Position tracking of a hexacopter using a geometric backstepping control law - Experimental results

In this paper a position tracking controller for a hexacopter is presented. The controller design exploits the fact that for position tracking, the control of the whole attitude is not needed, but only the control of the body-fixed z-axis. This results in a position controller which is independent of the heading controller. This is achieved by introducing the thrust vector as a system´s state, i.e. using the body-fixed z-axis as a reduced attitude parameter and extending the thrust input T dynamically. This parameter choice also avoids drawbacks of local attitude parameterizations like singularities or unwinding and thus maximizes the flight envelope. The position controller is designed using a three-step backstepping control law, such that no time-scale separation is needed. The performance of the controller is demonstrated in outdoor flight tests.