Autonomous aerial perching and unperching using omnidirectional tiltrotor and switching controller

TL;DR

The paper introduces a lightweight, fully actuated omnidirectional tiltrotor capable of hovering at 90° pitch, enabling autonomous perching and unperching on vertical ferromagnetic surfaces via a magnet-based module actuated by a single servo. A switching controller coordinates free-flight, perching, and transitions to prevent rotor saturation and excessive overshoot, incorporating a disturbance estimator and transition-mode freezing. The perching/unperching strategy uses carefully timed signals and minimum-jerk trajectory planning to avoid collisions and ensure robust contact interaction, even under measurement and control errors. Experimental validation, including ablation studies, demonstrates successful in-flight perching and unperching and highlights the importance of transition-aware control for reliable operation in confined spaces. This work advances autonomous aerial manipulation by enabling rapid, reversible attachment to vertical surfaces with a lightweight, scalable platform.

Abstract

Aerial unperching of multirotors has received little attention as opposed to perching that has been investigated to elongate operation time. This study presents a new aerial robot capable of both perching and unperching autonomously on/from a ferromagnetic surface during flight, and a switching controller to avoid rotor saturation and mitigate overshoot during transition between free-flight and perching. To enable stable perching and unperching maneuvers on/from a vertical surface, a lightweight ($\approx$ $1$ \si{kg}), fully actuated tiltrotor that can hover at $90^\circ$ pitch angle is first developed. We design a perching/unperching module composed of a single servomotor and a magnet, which is then mounted on the tiltrotor. A switching controller including exclusive control modes for transitions between free-flight and perching is proposed. Lastly, we propose a simple yet effective strategy to ensure robust perching in the presence of measurement and control errors and avoid collisions with the perching site immediately after unperching. We validate the proposed framework in experiments where the tiltrotor successfully performs perching and unperching on/from a vertical surface during flight. We further show effectiveness of the proposed transition mode in the switching controller by ablation studies where large overshoot and even collision with a perching site occur. To the best of the authors' knowledge, this work presents the first autonomous aerial unperching framework using a fully actuated tiltrotor.

Figures (10)

• Figure 1: Experimental results showing both autonomous perching ((a) to (b)) and unperching ((c) to (d)) on the fly. Alphabetic order from (a) to (d) indicates the time sequence.
• Figure 2: CAD drawings of the tiltrotor (a) and the perching/unperching mechanism (b), (c). The tiltrotor without the perching/unperching mechanism has total of $8$ actuators, including $4$ rotors and $4$ servomotors. The four servomotors rotate the thrust direction of each rotor, enabling full actuation and especially $90^\circ$ pitching while hovering. When unperching, a single perching/unperching module shown in the blue-shaded region in (b) and (c) moves only in a tangential direction to the contact surface, thereby suffering less from adhesion induced by magnets.
• Figure 3: A prototype of the proposed tiltrotor with the perching/unperching modules.
• Figure 4: Switching control laws with or without transition modes $F2P, P2F$. $\bm{u}=\bm{u}_n + \bm{u}_r$, $\bm{u}_n = [\bm{f}_n;\bm{\tau}]$, $\bm{u}_r = [\bm{f}_r;\bm{0}_{3}]$
• Figure 5: A timeline showing the perching and unperching timings $\eta_d$ with respect to switching signals of the switching controller. $\mu_c$ is the controller mode and $\mu$ is actual status of either perching $P$ or free-flight $F$.