Tail Assisted Pitch Control in a Lizard, Robot, and Dinosaur
Libby T*, Moore TY, Chang-Siu E, Li D, Cohen D, Jusufi A, Full RJ
University of California, Berkeley
Nature 481, 181–184 (12 January 2012) doi:10.1038/nature10710
Rapid limb or tail movements produce reaction torques that can induce body rotations. Such motions have been observed in several mammalian taxa, implicated in stabilizing walking and branch balancing, and have enabled aerial righting in lizards. By contrast, the effect of tail loss on lizard running performance is unclear. We contend that application of a control theoretic framework could advance our general understanding of inertial appendage use in locomotion.
To investigate the control of body attitude in the sagittal plane by a tail, we video recorded lizards (Agama agama) leaping toward a vertical surface by first vaulting onto an obstacle with variable traction to induce a large 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.
We found that lizards swing their tail upward or downward in a measured manner, as in the robot, to redirect angular momentum from their bodies to their tails, stabilizing body attitude. To compare diverse tails, we used a dynamic model to calculate tail-effectiveness, the amount of tailless body rotation a tail could stabilize per degree tail stroke.
We used the model to evaluate the hypothesis that small theropods used their tail as a dynamic stabilizer during rapid or irregular movements. We found that Velociraptor mongoliensis may have possessed a more effective tail than the Agamas. 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 highly maneuverable search-and-rescue robots.
Bibtex
@article{Libby2012,
author = {Libby, Thomas and Moore, Talia Yuki and Chang-Siu, Evan and Li, Deborah and Cohen, Daniel J and Jusufi, Ardian and Full, Robert J.},
journal = {Nature},
number = {7380},
pages = {181--184},
publisher = {Nature Publishing Group},
title = {{Tail-assisted pitch control in lizards, robots and dinosaurs}},
volume = {481},
year = {2012}
}
