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This paper introduces "dynamic symmetry," quantified by "dynamic isotropy," as a key design principle for robots, focusing on the uniformity of attainable center-of-mass accelerations. Through extensive simulations and the physical realization of the Argus robot family, the authors demonstrate that maximizing dynamic symmetry leads to significant improvements in trajectory tracking, robustness, energy efficiency, and overall task performance. The 20-leg Argus prototype achieves near-extreme dynamic isotropy, showcasing orientation-invariant locomotion, agile traversal of complex terrains, and resilience to actuator failures.
Forget static designs: robots that move with equal ease in all directions aren't just cooler, they're demonstrably more agile, robust, and energy-efficient.
Symmetry is a central organizing principle in natural systems, yet its use as a unifying design strategy in robotics has largely remained limited to geometric form. We show that symmetry can instead be leveraged at the level of dynamic actuation capability. We introduce dynamic symmetry, the uniformity of a robot鈥檚 attainable center-of-mass accelerations, and formalize it through a measure coined as dynamic isotropy. Across more than 1000 simulated morphologies, we found that higher dynamic symmetry consistently improved trajectory tracking, task success, robustness, resiliency, and energy efficiency, with the benefits becoming most pronounced as dynamic isotropy approached its theoretical limit. To study this regime systematically, we developed Argus, a family of spherical robots designed to explore the effects of increasing dynamic symmetry. Members of the Argus family vary in their actuation geometry and dynamic symmetry level while sharing a common architectural principle: radially oriented linear actuators that directly shape the robot鈥檚 center-of-mass dynamics. Among them, we built a physical 20-leg Argus variant that achieved near-extreme dynamic isotropy and demonstrated orientation-invariant locomotion, agile traversal of cluttered and deformable terrain, rapid self-stabilization, and resilience to partial actuator failures. Its distributed sensing further enabled omnidirectional perception and object interaction during continuous motion. These results show that designing robots for symmetry not only in morphology but also in their attainable dynamics provides a powerful and general pathway toward agility, robustness, and multifunctionality in uncertain terrestrial and extraterrestrial environments.
