet 9" x 9" origami paper square or other paper
40cm of Flexinol muscle wire
2 crimp beads
9V battery
9V battery snap
6" of copper foil tape
Sewing thread
Invisible office tape
Hook up wire

Materials The Electronic Origami Flapping Crane is a great beginner project for those wanting to see muscle wire in action and practice folding origami as well. The instructions are pretty straightforward, they just require a bit of an artistic touch to them.

First, make sure you have all of your materials gathered. If you do not have origami paper, you can use wrapping paper or other paper and cut to the 9" x 9" dimensions. Print out the wing flaps attached to the project to use for the construction of the muscle wire circuit. Once you have everything, it's time to start!

The first step is to fold the origami crane. If you're not practiced in origami, it helps to try the fold a few times until you're comfortable. The first one I made was not the most pretty, but after a few more tries, it looked great. Note that you will need to unfold a few steps in order to attach the muscle wire into the wings, so it helps to know the folding steps.

After cutting out the wing pattern, put the copper tape onto the area specified at the bottom of the wings. Cut the muscle wire into two pieces of about 20 centimeters, or a little less than 8 inches. If the wire pieces are too long the paper will not fold up nicely or fit on the pattern when the circuit is powered.

Sew the Muscle Wire Crimp the ends of the muscle wire to solder them to copper tape (the muscle wire itself is not solderable). Use invisible office tape to attach the top of the muscle wire to the wing pattern and make sure the crimp beads line up nicely to where you will solder them to the copper tape. Before you solder them together, make sure you tin the wire and add some solder on the copper tape. I will make it a lot easier to join them together. The solder space is a bit small, so try to make it fit as close to the pattern on the wings as much as possible.

After you solder, sew the muscle wire into place. This is to allow the muscle wire to move enough to cause the fold while keeping in intact. Make certain you know where the needle is going as you follow the pattern on the wing. Verify that the muscle wire is sewn tightly or it will not fold as much as it should.

Cut the wing flap patterns out of the rectangle and be careful to not cut the stitches. Solder each end of the battery snap onto each wing and again, be mindful of the space left on the copper tape. Solder two, four inch pieces of wire to two different pieces of copper tape. This is to be used as the switch to activate the flapping of the crane. Solder the other end of the wire to one of each of the wings. This finishes the circuit. Now it's time to test.

Finishes the Circuit Finishes the Circuit

When testing the circuit, make sure you have a fully charged 9V battery or else you may not have enough to power the muscle wire. As you are testing the muscle wire for contractions, try to limit it to about 5 seconds or until it stops curling. (If you hold it any longer, the muscle wire might burn out and stop contracting. It helps to remove the 9V battery each time after preheating.) The muscle wire can become a bit wavy, so pull on the copper tape to straighten it out and put it back down.

Now unfold the wings of the crane to insert the wing flaps of the circuit. Make it fit nicely and tape it into place. Then refold the crane and attach the switch side of the circuit to the inside of tail. Make sure they touch when you close the tail and open when you let go. Your crane is complete!

Finishes the Circuit Finishes the Circuit

You can 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 projects. What are your thoughts about muscle wire and which types of projects would you use it? Let us know at MyStory@Jameco.com.


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.