  Autonomous drone racing is becoming an excellent platform to challenge
quadrotors' autonomy techniques including planning, navigation and control
technologies. However, most research on this topic mainly focuses on single
drone scenarios. In this paper, we describe a novel time-optimal trajectory
generation method for generating time-optimal trajectories for a swarm of
quadrotors to fly through pre-defined waypoints with their maximum
maneuverability without collision. We verify the method in the Gazebo
simulations where a swarm of 5 quadrotors can fly through a complex 6-waypoint
racing track in a 35m * 35m space with a top speed of 14m/s. Flight tests are
performed on two quadrotors passing through 3 waypoints in a 4m * 2m flight
arena to demonstrate the feasibility of the proposed method in the real world.
Both simulations and real-world flight tests show that the proposed method can
generate the optimal aggressive trajectories for a swarm of autonomous racing
drones. The method can also be easily transferred to other types of robot
swarms.
