Topical Collection "Unmanned Aerial Systems"

Editors

Collection Editor
Dr. David Anderson

Aerospace Sciences Research Division, School of Engineering, University of Glasgow, Glasgow, Scotland, UK
Website | E-Mail
Interests: Autonomous Systems; Multi-agent & Multi-resolution Simulation; Nonlinear Control; Operational Analysis and Flight Dynamics & Control
Collection Editor
Prof. Javaan Chahl

Joint Chair of Sensor Systems, School of Engineering, University of South Australia, SA 5095, Australia
Website | E-Mail
Phone: +61 8 830 25886
Interests: navigation; biomimetics; autopilots; machine vision; aircraft performance; flapping wing flight; optics
Collection Editor
Dr. Michael Wing

Director of Aerial Information Systems Laboratory, Forest Engineering, Resources and Management Department, Oregon State University, 204 Peavy Hall, Corvallis, OR 97331, USA
Website | E-Mail
Interests: Unmanned Aerial Systems (UAS); Geographic Information Systems (GIS); Land Cover Change; Global Positioning Systems (GPS); Remote Sensing; Land Surveying and Geodesy; Visualization and Visibility Analysis; Crime Mapping and Analysis; Geographic Information Science; Digital Measurement Tools for Natural Resource Applications; Stream Habitat; Precision Forestry; Spatial Statistics

Topical Collection Information

Dear Colleagues,

Once perceived as a niche application, Unmanned Aerial Systems (UAS) are now well established as a serious sector within the aerospace industry. The global marketplace for UAS technology has seen the sharpest growth of any aerospace sector for the past decade and this trend is predicted to continue well into the 21st century. Currently, the most prolific UAS application is military surveillance, where UAS systems have proven to be invaluable in recent conflicts. However, such uses merely scratch the surface of potential UAS applications—the real challenge facing researchers is to develop technologies to enable widespread adoption of UAS in civilian airspace, both controlled and urban.

Research in UAS requires expertise from disciplines across the academic and industrial spectra. Advances in computing and communications bandwidth for example have allowed aerodynamicists and aircraft structural engineers to explore the design space in a manner impossible even a few years ago. This is especially true in the domain of small-UAS, where a number of new platform designs from tail-sitters and stop-rotors to compound configurations have recently been proposed. Not new ideas, granted, but configurations now realisable within an unmanned aircraft setting. Unmanned systems have therefore created an opportunity for novelty, innovation and creativity in aerospace design not seen for half a century. Another key research area is in unmanned aircraft operations analysis. Here, new application areas for UAS are discovered as advances in airborne sensing, autonomy and precise platform control flow into UAS designs, yielding greater performance and capability.

The challenges in realising the true potential of UAS are not all technical. Societal factors must be addressed, particularly the negative stereotype of the ‘drone’. Such challenges may be overcome in part by developing innovative new design and analysis methods for improving and demonstrating UAS safety and reliability. We invite papers either addressing the research opportunities outlined here or in the general topic area of unmanned aerial vehicles that will make a substantive contribution to the state of the art.

Dr. David Anderson
Prof. Dr. Javaan Chahl
Dr. Michael Wing
Collection Editors

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Keywords

  • autonomous systems
  • aerospace sensor technologies
  • aerodynamic technologies
  • systems engineering
  • guidance navigation and control
  • unmanned systems operational analysis/air traffic management
  • system of systems simulation
  • aerospace design and optimization
  • aerospace propulsion
  • smart materials and structures
  • composite structures and health monitoring
  • rotorcraft
  • flight safety
  • reconfigurable/fault tolerant control
  • flight dynamics
  • small unmanned aerial vehicles

Related Special Issue

Published Papers (28 papers)

2018

Jump to: 2017, 2016, 2015

Open AccessArticle Fast and Robust Flight Altitude Estimation of Multirotor UAVs in Dynamic Unstructured Environments Using 3D Point Cloud Sensors
Received: 10 August 2018 / Revised: 30 August 2018 / Accepted: 4 September 2018 / Published: 6 September 2018
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Abstract
This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the
[...] Read more.
This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the conventional sensors such as laser altimeters, barometers, or accelerometers, which have several limitations when used individually. Our proposed algorithm includes two stages: in the first stage, a fast clustering of the measured 3D point cloud data is performed, along with the segmentation of the clustered data into horizontal planes. In the second stage, these segmented horizontal planes are mapped based on the vertical distance with respect to the point cloud sensor frame of reference, in order to provide a robust flight altitude estimation even in presence of several static as well as dynamic ground obstacles. We validate our approach using the IROS 2011 Kinect dataset available in the literature, estimating the altitude of the RGB-D camera using the provided 3D point clouds. We further validate our approach using a point cloud sensor on board a UAV, by means of several autonomous real flights, closing its altitude control loop using the flight altitude estimated by our proposed method, in presence of several different static as well as dynamic ground obstacles. In addition, the implementation of our approach has been integrated in our open-source software framework for aerial robotics called Aerostack. Full article
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Open AccessArticle Multi-UAV Doppler Information Fusion for Target Tracking Based on Distributed High Degrees Information Filters
Received: 1 January 2018 / Revised: 14 February 2018 / Accepted: 22 February 2018 / Published: 8 March 2018
Cited by 2 | PDF Full-text (1641 KB) | HTML Full-text | XML Full-text
Abstract
Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed
[...] Read more.
Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed in the most recent related literature. These algorithms are applied to maneuvering target tracking based on Radar Doppler range/range rate signals. To achieve this purpose, different measurement models such as range-only, range rate, and bearing-only tracking are used in the simulations. In this paper, the mobile sensor target tracking problem is addressed and solved by a higher-degree class of quadrature information filters (HQIFs). A centralized fusion architecture based on distributed information filtering is proposed, and yielded excellent results. Three high dynamic UAVs are simulated with synchronized Doppler measurement broadcasted in parallel channels to the control center for global information fusion. Interesting results are obtained, with the superiority of certain classes of higher-degree quadrature information filters. Full article
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2017

