Geranos: a Novel Tilted-Rotors Aerial Robot for the Transportation of Poles

TL;DR

Geranos addresses the risk and inaccuracy of conventional sling-load operations by introducing a ring-shaped, tilted-rotor UAV designed for precise aerial transportation and vertical assembly of long poles. It couples a two-part centering and lifting gripper with an eight-rotor propulsion layout to maintain near-vertical orientation while enabling lateral motion, and it integrates a model-based controller with a QP-based wrench allocation that accounts for pole dynamics. Experimental results demonstrate sub-5 cm placement accuracy and successful stacking of poles up to 2 m long and 3 kg in mass, using autonomous grasping and release without human intervention. The work provides a scalable blueprint for autonomous aerial assembly tasks in challenging terrains, with future work focused on onboard perception and outdoor validation.

Abstract

In challenging terrains, constructing structures such as antennas and cable-car masts often requires the use of helicopters to transport loads via ropes. The swinging of the load, exacerbated by wind, impairs positioning accuracy, therefore necessitating precise manual placement by ground crews. This increases costs and risk of injuries. Challenging this paradigm, we present Geranos: a specialized multirotor Unmanned Aerial Vehicle (UAV) designed to enhance aerial transportation and assembly. Geranos demonstrates exceptional prowess in accurately positioning vertical poles, achieving this through an innovative integration of load transport and precision. Its unique ring design mitigates the impact of high pole inertia, while a lightweight two-part grasping mechanism ensures secure load attachment without active force. With four primary propellers countering gravity and four auxiliary ones enhancing lateral precision, Geranos achieves comprehensive position and attitude control around hovering. Our experimental demonstration mimicking antenna/cable-car mast installations showcases Geranos ability in stacking poles (3 kg, 2 m long) with remarkable sub-5 cm placement accuracy, without the need of human manual intervention.

Figures (7)

• Figure 1: (a) Common sling load operation for load; (b) An example of a commercial solution for load stabilization by Verton; (c) Fly-Crane system for cooperative sling load transportation jimenez2022precise; (d) The PrisMAV omnidirectional aerial manipulator with a linear delta arm PrisMAV
• Figure 2: This figure illustrates the working principles of the Geranos UAV. For greater clarity the vehicle is split into three parts: the lifting mechanism (red), the centering mechanism (blue) and the actuation (green). On the left, a picture of the full system is displayed, while in the middle an explosion view illustrates the three main parts of the UAV. The top right picture shows the relevant forces acting between the pole and one of the folding triangles used in the lifting mechanism. The picture in the middle right depicts the actuation setup and the spinning directions of all rotors (green for clockwise and blue for counter clockwise). The working principle of the centering mechanism is illustrated on the bottom of this figure. The yellow lines symbolize cables equipped with a spring while the green, orange and red lines represent inelastic cables. Cable fixations are represented by filled circles matching the color of the respective cables.
• Figure 3: Full gripping procedure: Once the pole is located within the vertical clearance of Geranos (a), the gripping procedure begins. The centering mechanism aligns the pole (or rather the UAV, when airborne), such that the central axis of the pole is as close as possible to the the $z$-axis of $\mathcal{F}_b$ (b). Once the centering procedure has finished (c), the self locking lifting mechanism comes in to play (d). By folding down all three hinged triangles (e), they will come in contact with the pole (f), effectively clamping it in place. When releasing the pole, this operation is done in reverse. This, however, only works if the pole is placed on the ground, since the self-locking mechanism can only be released if the weight of the pole is counteracted by an external force, e.g., the ground reaction.
• Figure 4: System Architecture of Geranos. The System comprises of three main categories: The commands sent from the ground station, a control loop running the onboard computer, and the sensors and actuators mounted on the robot. To estimate the robot's state, sensor measurements from an onboard IMU and an external motion capture system are fused with an Extended Kalman Filter. In case a node runs periodically, its frequency is specified above it.
• Figure 5: Position and attitude misalignment between Geranos and the pole depending on the applied acceleration.