Simultaneous Planning and Execution for Quadrotors Flying Through a Narrow Gap Under Disturbance

The dynamics of a quadrotor exhibit the challenges of underactuation, strong coupling, and external disturbances. In order to handle these difficulties and enable quadrotors to align the six-degree-of-freedom (6-DOF) pose of the tilted narrow gap during the traversing maneuver, this article proposes a strategy based on simultaneous planning and execution (SPAE). In this strategy, the unknown disturbance is considered in both the planning and execution of the trajectory simultaneously. Specifically, the disturbance is estimated online during system execution and then combined with the attitude angle of the narrow gap and maximum thrust to constraint acceleration of trajectory. Given the state constraints and physical limitations in thrust, velocity, and jerk, a minimum time trajectory planning algorithm is developed based on a piecewise cubic function to realize aggressive flight. In this algorithm, the coupled maximum thrust is decoupled into three independent axes. Each axis can then generate time-efficient third-order trajectories that satisfy arbitrary state constraints and dynamic feasibility. The average computing time of the algorithm is less than
$150 ~\mu \text{s}$
on the STM32 embedded platform, which is suitable for quadrotors with limited onboard computing capability. Finally, simulations and outdoor experiments were conducted to verify the effectiveness of the proposed system strategy. The outdoor results demonstrate that the proposed strategy can enable the quadrotor to carry out aggressive flying through a narrow gap in a natural disturbance environment.