Kangli Wang

Design and Implementation of a Thrust-Vectored Unmanned Tail-Sitter with Reconfigurable Wings

In this paper, we present the development of a reconfigurable hybrid unmanned aerial vehicle (UAV): U-Lion [Ang et al., 11th IEEE Int. Conf. Control Automation (ICCA), pp. 750–755]. U-Lion is a small-scale UAV that is capable of vertical takeoff and landing (VTOL) and fixed-wing Cruise modes through its unique mechanical design. Mainly built with carbon fiber and expanded polyolefin (EPO) foam, U-Lion is equipped with an array of avionic components which enable stable control of the UAV both in VTOL and Cruise modes. It was employed by the National University of Singapore (NUS) Unmanned System Research Group to participate in the 2013 UAV Grand Prix (UAVGP) competition held in Beijing, China. Its design adopts a reconfigurable wing and a tail-sitter structure, which combines the advantages of a fixed-wing plane and a rotor helicopter effectively. U-Lion could transit from vertical takeoff to a hovering stage before flying in Cruise mode to realize efficient long duration flight. The propulsion of U-Lion comes from a self-fabricated contra-rotating motor fixed on a gimbal mechanism which can change the direction of the motor for the required thrust. This thrust-vectored propulsion system primarily provides control in the VTOL mode but also enhances flight capabilities in Cruise mode. The maximum thrust provided by the motor can be as high as 40 N and it provides six degree of motion controls in VTOL mode. U-Lion has a few special internal designs to empower its capabilities: (1) Reconfigurable wings allow the U-Lion to adapt to different flying modes. (2) Adaptive center of gravity (CG) by adjusting the battery position to fulfill the different requirements of CG for VTOL mode and Cruise mode. (3) Unique contra-rotating thrust-vectored propulsion system. The detailed design and implementation procedure have been presented in this paper along with our computational fluid dynamics (CFD) simulation results, real flight tests and competition performance.

Autonomous reconfigurable hybrid tail-sitter UAV U-Lion

We present in this work the development of a novel hybrid unmanned aircraft platform, U-Lion, which has both vertical take-off and landing (VTOL) and cruising flight capabilities. Our design is in tail-sitter structure with reconfigurable wings, which combines the advantages of a fixed-wing plane and a rotor helicopter effectively. This allows it to transit from vertical take-off to hovering, before flying in cruise mode for efficient long duration flight. The propulsion comes from two coaxial contra-rotating motors fixed on a gimbal mechanism, which can change the direction of the motors for the required thrust. This thrust-vectored propulsion system primarily provides control in the VTOL mode but also enhances flight capabilities in the cruise mode. The hybrid aircraft is equipped with GPS and airspeed sensors, and has an onboard avionic system with advanced flight control algorithms to perform fully autonomous VTOL and cruising flights, in addition to transiting effectively between VTOL and cruising flight modes. The overall design has been successfully verified by actual flight experiments.

Design and implementation of an unmanned aerial vehicle for autonomous firefighting missions

This paper presents a design and implementation of an unmanned aerial vehicle (UAV) for outdoor firefighting application. The proposed UAV firefighting system consists of a self-designed quadcopter as platform, a transmission system to collect and release water, a real time kinematic (RTK) based navigation system and a mission control system to monitor and coordinate the UAV. In our proposed autonomous cooperative framework, the UAV finds an optimal path (with respect to distance and power consumption) to the fire spot at first. After arriving at the target on fire, the mission control system will guide the UAV to suppress the fire. The proposed framework has been demonstrated in the 2015 International Micro Aerial Vehicle Outdoor Competition, held in Aachen, Germany and help our team V-Lion obtain the second place. Our designed framework has successfully achieved all the requirements in firefighting mission even in a challenging wind gusts environment. The video of the firefighting mission can be found at: https://youtu.be/YREngbun7zQ.

Search and Rescue Using Multiple Drones in Post-Disaster Situation

We present the development and application of multiple autonomous aerial vehicles in urban search and rescue missions. The missions are designed by the 2014 International Micro Aerial Vehicle Competition, held in Delft, the Netherlands, August 2014. Different mission tasks are identified for search and rescue missions, such as aerial photography, low altitude flight in urban environment, indoor navigation and rooftop landing. These tasks are all of paramount importance for rescuers in a disaster-hit place. We have designed a team of micro aerial vehicles with specific configurations to meet the mission requirements. A range of key technologies have been developed, including robust controller design, real-time map stitching, indoor navigation and roof-top perching. The proposed solutions are successfully demonstrated in the competition.

Development of autonomous hybrid UAV U-Lion with VTOL and cruise flying capabilities

In this paper, we present a novel hybrid UAV, U-Lion, which has autonomous VTOL and cruise flying capabilities. The reconfigurable wings are designed so that the structure of U-Lion is aerodynamically efficient in both flying modes. Vectoring thrust and the multiple control surfaces tail are implemented to increase the controllability for better maneuverability and stronger rejection to wind gust disturbance. A complete control framework is developed for the autonomous flight for both flying modes as well as the bi-directional transitions. An autonomous outdoor flight test result is presented to demonstrate the effectiveness of the platform design and the entire control framework.