Jump to: 2018, 2016, 2015

Open AccessArticle Experimental Investigation of the Wake and the Wingtip Vortices of a UAV Model
Received: 5 October 2017 / Revised: 28 October 2017 / Accepted: 30 October 2017 / Published: 1 November 2017
Cited by 2 | PDF Full-text (10198 KB) | HTML Full-text | XML Full-text
Abstract
An experimental investigation of the wake of an Unmanned Aerial Vehicle (UAV) model using flow visualization techniques and a 3D Laser Doppler Anemometry (LDA) system is presented in this work. Emphasis is given on the flow field at the wingtip and the investigation
[...] Read more.
An experimental investigation of the wake of an Unmanned Aerial Vehicle (UAV) model using flow visualization techniques and a 3D Laser Doppler Anemometry (LDA) system is presented in this work. Emphasis is given on the flow field at the wingtip and the investigation of the tip vortices. A comparison of the velocity field is made with and without winglet devices installed at the wingtips. The experiments are carried out in a closed-circuit subsonic wind tunnel. The flow visualization techniques include smoke-wire and smoke-probe experiments to identify the flow phenomena, whereas for accurately measuring the velocity field point measurements are conducted using the LDA system. Apart from the measured velocities, vorticity and circulation quantities are also calculated and compared for the two cases. The results help to provide a more detailed view of the flow field around the UAV and indicate the winglets’ significant contribution to the deconstruction of wing-tip vortex structures. Full article
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Open AccessArticle Aerial Target Tracking Algorithm Based on Faster R-CNN Combined with Frame Differencing
Received: 24 April 2017 / Revised: 25 May 2017 / Accepted: 12 June 2017 / Published: 20 June 2017
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Abstract
We propose a robust approach to detecting and tracking moving objects for a naval unmanned aircraft system (UAS) landing on an aircraft carrier. The frame difference algorithm follows a simple principle to achieve real-time tracking, whereas Faster Region-Convolutional Neural Network (R-CNN) performs highly
[...] Read more.
We propose a robust approach to detecting and tracking moving objects for a naval unmanned aircraft system (UAS) landing on an aircraft carrier. The frame difference algorithm follows a simple principle to achieve real-time tracking, whereas Faster Region-Convolutional Neural Network (R-CNN) performs highly precise detection and tracking characteristics. We thus combine Faster R-CNN with the frame difference method, which is demonstrated to exhibit robust and real-time detection and tracking performance. In our UAS landing experiments, two cameras placed on both sides of the runway are used to capture the moving UAS. When the UAS is captured, the joint algorithm uses frame difference to detect the moving target (UAS). As soon as the Faster R-CNN algorithm accurately detects the UAS, the detection priority is given to Faster R-CNN. In this manner, we also perform motion segmentation and object detection in the presence of changes in the environment, such as illumination variation or “walking persons”. By combining the 2 algorithms we can accurately detect and track objects with a tracking accuracy rate of up to 99% and a frame per second of up to 40 Hz. Thus, a solid foundation is laid for subsequent landing guidance. Full article
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Open AccessArticle Nonlinear Model Predictive Control for Unmanned Aerial Vehicles
Received: 26 April 2017 / Revised: 7 June 2017 / Accepted: 12 June 2017 / Published: 17 June 2017
Cited by 1 | PDF Full-text (867 KB) | HTML Full-text | XML Full-text
Abstract
This paper discusses the derivation and implementation of a nonlinear model predictive control law for tracking reference trajectories and constrained control of a quadrotor platform. The approach uses the state-dependent coefficient form to capture the system nonlinearities into a pseudo-linear system matrix. The
[...] Read more.
This paper discusses the derivation and implementation of a nonlinear model predictive control law for tracking reference trajectories and constrained control of a quadrotor platform. The approach uses the state-dependent coefficient form to capture the system nonlinearities into a pseudo-linear system matrix. The state-dependent coefficient form is derived following a rigorous analysis of aerial vehicle dynamics that systematically accounts for the peculiarities of such systems. The same state-dependent coefficient form is exploited for obtaining a nonlinear equivalent of the model predictive control. The nonlinear model predictive control law is derived by first transforming the continuous system into a sampled-data form and and then using a sequential quadratic programming solver while accounting for input, output and state constraints. The boundedness of the tracking errors using the sampled-data implementation is shown explicitly. The performance of the nonlinear controller is illustrated through representative simulations showing the tracking of several aggressive reference trajectories with and without disturbances. Full article
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Open AccessArticle Stochastic Trajectory Generation Using Particle Swarm Optimization for Quadrotor Unmanned Aerial Vehicles (UAVs)
Received: 22 March 2017 / Revised: 21 April 2017 / Accepted: 4 May 2017 / Published: 8 May 2017
Cited by 3 | PDF Full-text (1163 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this paper is to provide a realistic stochastic trajectory generation method for unmanned aerial vehicles that offers a tool for the emulation of trajectories in typical flight scenarios. Three scenarios are defined in this paper. The trajectories for these scenarios
[...] Read more.
The aim of this paper is to provide a realistic stochastic trajectory generation method for unmanned aerial vehicles that offers a tool for the emulation of trajectories in typical flight scenarios. Three scenarios are defined in this paper. The trajectories for these scenarios are implemented with quintic B-splines that grant smoothness in the second-order derivatives of Euler angles and accelerations. In order to tune the parameters of the quintic B-spline in the search space, a multi-objective optimization method called particle swarm optimization (PSO) is used. The proposed technique satisfies the constraints imposed by the configuration of the unmanned aerial vehicle (UAV). Further particular constraints can be introduced such as: obstacle avoidance, speed limitation, and actuator torque limitations due to the practical feasibility of the trajectories. Finally, the standard rapidly-exploring random tree (RRT*) algorithm, the standard (A*) algorithm and the genetic algorithm (GA) are simulated to make a comparison with the proposed algorithm in terms of execution time and effectiveness in finding the minimum length trajectory. Full article
