After some trial and error, I got the muscle wire to lift via a resistive heater!
I’m working with several ideas right now in terms of integrating the heating element into the muscle wires, but the simplest and most immediate test I could carry out was to simply coil the Litz wire around the prepared muscle wire.
Here is a demonstration video:
And one more video, where you can see the voltage/amperage I put through the Litz wire:
So it’s working! A couple of notes:
You might say that it lifts the weight only a very short distance, and you would be correct. I think this can be improved outright, but consider a few things:
- You can integrate this actuator into a larger construction that takes advantage of this. Think of your bicep as you arm flexes in a curl. I would be willing to bet that the bicep length (and by analogy, our muscle wire length) doesn’t change much.
- It lifts a very considerable weight for its size: 80 grams.
Better yet, as I changed the voltage of the circuit in the variable power supply, the muscle wire seemed to happily stay tense at a particular location. This is a rough guess (and a hope), but it seems like for a particular temperature maintained in the resistive heater, a particular position is maintained by the muscle wire. This remains to be really proven and tested, but if true that would be very promising for positional robotic control via the muscle wires.
Another experiment I’m working on–and I’m not sure this will work in its current form–is to form a weave, where a series of parallel muscle wires (the warp, for the fabric and textile savvy) is woven together by the resistive heating element (the weft).
The problem I’m having with this experiment is how laborious it is to weave by hand (certainly that can be improved) and how much wire is required for the weaving. This small, approximately 3″ section seems like it will take about 8′ of the thin Litz wire to weave completely. This is going to require a lot of juice to heat up, and I’m not sure it’s necessary. I will keep the idea in mind — there is an elegance to it, and I always enjoy when an unexpected technique (weaving, of all things!) shows up in robotics.