Robust Trajectory Planning for a Multirotor against Disturbance based on HamiltonJacobi Reachability Analysis Ensuring safety in trajectory planning of multirotor systems is an essential element for riskfree operation. Even if the generated trajectory is known to be safe in the planning phase, unknown disturbance during an actual operation can lead to a dangerous situation. This paper proposes safetyguaranteed receding horizon planning against unknown, but bounded, disturbances. We first characterize forward reachable set (FRS) of the system, the set of states after a certain duration considering all possible disturbances, using HamiltonJacobi (HJ) reachability analysis. To compute the FRSs in realtime, we conservatively approximate the true FRS and perform ellipsoidal parameterization on the FRSs. Using the FRSs, we can plan a robust trajectory that avoids risky regions and rapidly replan the trajectory when the system encounters sudden disturbance. The proposed method is validated through an experiment of avoiding obstacles in a wind.

Fast Trajectory Planning for Multiple Quadrotors using Relative Safe Flight Corridor This paper presents a new trajectory planning method for multiple quadrotors in obstacledense environments. We suggest a relative safe flight corridor (RSFC) to model safe region between a pair of agents, and it is used to generate linear constraints for intercollision avoidance by utilizing the convex hull property of relative Bernstein polynomial. Our approach employs a graphbased multiagent pathfinding algorithm to generate an initial trajectory, which is used to construct a safe flight corridor (SFC) and RSFC. We express the trajectory as a piecewise Bernstein polynomial and formulate the trajectory planning problem into one quadratic programming problem using linear constraints from SFC and RSFC. The proposed method can compute collisionfree trajectory for 16 agents within a second and for 64 agents less than a minute, and it is validated both through simulation and indoor flight test.