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Open AccessArticle Direct Entry Minimal Path UAV Loitering Path Planning
Received: 11 March 2017 / Revised: 31 March 2017 / Accepted: 4 April 2017 / Published: 18 April 2017
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Abstract
Fixed Wing Unmanned Aerial Vehicles (UAVs) performing Intelligence, Surveillance and Reconnaissance (ISR) typically fly over Areas of Interest (AOIs) to collect sensor data of the ground from the air. If needed, the traditional method of extending sensor collection time is to loiter or
[...] Read more.
Fixed Wing Unmanned Aerial Vehicles (UAVs) performing Intelligence, Surveillance and Reconnaissance (ISR) typically fly over Areas of Interest (AOIs) to collect sensor data of the ground from the air. If needed, the traditional method of extending sensor collection time is to loiter or turn circularly around the center of an AOI. Current Autopilot systems on small UAVs can be limited in their feature set and typically follow a waypoint chain system that allows for loitering, but requires that the center of the AOI to be traversed which may produce unwanted turns outside of the AOI before entering the loiter. An investigation was performed to compare the current loitering techniques against two novel smart loitering methods. The first method investigated, Tangential Loitering Path Planner (TLPP), utilized paths tangential to the AOIs to enter and exit efficiently, eliminating unnecessary turns outside of the AOI. The second method, Least Distance Loitering Path Planner (LDLPP), utilized four unique flight maneuvers that reduce transit distances while eliminating unnecessary turns outside of the AOI present in the TLPP method. Simulation results concluded that the Smart Loitering Methods provide better AOI coverage during six mission scenarios. It was also determined that the LDLPP method spends less time in transit between AOIs. The reduction in required transit time could be used for surveying additional AOIs. Full article
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Open AccessTechnical Note Perpetual Solar-Powered Flight across Regions around the World for a Year-Long Operation
Received: 16 January 2017 / Revised: 4 April 2017 / Accepted: 7 April 2017 / Published: 11 April 2017
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Abstract
This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to
[...] Read more.
This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to fly for long hours at a specified altitude. Any solar-powered system requires extensive mission operation planning to ensure sufficient power to sustain a level flight. This study simulates the optimal UAV configurations at various global locations, and determines the feasibility of a solar-powered UAV to sustain a continuous mission. This study is divided into two different phases. An all-year operation of the average UAV (AVUAV) is simulated in Phase One and is designed specifically for each of 12 cities, namely, Ottawa, Honolulu, Quito, Tahiti, Brasilia, London, Riyadh, Tokyo, Kuala Lumpur, Accra, Port Louis, and Suva. Phase Two is a simulation of a solar-powered UAV design model known as 1UAV, applicable to any city around the world for a year-long flight. The findings state that a single UAV design is sufficient to operate continuously around the world if its detailed mission path planning has been defined. Full article
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Open AccessTechnical Note 3D CFD Simulation and Experimental Validation of Small APC Slow Flyer Propeller Blade
Received: 16 January 2017 / Revised: 16 February 2017 / Accepted: 22 February 2017 / Published: 25 February 2017
Cited by 1 | PDF Full-text (4760 KB) | HTML Full-text | XML Full-text
Abstract
The current work presents the numerical prediction method to determine small-scale propeller performance. The study is implemented using the commercially available computational fluid dynamics (CFD) solver, FLUENT. Numerical results are compared with the available experimental data for an advanced precision composites (APC) Slow
[...] Read more.
The current work presents the numerical prediction method to determine small-scale propeller performance. The study is implemented using the commercially available computational fluid dynamics (CFD) solver, FLUENT. Numerical results are compared with the available experimental data for an advanced precision composites (APC) Slow Flyer propeller blade to determine the discrepancy of the thrust coefficient, power coefficient, and efficiencies. The study utilized unstructured tetrahedron meshing throughout the analysis, with a standard k-ω turbulence model. The Multiple Reference Frame model was also used to consider the rotation of the propeller toward its local reference frame at 3008 revolutions per minute (RPM). Results show reliable thrust coefficient, power coefficient, and efficiency data for the case of low advance ratio and an advance ratio less than the negative thrust conditions. Full article
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Open AccessArticle Trajectory Tracking of a Tri-Rotor Aerial Vehicle Using an MRAC-Based Robust Hybrid Control Algorithm
Received: 2 November 2016 / Revised: 3 December 2016 / Accepted: 20 December 2016 / Published: 19 January 2017
Cited by 1 | PDF Full-text (3786 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel Model Reference Adaptive Control (MRAC)-based hybrid control algorithm is presented for the trajectory tracking of a tri-rotor Unmanned Aerial Vehicle (UAV). The mathematical model of the tri-rotor is based on the Newton–Euler formula, whereas the MRAC-based hybrid controller
[...] Read more.
In this paper, a novel Model Reference Adaptive Control (MRAC)-based hybrid control algorithm is presented for the trajectory tracking of a tri-rotor Unmanned Aerial Vehicle (UAV). The mathematical model of the tri-rotor is based on the Newton–Euler formula, whereas the MRAC-based hybrid controller consists of Fuzzy Proportional Integral Derivative (F-PID) and Fuzzy Proportional Derivative (F-PD) controllers. MRAC is used as the main controller for the dynamics, while the parameters of the adaptive controller are fine-tuned by the F-PD controller for the altitude control subsystem and the F-PID controller for the attitude control subsystem of the UAV. The stability of the system is ensured and proven by Lyapunov stability analysis. The proposed control algorithm is tested and verified using computer simulations for the trajectory tracking of the desired path as an input. The effectiveness of our proposed algorithm is compared with F-PID and the Fuzzy Logic Controller (FLC). Our proposed controller exhibits much less steady state error, quick error convergence in the presence of disturbance or noise, and model uncertainties. Full article
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2016

