A yaw angle, different from zero, introduces highly nonlinear couplings in the rotational and translational quadrotor dynamics, implying undesirable motions. This argument has motivated that the position control problem of quadrotors is studied generally regulating yaw at zero. However, zeroing yaw limits the maneuverability of underactuated quadrotors because yaw is one of the four actuated motions. In this paper, the simultaneous tracking of position and time-varying heading is proposed, based on an integral sliding mode control with a quaternion-based sliding surface. An exponential tracking with chattering-free is obtained without requiring any knowledge of the dynamic model or its parameters for implementation. Since a linear invariant orientation error manifold is enforced for all time, a time-varying gain is introduced for a well-posed finite time convergence, which is useful not only to realize the virtual position control scheme, due to underactuation, but also to guarantee a desired contact in a given point at a given desired contact time for the yaw motion. Illustrative applications are explored in a simulation study which shows the viability and versatility of position–yaw tracking in the surveillance of a field-of-view (FoV) target, aerial screw driver, and aerial grasping.
Quadrotors are highly maneuverable light weight drones, which are prone to aerodynamic disturbances, vibrations and uncertainties. These factors stand for a problem that demands robust control laws. For position tracking, the control problem is exacerbated because the plant is underactuated in the coordinates of interest, requiring a high performance attitude tracking to resolve underactuation. In this paper, a novel fractional-order controller is proposed by considering a well-posed map that relates the position/yaw control to desired attitude references. The attitude control is continuous and enforces and sustains a sliding motion in finite-time for exponential convergence of the tracking errors to fulfill a "virtual" position controller. The resulting closed-loop system is robust against continuous disturbances that are not necessarily differentiable in the conventional sense. A numerical study based on simulations is presented to analyze the advantages of the fractional actions to design a physically realizable controller, and experiments are discussed to expose the reliability of the proposed fractional scheme implemented in an 'X' configuration quadrotor.
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