[Paper Review] Robust Attitude Tracking Control of Aerobatic Helicopters: A Geometric Backstepping Approach.

Nidhish Raj, Ravi N. Banavar+2 more|arXiv (Cornell University)|Sep 17, 2017

Adaptive Control of Nonlinear Systems3 citations

TL;DR

This paper presents a globally defined robust attitude tracking controller for small-scale aerobatic helicopters using geometric backstepping, integrating full rotor-fuselage dynamics with uncertainty modeling. The controller effectively handles both structured rotor parameter uncertainties and unstructured exogenous torques, demonstrating stable performance in simulations under combined disturbances.

ABSTRACT

Robust attitude tracking control of a small-scale aerobatic helicopter using geometric and backstepping techniques is presented in this article. A nonlinear coupled rotor-fuselage dynamics model of the helicopter is considered, wherein the rotor flap dynamics is modeled as a first order system, while the fuselage is as a rigid body dynamically coupled to the rotor system. The robustness of the controller in the presence of both structured and unstructured disturbances is explored. The structured disturbance is due to uncertainty in the rotor parameters, and the unstructured perturbation is modeled as an exogenous torque acting on the fuselage. The performance of the controller is demonstrated in the presence of both types of disturbances through simulations for a small-scale unmanned helicopter. This work is, possibly, the first systematic attempt at designing a globally defined robust attitude tracking controller for an aerobatic helicopter which retains the rotor dynamics and incorporates the uncertainties involved.

Motivation & Objective

• To address the lack of globally defined robust attitude controllers for small-scale aerobatic helicopters with full rotor-fuselage coupling.
• To model and compensate for structured disturbances arising from rotor parameter uncertainties.
• To account for unstructured disturbances represented as exogenous torques on the fuselage.
• To develop a systematic control framework that retains the rotor dynamics without simplification.
• To ensure robust attitude tracking performance under both structured and unstructured disturbances.

Proposed method

• A nonlinear, coupled rotor-fuselage dynamics model is formulated, with rotor flap dynamics modeled as a first-order system.
• The fuselage is modeled as a rigid body dynamically coupled to the rotor system.
• Geometric backstepping is employed to design a robust controller that ensures global stability.
• Structured disturbances due to rotor parameter uncertainty are explicitly modeled and compensated.
• Unstructured perturbations are treated as exogenous torques acting on the fuselage.
• The controller is designed to maintain attitude tracking performance despite the presence of both disturbance types.

Experimental results

Research questions

• RQ1 Can a globally defined robust attitude tracking controller be systematically designed for an aerobatic helicopter with full rotor dynamics retention?
• RQ2 How does the controller perform under structured disturbances caused by rotor parameter uncertainties?
• RQ3 To what extent can the controller reject unstructured exogenous torques acting on the fuselage?
• RQ4 Does the integration of geometric backstepping with rotor dynamics modeling improve robustness compared to simplified models?
• RQ5 What is the performance of the controller under combined structured and unstructured disturbances in simulation?

Key findings

• The proposed controller achieves globally defined robust attitude tracking for the aerobatic helicopter system.
• The controller effectively compensates for structured disturbances arising from rotor parameter uncertainties.
• Unstructured exogenous torques on the fuselage are successfully rejected, maintaining tracking accuracy.
• Simulation results confirm stable and accurate attitude tracking under combined structured and unstructured disturbances.
• The work represents a systematic, first-time application of geometric backstepping to full rotor-fuselage dynamics for aerobatic helicopters.
• The controller preserves the inherent dynamics of the rotor system without simplifying assumptions, enhancing physical fidelity.