Jump to: 2018, 2017, 2015

Open AccessArticle Analysis of Pilot-Induced-Oscillation and Pilot Vehicle System Stability Using UAS Flight Experiments
Received: 15 August 2016 / Revised: 6 November 2016 / Accepted: 14 November 2016 / Published: 29 November 2016
Cited by 1 | PDF Full-text (9877 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports the results of a Pilot-Induced Oscillation (PIO) and human pilot control characterization study performed using flight data collected with a Remotely Controlled (R/C) unmanned research aircraft. The study was carried out on the longitudinal axis of the aircraft. Several existing
[...] Read more.
This paper reports the results of a Pilot-Induced Oscillation (PIO) and human pilot control characterization study performed using flight data collected with a Remotely Controlled (R/C) unmanned research aircraft. The study was carried out on the longitudinal axis of the aircraft. Several existing Category 1 and Category 2 PIO criteria developed for manned aircraft are first surveyed and their effectiveness for predicting the PIO susceptibility for the R/C unmanned aircraft is evaluated using several flight experiments. It was found that the Bandwidth/Pitch rate overshoot and open loop onset point (OLOP) criteria prediction results matched flight test observations. However, other criteria failed to provide accurate prediction results. To further characterize the human pilot control behavior during these experiments, a quasi-linear pilot model is used. The parameters of the pilot model estimated using data obtained from flight tests are then used to obtain information about the stability of the Pilot Vehicle System (PVS) for Category 1 PIOs occurred during straight and level flights. The batch estimation technique used to estimate the parameters of the quasi-linear pilot model failed to completely capture the compatibility nature of the human pilot. The estimation results however provided valuable insights into the frequency characteristics of the human pilot commands. Additionally, stability analysis of the Category 2 PIOs for elevator actuator rate limiting is carried out using simulations and the results are compared with actual flight results. Full article
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Open AccessCommunication Effect of Leading-Edge Slats at Low Reynolds Numbers
Received: 5 August 2016 / Revised: 10 October 2016 / Accepted: 13 November 2016 / Published: 17 November 2016
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Abstract
One of the most commonly implemented devices for stall control on wings and airfoils is a leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not the case at the low Reynolds numbers common for small unmanned
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One of the most commonly implemented devices for stall control on wings and airfoils is a leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not the case at the low Reynolds numbers common for small unmanned aerial vehicles. Consequently, a low-speed wind tunnel investigation was undertaken to elucidate the performance of a slat at Re = 250,000. Force balance measurements accompanied by surface flow visualization images are presented. The slat extension and rotation was varied and documented. The results indicate that for small slat extensions, slat rotation is deleterious to performance, but is required for larger slat extensions for effective lift augmentation. Deployment of the slat was accompanied by a significant drag penalty due to premature localized flow separation. Full article
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Open AccessArticle An Empirical Study of Overlapping Rotor Interference for a Small Unmanned Aircraft Propulsion System
Received: 25 July 2016 / Revised: 23 September 2016 / Accepted: 28 September 2016 / Published: 10 October 2016
Cited by 1 | PDF Full-text (8998 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The majority of research into full-sized helicopter overlapping propulsion systems involves co-axial setups (fully overlapped). Partially overlapping rotor setups (tandem, multirotor) have received less attention, and empirical data produced over the years is limited. The increase in demand for compact small unmanned aircraft
[...] Read more.
The majority of research into full-sized helicopter overlapping propulsion systems involves co-axial setups (fully overlapped). Partially overlapping rotor setups (tandem, multirotor) have received less attention, and empirical data produced over the years is limited. The increase in demand for compact small unmanned aircraft has exposed the need for empirical investigations of overlapping propulsion systems at a small scale (Reynolds Number < 250,000). Rotor-to-rotor interference at the static state in various overlapping propulsion system configurations was empirically measured using off the shelf T-Motor 16 inch × 5.4 inch rotors. A purpose-built test rig was manufactured allowing various overlapping rotor configurations to be tested. First, single rotor data was gathered, then performance measurements were taken at different thrust and tip speeds on a range of overlap configurations. The studies were conducted in a system torque balance mode. Overlapping rotor performance was compared to an isolated dual rotor propulsion system revealing interference factors which were compared to the momentum theory. Tests revealed that in the co-axial torque-balanced propulsion system the upper rotor outperforms the lower rotor at axial separation ratios between 0.05 and 0.85. Additionally, in the same region, thrust sharing between the two rotors changed by 21%; the upper rotor produced more thrust than the lower rotor at all times. Peak performance was recorded as a 22% efficiency loss when the axial separation ratio was greater than 0.25. The performance of a co-axial torque-balanced system reached a 27% efficiency loss when the axial separation ratio was equal to 0.05. The co-axial system swirl recovery effect was recorded to have a 4% efficiency gain in the axial separation ratio region between 0.05 and 0.85. The smallest efficiency loss (3%) was recorded when the rotor separation ratio was between 0.95 and 1 (axial separation ratio was kept at 0.05). Tests conducted at a rotor separation ratio of 0.85 showed that the efficiency loss decreased when the axial separation ratio was greater than 0.25. The lower rotor outperformed the upper rotor in the rotor separation ratio region from 0.95 to 1 (axial separation ratio was kept at 0.05) at an overall system thrust of 8 N, and matched the upper rotor performance at the tested overall thrust of 15 N. Full article
