The Consequences of Speed: Studies of Cavitation During the Mantis Shrimp Strike and the Control of Rapid Deceleration During Toad Landing

There are consequences of moving quickly in this world. Here we investigate how two very different species, mantis shrimp (Odontodactylus scyllarus) and cane toads (Bufo marinus), negotiate forces that result from moving rapidly in different environments. To study the mechanical principles and fluid dynamics of ultrafast power-amplified systems, we built Ninjabot, a physical model of the extremely fast mantis shrimp. While mantis shrimp produce damaging cavitation upon impact with their prey, they do not cavitate during the forward portion of their strike despite extreme speeds. In order to study cavitation onset in non-linear flows common during the mantis shrimp strike, we used Ninjabot to produce strikes of varying kinematics and measured cavitation presence or absence. We found that in rotating and accelerating biological conditions, cavitation inception is best explained only by maximum linear velocity. Thus, studies of cavitation onset in biological conditions only need to focus on maximum velocity. On land, moving quickly requires avoiding or preparing for impact with other objects, often the ground. Within anurans (frogs and toads), a group well known for jumping, cane toads are known to perform particularly controlled landings in which the forelimbs are used to decelerate and balance the body after impact as the hind limbs are lowered to the ground. Here I explore whether and how toads modulate landing preparation depending on hopping and landing conditions and what this can tell us about how they utilize sensory information to help them perform controlled landings. We found that toads modulate three components of impact preparation to specific hop conditions: 1) They position the forelimbs to hit the ground first by protracting and abducting the humeri, 2) They prepare and brace for impact by extending the elbows and activating underlying musculature to stiffen the joint and 3) they control torques during the landing by retracting the hind limbs and rotating the forelimbs to align with the impact angle. By perturbing landing conditions we found that toads tune these components to specific landing conditions with a combination of passive and active control and toads do so by primarily relying on non-visual sensory feedback

The biomechanics of tree frogs climbing curved surfaces: a gripping problem

The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that, on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the two smaller diameter cylinders (44 mm and 13 mm), frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualize substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots

The jumping mechanism of flea beetles (Coleoptera, Chrysomelidae, Alticini), its application to bionics and preliminary design for a robotic jumping leg

Flea beetles (Coleoptera, Chrysomelidae, Galerucinae, Alticini) are a hyperdiverse group of organisms with approximately 9900 species worldwide. In addition to walking as most insects do, nearly all the species of flea beetles have an ability to jump and this ability is commonly understood as one of the key adaptations responsible for its diversity. Our investigation of flea beetle jumping is based on high-speed filming, micro- CT scans and 3D reconstructions, and provides a mechanical description of the jump. We reveal that the flea beetle jumping mechanism is a catapult in nature and is enabled by a small structure in the hind femur called an ‘elastic plate’ which powers the explosive jump and protects other structures from potential injury. The explosive catapult jump of flea beetles involves a unique ‘high-efficiency mechanism’ and ‘positive feedback mechanism’. As this catapult mechanism could inspire the design of bionic jumping limbs, we provide a preliminary design for a robotic jumping leg, which could be a resource for the bionics industry

The importance of muscle mechanics during movement: investigating power production and dynamic stability using a closed-loop system

Animals effectively move and negotiate a variety of environments exemplifying the neuromuscular system's ability to produce complex coordinated movements. Our central thesis is that the nonlinear dynamical properties of muscle play a critical role in power production and stability during such movements. We have developed a closed-loop system that couples an isolated muscle to a physical or computational load, facilitating the study of the interactions between intrinsic muscle properties and external forces. We used this system to determine how elastic elements in the frog semimembranosus can improve power production during a jumping task and how the contractile element automatically manages energy to maintain a stable bouncing gait. Our results reveal that, during ballistic movements (e.g. jumping), series elastic elements stretch and shorten to temporally concentrate energy transfer from the contractile element to the body, amplifying power production. We measured peak instantaneous power greater than twice the maximum power the contractile element could produce alone. Our results show how, during a bouncing gait, the contractile and elastic elements autonomously interact to produce, dissipate, and recycle energy and to maintain dynamic stability without sensory feedback. Our data suggest that muscles can recover over 75% of the kinematic energy from one step and apply it to the next. These results demonstrate the effects and importance of intrinsic muscle properties during movements. Ultimately, this research can guide the development of biomimetic robotic and prosthetic technologies capable of life-like mobility.Ph.D.Committee Chair: DeWeerth, Stephen P.; Committee Co-Chair: Ting, Lena H.; Committee Member: Burkholder, Thomas J.; Committee Member: Nichols, T. Richard; Committee Member: Tresch, Matthew C

Bio-Inspired Robotics

Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field