Exploiting Linear Structure for Precision Control of Highly Nonlinear Vehicle Dynamics

Drifting - operating a vehicle at a high sideslip angle - offers intriguing possibilities for controlling autonomous vehicles in critical situations. While drifting is a very dynamic process, occurring in a region of the state space with saturated tires and unstable equilibria, autonomous vehicles have been successfully controlled in this region. Previous control approaches to path tracking while drifting have relied on nonlinear vehicle models. In this paper, however, we demonstrate that linearized models capture the necessary dynamics for control in a large region surrounding a drift equilibrium. Using this linearized model, we develop a controller based on a linear quadratic regulator. This controller uses steering, throttle, and brakes to track both a desired path and a desired speed profile, making the system fully actuated. We demonstrate the fidelity of this linearized model and the utility of this controller by implementing this controller on MARTY, an electric DMC DeLorean, and accurately tracking equilibrium and quasi-equilibrium paths with centimeter-level accuracy that exceeds prior work.