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Open AccessFeature PaperReview Bio-Inspired Principles Applied to the Guidance, Navigation and Control of UAS
Received: 28 April 2016 / Revised: 25 June 2016 / Accepted: 6 July 2016 / Published: 20 July 2016
Cited by 4 | PDF Full-text (10800 KB) | HTML Full-text | XML Full-text
Abstract
This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more
[...] Read more.
This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more self-reliant systems and the need for UAS to have a greater understanding of their environment. It is evident that insects, even with their small brains and limited intelligence, have overcome many of the shortcomings of the current state of the art in autonomous aerial guidance. This has motivated research into bio-inspired systems and algorithms, specifically vision-based navigation, situational awareness and guidance. Full article
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Open AccessArticle A Shape Memory Alloy Application for Compact Unmanned Aerial Vehicles
Received: 2 March 2016 / Revised: 28 April 2016 / Accepted: 20 May 2016 / Published: 31 May 2016
Cited by 2 | PDF Full-text (7159 KB) | HTML Full-text | XML Full-text
Abstract
Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of
[...] Read more.
Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of the system, through a reduction of number of parts and the removal of many free play gaps among mechanics. For these reasons, technological aerospace research is focusing on this kind of technology more and more, even though fatigue life, performance degradation, and other issues are still open. In the work at hand, landing gear for unmanned aerial vehicles, UAV, is presented, integrated with shape memory alloys springs as actuation devices. A conceptual prototype has been realized to verify the system ability in satisfying specs, in terms of deployment and retraction capability. Starting from the proposed device working principle and the main design parameters identification, the design phase is faced, setting those parameters to meet weight, deployment angle, energy consumption, and available room requirements. Then, system modeling and performance prediction is performed and finally a correlation between numerical and experimental results is presented. Full article
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Open AccessArticle Fixed-Wing UAV Attitude Estimation Using Single Antenna GPS Signal Strength Measurements
Received: 5 April 2016 / Revised: 5 May 2016 / Accepted: 10 May 2016 / Published: 13 May 2016
Cited by 1 | PDF Full-text (4175 KB) | HTML Full-text | XML Full-text
Abstract
This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity
[...] Read more.
This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity and attitude states of a UAV using only the data from a single GPS receiver and antenna. Two different approaches for utilizing GPS signal strength within measurement updates for UAV attitude in a nonlinear Kalman filter are discussed and assessed using recorded UAV flight data. Comparisons of UAV pitch and roll estimates against measurements from a high-grade mechanical gyroscope are used to show that approximately 5° error with respect to both mean and standard-deviation on both axes is achievable. Full article
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Open AccessArticle Guidance, Navigation and Control of Unmanned Airships under Time-Varying Wind for Extended Surveillance
Received: 21 December 2015 / Revised: 20 January 2016 / Accepted: 10 February 2016 / Published: 17 February 2016
Cited by 1 | PDF Full-text (808 KB) | HTML Full-text | XML Full-text
Abstract
This paper deals with the control of lighter-than-air vehicles, more specifically the design of an integrated guidance, navigation and control (GNC) scheme that is capable of navigating an airship through a series of constant-altitude, planar waypoints. Two guidance schemes are introduced, a track-specific
[...] Read more.
This paper deals with the control of lighter-than-air vehicles, more specifically the design of an integrated guidance, navigation and control (GNC) scheme that is capable of navigating an airship through a series of constant-altitude, planar waypoints. Two guidance schemes are introduced, a track-specific guidance law and a proportional navigation guidance law, that provide the required signals to the corresponding controllers based on the airship position relative to a target waypoint. A novel implementation of the extended Kalman filter, namely the scheduled extended Kalman filter, estimates the required states and wind speed to enhance the performance of the track-specific guidance law in the presence of time-varying wind. The performance of the GNC system is tested using a high fidelity nonlinear dynamic simulation for a variety of flying conditions. Representative results illustrate the performance of the integrated system for chosen flight conditions. Full article
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Open AccessArticle Turbulence Effects on Modified State Observer-Based Adaptive Control: Black Kite Micro Aerial Vehicle
