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).