Adaptive Trajectory Control for Autonomous Helicopters

TLDR

Autonomous helicopter flight typically separates control into an inner attitude loop and an outer translational trajectory loop. The study introduces adaptive control to handle attitude and translational uncertainties, aiming to reduce model error across all six degrees of freedom and improve position tracking, and presents the theory, implementation, and flight‑test results. The approach employs dynamic inversion with neural‑network adaptation, pseudocontrol hedging to safeguard against actuator limits, a novel outer‑loop adaptation scheme, and a pole‑placement strategy that aligns outer‑loop bandwidth with the inner loop to enhance tracking. Flight tests demonstrate that even with a simplistic attitude model and basic kinematics, the adaptive controller achieves accurate position tracking.

Abstract

For autonomous helicopter flight, it is common to separate the flight control problem into an inner loop that controls attitude and an outer loop that controls the translational trajectory of the helicopter. In previous work, dynamic inversion and neural-network-based adaptation was used to increase performance of the attitude control system and the method of pseudocontrol hedging (PCH) was used to protect the adaptation process from actuator limits and dynamics. Adaptation to uncertainty in the attitude, as well as the translational dynamics, is introduced, thus, minimizing the effects of model error in all six degrees of freedom and leading to more accurate position tracking. The PCH method is used in a novel way that enables adaptation to occur in the outer loop without interacting with the attitude dynamics. A pole-placement approach is used that alleviates timescale separation requirements, allowing the outer-loop bandwidth to be closer to that of the inner loop, thus, increasing position tracking performance. A poor model of the attitude dynamics and a basic kinematics model is shown to be sufficient for accurate position tracking. The theory and implementation of such an approach, with a summary of flight-test results, are described.