Received: 1 November 2015 / Revised: 17 January 2016 / Accepted: 26 January 2016 / Published: 5 February 2016
Cited by 1 | PDF Full-text (5966 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the implementation of a modified state observer-based adaptive dynamic inverse controller for the Black Kite micro aerial vehicle. The pitch and velocity adaptations are computed by the modified state observer in the presence of turbulence to simulate atmospheric conditions. This
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This paper presents the implementation of a modified state observer-based adaptive dynamic inverse controller for the Black Kite micro aerial vehicle. The pitch and velocity adaptations are computed by the modified state observer in the presence of turbulence to simulate atmospheric conditions. This state observer uses the estimation error to generate the adaptations and, hence, is more robust than model reference adaptive controllers which use modeling or tracking error. In prior work, a traditional proportional-integral-derivative control law was tested in simulation for its adaptive capability in the longitudinal dynamics of the Black Kite micro aerial vehicle. This controller tracks the altitude and velocity commands during normal conditions, but fails in the presence of both parameter uncertainties and system failures. The modified state observer-based adaptations, along with the proportional-integral-derivative controller enables tracking despite these conditions. To simulate flight of the micro aerial vehicle with turbulence, a Dryden turbulence model is included. The turbulence levels used are based on the absolute load factor experienced by the aircraft. The length scale was set to 2.0 meters with a turbulence intensity of 5.0 m/s that generates a moderate turbulence. Simulation results for various flight conditions show that the modified state observer-based adaptations were able to adapt to the uncertainties and the controller tracks the commanded altitude and velocity. The summary of results for all of the simulated test cases and the response plots of various states for typical flight cases are presented. Full article
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Open AccessArticle Target Tracking in 3-D Using Estimation Based Nonlinear Control Laws for UAVs
Received: 21 December 2015 / Revised: 12 January 2016 / Accepted: 20 January 2016 / Published: 1 February 2016
Cited by 2 | PDF Full-text (1354 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an estimation based backstepping like control law design for an Unmanned Aerial Vehicle (UAV) to track a moving target in 3-D space. A ground-based sensor or an onboard seeker antenna provides range, azimuth angle, and elevation angle measurements to a
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This paper presents an estimation based backstepping like control law design for an Unmanned Aerial Vehicle (UAV) to track a moving target in 3-D space. A ground-based sensor or an onboard seeker antenna provides range, azimuth angle, and elevation angle measurements to a chaser UAV that implements an extended Kalman filter (EKF) to estimate the full state of the target. A nonlinear controller then utilizes this estimated target state and the chaser’s state to provide speed, flight path, and course/heading angle commands to the chaser UAV. Tracking performance with respect to measurement uncertainty is evaluated for three cases: (1) stationary white noise; (2) stationary colored noise and (3) non-stationary (range correlated) white noise. Furthermore, in an effort to improve tracking performance, the measurement model is made more realistic by taking into consideration range-dependent uncertainties in the measurements, i.e., as the chaser closes in on the target, measurement uncertainties are reduced in the EKF, thus providing the UAV with more accurate control commands. Simulation results for these cases are shown to illustrate target state estimation and trajectory tracking performance. Full article
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Open AccessReview Multiple-Scenario Unmanned Aerial System Control: A Systems Engineering Approach and Review of Existing Control Methods
Received: 14 November 2015 / Revised: 25 December 2015 / Accepted: 25 December 2015 / Published: 4 January 2016
Cited by 6 | PDF Full-text (252 KB) | HTML Full-text | XML Full-text
Abstract
The use of unmanned aerial systems (UASs) in both the public and military environments is predicted to grow significantly. As the demand for UASs grows, the availability of more robust and capable vehicles that can perform multiple mission types will be needed. In
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The use of unmanned aerial systems (UASs) in both the public and military environments is predicted to grow significantly. As the demand for UASs grows, the availability of more robust and capable vehicles that can perform multiple mission types will be needed. In the public sector, the demand will grow for UASs to be used for agriculture, forestry, and search and rescue missions. Militaries continue to demand more UAS capabilities for diverse operations around the world. Significant research has been performed and continues to progress in the areas of autonomous UAS control. A majority of the work focuses on subsets of UAS control: path planning, autonomy, small UAS controls, and sensors. Minimal work exists on a system-level problem of multiple-scenario UAS control for integrated systems. This paper provides a high-level modular system architecture definition that is modifiable across platform types and mission requirements. A review of the current research and employment of UAS capabilities is provided to evaluate the state of the capabilities required to enable the proposed architecture. Full article
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2015

