RI: Small: Hierarchical Planning, Estimation, and Control for Hybrid Mechanical Systems

Northwestern University, Evanston IL

Investigators

Abstract

Hybrid mechanical systems arise in many applications, including hopping, walking, and climbing robots where contact with the ground changes; skid-steering vehicles where Coulomb friction introduces stick/slip behavior; and prosthetic devices that interact with objects. All of these applications are influenced by nonlinearity, nonsmooth transitions, and uncertainty, and these systems demand new tools in motion planning and control. This work takes advantage of the specific structure of mechanical systems to bound the propagation of uncertainty and to develop feedback controllers that maximize robustness of execution. The work builds on state-of-the-art techniques in motion planning and estimation, including sample-based and optimization-based planning, leading to tools for uncertain hybrid mechanical systems that are analogous to control and estimation tools used for linear systems. Example systems are used to drive algorithm development as well as to verify performance. These include 1) the Monkeybot, a robot that uses electromagnets and a single motor to locomote along a vertical wall; 2) a parkour robot that uses mechanical contact and jumping to climb narrow passages; and 3) a skid-steered vehicle that experiences discontinuous dynamics due to stick/slip friction effects. All phases of this work include participation of undergraduates and minority students. In addition to dissemination in conferences and journals, results are disseminated on a publicly viewable wiki.