Unmodeled aerodynamic disturbances pose a key challenge for multirotor flight when multiple vehicles are in close proximity to each other. However, certain missions \textit{require} two multirotors to approach each other within 1-2 body-lengths of each other and hold formation -- we consider one such practical instance: vertically docking two multirotors in the air. In this leader-follower setting, the follower experiences significant downwash interference from the leader in its final docking stages. To compensate for this, we employ a learnt downwash model online within an optimal feedback controller to accurately track a docking maneuver and then hold formation. Through real-world flights with different maneuvers, we demonstrate that this compensation is crucial for reducing the large vertical separation otherwise required by conventional/naive approaches. Our evaluations show a tracking error of less than 0.06m for the follower (a 3-4x reduction) when approaching vertically within two body-lengths of the leader. Finally, we deploy the complete system to effect a successful physical docking between two airborne multirotors in a single smooth planned trajectory.

翻译：未建模的气动干扰对多旋翼飞行器在近距离编队飞行中构成关键挑战。然而，某些任务要求两架多旋翼相互接近至1-2倍机体长度范围内并保持编队——我们考虑一个实际场景：在空中垂直对接两架多旋翼。在此领航-跟随框架中，跟随者在最终对接阶段会受到来自领航者的显著下洗流干扰。为补偿该效应，我们在线采用一个学习得到的下洗流模型，在最优反馈控制器内精确追踪对接机动并保持编队。通过不同机动类型的实际飞行实验，我们证明这种补偿对于缩小传统/朴素方法所需的大垂直间距至关重要。评估结果显示，当跟随者垂直接近至领航者两倍机体长度时，其追踪误差小于0.06米（误差降低3-4倍）。最后，我们部署完整系统，通过单一平滑规划轨迹成功实现两架空中多旋翼的物理对接。