Almost-Global Exponential Tracking of a Variable Pitch Quadrotor on SE(3)

Abstract

Abstract This paper presents a coordinate-free trajectory tracking control design for the nonlinear dynamics of a variable pitch quadrotor. Unlike conventional quadrotors, the rotor thrust is varied by changing its blade pitch angle as opposed to its RPM. It has been shown that such an actuation mechanism has a very high control bandwidth and is capable of producing negative thrust, which facilitates aggressive trajectory tracking. However, the control allocation in the actuator for generating the commanded thrust and torque is not a static, linear relation, but is nonlinear and dynamic. Further, transient disturbances are present due to rapid variations in aerodynamic load on the rotor dynamics while varying the blade pitch angle. The proposed control law consists of a robust attitude controller augmented with a saturated thrust-feedback position controller. The control law is shown to almost-globally stabilize the tracking errors on SE(3) at an exponential rate. Numerical simulations on a model of a variable pitch quadrotor have been presented.