Nonlinear Adaptive Control of Quadrotor Multi-Flipping Maneuvers in the Presence of Time-Varying Torque Latency

Abstract

The dynamics of quadrotors are affected by time-varying torque latency, which can greatly alter the stability robustness and performance of the closed-loop control schemes employed for flight; this issue is especially relevant during the execution of aerobatic maneuvers such as high-speed multi-flips. To address this problem, we propose two controller synthesis methods associated with two different modeling approaches. In the first approach, we describe torque latency with a linear time-invariant (LTI)model, identified through ground experiments, which is then used to design a backstepping-based nonlinear controller. In the second approach, we employ an improved linear time-varying (LTV)model with a priori unknown parameters, which is used to synthesize and implement a novel nonlinear adaptive control scheme updated in real time using the recursive least-squares (RLS)algorithm. Empirical observations suggest that the torque delay affecting the system depends on the time-varying angular speed of the flyer and its derivative. This phenomenon is explained by the fact that the aerodynamic forces produced by, and acting on, the rotating propellers vary with the local velocity of the incident flows. Hence, in the proposed adaptive structure, we define the parameters of the LTV latency model as linear functions of the angular speed reference and its derivative. Experimental results compellingly demonstrate the efficacy of the methods introduced in this paper; compared to the highperformance linear controller in [1]-[3], the backstepping-based control scheme and adaptive controller decrease the average root mean square (RMS)value of the control error by 17.82 % and 38.42 %, respectively.