Robot mimics the powerful punch of the mantis shrimp
Research answers long-standing biological questions, paves the way for
small but mighty robots

Date:
August 25, 2021
Source:
Harvard John A. Paulson School of Engineering and Applied Sciences
Summary:
Mantis shrimp pack the strongest punch of any creature in the
animal kingdom. How mantis shrimp produce these deadly, ultra-fast
movements has long fascinated biologists. Now, an interdisciplinary
team of roboticists, engineers and biologists have modeled the
mechanics of the mantis shrimp's punch and built a robot that
mimics the movement. The research sheds light on the biology of
these pugnacious crustaceans and paves the way for small but mighty
robotic devices.



FULL STORY ========================================================================== Mantis shrimp pack the strongest punch of any creature in the animal
kingdom.

Their club-like appendages accelerate faster than a bullet out of a
gun and just one strike can knock the arm off a crab or break through
a snail shell.

These small but mighty crustaceans have been known to take on octopus
and win.


==========================================================================
How mantis shrimp produce these deadly, ultra-fast movements has long fascinated biologists. Recent advancements in high-speed imaging make
it possible to see and measure these strikes but some of the mechanics
have not been well understood.

Now, an interdisciplinary team of roboticists, engineers and biologists
have modeled the mechanics of the mantis shrimp's punch and built a
robot that mimics the movement. The research sheds light on the biology
of these pugnacious crustaceans and paves the way for small but mighty
robotic devices.

The research is published in the Proceedings of the National Academy
of Sciences.

"We are fascinated by so many remarkable behaviors we see in nature,
in particular when these behaviors meet or exceed what can be achieved
by human- made devices," said Robert Wood, the Harry Lewis and Marlyn
McGrath Professor of Engineering and Applied Sciences at the Harvard John
A. Paulson School of Engineering and Applied Sciences (SEAS) and senior
author of the paper. "The speed and force of mantis shrimp strikes,
for example, are a consequence of a complex underlying mechanism. By constructing a robotic model of a mantis shrimp striking appendage,
we are able to study these mechanisms in unprecedented detail."
Many small organisms -- including frogs, chameleons, even some kinds
of plants -- produce ultra-fast movements by storing elastic energy
and rapidly releasing it through a latching mechanism, like a mouse
trap. In mantis shrimp, two small structures embedded in the tendons of
the muscles called sclerites act as the appendage's latch. In a typical spring-loaded mechanism, once the physical latch is removed, the spring
would immediately release the stored energy.



==========================================================================
But when the sclerites unlatch in a mantis shrimp appendage, there is
a short but noticeable delay.

"When you look at the striking process on an ultra-high-speed camera,
there is a time delay between when the sclerites release and the appendage fires," said Nak-seung Hyun, a postdoctoral fellow at SEAS and co-first
author of the paper.

"It is as if a mouse triggered a mouse trap but instead of it snapping
right away, there was a noticeable delay before it snapped. There is
obviously another mechanism holding the appendage in place, but no one
has been able to analytically understand how the other mechanism works."
"We know that mantis shrimp don't have special muscles compared to other crustaceans, so the question is, if it's not their muscles creating the
fast movements, then there must be a mechanical mechanism that produces
the high accelerations," said Emma Steinhardt, a graduate student at
SEAS and first author of the paper.

Biologists have hypothesized that while the sclerites initiate
unlatching, the geometry of the appendage itself acts as a secondary
latch, controlling the movement of the arm while it continues to store
energy. But this theory had not been tested.

The research team tested this hypothesis first by studying the linkage mechanics of the system, then building a physical, robotic model. Once
they had the robot, the team was able to develop a mathematical model
of the movement.

The researchers mapped four distinct phases of the mantis strike,
starting with the latched sclerites and ending with the actual strike
of the appendage. They found that, indeed, after the sclerites unlatch, geometry of the mechanism takes over, holding the appendage in place
until it reaches an over-centering point and then the latch releases.



========================================================================== "This process controls the release of stored elastic energy and actually enhances the mechanical output of the system," said Steinhardt. "The
geometric latching process reveals how organisms generate extremely
high acceleration in these short duration movements, like punches."
The researchers mimicked this process in a 1.5-gram, shrimp-scale
robot. While the robot didn't reach the speed of a mantis shrimp
strike, its speed clocked in at 26 meters per second in air -- with an acceleration equivalent to a car reaching 58 mph in four milliseconds. The device is faster than any similar devices at the same scale to date.

"This study exemplifies how interdisciplinary collaborations can
yield discoveries for multiple fields," said co-author Sheila Patek,
Professor of Biology at Duke University. "The process of building a
physical model and developing the mathematical model led us to revisit
our understanding of mantis shrimp strike mechanics and, more broadly,
to discover how organisms and synthetic systems can use geometry to
control extreme energy flow during ultra- fast, repeated-use, movements."
This approach of combining physical and analytical models could help
biologists understand and roboticists mimic some of nature's other extraordinary feats, such as how trap jaw ants snap their jaws so quickly
or how frogs propel themselves so high.

This research was co-authored by Je-sung Koh, Gregory Freeburn,
Michelle H.

Rosen and Fatma Zeynep Temel. It was supported by the U. S. Army Research Laboratory and the U. S. Army Research Office under contract/grant
number W911NF1510358.

========================================================================== Story Source: Materials provided by Harvard_John_A._Paulson_School_of_Engineering_and_Applied
Sciences. Original written by Leah Burrows. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Emma Steinhardt, Nak-seung P. Hyun, Je-sung Koh, Gregory Freeburn,
Michelle H. Rosen, Fatma Zeynep Temel, S. N. Patek, Robert
J. Wood. A physical model of mantis shrimp for exploring the
dynamics of ultrafast systems. Proceedings of the National
Academy of Sciences, 2021; 118 (33): e2026833118 DOI:
10.1073/pnas.2026833118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210825153749.htm

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