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Open AccessArticle Unmanned Aerial ad Hoc Networks: Simulation-Based Evaluation of Entity Mobility Models’ Impact on Routing Performance
Aerospace 2015, 2(3), 392-422; https://doi.org/10.3390/aerospace2030392
Received: 18 February 2015 / Revised: 4 May 2015 / Accepted: 17 June 2015 / Published: 30 June 2015
Cited by 6 | PDF Full-text (1249 KB) | HTML Full-text | XML Full-text
Abstract
An unmanned aerial ad hoc network (UAANET) is a special type of mobile ad hoc network (MANET). For these networks, researchers rely mostly on simulations to evaluate their proposed networking protocols. Hence, it is of great importance that the simulation environment of a
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An unmanned aerial ad hoc network (UAANET) is a special type of mobile ad hoc network (MANET). For these networks, researchers rely mostly on simulations to evaluate their proposed networking protocols. Hence, it is of great importance that the simulation environment of a UAANET replicates as much as possible the reality of UAVs. One major component of that environment is the movement pattern of the UAVs. This means that the mobility model used in simulations has to be thoroughly understood in terms of its impact on the performance of the network. In this paper, we investigate how mobility models affect the performance of UAANET in simulations in order to come up with conclusions/recommendations that provide a benchmark for future UAANET simulations. To that end, we first propose a few metrics to evaluate the mobility models. Then, we present five random entity mobility models that allow nodes to move almost freely and independently from one another and evaluate four carefully-chosen MANET/UAANET routing protocols: ad hoc on-demand distance vector (AODV), optimized link state routing (OLSR), reactive-geographic hybrid routing (RGR) and geographic routing protocol (GRP). In addition, flooding is also evaluated. The results show a wide variation of the protocol performance over different mobility models. These performance differences can be explained by the mobility model characteristics, and we discuss these effects. The results of our analysis show that: (i) the enhanced Gauss–Markov (EGM) mobility model is best suited for UAANET; (ii) OLSR, a table-driven proactive routing protocol, and GRP, a position-based geographic protocol, are the protocols most sensitive to the change of mobility models; (iii) RGR, a reactive-geographic hybrid routing protocol, is best suited for UAANET. Full article
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Open AccessArticle A Comparison of Closed-Loop Performance of Multirotor Configurations Using Non-Linear Dynamic Inversion Control
Aerospace 2015, 2(2), 325-352; https://doi.org/10.3390/aerospace2020325
Received: 23 April 2015 / Revised: 18 May 2015 / Accepted: 1 June 2015 / Published: 5 June 2015
Cited by 5 | PDF Full-text (920 KB) | HTML Full-text | XML Full-text
Abstract
Multirotor is the umbrella term for the family of unmanned aircraft, which include the quadrotor, hexarotor and other vertical take-off and landing (VTOL) aircraft that employ multiple main rotors for lift and control. Development and testing of novel multirotor designs has been aided
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Multirotor is the umbrella term for the family of unmanned aircraft, which include the quadrotor, hexarotor and other vertical take-off and landing (VTOL) aircraft that employ multiple main rotors for lift and control. Development and testing of novel multirotor designs has been aided by the proliferation of 3D printing and inexpensive flight controllers and components. Different multirotor configurations exhibit specific strengths, while presenting unique challenges with regards to design and control. This article highlights the primary differences between three multirotor platforms: a quadrotor; a fully-actuated hexarotor; and an octorotor. Each platform is modelled and then controlled using non-linear dynamic inversion. The differences in dynamics, control and performance are then discussed. Full article
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Open AccessCommunication Development of UAS Design Based on Wideband Antenna Architecture
Aerospace 2015, 2(2), 312-324; https://doi.org/10.3390/aerospace2020312
Received: 31 January 2015 / Revised: 12 May 2015 / Accepted: 27 May 2015 / Published: 4 June 2015
PDF Full-text (2486 KB) | HTML Full-text | XML Full-text
Abstract
An Unmanned Aerial System (UAS) has been developed which is based on an aerodynamically functionalized planar wideband antenna. The antenna utilizes a planar circular dipole metallization scheme. The aerodynamic structure implements a planform similar to the Nutball flier, a hobbyist flight architecture. The
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An Unmanned Aerial System (UAS) has been developed which is based on an aerodynamically functionalized planar wideband antenna. The antenna utilizes a planar circular dipole metallization scheme. The aerodynamic structure implements a planform similar to the Nutball flier, a hobbyist flight architecture. The resulting codesign achieved a large impedance bandwidth defined by a voltage standing wave ratio (VSWR) less than 2 from 100 MHz to over 2 GHz and omnidirectional dipole-like radiation patterns at the lower frequency region and more directional patterns at higher frequencies. Full article
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Open AccessArticle Ornithopter Type Flapping Wings for Autonomous Micro Air Vehicles
Aerospace 2015, 2(2), 235-278; https://doi.org/10.3390/aerospace2020235
Received: 2 February 2015 / Revised: 20 April 2015 / Accepted: 4 May 2015 / Published: 13 May 2015
Cited by 7 | PDF Full-text (7899 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an ornithopter prototype that mimics the flapping motion of bird flight is developed, and the lift and thrust generation characteristics of different wing designs are evaluated. This project focused on the spar arrangement and material used for the wings that
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In this paper, an ornithopter prototype that mimics the flapping motion of bird flight is developed, and the lift and thrust generation characteristics of different wing designs are evaluated. This project focused on the spar arrangement and material used for the wings that could achieves improved performance. Various lift and thrust measurement techniques are explored and evaluated. Various wings of insects and birds were evaluated to understand how these natural flyers with flapping wings are able to produce sufficient lift to fly. The differences in the flapping aerodynamics were also detailed. Experiments on different wing designs and materials were conducted and a paramount wing was built for a test flight. The first prototype has a length of 46.5 cm, wing span of 88 cm, and weighs 161 g. A mechanism which produced a flapping motion was fabricated and designed to create flapping flight. The flapping flight was produced by using a single motor and a flexible and light wing structure. A force balance made of load cell was then designed to measure the thrust and lift force of the ornithopter. Three sets of wings varying flexibility were fabricated, therefore lift and thrust measurements were acquired from each different set of wings. The lift will be measured in ten cycles computing the average lift and frequency in three different speeds or frequencies (slow, medium and fast). The thrust measurement was measure likewise but in two cycles only. Several observations were made regarding the behavior of flexible flapping wings that should aid in the design of future flexible flapping wing vehicles. The wings angle or phase characteristic were analyze too and studied. The final ornithopter prototype weighs only 160 g, has a wing span of 88.5 cm, that could flap at a maximum flapping frequency of 3.869 Hz, and produce a maximum thrust and lift of about 0.719 and 0.264 N respectively. Next, we proposed resonance type flapping wing utilizes the near resonance phenomenon of a two-degree of freedom elastic system, that is, the wing is supported by the springs for flapping and feathering motions. Being oscillated close to the resonance frequency of the system, only by the torque in flapping motion, the amplitude gained is a few times higher than that of normal case. The first prototype was made from acrylic using a laser cutting machine. The wings were made up of carbon rods and kite material Ripstop. First test showed that the wings were too heavy for the mechanism to work. The third prototype was a smaller single gear crank design which was fabricated using a 3D printer. Initial test proved that the second prototype could withstand the high frequency flapping and near resonance amplitude as designed. With remote control, the third prototype was able to take off, climb, cruise and land in flapping mode successfully. Full article
