Tag Archives: nitinol

Nitinol and Origami

Jie Qi at the High-Low Tech lab at MIT’s Media Lab, posted a HOWTO on nitinol and origami. In the HOWTO she mentions that you can’t solder the nitinol directly, and so you’ll have to have create a soldering pad for it. (She used a craft crimp bead.) Another tip she gives is the need to preheat the nitinol by running a 9 volt charge through it for five seconds. When the wire relaxes, it will become be longer than it was originally, and so you’ll need to retention the wire. Last of all, she warns against keeping the wire energized too long, lest your “burn out” the nitinol. In another project, Qi mentions she used 0.006 inch flexinol for the origami, but used 0.01 inch for the more rapid vine/snake project.

I have had a fairly long interest in synthetic plants and was thinking if nitinol could be used to in a heliostat or some sort of dinural deployable structure, but I never knew the reaction time of nitinol. Seeing it used understanding what voltages are required was helpful. (Poking around just now, I also ended up finding a handy nitinol wire width-voltage-time-force table.) While I doubt that I will ever actually build whatever vague idea idea I have for synthetic plant, I’ve come to conclusion that nitinol perhaps isn’t the best choice of materials if you want it to hold position for any considerable length of time (or at least not without some sort of mechanical latching).

Previously.

Autorigami

MIT has published a paper entitled Programmable Matter by Folding (full article) that describes paper that can fold itself into a variety of shapes. The paper is covered by is divided into triangular sections that are joined by a network of thin nitinol actuators that contract under voltage. At the center of each section is a magnet that is used to retain the paper’s shape.

While I’m sure MIT had bigger plans for this tech (Well if it was the Media Lab, perhaps not.), I immediately thought that this was the perfect thing for synthetic plants. I’ve been thinking about how nitinol wires, or at least something like them, could deform a paper but thought that the being able to compresses only about 4% was a problem. When I first saw this video, I thought they were using something else besides nitinol, but they’re not. The trick they they used to get 180 degree bending is folding and annealing the 100μm foil so that the nitinol will remember the folded shape. Once it cooled, the foil is manually flattened, and then reheating the foil with electrical current will cause it return to the folded shape.

Guess it’s time to get some nitinol sheets.

Synthetic Plants

I’ve been thinking more about solar plants recently. I like how these projects combine both form and function. I’ve been thinking about what I’d like in one of these, and how one would be made. First, the power being collected by the solar cells needs to go somewhere. It could just feed back into the device, which is exactly what happens with plants, but part of me likes the idea of having the sculpture(?) have a practical use as well. If I want practicality, then USB ports for charging an iPod or a phone that I don’t have would be nice. At least one port, but four would be more than plenty. I’m leaning towards the solar cells charging some li-ion or nicad battery coupled with something like a Minty Boost.

The second feature I’ve been hammering the previous electronic plants I’ve looked at is the movement, specifically heliotropism (i.e. sun tracking). It’s an interesting feature, and it would increase the power to the photovoltaics. I don’t like the idea of the hearing servos move, so that means nitinol wires, which also have the quality of more closely resembling natural motion by simply expanding and contracting. The next question then becomes, what form would the motion would take?

If rigid photovoltaics are used, then panel could be mounted to a universal joint with the two outside corners independently controlled by nitinol. The other idea is to use flexible photovoltaics and hopefully no hinges and joints.

Another interesting idea is to think about deployable structures, which would seem to imply the use of flexible photovoltaics. It’s not exactly the heliotropism I was thinking of, but it would be cool if the “leaves” opened up in the day, tracked the light, and then closed at night.

Doing all of this nitinol might be kind of difficult. Heating nitinol causes it to contract in the 3 – 5 % range, doesn’t seem like much. This also means that for a deployable structure, it needs to collapse when the wires are extended,

Will I actually build this? Probably not, but it is something I’ve been thinking about. Perhaps it would give me an excuse to visit Noisebridge.