Flight coordination solutions for multirotor unmanned aerial vehicles

[EN] As the popularity and the number of Unmanned Aerial Vehicles (UAVs) increases, new protocols are needed to coordinate them when flying without direct human control, and to avoid that these UAVs collide with each other. Testing such novel protocols on real UAVs is a complex procedure that requires investing much time, money and research efforts. Hence, it becomes necessary to first test the developed solutions using simulation. Unfortunately, existing tools present significant limitations: some of them only simulate accurately the flight behavior of a single UAV, while some other simulators can manage several UAVs simultaneously, but not in real time, thus losing accuracy regarding the mobility pattern of the UAV. In this work we address such problem by introducing Arducopter Simulator (ArduSim), a novel simulation platform that allows controlling in soft real-time the flight and communications of multiple UAVs, being the developed protocols directly portable to real devices. Moreover, ArduSim includes a realistic model for the WiFi communications link between UAVs, which was proposed based on real experiments. The chances that two UAVs get close to each other during their flights is increasing as more and more of them populate our skies, causing concerns regarding potential collisions. Therefore, this thesis also proposes the Mission Based Collision Avoidance Protocol (MBCAP), a novel UAV collision avoidance protocol applicable to all types of multicopters flying autonomously. It relies on wireless communications in order to detect nearby UAVs, and to negotiate the procedure to avoid any potential collision. Experimental and simulation results demonstrate the validity and effectiveness of the proposed solution, which typically introduces a small overhead in the range of 15 to 42 seconds for each risky situation successfully handled. The previous solution aims at UAVs performing independent flights, but they can also form a swarm, where more constraints have to be met to avoid collisions among them, and to allow them to complete their task efficiently. Deploying an UAV swarm instead of a single UAV can provide additional benefits when, for example, cargo carrying requirements exceed the lifting power of a single UAV, or when the deployment of several UAVs simultaneously can accelerate the accomplishment of the mission, and broaden the covered area. To this aim, in this work we present the Mission-based UAV Swarm Coordination Protocol (MUSCOP), a solution that allows multiple UAVs to perfectly coordinate their flight when performing planned missions. Experimental results show that the proposed protocol is able to achieve a high degree of swarm cohesion independently of the flight formation adopted, and even in the presence of very lossy channels, achieving minimal synchronization delays and very low position offsets with regard to the ideal case. Currently, there are some other scenarios, such as search and rescue operations, where the deployment of manually guided swarms of UAVs can be necessary. In such cases, the pilot's commands are unknown a priori (unpredictable), meaning that the UAVs must respond in near real-time to the movements of the leader UAV in order to maintain swarm consistency. Hence, in this thesis we also propose the FollowMe protocol for the coordination of UAVs in a swarm where the swarm leader is controlled by a real pilot, and the other UAVs must follow it in real-time to maintain swarm cohesion. Simulation results show the validity of the proposed swarm coordination protocol, detailing the responsiveness limits of our solution, and finding the minimum distances between UAVs to avoid collisions.[ES] A medida que la popularidad de los Vehículos Aéreos No Tripulados (VANTs) se incrementa, también se hacen necesarios nuevos protocolos para coordinarlos en vuelos sin control humano directo, y para evitar que colisionen entre sí. Probar estos nuevos protocolos en VANTs reales es un proceso complejo que requiere invertir mucho tiempo, dinero y esfuerzo investigador. Por lo tanto, es necesario probar en simulación las soluciones previamente implementadas. Lamentablemente, las herramientas actuales tienen importantes limitaciones: algunas simulan con precisión el vuelo de un único VANT, mientras que otros simuladores pueden gestionar varios VANTs simultáneamente aunque no en tiempo real, perdiendo por lo tanto precisión en el patrón de movilidad del VANT. En este trabajo abordamos este problema introduciendo Arducopter Simulator (ArduSim), una nueva plataforma de simulación que permite controlar en tiempo real el vuelo y la comunicación entre múltiples VANTs, permitiendo llevar los protocolos desarrollados a dispositivos reales con facilidad. Además, ArduSim incluye un modelo realista de un enlace de comunicaciones WiFi entre VANTs, el cual está basado en el resultado obtenido de experimentos con VANTs reales. La posibilidad de que dos VANTs se aproximen entre sí durante el vuelo se incrementa a medida que hay más aeronaves de este tipo surcando los cielos, introduciendo peligro por posibles colisiones. Por ello, esta tesis propone Mission Based Collision