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Re: Tail assisted pitch control in lizards, robots and dinosaurs

From: Ben Creisler
Here's the full ref and a link to a Nature news article with a video:
 Thomas Libby, Talia Y. Moore, Evan Chang-Siu, Deborah Li, Daniel J. Cohen, 
Ardian Jusufi & Robert J. Full (2012)
Tail-assisted pitch control in lizards, robots and dinosaurs.
Nature (advance online publication)
In 1969, a palaeontologist proposed that theropod dinosaurs used their tails as 
dynamic stabilizers during rapid or irregular movements, contributing to their 
depiction as active and agile predators. Since then the inertia of swinging 
appendages has been implicated in stabilizing human walking, aiding acrobatic 
manoeuvres by primates and rodents, and enabling cats to balance on branches. 
Recent studies on geckos suggest that active tail stabilization occurs during 
climbing, righting and gliding. By contrast, studies on the effect of lizard 
tail loss show evidence of a decrease, an increase or no change in performance. 
Application of a control-theoretic framework could advance our general 
understanding of inertial appendage use in locomotion. Here we report that 
lizards control the swing of their tails in a measured manner to redirect 
angular momentum from their bodies to their tails, stabilizing body attitude in 
the sagittal plane. We video-recorded
 Red-Headed Agama lizards (Agama agama) leaping towards a vertical surface by 
first vaulting onto an obstacle with variable traction to induce a range of 
perturbations in body angular momentum. To examine a known controlled tail 
response, we built a lizard-sized robot with an active tail that used sensory 
feedback to stabilize pitch as it drove off a ramp. Our dynamics model revealed 
that a body swinging its tail experienced less rotation than a body with a 
rigid tail, a passively compliant tail or no tail. To compare a range of tails, 
we calculated tail effectiveness as the amount of tailless body rotation a tail 
could stabilize. A model Velociraptor mongoliensis supported the initial tail 
stabilization hypothesis1, showing as it did a greater tail effectiveness than 
the Agama lizards. Leaping lizards show that inertial control of body attitude 
can advance our understanding of appendage evolution and provide biological 
inspiration for the next
 generation of manoeuvrable search-and-rescue robots.
News Article with video: