
Artificial “muscles” achieve powerful pulling force - xVedun
https://news.mit.edu/2019/artificial-fiber-muscles-0711
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GlenTheMachine
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.

~~~
ls612
What kind of efficiency do human muscles get?

~~~
GlenTheMachine
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/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144848/)

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kscz
This looks like a re-discovery of a 2014 University of Texas at Dallas paper -
[https://science.sciencemag.org/content/343/6173/868](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...](https://hackaday.com/2014/02/21/researchers-create-synthetic-
muscle-100-times-stronger-than-the-real-thing/)

Here is another, earlier iteration also from MIT: [https://gizmodo.com/mits-
new-plastic-muscles-could-bring-us-...](https://gizmodo.com/mits-new-plastic-
muscles-could-bring-us-one-step-closer-1789302210)

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

~~~
anonoholic
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.

~~~
stellar678
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.

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

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cr0sh
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.

~~~
clairity
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).

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gene-h
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.

~~~
m463
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?

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

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dmitrygr
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...](https://www.dfrobot.com/product-761.html?gclid=Cj0KCQjwyLDpBRCxARIsAEENsrL_Oi_rQoj3awOnWr-
kaEszjOmsOP-jefcs7PU4BoIaoyOZ9sQJBZUaAkssEALw_wcB)

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peter_d_sherman
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...

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unnouinceput
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.

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cwkoss
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.

