There are a lot of these. You see a couple of papers on different types of linear actuator materials every year at ICRA, just to pick a robotics conference at random.

To date they’ve all had the same problem, which is that their energy efficiency is usually less than 5%, and often less than 1%. Compare this to a decent brushless DC motor, which will have an energy efficiency of 85%. Often their bandwidth is very low as well, like less than half a hertz. So they work okay if all you’re interested in is pull force and compactness, but they turn out to be really unsuitable for most robotic applications.

Note that this particular article gives neither an energy efficiency nor a bandwidth figure.

This looks like a re-discovery of a 2014 University of Texas at Dallas paper - https://science.sciencemag.org/content/343/6173/868 ?

I am missing something? You can see the hackaday article about this here: https://hackaday.com/2014/02/21/researchers-create-synthetic...

Here is another, earlier iteration also from MIT: https://gizmodo.com/mits-new-plastic-muscles-could-bring-us-...

What I've noticed about all of these thermally based systems - this one, the earlier (and DIY capable) one made of fishing line, and heck, even shape memory alloys - they all seem to have relatively slow cycling rates for either the entire cycle, or one half of it.

It might take several seconds to contract or relax; or it's fast contracting, but slow to relax. Much of it I think has to do with the thermal mass of the fibers/material, and how it takes longer to relax because the heat is being dissipated slower. Perhaps this could be mitigated using an active cooling system, but that also adds more complexity and takes up more space.

Hopefully these issues can be overcome in time, as such muscles and fibers are simpler, relatively cheaper, and more compact than many other actuators.

And unfortunately, their operation is thermally based. This means they are inherently inefficient and as you scale up fine control becomes more difficult due to increased thermal mass.

This looks like the same thing we've had for almost a decade, and is so easily and widely accessible that it is used in cheap super-miniature hobby servos (usually under the MuscleWire name)

Eg: https://www.dfrobot.com/product-761.html?gclid=Cj0KCQjwyLDpB...

Theoretical musing to future self: Is magnetism in some way analogous to this phenomena? In other words, might there be (that we can't see) two (or more) "strings"/"streams" of twisted space (for lack of a better term) that comprise a magnetic field, and if so, does this idea of two wrapped strings with one becoming a region of more tension have any application to the understanding of the physical phenomena of Magnetism?

Perhaps not, perhaps there is no relation.

But, it might be an interesting subject of future investigation...

So to make an easy commercial usefulness, one needs to make them from cheap metal alloys, apply enough electrical power (V vs A) to make them go hotter then any environmental changes and voila!, you'll have a better then current hydraulic solutions. I hope this takes off since I never liked hydraulic ones due to danger of spilling fluids and not so easy maintenance requirements.

These will be really cool for use in autonomous solar-powered systems. Can use sun's heat to make these do 1 work cycle per day, maybe a few if it's windy.