Smooth and Robust Trajectory Tracking of Single-Actuator Monocopters via Incremental Nonlinear Dynamic Inversion

This letter presents a comprehensive comparative study of Incremental Nonlinear Dynamic Inversion (INDI) and standard Nonlinear Dynamic Inversion (NDI) for smooth trajectory tracking on Samara Seed-Inspired Single-Actuator Monocopters (SAM). While prior work on SAMs has largely focused on hover stabilization, smooth robust control for aggressive translational motion remains a largely uncharted frontier. Leveraging the precession-prone dynamics inherent to the SAM, we analyze the tracking performance of INDI across varying flight speeds, trajectories, and wing morphologies (long, short, ultralight). Our experiment results demonstrate that INDI on the long-wing consistently achieves lower angular acceleration tracking errors, reducing mean and RMS by up to 13.8% and 13.0%, respectively, while also improving motor efficiency with up to 8.4% less PWM usage compared to NDI. Additionally, INDI produces tighter and more stable body yaw rates ( $\pm$ 0.1 Hz) and delivers up to 65% improvement in position tracking over traditional purely attitude control (ATT). Finally, even under severe actuation constraints with an ultralight-wing operating at reduced thrust, INDI maintains robust performance, validating its resistance towards precession and robust control of highly under-actuated SAMs.