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Disappearing by Rapid Inversion


IGERT Trainee Jean-Michel Mongeau, Principal Investigator (PI) Robert Full, Co-PI Ron Fearing and our team of biologists and engineers from the University of California at Berkeley discovered a new behavior in animals and translated this capability to a search-and-rescue robot prototype. Support by a National Science Foundation-sponsored Integrative Graduate Education and Research Traineeship (IGERT) in Bio- and Bio-inspired Motion Systems Operating in Complex Environments provided the unique interdisciplinary research opportunity in UC Berkeley’s Center for interdisciplinary Biological-inspiration in Education and Research (CiBER) where it became possible.

Serendipitously, our team found that rapid running insects and geckos seemingly disappear as they approach a ledge by using a rapid inversion behavior to swing underneath like a pendulum (Fig. 1). Our IGERT team’s discovery was published in PLoS ONE, presented at the Society of Integrative and Comparative Biology Meeting and featured in the NY Times and Science NOW. The discovery highlights the IGERT’s interdisciplinary nature benefiting from a collaboration among biologists and engineers in five different departments. We all have had the experience of chasing tiny animal pests with the intention of their demise only to find that they have seemingly disappeared. Our IGERT team discovered a new behavior revealing the stealthy nature of small animals. Our team found that cockroaches and geckos can disappear from predators by running rapidly toward a ledge, diving off, attaching their feet by claws like a grappling hook, and using a pendular-like motion that can exceed one-meter-second can swing under a ledge to an inverted position, out of sight, in less time than a human can react, two-tenths of a second. “Small animals are incredibly maneuverable in part because they are small,” emphasizes Jean-Michel Mongeau, lead author, graduate student in biophysics and IGERT Trainee. He noted that animals the size of a one gram insect have an eight-fold greater ability to rotate than humans, making the animal’s extraordinary gymnastic-like maneuvers effortless.

Serendipitously, the team discovered the behavior in cockroaches while testing the animal’s athleticism in crossing gaps using their antennae. Brian McRae, undergraduate bioengineer, described, “While studying a completely different behavior with our high-speed video cameras, we were surprised to find the insect gone. After searching, we discovered it upside-down under the ledge.” After close inspection of the video, our team discovered that the cockroach was using its legs as grappling hooks by engaging its claws at the tip of the ledge (Fig. 2). Removing the claws caused the animal to fail by flipping over and falling to the ground. Our team then questioned if this behavior was unique to cockroaches, so we suggested that the students try geckos. A previous discovery from IGERT PI Full’s laboratory has shown lizards to be highly acrobatic, using their tails to right themselves when falling, stabilize their body during leaping, and even steer during gliding. To our astonishment, the gecko showed the same rapid inversion behavior, swinging under the ledge at nearly one thousand degrees per second (Fig. 1b,2).

Escaping in the fields of Southeast Asia. Our team wondered whether rapid inversion was a behavior used in the field to escape predators. Fortuitously, Integrative Biology graduate student, Ardian Jusufi, was in a lowland tropical rainforest at the Wildlife Reserve in Singapore studying the gliding of the very same geckos. To his surprise, he found that a gecko chased to the end of a broken Bird’s Nest Fern leaf disappeared. Using high-speed video, he showed that geckos used rapid inversion, just as observed in the laboratory, suggesting they could escape predators with this behavior.

