Circumnavigation with a group of quadrotor helicopters

Abstract: The primary goal of this thesis has been to implement Collective Circumnavigation. Given a group of unmanned aerial vehicles (UAVs) and the position of a target, the UAVs should approach the target and start circulating around it at a desired distance while forming a regular polygon. In this project quadrotor helicopters were used to conduct experiments and so a secondary goal was to study and implement control of quadrotors. The overall control of a quadrotor can be divided into three layers; attitude control, position control and path planning. The attitude of a quadrotor describes the orientation, i.e. how much the quadrotor is tilted, with respect to a referance frame. The attitude controller represents the innermost layer of the controller since all translational motions are achieved by tilting the quadrotor. A position controller represents the middle layer and is used to determine how much the quadrotor needs to tilt to get to a certain desired position. The outermost layer is the path planner which decides the trajectory of the quadrotor. The path planner is in this project given by the Circumnavigation algorithm. For both attitude and position control, the chosen controllers focus on the orientation of the thrust vector. The thrust vector points straight up from the center of mass of the quadrotor and is the sum of the thrust forces caused by the four rotors. The position controller calculates the desired direction of the thrust vector while the attitude controller aligns the real thrust vector with the desired one. Both controllers uses quaternions to describe the orientation of the thrust vector and to prioritize the alignment. Simulation results show that it was possible to merge the chosen controllers and experimental results show the feasibility of Collective Circumnavigation.