Sandfish robotics: the story continues

Almost exactly a year ago, I wrote
about the remarkable abilities of Scincus scincus, otherwise known as the sandfish, sand skink or sand swimmer. This little Saharan
lizard can swim through sand like a fish through water, and the way in which it
does it remained a mystery until researchers at Georgia Tech set out to tackle
the problem. It turns out that the sandfish undulates its body in a sinusoidal
wave motion, tucking in its limbs and modifying the frequency of undulation in
order to control speed and manage its movement in sands of greater or lesser
compaction.

At the “CRAB lab” at Georgia Tech,  Daniel Goldman and
Ryan Maladen’s team have continued their research, moving further into
mathematical modelling, iterated and integrated with lab experiments; they have
also worked in collaboration with Paul
Umbanowar at Northwestern University in Illinois who is one of the gurus of
the bizarre world of granular materials, and who kindly helped with several
illustrations in my book. The results not only shed light on one of nature’s
wonders, but generate important advances in robotics. Recently, the team has
reported on a newly developed prototype robot, constructed from easily available
components, that directly simulates the skills of Scincus scincus, and
could lead, for example, to vital developments in post-earthquake search and
rescue efforts. The complete paper by the group is available
online (the illustrations at the head of this post are taken from there),
and the Canadian Discovery Channel has a great video
report (although I do rather resent the presenters referring to sand as
“dirt”). The work was described briefly in the New
Scientist, but since the full version, by James Urquart, is
only available by subscription, I’ll take the liberty of reproducing it
here:

Lizard-like robot can ‘swim’ through sand

TO ADD to the robots that can crawl
over land, fly
through air and swim
underwater comes one that can swim through sand. Such robots could help find
people trapped in the loose debris resulting from an earthquake.
Navigating through sand is harder than moving through water or air because
sand can behave as both a solid and a fluid. We have no equations to describe
how such substances flow, let alone to predict how an object can “swim”
efficiently through them.
But the sandfish lizard, Scincus scincus, can travel through sand
effortlessly, so Daniel Goldman and
Ryan Maladen’s team at the Georgia Institute of Technology in Atlanta decided to
find out how they do it. They found that once the sandfish is submerged, it
tucks its limbs into its sides and propels itself forward by wiggling from side
to side.
Working with Paul
Umbanhowar of Northwestern University in Evanston, Illinois, the team
plugged their results into a computer model, which they used to show that a
snake-like robot with just seven body segments could travel through a granular
medium like sand.
Encouraged, the team built a 35-centimetre-long version of the robot, made
from seven aluminium segments linked by six motors, all clothed in spandex to
prevent the motors from becoming jammed.
The team then tested their robot by burying it in a container filled with
plastic spheres 6 millimetres across. When the robot undulated its body at a
frequency similar to the lizard, they found it could move forward at speeds of
up to 0.3 body lengths per wave cycle - just below the 0.4 body lengths per
cycle that a submerged lizard can achieve.
The robot could eventually match the lizard for speed, says Goldman, if more
jointed segments are added to make its movements smoother.
Howie Choset, a roboticist at
Carnegie Mellon University in Pittsburgh, Pennsylvania, thinks that the physics
and the biology-inspired approaches to robot movement will one day meet and “at
the intersection will be a deeper understanding of how biology works and how to
make robots better”.

Amongst the many things that I find fascinating about this work is the fact
that it is a carefully executed project that uses mathematical modelling in
intimate combination with laboratory experiment – the “fieldwork” informs the
maths which, in turn, informs the next phase of laboratory investigation. In a
world where, in my view, we place undue faith in the validity of mathematical
models alone, particularly when evaluating complex natural processes, this kind
of “continuous feedback” approach is to be admired and emulated.

[ The Georgia
Tech press release page has links to further sources] SIGNATURE

Comments

Richard Bready (2010-07-23):

Interesting too that traditional design so closely approximated technical findings, as in this example of a fond early memory:
http://www.letterbox.co.uk/20670-04382-LBPOCKETMONEYTOYS3-2/pocket-money-toys/up-to-3-pounds/jointed-snake
Greetings, Michael. I have been keeping up with your postings, and greatly enjoyed the set on writing a successful work of popular science.
Best wishes,
Richard

Sandglass (2010-07-23):

Greetings Richard - and thanks for the analogy. I hadn’t even thought of the design correlation with those toy snakes - but I remember them well myself!

F (2010-07-23):

I thought you had another entry related to this aside from the one at your link:
http://throughthesandglass.typepad.com/through_the_sandglass/2009/06/of-reptiles-and-robots---locomotion-in-sand.html
Apparently, my memory is still intact. :)
The tight coupling between modeling and experimentation is a really fantastic situation when it comes along. I’m sure it would be difficult to accomplish in some studies, but certainly more researchers could bring these together more often. Perhaps I have always been naive, but I have always thought that this was the core of the scientific method.

pcb prototype (2011-12-07):

Hmmm! That’s a creative ideas to use robot for right purpose.

Originally published at: https://throughthesandglass.typepad.com/through_the_sandglass/2010/07/sandfish-robotics-the-story-continues.html