Improving Multicopter Feedback Controllers for Flight in Vertically Narrow Space Using Robust Controller Bode Plot

Multicopters have attracted significant attention in recent years owing to their potential to revolutionize various fields. Maintaining stable flight in vertically narrow spaces is critical for broadening their applications. However, controllers designed for open environments often overlook pressure differentials that develop in confined spaces, thereby increasing the risk of ceiling collisions. To address this challenge, this study proposes a method for improving the feedback controllers of multicopters by employing the Robust Controller Bode (RCBode) plot. This intuitive loop-shaping technique enables the development of robust controllers using only classical control theory, a crucial consideration given that most commercially deployed multicopters rely on PID controllers. In addition, our approach avoids the substantial modeling efforts typically required to capture the complex dynamic characteristics of fluid flows by utilizing a simple nominal model capable of compensating for unknown external disturbances. Validation results demonstrate that multicopters equipped with the enhanced thrust controller can navigate vertically constrained spaces without ceiling collisions. Additionally, experimental findings confirm that tracking performance is improved not only by adjusting the thrust but also by reducing oscillations in roll and pitch.