Credit: Nature 2012

From Jurassic Park’s Velociraptor to geckos to cats, tails are thought to provide stabilization that contributes to these organisms’ agility. In a recent report in Nature, Robert Full’s lab in the Department of Integrative Biology at UC Berkeley, in collaboration with Masayoshi Tomizuka and the Mechanical Systems Control Lab in the Department of Mechanical Engineering, have shown that lizards use their tails for body stabilization by transferring angular momentum from their bodies to their tails. Using high-speed video, researchers recorded the body and tail positions of Red-Headed Agama lizards (Agama agama) as they leaped toward a vertical surface. By varying the traction of the vault, the researchers introduced different perturbations in body angular momentum, and evaluated the effect of tail stabilization by mathematical models, and by building an Agama-sized robot designed to use feedback from the tail to control and stabilize body angle. The angle of tail swing was proportional to the change in body angle, and lizards could swing their tails upward or downward to compensate for downward or upward perturbations, respectively. The researchers found that by actively controlling their tails, Agama lizards are much less sensitive to perturbation than tailless, rigid-tailed, or compliant-tailed models. They calculated that Agama lizards could completely stabilize a perturbation that would rotate a tailless lizard by almost 80 degrees and that Velociraptor mongoliensis could theoretically completely stabilize a 110-degree perturbation, supporting an earlier proposal of tail stabilization in dinosaurs. “The next big steps,” said first author Tom Libby, “will come in understanding the control of multi-axis rotations, and how animals coordinate tail motions with limb motions during fast running.” Already, by furthering our understanding of how appendages confer inertial control of movement, these findings have generated excitement because of their implications for improved tail design in robots and, ultimately, the design of exceptionally agile and maneuverable robots for use in search-and-rescue and other applications.