FLOAT Drone: A Fully-actuated Coaxial Aerial Robot for Close-Proximity Operations

Abstract

How to endow aerial robots with the ability to operate in close proximity remains an open problem. The core challenges lie in the propulsion system's dual-task requirement: generating manipulation forces while simultaneously counteracting gravity. These competing demands create dynamic coupling effects during physical interactions. Furthermore, rotor-induced airflow disturbances critically undermine operational reliability. Although fully-actuated unmanned aerial vehicles (UAVs) alleviate dynamic coupling effects via six-degree-of-freedom (6-DoF) force-torque decoupling, existing implementations fail to address the aerodynamic interference between drones and environments. They also suffer from oversized designs, which compromise maneuverability and limit their applications in various operational scenarios. To address these limitations, we present FLOAT Drone (FuLly-actuated cOaxial Aerial roboT), a novel fully-actuated UAV featuring two key structural innovations. By integrating control surfaces into fully-actuated systems for the first time, we significantly suppress lateral airflow disturbances during operations. Furthermore, a coaxial dual-rotor configuration enables a compact size while maintaining high hovering efficiency. Through dynamic modeling, we have developed hierarchical position and attitude controllers that support both fully-actuated and underactuated modes. Experimental validation through comprehensive real-world experiments confirms the system's functional capabilities in close-proximity operations.

Figures (9)

• Figure 1: Our proposed FLOAT Drone demonstrates diverse close-proximity operation tasks. (a) Carrying a watering can and watering flowers via a tilted hovering posture. (b) Traversing a narrow gap inclined at 20 degrees, with a width of 25 cm. (c) Pulling and pushing a deformable curtain within a minimum workspace of only 30 cm. Videos on the https://zju-jxlin.github.io/float-drone.github.io/.
• Figure 2: Visualization of $S_{c}(n)$. Y-axis represents the area of the circumscribed circle for different numbers of rotors, with the single rotor as the baseline. The values within circumscribed circles represent the diameter ratio of the circumscribed circle.
• Figure 3: Comparison of horizontal force generation among different UAV configurations. The red arrows denote the direction of the horizontal thrust generated by the drone, while the blue arrows indicate the direction of the forces exerted on the object by the downwash airflow.
• Figure 4: Schematic diagram for the implementation of full actuation. $T_1$ and $T_2$ represent the thrusts generated by the upper and lower rotors, respectively. $T_z$ is the total thrust in the vertical direction of the drone. $F_{cs1}$ and $F_{cs2}$ denote the lift forces produced by the upper and lower control surfaces, respectively. $T_x$ and $\tau_y$ are the total force and torque in the horizontal direction of the UAV. $G$ represents the gravity of the drone.
• Figure 5: Prototype and hardware configuration of FLOAT Drone.