Yijie Ke

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.

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.

A systematic design approach for an unconventional UAV J-Lion with extensible morphing wings

This paper presents a systematic design approach for an unconventional UAV, J-Lion. J-Lion is a UAV featured by its hybrid flight capability in both VTOL and fixed-wing modes. Besides, a morphing wing concept is also realized by the extensible wing design. To reduce the development cycle, our approach takes into account the common factors systematically in the conceptual design phase, including overall configuration, aerodynamics, internal subsystems, etc. Initial VTOL experiment results prove the design concept and verify the effectiveness of the proposed approach.

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.

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.

Drones for cooperative search and rescue in post-disaster situation

In this work, we report our solutions to the problems given in the 2014 International Micro Aerial Vehicle Competition, held in Delft, the Netherlands, August 2014, which involves using micro air vehicles in urban post-disaster search and rescue missions. Solutions to all key mission elements of the competition, including real-time map stitching, indoor navigation and roof-top perching, are documented and highlighted in this manuscript. The proposed solutions are successfully demonstrated in the competition and help us win the championship.

Model-based optimal auto-transition and control synthesis for tail-sitter UAV KH-Lion

This paper presents a systematic control synthesis method in order to achieve auto-transition for KH-Lion, a tail-sitter hybrid UAV. Although there are huge potentials in various applications of the hybrid tail-sitter UAVs, the transition between vertical take-off and landing mode and cruise mode is still a challenge now. Due to the complex behaviour that the transition can generate, it is very difficult to implement the auto-transition as the reference transition trajectory is hard to obtain. In this paper, we propose to use the model validated from the experiments to generate an optimal reference trajectory for transition. A constrained dynamic programming technique is applied to the model with the consideration of all necessary constraints. A feedback control algorithm is also designed to track the desired transition trajectory. Simulation result and successful flight experiments have demonstrated the effectiveness of the proposed synthesis method.