Autonomous Aerial Recovery System of a Compound Mother-Daughter UAV System

Micro aerial vehicles (MAVs) are usually chosen as daughter-UAVs for many complicated missions in mother-daughter UAV system, and their recovery method is significant for the coordination between mother-UAV and daughter-UAVs. This paper aims to develop a autonomous recovery system for mother-daughter UAV system, which consists of a recovery mechanism subsystem and its corresponding recovery algorithms. The recovery system relies on a finite state machine architecture, and a relocation state is included for the daughter-UAVs to re-locate the corresponding recovery platform. The recovery mechanism is designed as a shelter, which includes three layers of the rolling-shutter platform and one layer of the bottom platform. The proposed recovery algorithms include the part of detection and the tracking controller. The detection subsystem based on a multi-state visual marker is developed, which helps the daughter-UAVs locate the recovery platform quickly and accurately. Then, a state-based PID controller and a reference-speed compensation controller are developed for the tracking subsystem, in order to transform a “moving platform” recovery problem into a “static platform” recovery problem. The proposed recovery system is tested in the simulation environment (Gazebo), in which the mother-UAV’s motion mode includes static and moving. Through the quantitative analyses of the experimental results, it is verified that the state-based PID controller with reference-speed compensation presents a better tracking effect, and the proposed system is effective for the autonomous recovery of four daughter-UAVs in aerial.