Contact with the outside world is challenging for robots due to its inherently discontinuous nature – when a foot or hand is touching a surface the forces are completely different than if it is just above the surface. However, most of our computational and analytic tools for planning, learning, and control assume continuous (if not smooth or even linear) systems. Simple models of contact make assumptions (like plasticity and coulomb friction) that are known to not only be wrong physically but also inconsistent. In this talk I will present techniques for overcoming these challenges in order to adapt smooth methods to systems that have changing contact conditions. In particular I will focus on three topics: First, I will present the “Salted Kalman Filter” for state estimation over hybrid systems. Second, I will present an analysis approach that unifies and extends different strategies for stabilizing and controlling systems through contact. Finally, I will talk about when these hybrid models of contact break down, especially when driving on sand.

“I developed and teach a graduate class called Robot Dynamics and Analysis. Unlike most other robot dynamics classes, this new class focused on contact, impacts, and how to handle changing contact conditions in simulation and optimization. However, while the first half used a standard textbook, I could not find any good educational resources that covered hybrid systems, changing contact conditions, and impacts at the level needed for this class. Instead, I used two of my own research papers and a collection of other sources. The problem with these resources are that: 1) research papers are not written like textbooks, and generally lack the detailed explanations and example problems necessary; and 2) they lack a coherent dialog and notation, as each was written by a different author with a different audience in mind.

To remedy these issues, I am writing a textbook to cover the topics listed below over the course of several years. This will allow for a cohesive treatment of contact and related topics in a form that will be more approachable for students, following research-based best practices for textbook design. The text will be based on my papers, class notes, and translation guides, which comments back from students indicated were more helpful than many of the assigned readings. The textbook will be available for free online, and I will solicit input from the community during its development to help ensure it is of use to a wider range of researchers”

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