An Introduction to Nonlinear Robust Control for Unmanned Quadrotor Aircraft: How to Design Control Algorithms for Quadrotors Using Sliding Mode Control and Adaptive Control Techniques [Focus on Education]

TLDR

Quadrotor aircraft attract attention for their high mobility and autonomous capabilities, yet their underactuation and other limitations make them ideal testbeds for innovative control approaches, prompting extensive research into guidance, navigation, and control systems. The article aims to analyze and synthesize nonlinear robust control systems for quadrotors. The authors analyze quadrotor equations of motion under three progressively restrictive modeling assumptions: time‑varying inertial properties, a rigid main frame with thin spinning disc propellers, and small pitch and roll angles.

Abstract

Quadrotor aircraft are drawing considerable attention for their high mobility and capacity to perform tasks with complete autonomy, while minimizing the costs and risks involved with the direct intervention of human operators. Moreover, several limitations characterizing these rotary-wing unmanned aerial systems (UASs), such as their underactuation, make quadrotors ideal testbeds for innovative theoretical approaches to the problem of controlling mechanical systems. Designing autopilots for autonomous quadrotors is a challenging task, which involves multiple interconnected aspects. Numerous researchers are currently addressing the problem of designing autonomous guidance systems, navigation systems, and control systems for quadrotors. The primary goal of this article is to present an analysis and synthesis of several nonlinear robust control systems for quadrotors, as discussed in “Summary.” First, the article presents and analyzes the equations of motion of quadrotors under three sets of progressively restrictive modeling assumptions: 1) the vehicle's inertial properties (such as the mass and matrix of inertia) vary in time, 2) the quadrotor's main frame is a rigid body and the propellers are thin spinning discs, and 3) the pitch and roll angles are small.