Rapid Inversion: Running Animals and Robots Swing like a Pendulum under Ledges

Abstract

Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. Here, we report a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12–15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot.

Cockroaches traverse crevices, crawl rapidly in confined spaces, and inspire a soft, legged robot

“…Cockroaches use rigid, jointed exoskeletons to run rapidly at speeds approaching 1.5 m·s −1 (31), climb up walls (11,32), race along ceilings (33), and swing stealthily under ledges out of sight (34). However, materials science has revealed that the stiffness of exoskeletal tissue can differ by eight orders of magnitude (35)(36)(37)(38), permitting the possibility that cockroaches with powerful propulsive appendages might also retain the advantages of soft-bodied animals capable of conforming to their environment (39).…”

“…We selected the American cockroach, Periplaneta americana, because of its high speed (31), maneuverability (34,40), robustness (41), and tenacity to enter and leave spaces. To determine the smallest horizontal crevice that a cockroach could traverse, we challenged animals with a series of decreasing crevice heights.…”

Exceptional running and turning performance in a mite

“…Given the mites' ability to turn through 180 deg in 6-7 gait cycles, and assuming a stride frequency in the field of 100 Hz, they would be able to accomplish such a turn in less than 0.1 s. The peak angular velocity achieved by a pivoting mite in the current lab trials exceeded 1250 deg s −1 . This pivoting, lateral turn by the mite is comparable in angular velocity to the inversion behavior seen in the cockroach Periplaneta, which uses a similar grappling hook mechanism to pivot vertically around the tarsus of a limb during escape (>1200 deg s −1 ; Mongeau et al, 2012). Unlike Periplaneta, however, the mites continued to cycle their other limbs to move through the turn about the pivoted leg (Fig.…”

“…Although the pivoting (or grappling hook) mechanism has been described in inverting cockroaches and geckos (Mongeau et al, 2012), this use of a grappling hook during turning in P. macropalpis differs substantially from that described for most other arthropods. The octopodal gait in the tarantula Grammostola mollicoma uses a gait cycle where the ipsilateral legs are reversed during a sharp turn (Biancardi et al, 2011).…”

Animal-inspired design and aerodynamic stabilization of a hexapedal millirobot

“…The American cockroach, Periplaneta americana, is a highly dynamic running insect, exhibiting a variety of robust and high speed gaits that we use as a model of study for the design of VelociRoACH. P. americana is capable of running at over 50 body-lengths per second (bl/s) and is capable of hexapedal, quadrupedal, and even bipedal locomotion [9], as well as high-speed climbing and rapid inversion [19].…”