Full Attitude Control of an Efficient Quadrotor Tail-sitter VTOL UAV with Flexible Modes

TL;DR

This paper develops a full attitude and altitude control system for an efficient quadrotor tail-sitter VTOL UAV that operates across all flight modes using motor differential thrusts, with optimized controllers for robustness and performance.

Contribution

It introduces a novel control system design that handles flexible modes and achieves superior tracking and robustness without control surfaces.

Findings

Achieved superior attitude tracking performance.

Demonstrated robustness in flexible mode compensation.

Validated control system through various flight tests.

Abstract

In this paper, we present a full attitude control of an efficient quadrotor tail-sitter VTOL UAV with flexible modes. This control system is working in all flight modes without any control surfaces but motor differential thrusts. This paper concentrates on the design of the attitude controller and the altitude controller. For the attitude control, the controller's parameters and filters are optimized based on the frequency response model which is identified from the sweep experiment. As a result, the effect of system flexible modes is easily compensated in frequency-domain by using a notch filter, and the resulting attitude loop shows superior tracking performance and robustness. In the coordinated flight condition, the altitude controller is structured as the feedforward-feedback parallel controller. The feedforward thrust command is calculated based on the current speed and the pitch angle. Tests in hovering, forward accelerating and forward decelerating flights have been conducted to verify the proposed control system.