Ramesh, DivyaKathail, AnmolKoditschek, Daniel E.Qian, Feifei2023-05-222023-05-222020-01-312020-03-09https://repository.upenn.edu/handle/20.500.14332/34112We study a quadrupedal robot traversing a structured (i.e., periodically spaced) obstacle field driven by an open-loop quasi-static trotting walk. Despite complex, repeated collisions and slippage between robot legs and obstacles, the robot’s horizontal plane body orientation (yaw) trajectory can converge in the absence of any body level feedback to stable steady state patterns. We classify these patterns into a series of “types” ranging from stable locked equilibria, to stable periodic oscillations, to unstable or mixed period oscillations. We observe that the stable equilibria can bifurcate to stable periodic oscillations and then to mixed period oscillations as the obstacle spacing is gradually increased. Using a 3D-reconstruction method, we experimentally characterize the robot leg-obstacle contact configurations at each step to show that the different steady patterns in robot orientation trajectories result from a self-stabilizing periodic pattern of leg-obstacle contact positions. We present a highly-simplified coupled oscillator model that predicts robot orientation pattern as a function of the leg-obstacle contact mechanism. We demonstrate that the model successfully captures the robot steady state for different obstacle spacing and robot initial conditions. We suggest in simulation that using the simplified coupled oscillator model we can create novel control strategies that allow multi-legged robots to exploit obstacle disturbances to negotiate randomly cluttered environments. For more information: Kod*lab (link to kodlab.seas.upenn.edu)flash_audioAuthors may post their preprints in the following locations: Author’s personal website Author’s employer’s website arXiv.org TechRxiv.org This does not count as a prior publication. If copyright to the article was transferred to IEEE through the completion of an IEEE Copyright Form before the preprint is posted, IEEE must be credited as the copyright holder with the following statement included on the initial screen displaying IEEE-copyrighted material: “© 20XX IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.” Upon publication of the article, the article’s Digital Object Identifier (DOI) should be added.GRASPKodlabDynamicsLegged RobotsContact ModelingElectrical and Computer EngineeringEngineeringSystems EngineeringArticle