Design and Development of Novel Quadcopters for Reliable Operations in Cluttered Environments

Abstract

This thesis presents innovative designs and control strategies for enhancing the performance and reliability of quadcopters, particularly in demanding and cluttered environments. The primary contributions include the development of two novel quadcopter prototypes—Scissorbot and Heliquad—both of which address fundamental limitations in current quadcopter technology, such as mid-flight flipping, control under actuator failures, and shape-changing ability.

The first major contribution is the design of Scissorbot, a morphing quadcopter with a mid-flight reconfigurable geometry that allows the lateral span to reduce significantly (up to 88%) using a servo-motor and bevel differential gearbox. This design enables safe operation in cluttered environments by minimising the risk of propeller tip collisions, even when adjacent propellers are positioned in different planes. A robust attitude control system is implemented, ensuring precise tracking even in the presence of disturbances. Multi-body simulations and real-world experiments validate Scissorbot’s performance and fault tolerance, with the findings confirming its ability to handle reconfiguration and scale effectively for future applications.

The second major contribution focuses on Heliquad, a Variable-Pitch-Propeller (VPP) quadcopter featuring cambered airfoil propellers. This design ensures full attitude control even after the complete failure of one actuator. The use of cambered airfoil propellers increases torque generation, particularly for yaw control, allowing the system to maintain full control with only three actuators. A unified fault-tolerant control system integrates a position tracking controller, an attitude controller, and a neural-network-based reconfigurable control allocation scheme, all tested through high-fidelity simulations and real-world experiments. The results demonstrate the Heliquad's ability to recover and land safely post-actuator failure, validating the effectiveness of the VPP mechanism.

Further contributions include the design and validation of the VPP mechanism for Heliquad, which involves detailed analysis of the input-output relationships, actuator sizing, and the control challenges associated with non-linear relationships in the system. The prototype demonstrates superior flight characteristics, particularly in mid-flight flipping maneuvers, and ensures full attitude control under the complete failure of an actuator.

The research highlights the potential of combining morphing geometries and VPP mechanisms to enhance quadcopter performance, particularly in fault-tolerant, high-stress scenarios. Future work may involve merging the morphing capabilities of Scissorbot with the VPP mechanism of Heliquad, providing a more robust solution to control and efficiency challenges in complex operational environments. This work paves the way for more adaptive, resilient UAV systems capable of performing critical missions in cluttered and dynamic environments.