Science fiction often envisions worlds populated by humanoid robots. In reality, insects, reptiles and nonhuman animals often serve as a more practical template for automatons. The more legs a robot has, the more easily it can navigate tough terrain. Likewise, claws are less challenging to emulate than primate-esque hands, and, as a team of researchers reported recently, tails are an incredibly versatile stabilizing mechanism.

The back end of snakes, ants or even grasshoppers has served as such an inspiration to some roboticists. Now Robert J. Full, a biologist at the Univer­sity of California, Berkeley, and his colleagues have turned to the red-headed African Agama lizard. The researchers’ work, published in the January 12 issue of Nature, describes how a careful study of the Agama’s approach to leaping on slippery surfaces led to improvements in robotic design.

High-speed videography and motion capture revealed how the Agama raises its tail to counteract a lack of footing on slippery surfaces when vaulting from a flat, rectangular block to a vertical sur­face. When the block was covered with sandpaper, the lizard required less stabilization and its tail remained in a down position during a leap.

Full and his team applied the lizard’s tail-raising schemes to a small, robotic four-wheeled vehicle dubbed Tailbot. After attaching a stabilizing tail to the rear of the vehicle and sending it off a ramp, the researchers noted that Tail­bot sank nose down with its tail in the down position. When the tail was raised like the Agama’s, based on the Tailbot’s attitude coming off the ramp, the robot was able to land on its wheels in a more balanced position. Full and his students are now investigating the role of the tail in controlling roll—and pitch and yaw—while running.

These are just the latest developments in Full’s full-on flirtations with lizard-inspired robots. Stickybot, a mechanical collaboration with Stanford University in 2006 that could walk up smooth surfaces such as windows using an adhesive, was modeled after microscopic hairs found on the feet of geckos.

Other examples of so-called bio­mimetic machines include Boston Dynamics’s Legged Squad Support System (LS3), which resembles a headless pack mule, and a wormlike robot under development at Harvard University.

By focusing on these nonhuman robot models, investigators can improve robotic design piece by piece, examining specific problems and learning from the ways in which animals solve them.

This article was published in print as "It's All in the Tail."