Voliro: An Omnidirectional Hexacopter With Tiltable Rotors (1801.04581v1)

Abstract: Extending the maneuverability of unmanned areal vehicles promises to yield a considerable increase in the areas in which these systems can be used. Some such applications are the performance of more complicated inspection tasks and the generation of complex uninterrupted movements of an attached camera. In this paper we address this challenge by presenting Voliro, a novel aerial platform that combines the advantages of existing multi-rotor systems with the agility of omnidirectionally controllable platforms. We propose the use of a hexacopter with tiltable rotors allowing the system to decouple the control of position and orientation. The contributions of this work involve the mechanical design as well as a controller with the corresponding allocation scheme. This work also discusses the design challenges involved when turning the concept of a hexacopter with tiltable rotors into an actual prototype. The agility of the system is demonstrated and evaluated in real- world experiments.

• The paper presents Voliro, a hexacopter with tiltable rotors that enables omnidirectional control by decoupling position and orientation.
• Experimental validation demonstrates Voliro's enhanced agility with capabilities like upside-down flight and wall interaction, showcasing potential for complex inspection tasks.
• Voliro broadens UAV applications requiring precise control, such as inspections, and serves as a framework for research on tiltable rotor dynamics and control.

Overview of Voliro: An Omnidirectional Hexacopter With Tiltable Rotors

The paper "Voliro: An Omnidirectional Hexacopter With Tiltable Rotors" introduces a novel UAV platform aiming to extend maneuverability beyond conventional multi-rotor systems. The central innovation lies in Voliro's hexacopter with tiltable rotors, which decouples the control of position and orientation, thereby enhancing operational agility. This paper elucidates the mechanical design, control strategy, and prototype evaluation, focusing on overcoming the intrinsic limitations of traditional multi-copters concerning dynamic agility and operational versatility.

Mechanical Design and System Architecture

Voliro's design features six rotors arranged in a traditional hexacopter manner, each capable of rotating around its arm axis through brushless DC motors. This configuration offers hexacopter benefits while granting omnidirectional control. The system's architecture incorporates the Pixhawk flight controller, with sensor integration from an IMU, magnetometer, and barometer, fused with external pose information such as Vicon or GNSS data. The innovative mechanical design successfully integrates high-performance tilt motors with attributes such as high rotational speed and precise control.

Control Strategy

Controlling such an omnidirectional system poses unique challenges, most notably in aligning rotor orientation with desired motion vectors. The paper introduces a control allocation mechanism based on decomposing rotor forces into vertical and lateral components, effectively minimizing the total thrust and producing more consistent rotor speeds through the setup's Moore-Penrose pseudo-inverse approach. This configuration supports a PID-based position control and cascade attitude control structure, optimizing for agility while facilitating reliable control dynamics across the UAV's full range of motion.

Evaluation and Experimental Validation

Experimental results validate Voliro's enhanced agility, showcasing maneuvers not feasible for standard UAV configurations, such as upside-down flight and lateral motion at inclined orientations. A particularly striking demonstration includes wall interactions using a passive three-sphere module mounted for contact, highlighting the vehicle's capabilities in complex environments and supporting operations like aerial inspections that require nuanced positional control.

Implications and Future Directions

Voliro signifies a substantive leap in UAV design, addressing gaps in dynamic agility and control precision. Practically, it broadens the scope for UAV deployment in domains requiring intricate positional adjustments and uninterrupted motion sequences, such as film production and structural inspections. Theoretically, its design challenges prevailing assumptions in rotor-based UAVs, suggesting pathways for future research, notably in control allocation for underactuated systems and optimizing rotor dynamics for even broader flight envelopes.

This platform may serve as a catalyst for further exploration into tiltable rotor designs, emphasizing the balance between agility and power consumption—a traditional trade-off magnified by the omnidirectional control capabilities. Researchers and developers in UAV technologies could leverage this framework to refine control systems and explore novel applications enhanced by dynamic aerial maneuvering. Overall, Voliro presents a compelling case for reevaluating multi-rotor systems' limitations, promising operational advancements and stimulating theoretical discussions on UAV dynamics.