In this project the PI will investigate, experimentally and theoretically, the role of complex biological integuments in animal locomotion. Two parallel research thrusts are planned: one investigation on the terrestrial limbless locomotion of snakes, and the other on the collective locomotion of semi-aquatic insects. A series of integrated experimental and theoretical investigations will be conducted on the propulsion of snakes on horizontal surfaces. Snakes exhibit four modes of locomotion, including lateral undulation, side winding, rectilinear progression and an accordion-like concertina motion. The goal of this research is to rationalize these limbless propulsion mechanisms. An existing theoretical framework will be adapted for investigation of the snake gaits. Particular attention will be given to assessing the snake's gains in efficiency and speed from dynamic lifting of its body during locomotion. Measurements of the snake's weight distribution during slithering will be obtained qualitatively using birefringent gelatin techniques and quantitatively using arrays of pressure transducers. An understanding of dynamic load-bearing mechanisms will shed insight onto the snake's energy budget and mechanisms for reducing abrasive wear. For the second part of the project, combined experimental and theoretical investigations will be made on the locomotion of insects that live above and below the water surface. An exploratory investigation will be conducted on the mechanisms by which fire ant colonies, whose individuals are hydrophilic and cannot swim, collectively form floating structures, ant balls that allow them to survive floods. Contact angles of the individuals and frozen ant balls will be measured and the dynamics of ants within the ball observed. A series of investigations of the locomotion of aquatic insects and gastropods will also be conducted, focusing on their wetting properties, propulsion using cilia and the body shapes which give them underwater stability near the free surface. The PI will develop an interdisciplinary undergraduate course in animal bio-locomotion in order to draw together students of biology and engineering and increase the visibility of integrative research. A bio-inspired walking-on-water theme will be planned for the school's annual design competition for mechanical engineering juniors. The PI will mentor two local high school students under the Intel Science Talent Search, in which he once participated.
Introduction Snakes are one of the world’s most versatile organisms, at ease slithering through rubble or climbing vertical tree trunks. Their adaptations for conquering complex terrain thus serve naturally as inspirations for search and rescue robotics. In a combined experimental and theoretical investigation, we elucidate the propulsion mechanisms of snakes on both hard and granular substrates. The focus of this study is on physics of snake interactions with its environment. Snakes use one of several modes of locomotion, such as slithering on flat surfaces, sidewinding on sand, or accordion-like concertina and worm-like rectilinear motion to traverse crevices. Particular attention is paid to a novel paradigm in locomotion, a snake’s active control of its scales, which enables it to modify its frictional interactions with the ground. We use this discovery to build bio-inspired limbless robots that have improved sensitivity to the current state of the art: Scalybot has individually controlled sets of belly scales enabling it to climb slopes of 55 degrees. These findings will result in developing new functional materials and control algorithms that will guide roboticists as they endeavor towards building more effective all-terrain search and rescue robots. Background More than 450 million people were affected by 700 natural disasters worldwide over the past two years. Robotic search and rescue is crucial for fast and effective rescue operations after such disasters. In addition to search and rescue, limbless and wheel-less propulsive devices can be designed for "robotic colonoscopy" to maneuver while minimizing pain and damage to the surrounding tissue, or exploratory missions in deserts and on other planets. In all these situations, terrain is complex, involving topography over a range of length scales and surface textures. Snakes are one of the most versatile animals at ease traversing complex terrain, climbing steep inclinations, and advancing through narrow openings. They have been studied for over 200 years and have been source of inspiration for many great engineering discoveries. Snakes have four different modes of terrestrial locomotion: concertina locomotion, rectilinear, lateral undulation, and sidewinding. When a snake climbs inclined channels it usually uses an accordion-like motion called concertina. In rectilinear motion, a snake propagates a longitudinal traveling wave along its body to move in limited spaces. Lateral undulation is the fastest mode of snake locomotion and most snakes are capable of performing this gait on flat surfaces. During lateral undulation, snakes generate a 2- dimensional traveling wave propagating from head to tail. When traversing a granular substrate such as sand, a snake usually uses the sidewinding gait, the second fastest and most energetically efficient gait of snake locomotion. Understanding the kinematics and energetics of these gaits and mechanisms snakes use for making effective interactions with their environment is a major step forward for developing effective all-terrain search and rescue robots. Scope and objectives The main objective of this study is to study the underlying physics of snakes’ interactions with their deformable or granular environment. We develop novel experimental and theoretical techniques to discover some of the mechanisms snakes use to effectively move on a variety of complex terrain. Snakes have four different modes of motion or gaits. In this research, we study three of these gaits using the aforementioned approach. We begin with a study of snakeskin tribology and the interaction of a snake scale with its deformable substrate. We present an experimental and computational methodology to understand how friction is generated during the interaction of two flexible beams: snake scale and a transparency film. We proceed with a study of concertina locomotion with a focus on the mechanisms snakes use to enhance frictional forces required for climbing. We also present two snake-like robots we developed inspired by concertina locomotion. In Scalybot 1 and 2, we control their ventral scales to adjust frictional forces as a function of position and time. We then develop a novel methodology for measuring total energetic cost of animal locomotion. We use Magnetic Resonance Spectroscopy (MRS) to measure cost of concertina locomotion on slopes of varying inclinations. We also study kinematics, optimality, and energetics of rectilinear locomotion of snakes. Finally, we study sidewinding on granular media. We present a control strategy sidewinders use to effectively climb on sand at highest possible inclinations.
