here are some pictures of what you can do with memory alloy. I have used an alloy made of nickel and titanium called Nitinol.The wire is 0,40 mm diameter and can (after stretched) contract with a force of 4 kg´s. It can be heated by sending electricity through it. To make it contract it must be stretched first. if you use thick wire it can take some time to stretch it after heated and contracted. You can visit mondotronics robotstore about memory alloys at http://www.robotstore.com . They do even have motors, robotkits and other useful stuff.