An efficient UAV navigation solution for confined but partially known indoor environments

This paper presents a robust and efficient navigation solution for a quadrotor UAV to perform autonomous flight in a confined but partially known indoor environment. The main sensors used onboard of the UAV are two scanning laser range finders and an inertial measurement unit. When the indoor environment is structured and the coordinates of its key corner features are known, the UAV planer position can be efficiently calculated via the measurements from the first horizontally scanning laser range finder. The height of the UAV with respect to the ground can be robustly estimated by the second laser scanner which is mounted orthogonally to the first. Besides, this work also adopts a robust and perfect tracking control method with integral action to enable the UAV to track any smooth 3-D trajectories responsively and precisely. All computation is done onboard by an ARM-based embedded computer with limited processing power. The whole system was successfully tested in the 2013 Singapore Amazing Flying Machine Competition and helped the Unmanned Aircraft Systems Group from the National University of Singapore win the overall championship in the fully autonomous category.

Development of an unmanned tail-sitter with reconfigurable wings: U-Lion

In this paper, we present the development of a reconfigurable hybrid unmanned aerial vehicle (UAV): U-Lion. U-Lion is a small-scale UAV that is capable of vertical takeoff and landing (VTOL) and fixed-wing flight modes through its unique mechanical design. Mainly built with carbon fiber and Expanded PolyOlefin (EPO) foam, U-Lion is equipped with an array of electronic avionic components which enable stable control of the UAV both in VTOL and Cruise modes. It was employed by the National University of Singapore (NUS) Unmanned System Research Group to participate in the 2013 UAV Grand Prix (UAVGP) competition held in Beijing, China. Its design adopts a reconfigurable wing and a tailsitter structure, which combines the advantages of a fixed-wing plane and a rotor helicopter effectively. U-Lion could transit from vertical takeoff to a hovering stage before flying in cruise mode to realize efficient long duration flight. The propulsion of U-Lion comes from a self-fabricated contra-rotating motor fixed on a gimbal mechanism which can change the direction of the motor for the required thrust. This thrust-vectored propulsion system primarily provides control in the VTOL mode but also enhances flight capabilities in the cruise mode. The detailed design and implementation procedure have been presented in this paper along with our Computational Fluid Dynamics (CFD) simulation results, real flight tests and competition performance.

Vision-aided tracking of a moving ground vehicle with a hybrid UAV

In this work, we present the development of a target tracking and following system using a self-customized hybrid UAV, KH-Lion. KH-Lion is a small and autonomous tail-sitter UAV stabilized and controlled by two vectored propulsion systems. A target tracking system was developed on this platform for autonomous target following on a predetermined moving object on the ground. A customized AprilTag marker was attached on a radio-controlled car, and the target tracking algorithm was verified in actual flight experiment in which the moving car is tracked. Experiments were conducted in the environment of VICON motion tracking system, which provides us with a ground truth to evaluate the performance of the tracking. The system was verified and tested with a moving speed of approximately 0.5 m/s.

Development of autonomous quadrotor system for vertical replenishment

Cargo transportation between moving platforms is one of the most meaningful potential applications of UAVs. However, to fully autonomously transport the cargos, the UAV is required to have high position precision and high intelligence to tackle all the emergencies, on which the technology is not mature yet. In this article, we present a quadrotor system targeting at fully autonomous cargo transportation missions. A large payload, long endurance quadorotor is utilized as the UAV platform. A novel navigation framework is proposed for the UAV to navigate between moving platforms. A robust vision algorithm is presented for localizing visual target under changing illumination conditions with auto-adjustment of exposure and HSV values. Sophisticated mission planning algorithm is developed with highly modular software structure for managing the complex mission requirements and tackling different emergencies. The developed quadrotor system has taken part in the 3rd AVIC Cup - International UAV Innovation Grand Prix 2015 and our team won the championship.

A stereo and rotating laser framework for UAV navigation in GPS denied environment

Recent developments in robotics sensing using either the active sensor-laser range finder (LRF) or passive sensors-camera systems have shown that the existing approaches are able to estimate the motion and reconstruct the environment in a typical GPS-denied environment such as indoor environments. However, for a 2D LRF, it can only provide a planar measurement due to the hardware limitations and the cost for 3D LRF is still too high for robotic systems. For camera systems, the 3D perception capability and lightweight are promising while it is not effective in long range, low illumination and low textured environment compared to the LRF. In the proposed framework, our first contribution is a senor integration system that combines a stereo camera with a rotating LRF. The stereo camera can achieve a fast and smooth motion estimation and the rotating LRF could construct a dense 3D environment. Our second contribution is an integration of a fast feature-based motion estimation with an accurate shape matching refinement. The proposed approaches have been built in our customized unmanned aerial vehicle (UAV) platform. We have verified our proposed approach through a series of extensive evaluations in clustered indoor environments and open outdoor environments.