Artificial “muscles” achieve powerful pulling force | Hacker News Reader

Artificial “muscles” achieve powerful pulling force

news.mit.edu

107 pointsxVedun24 comments

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.

yup, as part of a research project way back in college, we even made crude artificial muscles out of mesh wire sheathing[0] and custom-formed long, thin rubber "balloons" actuated using compressed air. the efficiency was horrible, but we were primarily interested in the gait dynamics of our robot, not efficiency. it was a fast little bugger though!

[0] something like this: https://www.donathenrc.com/mesh-sheathing

What kind of efficiency do human muscles get?

Depends on the human and, I suspect, the task. Also, it's hard to compare since muscles are not powered electrically, they are powered chemically. But the estimates I'm familiar with say somewhere north of 50%. Wikipedia says 25%.

Human muscle also has a bandwidth in the ~2-5 Hz range.

See:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144848/

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-...

This appears to be two materials bonded together who expand at different temperatures causing a coiling effect vs a single material changing properties.

The 2014 University of Texas example is also two materials - "fishing line and sewing thread", so the unique is this new research is something else.

The University of Texas approach was fishing line OR sewing thread. (Just a twisted single-material polymer line.)

At the start of this MIT article, I was wondering if it was just a re-hash of the fishing-line 'muscle' discovery as well.

But it's clear that the MIT muscle coils up because of the difference in thermal expansion between two bonded materials, while the Texas one seems to be more about a coiling pattern that multiplies the effect of a thermal expansion or contraction of a single material.

Hmm, yes. Re-reading the synopsis, I can see I was mislead by the heading.

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.

must these relax only by dissipating heat, or can an applied force stretch them out again quicker?

that would make it like real muscular systems, which must work in systems of opposition since actuation is one-way only (relaxation requires an opposing muscle, or some other force like gravity, to stretch it back out).

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.

I'm sure there are modest situations where something that can lift 650 times it's weight is more valuable than the thermal limitations. Or maybe super-cold environments?

Indeed - the cooling requirements of maglev don't seem to have prohibited it from existing

Pneumatic air muscles are in the same strength to weight range - for example, the Shadow 30mm version is ~470 minimum. They can also be simply manufactured today, cycle very quickly, and are easy to control.

Pneumatic actuation is also very powerful, and has been used for a while in rockets and are relatively reliable, even in various extreme conditions.

Not to mention it would be susceptible to environmental changes. A prosthetic device would spaz out going from an air conditioned room out into a hot day, for example.

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.

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