Science Codex, June 30, 2012
Lizards, just like cats, have a knack for turning right side up
and landing on their feet when they fall. But how do they do it? Unlike cats,
which twist and bend their torsos to turn upright, lizards swing their large
tails one way to rotate their body the other, according to a recent study that
will be presented at the Society for Experimental Biology meeting on 29th June
in Salzburg, Austria. A lizard-inspired robot, called 'RightingBot', replicates
the feat.
This work, carried out by Ardian Jusufi, Robert Full and
colleagues at the University of California, Berkeley, explains how large-tailed
animals can turn themselves right side up while falling through the air. It
could also help engineers to design air- or land-based robots with better
stability.
"It is not immediately obvious which mechanism an animal
will use to accomplish aerial righting and recover from falling in an
upside-down posture. Depending on body size, morphology and mass distribution
there are multiple strategies for animals to execute this behavior," said
Ardian Jusufi, lead author of the study.
Lizards in their natural environment encounter various
situations where they could fall. For instance, they could fall while fighting
over territory, seeking food, or even mating. To avoid injuries, they must have
a way to turn themselves during a fall to land safely on their feet.
For over a century, people have been studying if and how cats
and other mammals right themselves when they fall. Other animals like lizards,
which have different body plans and probably use different strategies, have
been largely unexplored.
The researchers used high-speed videography to dissect the
motion of two common lizards – the flat-tailed house gecko and green anole – as
they fall, starting upside down. Watching as the lizards righted themselves in
mid-air before alighting on extended legs, the researchers discovered that both
lizards swing their tails in one direction, causing their bodies to turn in the
other.
The team also compared the righting movement of the two lizards,
which have similar body sizes but different tail lengths and inertial
properties. The gecko, with its shorter tail, has to swing its tail further to
the side to right itself, making a larger angle relative to its body. By
contrast, relatively smaller movements of the anole tail, which is twice as
long, are enough to reorient its body.
"A comparative approach provides useful insights in the
study of aerial righting responses and could be beneficial to the design of
robots that navigate complex environments," said Ardian Jusufi.
For the study, Jusufi and his colleagues developed a
three-dimensional mathematical model to test their understanding of the
lizards' righting movement.
To further test the mathematical model's predictions the team
then built a simple robot. 'RightingBot' consists of just two parts: a body
joined to a tail. Despite its simple design, RightingBot rights itself in
mid-air with a swing of its tail just like the lizards that inspired it,
showing how useful a tail can be for that purpose.
Posts
