Meeting Abstract
S5.10 Wednesday, Jan. 5 Biomechanical Analyses of Goats and Dogs in the BigDog Project LEE, David/V*; BIEWENER, Andrew/A; University of Nevada Las Vegas; Harvard University david.lee@unlv.edu
Biomechanical experiments to inform the design and locomotor dynamics of Boston Dynamic’s BigDog robot have proceeded along two main lines. Analysis of limb mechanics in dogs and goats has guided the mechanical design and compliance characteristics of BigDog’s legs, while, more recently, a collision-based analysis of center of mass (CoM) mechanics across gait and species has helped to explain the physical principles underlying the walk, trot and gallop – as well as interspecific differences within these gaits. Understanding the functional connections between limb compliance, CoM mechanics and gait will help to integrate mechanical design with desired locomotor dynamics of quadrupedal robots. The overarching goal of these studies has been to transfer functional principles to BigDog, as opposed to explicit mimicry of biological limb design and gait patterns. The joint and radial leg mechanics of goats and dogs of similar size were examined using a serial actuator-spring model to determine their spring characteristics and actuation requirements. This model shows that radial leg spring constants are significantly greater in goats than in dogs. Forelegs and hindlegs of goats are, respectively, 75% and 65% stiffer. This dramatic difference in radial leg spring characteristics reflects limb postural differences resulting in reduced GRF moment arms about the MCP, wrist, and ankle joints of goats compared to dogs. Greater compliance in the legs of dogs may ‘smooth-out’ the redirection of CoM velocity by the legs, thereby reducing collision-based energy loss and mechanical cost of transport in dogs compared to goats. Our analysis of CoM mechanics has shown substantial collision reduction in walking and galloping but not in trotting. During walking and galloping, collision reduction is significantly greater in dogs than goats.
