Design and Development of a Variable-Pitch-Propeller Quadcopter with Mid-flight Flipping and Fault-Tolerant Control Capabilities

Core Concepts

This paper presents the design and development of a quadcopter named Heliquad that utilizes Variable-Pitch-Propellers (VPP) to demonstrate unique capabilities beyond traditional Fixed-Pitch-Propeller quadcopters, including mid-flight flipping and full-attitude control on three working actuators.

Abstract

The paper begins by deriving the input-output relationship for a generic VPP mechanism design and analyzing its kinematic singularities. It then formulates the dynamics of the Heliquad quadcopter and develops a unified non-switching cascaded attitude-rate controller. A Neural Network-based control allocation is employed to handle the nonlinearities in propeller aerodynamics.
The Heliquad prototype is built and experimentally validated. The mid-flight flipping experiments demonstrate the controller's tracking performance in both upright and inverted conditions. The prototype is then flown with full-attitude control, including yaw-rate, on only three working actuators. This is achieved by leveraging the cambered airfoil propeller design. Finally, the safe recovery and precise landing of the Heliquad after a mid-flight actuator failure is demonstrated. To the best of the authors' knowledge, this is the first experimental demonstration of full-attitude control on three working actuators in a VPP quadcopter.

Stats

The maximum estimated pitching moment generated by the prototype propeller is 0.0105 N-m at a pitch angle of 19 degrees and 15000 RPM.
The estimated torque acting on the servo-motor is 0.06 Kg-cm.

Quotes

"To the best of the authors' knowledge, this paper demonstrates full-attitude control, including the yaw-rate tracking, on three working actuators for the first time in VPP quadcopter literature."
"The role of a cambered airfoil in the propeller blades is pivotal to ensure the feasibility of the hover equilibrium point."

Key Insights Distilled From

Variable-Pitch-Propeller Mechanism Design, and Development of Heliquad for Mid-flight Flipping and Fault-Tolerant-Control

by Eeshan Kulka... at arxiv.org 04-09-2024

https://arxiv.org/pdf/2404.05591.pdf

Deeper Inquiries

How can the Heliquad's capabilities be further extended to handle complete loss of two or more actuators

To handle the complete loss of two or more actuators, the Heliquad's capabilities can be further extended by implementing a more advanced fault-tolerant control strategy. One approach could involve reconfiguring the control allocation to redistribute the control effort among the remaining actuators in a way that ensures stability and maneuverability. This could involve dynamically adjusting the propeller pitch angles and motor RPMs to compensate for the lost actuators and maintain control over the aircraft. Additionally, implementing redundancy in the control system, such as backup actuators or redundant control algorithms, could enhance the system's fault tolerance and robustness in the face of multiple actuator failures.

What are the potential drawbacks or limitations of the VPP mechanism design and control approach presented in this paper

While the VPP mechanism design and control approach presented in the paper offer unique capabilities for the Heliquad, there are potential drawbacks and limitations to consider. One limitation is the complexity of the VPP mechanism, which may introduce additional points of failure and maintenance challenges. The need for precise control of propeller pitch angles and motor RPMs adds complexity to the control system, requiring sophisticated algorithms and potentially increasing the computational load. Additionally, the reliance on cambered airfoil propellers for generating pitching moments may limit the design flexibility and performance in certain flight conditions. Furthermore, the use of Neural Networks for control allocation introduces the need for extensive training data and may require frequent recalibration to adapt to changing flight conditions.

How can the insights from this work on VPP quadcopters be applied to other types of multi-rotor systems or even fixed-wing UAVs

The insights gained from the work on VPP quadcopters can be applied to other types of multi-rotor systems and fixed-wing UAVs to enhance their performance and capabilities. For multi-rotor systems, the variable-pitch propeller mechanism design can be adapted to improve efficiency, maneuverability, and fault tolerance. By incorporating VPP systems, multi-rotors can achieve better control over thrust and torque distribution, leading to enhanced stability and agility. In fixed-wing UAVs, the principles of VPP mechanisms can be utilized to optimize propeller performance and control, enabling more precise and efficient flight maneuvers. The fault-tolerant control strategies developed for VPP quadcopters can also be applied to other UAVs to enhance their resilience to actuator failures and improve overall system reliability.