Synchronized mid-air drone docking during translational motion

While mid-air drone docking has been explored in the literature, these works have addressed the case where one drone hovers during docking. This paper considers the additional challenge where both drones may be in translational motion during the docking. Further, our work is entirely reactive and does not require that one drone receive trajectory information in advance from the other drone during docking. We describe a position-based visual-inertial navigation (PBVIN) control system utilizing an optimized Truncated Hexagonal Pyramid (THP) marker for multi-drone quasi-stationary midair docking. The THP marker enables position synchronization and continuous tracking across three translational planes, even during docking. A non-homogeneous gain adaptation model is implemented to minimize positioning errors during dynamic control. The oblique docking design compensates for turbulence and leverages gravity to facilitate payload handoff. The THP marker's development is compared against single and crossmarker positioning (CMP) methods, demonstrating a 23.7% increase in positional hold consistency and a 22% reduction in localization drift. Outdoor trials validate mid-air docking capabilities, integrating PBVIN with global positioning to maintain synchronization at speeds up to 5 m / s. Docking tests reveal average position correction deviations of 8.52 mm for front-back (pitch) movements and 17.2 mm for left-right (roll) adjustments, ensuring high-precision tracking. The THP marker achieves 61% higher detection accuracy than single markers, while PBVIN successfully synchronizes drone movements in quasistationary conditions.