first of all, I posted this under a somewhat misleading title - sorry about that.
The material I am working with is not regular Nitinol, but something called "Nitinol Memory Wire". Nitinol shrinks (or expands? i get it confused) when heated and then expands (or the other way round) when it cools again.
Nitinol Memory Wire has two phases. At room temperature you can freely shape it to anything you want and when you heat it, it will go back to its original shape. When it cools, it stays in that shape. So for bidirectional movement you need a counteracting force. Memory Wire is the material used in the above video.
I bought mine from a NYC based company called images. They sell all kinds of really cool nitinol-like products (they also sell actuators very similar to what retrolefty describes). Find them at www.imagesco.com
thanks, retrolefty & cyberteque for your input.
I have also come to the conclusion that nitinol is not really practical. I was hoping to get a setup which could animate flexible displays. My first thought was that the main problem would be the temperature changes which need to be taken into account. However, as retrolefty says, there is also the additional obsticle of really high current requirements.
btw @ retrolefty. You mention, that it is slow. However, if you get your setup right, it can be extremely fast. Ever tossed some into boiling water? I did it and the shape change was so abrupt it ricocheted back and flew through the entire room...
The observation of one direction beeing strongr than the other is possibly due to the fact that I just heat it up using a bunzen burner. I believe what happens is that I overheat it and slightly damage the material. Another effect which we have to deal with is that sometimes its physically impossible for it to return to its original shape - however I think the temperature of the cable (as we have no regulation on that what so ever) may rise to temperatures high enough to set it into the new shape, which in turn again will reduce its strength, making the cable weaker and weaker with every trial.
does anyone know of a sensor which could measure the heat? which is fine with temperatures abruptly changing from room temperature, to potentially several hundred degrees celsius?
@ cybertque ... I was playing around with PWM for led's and was thinking about trying something along the line of what you suggested. I will see if I can get around to trying that one of these days.
I played around a bit with regular nitinol (the dynalloy stuff...). My main problem with it is the ridiculously small gouge on it, which makes it really hard to handle ... its like trying to build something out of hair... when you where working with nitinol, do you remember what gouges your nitinol had? how did you manage the filigranness of it all?
@royboy
Once my project is done and if its cool I'll do an instructables on it or something. As of now, all the info I have can be found on my blog (fkeel.blogspot.com) and www.imegasco.com also has some good documentation on it. I'm happy you are interested in it though, and if you have specific questions feel free to ask or send me a pm or something.