Rapid inversion: running animals and robots swing like a pendulum under ledges.

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

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

Recent advances in the design and implementation of wearable resistive, capacitive, and optical strain sensors are summarized herein. Wearable and stretchable strain sensors have received extensive research interest due to their applications in personalized healthcare, human motion detection, human–machine interfaces, soft robotics, and beyond. The disconnection of overlapped nanomaterials, reversible opening/closing of microcracks in sensing films, and alteration of the tunneling resistance have been successfully adopted to develop high-performance resistive-type sensors. On the other hand, the sensing behavior of capacitive-type and optical strain sensors is largely governed by their geometrical changes under stretching/releasing cycles. The sensor design parameters, including stretchability, sensitivity, linearity, hysteresis, and dynamic durability, are comprehensively discussed. Finally, the promising applications of wearable strain sensors are highlighted in detail. Although considerable progress has been made so far, wearable strain sensors are still in their prototype stage, and several challenges in the manufacturing of integrated and multifunctional strain sensors should be yet tackled

The role of the tail in stability and maneuverability during running, climbing, mid-air orientation and gliding in both animals and robots.

Life above ground requires that animals navigate a highly three-dimensional world. Both cursorial and arboreal animals must rapidly negotiate a myriad of complex and often unpredictable substrata within their habitats (e.g. dense vegetation; forest canopy) in which discontinuous supports challenge secure footholds. Traveling rapidly through such demanding terrain necessitates a behavioral repertoire that consists of both terrestrial and aerial modes of locomotion. Lizards represent an important model system in the study of general principles of how animals move. Moreover, developing capabilities of ambulation in cluttered environments to assist in search and rescue operations is in demand in robotics. Within the scope of this dissertation, I investigate whether multiple coordinated tail reflexes and responses are necessary for the successful navigation of a highly three-dimensional environment that challenges animals' locomotor systems with numerous obstacles, discontinuous supports and slippery surfaces. In Chapter One, I present data on challenging single footholds in wall-running geckos, which lead to the discovery of a control structure the significance of which had not been previously recognized. Although the remarkable climbing performance of geckos has traditionally been attributed to specialized feet, I showed that a gecko's tail functions as an emergency fifth leg to prevent falling during rapid climbing. A response initiated by slipping causes the tail tip to push against the vertical surface, thereby preventing pitch-back of the head and upper body. When confronted with insurmountable gaps the lizards exhibited tail movement as they recovered from free fall. Lizards could also control body pitch and induce turning during simulated aerial descent. These experiments suggested that the secret to the gecko's arboreal acrobatics includes an active tail.In the context of measuring locomotor performance as a function of foot-substrate interaction, I perturbed geckos even further and found that when a gecko falls with its back to the ground, a swing of its tail induces the most rapid air-righting response yet measured. Chapter Two investigates the tail as an effective torque source first attempting to generatesimple, low parameter models of thesystem, then developing thee-dimensional analytical models of multi-body systems to investigate righting performance in two species of lizard, and how it is affected by variations in tail length, mass distribution, tail placement and orientation. These results suggest that large, active tails can function as effective control appendages. Lizards gliding in a vertical wind tunnel could use appendage inertia to induce turns in yaw whereby tails twice the torso length have better yield. Robots can also serve as physical models to test our understanding of animal locomotion. In this spirit, a physical model and robot prototype tests the model's predictive capacity further, while also demonstrating feasibility of tail use in robots. In Chapter Three, I present data from field research conducted in Southeast Asian lowland tropical rainforest, the natural habitat of my model system H. platyurus. A species heretofore not known to glide exhibits considerable horizontal transit of over 4m. Geckos with tails that glided to the tree trunk were able to remain attached to it upon landing in the majority of trials, whereas geckos without tails generally became dislodged upon impact. Moreover, I present how they carry out landing on vertical tree trunks despite approaching them at very high speeds. I propose a mechanically-mediated solution to how landing on a wall could be stabilized by the caudal appendage. In Chapter Four, I explore whether representatives of lizard taxa other than Gekkonidae night utilize their tails for improving the stability, maneuverability and overall robustness of a mode of terrestrial locomotion: Rapid climbing on tree bark. Observations from the field in Malaysian lowland tropical rainforest, where I observed these animals' behavior initiated this study. I discovered that they have specialized subcaudal scales which are keeled such as to engage with a rough substrate. I present materials testing measurements using an Instron machine, where we determined that each scale can support one to several times body weight, depending on species. Acanthosaurus crucigera, Gonocephalus grandis and Iguana iguana were sampled. When the scales are prevented from engaging the animals' performance decreases dramatically

Soft proprioceptive sensing enables soft robotic swimming with closed loop control and facilitates obstacle traversal

The 9.5th international symposium on Adaptive Motion of Animals and Machines. Ottawa，Canada (Virtual Platform). 2021-06-22/25. Adaptive Motion of Animals and Machines Organizing Committee

Strong, Ultrastretchable Hydrogel-Based Multilayered Soft Actuator Composites Enhancing Biologically Inspired Pumping Systems

10.1002/adem.202100121Advanced Engineering Materials2310210012

Active tails enhance arboreal acrobatics in geckos

Geckos are nature's elite climbers. Their remarkable climbing feats have been attributed to specialized feet with hairy toes that uncurl and peel in milliseconds. Here, we report that the secret to the gecko's arboreal acrobatics includes an active tail. We examine the tail's role during rapid climbing, aerial descent, and gliding. We show that a gecko's tail functions as an emergency fifth leg to prevent falling during rapid climbing. A response initiated by slipping causes the tail tip to push against the vertical surface, thereby preventing pitch-back of the head and upper body. When pitch-back cannot be prevented, geckos avoid falling by placing their tail in a posture similar to a bicycle's kickstand. Should a gecko fall with its back to the ground, a swing of its tail induces the most rapid, zero-angular momentum air-righting response yet measured. Once righted to a sprawled gliding posture, circular tail movements control yaw and pitch as the gecko descends. Our results suggest that large, active tails can function as effective control appendages. These results have provided biological inspiration for the design of an active tail on a climbing robot, and we anticipate their use in small, unmanned gliding vehicles and multisegment spacecraft

Rapid inversion: running animals and robots swing like a pendulum under ledges.

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

Modeling and Control of a Soft Robotic Fish with Integrated Soft Sensing

Soft robotics can be used not only as a means of achieving novel, more lifelike forms of locomotion, but also as a tool to understand complex biomechanics through the use of robotic model animals. Herein, the control of the undulation mechanics of an entirely soft robotic subcarangiform fish is presented, using antagonistic fast‐PneuNet actuators and hyperelastic eutectic gallium–indium (eGaIn) embedded in silicone channels for strain sensing. To design a controller, a simple, data‐driven lumped parameter approach is developed, which allows accurate but lightweight simulation, tuned using experimental data and a genetic algorithm. The model accurately predicts the robot's behavior over a range of driving frequencies and a range of pressure amplitudes, including the effect of antagonistic co‐contraction of the soft actuators. An amplitude controller is prototyped using the model and deployed to the robot to reach the setpoint of a tail‐beat amplitude using fully soft and real‐time strain sensing