A swinging pendulum as a model. When modeling the new behavior, our team could see that the motion was not comparable to a bungee-cord like dive or to a passively swinging pendulum. Gaining insight from the only comparable, well-studied behavior, the brachiation of Gibbons, our team showed the rapid inversion escape behavior in cockroaches and geckos could be explained by the same simple swinging pendulum, but with a starting velocity. IGERT Trainee Mongeau points out, “the animals could run at nearly a meter per second to the ledge and then transfer 75% of that energy into a swing we could only see by high-speed video.” From Nature to robot prototype. By forming an interdisciplinary team of biologists and engineers from five departments, the new rapid inversion behavior inspired the design of a legged robot that begins to demonstrate this enhanced maneuverability. Using the cockroach-inspired hexapedal robot DASH (Dynamic Autonomous Sprawled Hexapod), IGERT Co-PI Ron Fearing and his group of engineers simulated the claw action by attaching a pad of Velcro hooks on the hind legs of the robot. They glued the “loop” side of the Velcro on the substrate near and underneath the ledge. Although only a prototype and not quite as effective as the animals, the robot completed the new behavior (Fig 1c,3). Fearing concluded, “If we want search-and-rescue robots to assist us in the rubble left after an earthquake, tornado or explosion or have greater capability to more rapidly detect chemical, biological or nuclear hazards, we must build far more agile robots with animal-like maneuverability.”

Address Goals

Primary Strategic Goal: Discovery. The goal of UC Berkeley’s Center for interdisciplinary Biological-inspiration in Education and Research (CiBER) IGERT is to train biology and engineering PhD students how to develop mutualistic teams that energize transformative, interdisciplinary, basic research and translate fundamental discoveries into societal benefits. Current challenges in science, engineering, industry and society demand research-based skills as well as the ability to collaborate on diverse, interdisciplinary teams, but this is seldom taught explicitly. Our training program in Bio-inspired Motion Systems Operating in Complex Environments focuses on interdisciplinary collaboration to translate biological discoveries into engineered devices, and to apply new engineering approaches to generate hypotheses and tools for biological research.

The discovery of the rapid inversion behavior shows how an interdisciplinary approach can both advance the frontiers of knowledge and accelerate the translation towards a novel engineering advancement that can benefit society. Only through the unique combination of biologists, bioengineers, electrical, mechanical and control engineers could the present discovery and its translation have been made possible. Each group contributed knowledge and expertise so that the collective discovery was beyond what any single group could have imagined. In particular, the study shows the exceptional maneuverability of small animals. Animals the size of insects and geckos can seemingly maneuver in and around, up and down and sometimes through any degree of rubble at surprisingly fast speeds. Nature tells us that if we wish to rapidly find individuals trapped in rubble resulting from an earthquake or a terrorist bombing, then extracting the biomechanical principles from these acrobatic animals could provide just the needed solution to save lives. Engineers will now be able to further translate the inspiration from nature toward design of far more maneuverable search-and-rescue robots that will be able to save human lives directly or in disasters such as earthquakes, tornadoes, and explosions or by rapid detection of chemical, biological or nuclear hazards.

Secondary Strategic Goal: Learning. This IGERT sponsored research reinforced four important lessons. First, IGERT Trainee Jean-Michel Mongeau and an undergraduate researcher were actually attempting to test a hypothesis related to the potential gyroscopic function of insect antennae by attempting to have the insect jump a large gap. To their surprise, when the animal reached the ledge it seemed to disappear. After reorientation of the high-speed camera, they realized they had discovered a new behavior serendipitously. Students learned how important it is to be prepared to see observations that do not directly address those expected, but can be a solution to a completely novel question. Second, once the students discovered this novel behavior in the cockroach, they immediately wondered whether this was a general behavior or one restricted to a single species. To test generality, they chose to look at a legged runner from a completely separate taxa, an animal with an endoskeleton, a tail and four legs. To their surprise, again, a gecko could also execute the rapid conversion maneuver.

Students learned to search for general solutions and simple templates, like a swinging pendulum, that can apply to not only one species, but even to legged robots. Third, the study showed the importance of integrating both laboratory and field observations. After discovering the rapid inversion behavior, it was not clear if this simply was a laboratory artifact or something that animals can take advantage of in their natural habitat. Testing the hypothesis on gecko in the forests of South East Asia showed the relevance of this evasive maneuver for escape. Fourth, students were reminded once again, that you never know where fundamental research will lead. Students began by asking a question about a sensory structure, an antenna, but instead discovered a novel behavior that will increase the agility of future search-and-rescue robots.

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