A Self-rotating, Single-actuated UAV with Extended Sensor Field of View for Autonomous Navigation

Principal Investigator: Professor Fu Zhang (Assistant Professor, Department of Mechanical Engineering)

This project is showcased as the Research Highlight (January – February 2024) in the third exhibition – Technology for Future in Innovation Wing Two

Project information

Key features of PULSAR

The UAV is named Powered-flying Ultra-underactuated LiDAR-sensing Aerial Robot (PULSAR), whose motion in three-dimensional space is controlled by only a single actuator (i.e., motor). The single actuator design can naturally cause self-rotation motion of the UAV body, obviously extending the field of view (FoV) of the onboard LiDAR sensor. Furthermore, it also effectively reduces the energy loss of the propulsion system, allowing PULSAR to save 26.7% of energy consumption compared to a benchmarked quadrotor UAV. Utilizing the extended FoV and onboard computing resource, PULSAR can perform autonomous navigation in unknown environments and detect both static and dynamic obstacles in panoramic views without using any external instruments. PULSAR has large FoV, high flight efficiency, and autonomous navigation ability, which are all beneficial for the environmental observation and information collection. Therefore, it can be used in various applications, such as environment surveying, search and rescue, terrain mapping, and automatic 3D reconstruction.

Overview of PULSAR. (A) PULSAR uses one actuator (i.e., a motor) for full 3D position control and an onboard LiDAR sensor for autonomous navigation. (B) The uncompensated motor counter-torque naturally causes a self-rotation that extends the sensor horizontal FoV to 360°. (C) Autonomous flights of PULSAR in an unknown wooded environment at night; the flight trajectory is indicated by the onboard blue LED. (D) Autonomous flights in the woods in the daytime and the flight trajectory is shown as the red path.

Mechanical structure, avionics, and swashplateless mechanism. (A) Components description. (B) Interconnection among all electronic components. (C) Detailed mechanical structure of the swashplateless mechanism. (D) Assembly of the swashplateless mechanism, propeller blades, and motor. (E) Process of rotor acceleration causing the blades to lag from the rotor. (F) The illustration of the pitch angle variation of the blades.

Achievement of the Project

Nan Chen, Fanze Kong, Wei Xu, Yixi Cai, Haotian Li, Dongjiao He, Youming Qin, and Fu Zhang. A self-rotating, single-actuated UAV with extended sensor field of view for autonomous navigation. Sci. Robot. 8, eade4538 (2023). DOI:10.1126/scirobotics.ade4538

About the Scholar

Professor Fu Zhang is currently Assistant Professor of Mechanical Engineering at the University of Hong Kong (HKU). He received his B.E. degree in Automation from the University of Science and Technology of China (USTC) in 2011 and the Ph.D. degree in Controls from the University of California, Berkeley in 2015. His current research interests are on robotics and controls, with focus on UAV design, navigation, control, and LiDAR-based simultaneous localization and mapping.

Website: https://mars.hku.hk/people.html

Press release

Introducing PULSAR: HKU Team Develops Revolutionary Unpiloted Aerial Vehicle Inspired by Science Fiction

The press release article can be founded in HKU Press release (https://www.hku.hk/press/news_detail_26149.html)

The overview of PULSAR, showing its main structure, extended sensor field of view, and autonomous navigation flight in a wood environment.

Research members shot in the experimental site.

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Imagine a world where science fiction meets reality, where cutting-edge technology brings to life the awe-inspiring scenes from movies like Prometheus. This is the groundbreaking research led by Dr Fu Zhang, Assistant Professor of Department of Mechanical Engineering at the Faculty of Engineering, the University of Hong Kong (HKU), who has developed a Powered-flying Ultra-underactuated LiDAR-Sensing Aerial Robot (PULSAR) that is poised to redefine the world of unpiloted aerial vehicles (UAVs).

UAVs are already playing an increasingly vital role in search and rescue, cave surveying, and architectural mapping. The PULSAR, aptly named for its similarities to an astronomical pulsar’s self-rotation and scanning pattern, takes UAV technology to new heights. With a micro-computer and a LiDAR sensor, PULSAR boasts full onboard perception, mapping, planning, and control capabilities in both indoor and outdoor environments, all without requiring any external instruments.

The secret to PULSAR’s incredible functionality lies in its single actuator, which powers the swashplateless mechanism and provides both thrust and moment. Through a series of experiments, Dr Zhang’s team demonstrated PULSAR’s ability to detect static and dynamic obstacles in real-time, track complex trajectories, and navigate autonomously even in complete darkness. PULSAR’s robustness also extends to withstanding external wind disturbances, enabling safer and more stable flights in unpredictable conditions. At a maximum wind speed of 4.5 m/s, PULSAR can maintain its hover position within a small area. Such characteristic enables a safer and stable flight in a wild environment.

Besides its aforementioned capabilities, the sensor can also extend the field of view (FoV) through self-rotation motion, which enhances the UAV’s perception and task efficiency. Currently, there are two main approaches for extending the sensor FoV, but both of them consume a significant amount of power. The first approach involves using sensors with large FoVs, such as fisheye cameras, catadioptric cameras, or 360° LiDAR, which tend to produce distortions. However, 360° LiDAR has a narrow and low-resolution FoV in the vertical direction. The second approach involves using multiple sensors, such as a multi-camera or multi-LiDAR system, but this incurs additional costs and results in longer data processing times.

The invention of PULSAR can save 26.7% of energy consumption compared to a quadrotor UAV with the same propeller disk area and payload, while still maintaining good agility. Thanks to its single actuator propulsion system, PULSAR experiences less energy conversion loss, resulting in a high flight efficiency of 6.65g/W. Despite its small size, with a diameter of only 37.6 cm and a battery capacity of just 41 Wh, this 1234-g UAV achieved a hover time of over 12 minutes. By removing the LiDAR sensor and installing a larger propeller and battery, the hover time of PULSAR can be extended to more than 40 minutes.

The research finding is presented in the paper entitled “A self-rotating, single-actuated UAV with extended sensor field of view for autonomous navigation”, published in Science Robotics and highlighted as a visual feature on the official website of Science.

Dr Zhang said the research platform established by his team could be conducive to further exploration of self-rotating UAVs. “We believe that it will facilitate the research of UAV control methods under high-speed rotation and simultaneous localisation and mapping (SLAM) techniques under aggressive motion.”

Link to paper: https://mars.hku.hk/papers/scirobotics.ade4538_.pdf

For a demonstration video, please click here.

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