Terradynamically streamlined shapes in animals and robots enhance traversability through densely cluttered terrain

Abstract

Many animals, modern aircraft, and underwater vehicles use fusiform, streamlined body shapes that reduce fluid dynamic drag to achieve fast and effective locomotion in air and water. Similarly, numerous small terrestrial animals move through cluttered terrain where three-dimensional, multicomponent obstacles like grass, shrubs, vines, and leaf litter also resist motion, but it is unknown whether their body shape plays a major role in traversal. Few ground vehicles or terrestrial robots have used body shape to more effectively traverse environments such as cluttered terrain. Here, we challenged forest-floor-dwelling discoid cockroaches (Blaberus discoidalis) possessing a thin, rounded body to traverse tall, narrowly spaced, vertical, grass-like compliant beams. Animals displayed high traversal performance (79 ± 12% probability and 3.4 ± 0.7 s time). Although we observed diverse obstacle traversal strategies, cockroaches primarily (48 ± 9 % probability) used a novel roll maneuver, a form of natural parkour, allowing them to rapidly traverse obstacle gaps narrower than half their body width (2.0 ± 0.5 s traversal time). Reduction of body roundness by addition of artificial shells nearly inhibited roll maneuvers and decreased traversal performance.Inspired by this discovery, we added a thin, rounded exoskeletal shell to a legged robot with a nearly cuboidal body, common to many existing terrestrial robots. Without adding sensory feedback or changing the open-loop control, the rounded shell enabled the robot to traverse beam obstacles with gaps narrower than shell width via body roll. Terradynamically "streamlined" shapes can reduce terrain resistance and enhance traversability by assisting effective body reorientation Bioinspiration & Biomimetics (2015), 10, 046003; https://li.me.jhu.edu 2 via distributed mechanical feedback. Our findings highlight the need to consider body shape to improve robot mobility in real-world terrain often filled with clutter, and to develop better locomotor-ground contact models to understand interaction with 3-D, multi-component terrain. This image entitled 'Giant 'shrooms' has been obtained by the author from the Flickr website where it was made available by wonderferret under a CC BY 2.0 licence.] Here, we propose to advance terradynamics (Li et al. 2013) into three dimensions by going beyond relatively uniform, two-dimensional surfaces with three-dimensional obstacles of diverse, complex topology and mechanics, such as encountered in a forest floor with grass, shrubs, trees, and fungi (figure 1). In particular, small insects, arachnids, and reptiles face considerable challenges traversing such terrain, because these obstacles, which may be negligible for large animals, can be comparable or even much larger in size than themselves (Kaspari and Weiser 1999). Further, these obstacles can be densely cluttered with gaps, slits, and crevices comparable or even smaller than an animal's body, often pushing back against the animals, absorbing energy, and resisting locomotion, similar to surroun...

Dynamic traversal of large gaps by insects and legged robots reveals a template

“…Complex 3-D terrains such as leaf litter, fallen branches on a forest floor, and landslide debris (figure 1) can pose a major challenge for small animals and robots alike, because obstacles are often comparable to, or even larger than, the animal or robot itself [1] and can induce large perturbations [2][3][4][5][6][7][8].…”

“…More recently, thanks to cross-discipline collaborations between biologists, applied mathematicians, and engineers, the neuromechanical principles from biological studies have enabled many under-actuated bio-inspired robots [32,35,[59][60][61]. By combining high-level sensing and planning with mechanical feedback via mechanically tuned designs and control algorithms [62][63][64], these robots have achieved unprecedented locomotion performance on simple ground [32,59] and are beginning to traverse complex 3-D terrains [8,31,36,61].…”

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

“…Studies of locomotion over rough terrain (3), compliant surfaces (4), mesh-like networks (5), and sand (6)(7)(8), and through cluttered, 3D terrain (9) have resulted in the discovery of new behaviors and novel theory characterizing environments (10). The study of climbing has led to undiscovered templates (11) that define physical interactions through frictional van der Waals adhesion (12,13) and interlocking with claws (14) and spines (5).…”

Body-terrain interaction affects large bump traversal of insects and legged robots

“…Unlike locomotion on simpler 2-D surfaces where an animal can walk, run, or climb for extended time, when negotiating large obstacles in such complex 3-D terrains, animals more often use and transition between diverse locomotor modes [6,19,35]. Previous studies focused on how animals use sensory information to make decisions about which locomotor mode to use.…”