Dynamic attitude planning for trajectory tracking in underactuated VTOL UAVs
  This paper addresses the trajectory tracking control problem for
underactuated VTOL UAVs. According to the different actuation mechanisms, the
most common UAV platforms can achieve only a partial decoupling of attitude and
position tasks. Since position tracking is of utmost importance for
applications involving aerial vehicles, we propose a control scheme in which
position tracking is the primary objective. To this end, this work introduces
the concept of attitude planner, a dynamical system through which the desired
attitude reference is processed to guarantee the satisfaction of the primary
objective: the attitude tracking task is considered as a secondary objective
which can be realized as long as the desired trajectory satisfies specific
trackability conditions. Two numerical simulations are performed by applying
the proposed control law to a hexacopter with and without tilted propellers,
which accounts for unmodeled dynamics and external disturbances not included in
the control design model.
