External Forces Resilient Safe Motion Planning for Quadrotor

Adaptive autonomous navigation with no prior knowledge of extraneous disturbance is of great significance for quadrotors in a complex and unknown environment. The mainstream approach that considers external disturbance is to implement disturbance-rejected control and path tracking. However, the robust control to compensate for tracking deviations is not well-considered regarding energy consumption, and even the reference path will become risky and intractable with disturbance. As recent external forces estimation advances, it is possible to incorporate a real-time force estimator to develop more robust and safe planning frameworks. This letter proposes a systematic (re)planning framework that can resiliently generate safe trajectories under volatile conditions. Firstly, a front-end kinodynamic path is searched with force-biased motion primitives. Then we develop a nonlinear model predictive control (NMPC) as a local planner with Hamilton Jacobi (HJ) forward reachability analysis for error dynamics caused by external forces. It guarantees collision avoidance by constraining the ellipsoid of the quadrotor body expanded with the forward reachable sets (FRSs) within safe convex polytopes. Our method is validated in simulations and real-world experiments with different sources of external forces.

Automated summary

The letter proposes a systematic (re)planning framework that can resiliently generate safe trajectories under volatile conditions. By searching a front-end kinodynamic path with force-biased motion primitives and developing a nonlinear model predictive control (NMPC) as a local planner, error dynamics caused by external forces are analyzed using Hamilton Jacobi (HJ) forward reachability analysis. Collision avoidance is ensured by constraining the ellipsoid of the quadrotor body within safe convex polytopes expanded with the forward reachable sets (FRSs).