COMET: A Dual Swashplate Autonomous Coaxial Bi-copter AAV with High-Maneuverability and Long-Endurance

TL;DR

COMET tackles the enduring conflict between efficiency and maneuverability in compact coaxial bi-copters by implementing a dual swashplate cyclic pitch system. Through systematic rotor-spacing and blade-angle optimization, along with comprehensive bench tests and dynamic-model-based control, it demonstrates enhanced thrust authority, reduced rotor-interaction losses, and improved trajectory-tracking performance under various payloads. Endurance tests show competitive hover efficiency, while trajectory experiments reveal substantial gains over single-swashplate designs, and autonomous navigation experiments confirm robustness across sensing configurations. The work provides a practical pathway to deploy high-endurance, agile micro AAVs in GPS-denied or cluttered environments, with clear directions for extending high-speed capabilities.

Abstract

Coaxial bi-copter autonomous aerial vehicles (AAVs) have garnered attention due to their potential for improved rotor system efficiency and compact form factor. However, balancing efficiency, maneuverability, and compactness in coaxial bi-copter systems remains a key design challenge, limiting their practical deployment. This letter introduces COMET, a coaxial bi-copter AAV platform featuring a dual swashplate mechanism. The coaxial bi-copter system's efficiency and compactness are optimized through bench tests, and the whole prototype's efficiency and robustness under varying payload conditions are verified through flight endurance experiments. The maneuverability performance of the system is evaluated in comprehensive trajectory tracking tests. The results indicate that the dual swashplate configuration enhances tracking performance and improves flight efficiency compared to the single swashplate alternative. Successful autonomous flight trials across various scenarios verify COMET's potential for real-world applications.

Figures (8)

• Figure 1: (a). A center-of-gravity (CoG) shifting driven coaxial bi-copter AAV muFly by Bermes et al. bermes2008CoG (b). Aerodynamic control surfaces coaxial bi-copter AAV CanFly by Pan et al. canfly (c). A swashplateless duct coaxial bi-copter AAV Halo by Li et al. li2023halo (d). A servo-controlled coaxial bi-copter AAV by Chen et al. chen2024design (e). A gimbal-controlled coaxial bi-copter AAV GimbalHawk by Reddington et alreddington2021design. (f). A coaxial bi-copter AAV CoAX with swashplate cyclic pitch control by Fankhauser et al. fank2011
• Figure 2: (a). General schematic of COMET. (b). The folded overall dimensions of COMET are 450 mm in height and a maximum diameter of 66 mm. (c). Breakdown of the COMET's propulsion system, highlighting key structural components including the swashplates, brushless motors, propeller mount, and servos. The diagram also illustrates the vertical rotor separation distance $z$, (d). Blade installation angle, (e). Flapping hinges, and (f). Lead-lag hinges.
• Figure 3: (a)(b) Thrust and efficiency versus normalized separation distance ($z/D$). (c)(d) Thrust and efficiency versus installation angle of the lower rotor.
• Figure 4: Testbench torque results, blue for dual swashplate configuration, orange for single swashplate configuration on lower rotor, green for single swashplate configuration on upper rotor.
• Figure 5: Reference frame definition of COMET and visualization of the tilted thrust vector with tilt angles $\alpha_i$ and $\beta_i$.