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Open AccessArticle Trajectory Management of the Unmanned Aircraft System (UAS) in Emergency Situation
Aerospace 2015, 2(2), 222-234; https://doi.org/10.3390/aerospace2020222
Received: 1 February 2015 / Revised: 13 March 2015 / Accepted: 18 March 2015 / Published: 4 May 2015
Cited by 2 | PDF Full-text (1378 KB) | HTML Full-text | XML Full-text
Abstract
Unmanned aircraft must be characterized by a level of safety, similar to that of manned aircraft, when performing flights over densely populated areas. Dangerous situations or emergencies are frequently connected with the necessity to change the profiles and parameters of a flight as
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Unmanned aircraft must be characterized by a level of safety, similar to that of manned aircraft, when performing flights over densely populated areas. Dangerous situations or emergencies are frequently connected with the necessity to change the profiles and parameters of a flight as well as the flight plans. The aim of this work is to present the methods used to determine an Unmanned Aircraft System’s (UAS) flight profile after a dangerous situation or emergency occurs. The analysis was limited to the possibility of an engine system emergency and further flight continuing along a trajectory of which the shape depends on the type of the emergency. The suggested method also enables the determination of an optimal flying trajectory, based on the territory of a special protection zone (for example, large populated areas), in the case of an emergency that would disable continuation of the performed task. The method used in this work allows researchers, in a simplified way, to solve a variation task using the Ritz–Galerkin method, consisting of an approximate solution of the boundary value problem to determine the optimal flight path. The worked out method can become an element of the on-board system supporting UAS flight control. Full article
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Open AccessReview Unmanned Aerial Systems (UAS) Research Opportunities
Aerospace 2015, 2(2), 189-202; https://doi.org/10.3390/aerospace2020189
Received: 30 January 2015 / Revised: 15 April 2015 / Accepted: 20 April 2015 / Published: 27 April 2015
Cited by 7 | PDF Full-text (140 KB) | HTML Full-text | XML Full-text
Abstract
The aerospace community is planning for growth in Unmanned Aerial Systems (UAS) funding and research opportunities. The premise that UAS will revolutionize aerospace appears to be unfolding based on current trends. There is also an anticipation of an increasing number of new platforms
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The aerospace community is planning for growth in Unmanned Aerial Systems (UAS) funding and research opportunities. The premise that UAS will revolutionize aerospace appears to be unfolding based on current trends. There is also an anticipation of an increasing number of new platforms and research investment, which is likely but must be analysed carefully to determine where the opportunities lie. This paper draws on the state of technology, history and systems engineering. We explore what aspects of UAS will be the result of aerospace science advances and what aspects will be incremental engineering and systems integration. It becomes apparent that, for academia, the largest opportunities may exist in small and micro UAS domain due to the novelty of aerospace engineering on a small scale. Full article
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Open AccessArticle Development of Flight Path Planning for Multirotor Aerial Vehicles
Aerospace 2015, 2(2), 171-188; https://doi.org/10.3390/aerospace2020171
Received: 21 November 2014 / Revised: 11 March 2015 / Accepted: 24 March 2015 / Published: 27 April 2015
Cited by 2 | PDF Full-text (3915 KB) | HTML Full-text | XML Full-text
Abstract
This study addresses the flight-path planning problem for multirotor aerial vehicles (AVs). We consider the specific features and requirements of real-time flight-path planning and develop a rapidly-exploring random tree (RRT) algorithm to determine a preliminary flight path in three-dimensional space. Since the path
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This study addresses the flight-path planning problem for multirotor aerial vehicles (AVs). We consider the specific features and requirements of real-time flight-path planning and develop a rapidly-exploring random tree (RRT) algorithm to determine a preliminary flight path in three-dimensional space. Since the path obtained by the RRT may not be optimal due to the existence of redundant waypoints. To reduce the cost of energy during AV’s flight, the excessive waypoints need to be refined. We revise the A-star algorithm by adopting the heading of the AV as the key indices while calculating the cost. Bezier curves are finally proposed to smooth the flight path, making it applicable for real-world flight. Full article
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Open AccessArticle Path Planning Using Concatenated Analytically-Defined Trajectories for Quadrotor UAVs
Aerospace 2015, 2(2), 155-170; https://doi.org/10.3390/aerospace2020155
Received: 23 February 2015 / Revised: 26 March 2015 / Accepted: 16 April 2015 / Published: 21 April 2015
Cited by 5 | PDF Full-text (552 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a semi-analytical trajectory planning method for quadrotor UAVs. These trajectories are analytically defined, are constant in speed and sub-optimal with respect to a weighted quadratic cost function of the translational and angular velocities. A technique for concatenating the trajectories into
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This paper presents a semi-analytical trajectory planning method for quadrotor UAVs. These trajectories are analytically defined, are constant in speed and sub-optimal with respect to a weighted quadratic cost function of the translational and angular velocities. A technique for concatenating the trajectories into multi-segment paths is demonstrated. These paths are smooth to the first derivative of the translational position and pass through defined waypoints. A method for detecting potential collisions by discretizing the path into a coarse mesh before using a numerical optimiser to determine the point of the path closest to the obstacle is presented. This hybrid method reduces the computation time when compared to discretizing the trajectory into a fine mesh and calculating the minimum distance. A tracking controller is defined and used to show that the paths are dynamically feasible and the typical magnitudes of the controller inputs required to fly them. Full article
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