Flexinol + Arduino

Lately I have been experimenting with muscle wire with Arduino.

For those who haven’t heard of it, muscle wire is a type of shape memory wire made from the metal alloy nitinol. There are a few different types/brands available online, but the basic idea is when supplied with a current, the muscle wire is able to change form. I personal was interested in its potential for creating organic kinetic sculptural forms that have a feeling of “life” when controlled through Arduino.

The biggest problem I have encountered is understanding the limitations and properties of  muscle wire. Before you buy, make sure you understand which type you are getting. I have been using the brand Flexinol (which can be found on robotshop.com), which comes pre-annealed and is able to both contract (when supplied with a current) and relax (when their is no current). A lot of muscle wire does not come pre-annealed, and has to be set to contract to a certain shape using jigs, and will not relax once the current is gone. If you want the “contract and relax” motion, make sure to purchase Flexinol specifically!

Here is a visual of the type of motion you can achieve with Flexinol (from the YouTube channel of Jie Qi, who has many great examples of projects you can do with Flexion):

I found that once you have a form you would like to work with, a big challenge is creating the proper tension to get noticeable movement. You can see in this photo how closely I have sewn the wire into my forms:


(As a side note, I made these forms from coffee filters)

Here is a video of the first form I was able to make move:

In this video, I did not have the muscle wire hooked up with Arduino yet. I was simply attaching alligator clips to either end of the wire and to a 9v battery. Be careful when testing: only connect the wire to your battery for a few seconds at a time (I would say 5 seconds at the absolute maximum). If you connect it too long, you will damage your muscle wire. I also found that if you held the current to long, the wire would get so hot that it would start to burn the paper and thread that it was sewn into, and I would have to re-sew the form.  If you want to connect more than one form at once, I found that parallel circuits worked better than series circuits.

Once you have the forms you want, you can try controlling it with Arduino, allowing for the movement of your wire to pulse to a specific rhythm or be controlled by various input from sensors. The two important things: use pulse with modulation, still only allowing a few seconds of current through the wire at one time, and use a transistor.

Here is one form controlled by Arduino:

Here are pictures of the circuitry:


Unfortunately, I was not able at this point to make more than one form move at one time. I need to experiment with other transistors or another method of getting more voltage to the forms, because the setup I have now is not quite doing it.

Obviously I am still a beginner (not just to muscle wire, but to electronics in general), so I would love any suggestions or feedback! I am determined to get this project working, so I will make an update whenever that happens.