Principled understanding of dynamic multi-legged locomotion in complex terrain

Research on dynamic multi-legged locomotion on relatively flat, rigid surfaces significantly advanced our understanding of how animals walk and run and provided foundations for multi-legged robots that do so dynamically, stably, and efficiently. Here I review recent research building on these early insights to further understand dynamic multi-legged locomotion in complex terrain such as granular media like dry sand and cluttered large obstacles. An interdisciplinary approach at the interface of biology, engineering, and physics integrating rigorous, systematic experiments and first-principle modeling proved powerful in revealing novel insights and surprisingly general principles. Analogous to aero- and hydrodynamics that describe fluid-structure interaction and have advanced understanding of flight and swimming, these efforts are establishing a new field of terradynamics of locomotor-terrain interaction and have advanced understanding of animal and robot locomotion in complex terrain. Many questions still remain, calling for continued creation of new experimental tools and theoretical and computational models to address challenges of increasing complexity in measuring locomotion and defining environmental physics, as well as broad interdisciplinary training and collaboration.