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

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.

• The paper demonstrates a novel UAV design featuring a ring-shaped structure and dual-phase gripper for centering poles and ensuring secure load lifting.
• It employs a model-based control strategy with quadratic programming for optimal wrench allocation, enabling dynamic adjustments during transport.
• Experimental validation confirms sub-millimeter position errors and sub-5 cm placement accuracy, showcasing improved safety and efficiency over traditional methods.

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

The paper presents Geranos, a novel multi-rotor Unmanned Aerial Vehicle (UAV) specifically designed for the autonomous transportation and vertical assembly of poles. Traditional methods for such tasks, typically involving helicopters and cranes, suffer from inaccuracies due to swinging loads and necessitate manual intervention by ground crews, which poses significant risks and increases costs. This research successfully addresses these shortcomings, showcasing a UAV design that integrates precision, efficiency, and safety.

System Design

Geranos comprises several notable design features:

1. Structure: The UAV has a ring-shaped design, allowing it to pass over and grasp poles at their centers of mass (CoM). This minimizes the impact of the pole's inertia on the UAV's dynamics.
2. Gripper Mechanism: The gripper consists of a two-part mechanism:
   • Centering Mechanism: This mechanism ensures the pole is centered, reducing translational and rotational misalignments.
   • Lifting Mechanism: A friction-based self-locking mechanism uses folding triangles to securely hold poles without requiring continuous actuation.
3. Propeller Configuration: To enable accurate hovering and lateral movements without tilting, Geranos employs a combination of four primary propellers for lift and four auxiliary tilted propellers for lateral thrust. This configuration ensures full actuation, facilitating precise control over the UAV's position and orientation.

Control and Modeling

Geranos uses a model-based control approach grounded in the Newton-Euler formalism to derive the system dynamics. The control architecture includes:

• Controller: A proportional-derivative controller that computes a desired wrench based on state errors. This design includes integral terms to handle static errors, particularly useful during the assembly tasks.
• Wrench Allocation: A quadratic programming (QP) solver is employed for optimal wrench allocation, ensuring energy efficiency and adherence to actuator constraints.
• Dynamic Switching: The UAV's dynamics are adjusted in real-time upon grasping the pole, incorporating the load's mass and inertia into the system model. This switching ensures stability and precise control during the transport and assembly phases.

Experimental Validation

The paper thoroughly validates Geranos using both indoor experiments and simulations. Key results include:

• Gripper Performance: The UAV maintained a rigid connection with the pole, exhibiting minimal misalignment even under high accelerations (up to 21 m/s²). Position errors were maintained within 0.6 mm, and attitude deviations were around 1°.
• Precision in Assembly: Geranos demonstrated a sub-5 cm placement accuracy when positioning and stacking poles autonomously. The radial position errors during operations were consistently below the tolerance thresholds, confirming the UAV's precision in real-world tasks.

Implications and Future Work

From a theoretical perspective, Geranos contributes to the field by offering a fully actuated UAV system capable of achieving precise vertical load placement autonomously. Practically, it significantly enhances safety and efficiency in aerial transportation and construction tasks, reducing the need for manual intervention and minimizing risks associated with swinging loads.

Future developments will likely focus on:

• Scaling Up: Extending the system to handle heavier and larger poles for practical applications in construction sites.
• Autonomous Localization and Perception: Eliminating reliance on external systems (like motion capture) through advanced onboard sensing and localization technologies.
• Adaptability and Versatility: Improving the gripper to handle various pole shapes and materials, potentially using compliant materials and differentially actuated mechanisms.

In conclusion, this research marks a significant step towards integrating UAVs into complex construction roles, emphasizing precision, safety, and autonomy. Further advancements in scaling and perception will transform Geranos from a proof-of-concept to a viable tool in industrial applications.