Design and Control of a Midair-Reconfigurable Quadcopter using Unactuated Hinges (2103.16632v2)

Abstract: A novel quadcopter capable of changing shape mid-flight is presented, allowing for operation in four configurations with the capability of sustained hover in three. This is accomplished without requiring actuators beyond the four motors typical of a quadcopter. Morphing is achieved through freely-rotating hinges that allow the vehicle arms to fold downwards by either reducing or reversing thrust forces. Constraints placed on the control inputs of the vehicle prevent the arms from folding or unfolding unexpectedly. This allows for the use of existing quadcopter controllers and trajectory generation algorithms with only minimal added complexity. For our experimental vehicle at hover, we find that these constraints result in a 36% reduction of the maximum yaw torque the vehicle can produce, but do not result in a reduction of the maximum thrust or roll and pitch torques. Experimental results show that, for a typical maneuver, the added limits have a negligible effect on trajectory tracking performance. Finally, the ability to change configurations is shown to enable the vehicle to traverse small passages, perch on hanging wires, and perform limited grasping tasks.

• The paper introduces a reconfigurable quadcopter using unactuated hinges controlled solely by thrust, enabling shape changes midair without added actuators.
• The design utilizes passive hinges for multiple configurations and a control system managing transitions while accepting a 36% reduction in max yaw torque.
• Experimental results demonstrate the quadcopter's ability to navigate narrow passages and perform tasks like wire perching, showcasing practical utility in complex environments.

Midair-Reconfigurable Quadcopter: Design and Control Using Unactuated Hinges

The paper presents a novel design of a quadcopter capable of midair reconfiguration without the need for additional actuators beyond the conventional four motors. This design facilitates flight in multiple configurations, enabling sustained hover in select modes and enabling operations such as traversing narrow passages and performing manipulation tasks. The transformative feature is the implementation of passive hinges, allowing for arm folding through thrust manipulation, thereby placing minimal additional burden on the control system compared to traditional quadcopters.

Design and Implementation

The quadcopter is designed with freely rotating hinges at the arm connections. This structure permits three major configurations: unfolded, where it operates as a normal quadcopter; two-arms-folded, for narrow space navigation and grasping tasks; and four-arms-folded, facilitating passage through tight gaps. Unique arm geometries are introduced to enable sufficient control authority through thrust vector adjustments. The experimental vehicle reveals trade-offs with a calculated 36% reduction in maximum yaw torque due to control constraints ensuring stability across configurations. However, this does not affect the thrust or roll and pitch torques, sustaining agility.

Control Strategy

The control framework incorporates typical multicopter control techniques, supplemented by constraints that prevent unintended folding or unfolding of the arms. A hierarchical adjustment mechanism emphasizes retaining thrust direction accuracy over yaw, prioritizing critical position control. Transition strategies between configurations are elaborated, addressing the dynamics and control challenges, particularly in managing yaw disturbances due to asymmetric thrusts during transitions.

Performance and Applications

Experimental results underscore the vehicle's practical utility in scenarios demanding conventional and non-standard quadcopter functions. Successfully executing complex configurations such as tunnel traversal and wire perching illustrates the flexibility and potential utility in varied environments. These capabilities are achieved without additional mass from extraneous actuators, providing a clear advantage over existing morphing designs, particularly when autonomous operations in obstacle-rich environments are envisaged.

Future Prospects

The theoretical and practical enhancements displayed in this design present opportunities for further developments. Future work could explore expanded sensing capabilities and more sophisticated control techniques, including adaptive controls that dynamically modify constraints based on flight conditions. Integration with advanced localization methods could further extend the quadcopter's applicability in search and rescue missions, where quick adaptability to environmental constraints is crucial.

In conclusion, this paper offers a comprehensive analysis of a reconfigurable quadcopter design with significant implications for robotics and aerial vehicle engineering, fostering innovations that may redefine operational paradigms across diverse applications.