Kevin Z. Y. Ang

Development of an Unmanned Coaxial Rotorcraft for the DARPA UAVForge Challenge

In this paper, we present a comprehensive design for a fully functional unmanned rotorcraft system: GremLion. GremLion is a new smallscale unmanned aerial vehicle (UAV) concept using two contra-rotating rotors and one cyclic swash-plate. It can fit within a rucksack and be easily carried by a single person. GremLion is developed with all necessary avionics and a ground control station. It has been employed to participate in the 2012 UAVForge competition. The proposed design of GremLion consists of hardware construction, software development, dynamics modeling and flight control design, as well as mission algorithm investigation. A novel computer-aided technique is presented to optimize the hardware construction of GremLion to realize robust and efficient flight behavior. Based on the above hardware platform, a real-time flight control software and a ground control station (GCS) software have been developed to achieve the onboard processing capability and the ground monitoring capability respectively. A GremLion mathematical model has been derived for hover and near hover flight conditions and identified from experimental data collected in flight tests. We have combined H1 technique, a robust and perfect tracking (RPT) approach, and custom-defined flight scheduling to design a comprehensive nonlinear flight control law for GremLion and successfully realized the automatic control which includes take-off, hovering, and a variety of essential flight motions. In addition, advanced mission algorithms have been presented in the paper, including obstacle detection and avoidance, as well as target following. Both ground and flight experiments of the complete system have been conducted including autonomous hovering, waypoint flight, etc. The test results have been presented in this paper to verify the proposed design methodology.

A Robust Real-Time Vision System for Autonomous Cargo Transfer by an Unmanned Helicopter

Motivated by the 2013 International UAV Innovation Grand Prix, we design and implement a real-time vision system for an unmanned helicopter autonomously transferring cargoes between two platforms. In the competition, four cargoes are initially placed inside four circles on one platform, respectively. They are required to be transferred one by one into the four circles on the other platform. This paper presents the core algorithms of the proposed vision system on ellipse detection, ellipse tracking, and single-circle-based position estimation. Experiments and the great success of our team in the competition have verified the efficiency, accuracy, and robustness of the algorithms. Our team was ranked first in the final round competition.

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.

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 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.

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.

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.

High-Precision Multi-UAV Teaming for the First Outdoor Night Show in Singapore

Advancement in the development of automation in aerial robotics has created endless applications today by utilizing autonomous drones, or in other words, unmanned aerial vehicles (UAVs). Motivated ...

Comprehensive Safety System Design and Development for Unmanned Aerial Vehicles Formation Flight System

With Unmanned Aerial Vehicles(UAVs) becoming more popular, safety and robustness considerations turn out to be the most important matter for autonomous flight of UAVs. In this paper, a comprehensive approach on the implementation of safety features for multiple UAVs during outdoor formation flight is proposed. A hierarchical three layer safety architecture is designed based on the risk assessment matrix which categorizes each flight failure condition based on the severity and probability of each case. Moreover, safety exit routes and a return procedure for multiple UAVs are implemented to prevent them from mid-air collision while flying out of their flight zone and to ensure their safe return to their launch location. The safety system is implemented on sixteen UAVs formation flight demonstration and all the safety precautions are verified in extensive flight tests.

Simulation study of homography-based vision-aided inertial navigation for aerial vehicles

This research proposes a novel scheme for vision-aided inertial navigation based on planar homography. By exploiting the multiplicative group property of homography matrices, extended Kalman filter-based vision aiding is formulated with a measurement model of the group difference between image-estimated and navigation homographies. A simple compensation for depth distortion of the homography matrix is also proposed, and shown to be effective in simulation.