Three-Dimensional Trajectory Optimization for Quadrotor Tail-Sitter AAVs: Traversing Through Given Waypoints

Given the evolving application scenarios of current fixed-wing autonomous aerial vehicles (AAVs), it is necessary for AAVs to possess agile and rapid 3-D flight capabilities. Typically, the trajectory of a tail-sitter is generated separately for vertical and level flights. This limits the tail-sitter's ability to move in a 3-D airspace and makes it difficult to establish a smooth transition between vertical and level flights. In this article, a 3-D trajectory optimization method is proposed for quadrotor tail-sitters. Especially, the differential dynamics constraints are eliminated when generating the trajectory of the tail-sitter by utilizing the differential flatness method. In addition, the temporal parameters of the trajectory are generated using the State-of-the-Art trajectory generation method called MINCO (minimum control). Subsequently, we convert the speed constraint on the vehicle into a soft constraint by discretizing the trajectory in time. This increases the likelihood that the control input limits are satisfied, and the trajectory is feasible. Then, we utilize a kind of model-predictive control method to track trajectories. Even if restricting the tail-sitter's motion to a 2-D horizontal plane, the solutions still outperform those of the L1 Guidance Law and Dubins path.