Servo Integrated Nonlinear Model Predictive Control for Overactuated Tiltable-Quadrotors

TL;DR

This paper presents a nonlinear model predictive control method for tiltable quadrotors, enabling independent attitude and position control while considering servo dynamics, validated through simulation and real-world experiments.

Contribution

The proposed NMPC approach directly incorporates servo dynamics and full system nonlinearities, improving control performance over traditional methods.

Findings

Enhanced control accuracy with integrated servo dynamics

Successful real-world implementation at 100 Hz

Robust and smooth pose-tracking demonstrated

Abstract

Utilizing a servo to tilt each rotor transforms quadrotors from underactuated to overactuated systems, allowing for independent control of both attitude and position, which provides advantages for aerial manipulation. However, this enhancement also introduces model nonlinearity, sluggish servo response, and limited operational range into the system, posing challenges to dynamic control. In this study, we propose a control approach for tiltable-quadrotors based on nonlinear model predictive control (NMPC). Unlike conventional cascade methods, our approach preserves the full dynamics without simplification. It directly uses rotor thrust and servo angle as control inputs, where their limited working ranges are considered input constraints. Notably, we incorporate a first-order servo model within the NMPC framework. Simulation reveals that integrating the servo dynamics is not only an enhancement to control performance but also a critical factor for optimization convergence. To evaluate the effectiveness of our approach, we fabricate a tiltable-quadrotor and deploy the algorithm onboard at 100 Hz. Extensive real-world experiments demonstrate rapid, robust, and smooth pose-tracking performance.