Avoidance Protocol (MBCAP), un nuevo protocolo de evitación de colisiones para VANTs aplicable a todo tipo de multicópteros mientras vuelan autónomamente. MBCAP utiliza comunicaciones inalámbricas para detectar VANTs cercanos y para negociar el proceso de evitación de la colisión. Los resultados de simulaciones y experimentos reales demuestran la validez y efectividad de la solución propuesta, que introduce un pequeño aumento del tiempo de vuelo de entre 15 y 42 segundos por cada situación de riesgo correctamente resuelta. La solución anterior está orientada a VANTs que realizan vuelos independientes, pero también pueden formar un enjambre, donde hay que cumplir más restricciones para evitar que colisionen entre sí, y para que completen la tarea de forma eficiente. Desplegar un enjambre de VANTs en vez de uno solo proporciona beneficios adicionales cuando, por ejemplo, la necesidad de carga excede la capacidad de elevación de un único VANT, o cuando al desplegar varios VANTs simultáneamente se acelera la misión y se cubre un área mayor. Con esta finalidad, en este trabajo presentamos el protocolo Mission-based UAV Swarm Coordination Protocol (MUSCOP), una solución que permite a varios VANTs coordinar perfectamente el vuelo mientras realizan misiones planificadas. Los resultados experimentales muestran que el protocolo propuesto permite al enjambre alcanzar un grado de cohesión elevado independientemente de la formación de vuelo adoptada, e incluso en presencia de un canal de comunicación con muchas pérdidas, consiguiendo retardos en la sincronización insignificantes y desfases mínimos en la posición con respecto al caso ideal. Actualmente hay otros escenarios, como las operaciones de búsqueda y rescate, donde el despliegue de enjambres de VANTs guiados manualmente puede ser necesario. En estos casos, las órdenes del piloto son desconocidas a priori (impredecibles), lo que significa que los VANTs deben responder prácticamente en tiempo real a los movimientos del VANT líder para mantener la consistencia del enjambre. Por ello, en esta tesis proponemos el protocolo FollowMe para la coordinación de VANTs en un enjambre donde el líder es controlado por un piloto, y el resto de VANTs lo siguen en tiempo real para mantener la cohesión del enjambre. Las simulaciones muestran la validez del protocolo de coordinación de enjambres propuesto, detallando los límites de la solución, y definiendo la distancia mínima entre VANTs para evita[CA] A mesura que la popularitat dels Vehicles Aeris No Tripulats (VANTs) s'incrementa, també es fan necessaris nous protocols per a coordinar-los en vols sense control humà directe, i per a evitar que col·lisionen entre si. Provar aquests nous protocols en VANTs reals és un procés complex que requereix invertir molt de temps, diners i esforç investigador. Per tant, és necessari provar en simulació les solucions prèviament implementades. Lamentablement, les eines actuals tenen importants limitacions: algunes simulen amb precisió el vol d'un únic VANT, mentre que altres simuladors poden gestionar diversos VANTs simultàniament encara que no en temps real, perdent per tant precisió en el patró de mobilitat del VANT. En aquest treball abordem aquest problema introduint Arducopter Simulator (ArduSim), una nova plataforma de simulació que permet controlar en temps real el vol i la comunicació entre múltiples VANTs, permetent portar els protocols desenvolupats a dispositius reals amb facilitat. A més, ArduSim inclou un model realista d'un enllaç de comunicacions WiFi entre VANTs, que està basat en el resultat obtingut d'experiments amb VANTs reals. La possibilitat que dues VANTs s'aproximen entre si durant el vol s'incrementa a mesura que hi ha més aeronaus d'aquest tipus solcant els cels, introduint perill per possibles col·lisions. Per això, aquesta tesi proposa Mission Based Collision Avoidance Protocol (MBCAP), un nou protocol d'evitació de col·lisions per a VANTs aplicable a tota mena de multicòpters mentre volen autònomament. MBCAP utilitza comunicacions sense fils per a detectar VANTs pròxims i per a negociar el procés d'evitació de la col·lisió. Els resultats de simulacions i experiments reals demostren la validesa i efectivitat de la solució proposada, que introdueix un xicotet augment del temps de vol de entre 15 i 42 segons per cada situació de risc correctament resolta. La solució anterior està orientada a VANTs que realitzen vols independents, però també poden formar un eixam, on cal complir més restriccions per a evitar que col·lisionen entre si, i perquè completen la tasca de forma eficient. Desplegar un eixam de VANTs en comptes d'un només proporciona beneficis addicionals quan, per exemple, la necessitat de càrrega excedeix la capacitat d'elevació d'un únic VANT, o quan en desplegar diversos VANTs simultàniament s'accelera la missió i es cobreix una àrea major. Amb aquesta finalitat, en aquest treball presentem el protocol Mission-based UAV Swarm Coordination Protocol (MUSCOP), una solució que permet a diversos VANTs coordinar perfectament el vol mentre realitzen missions planificades. Els resultats experimentals mostren que el protocol proposat permet a l'eixam aconseguir un grau de cohesió elevat independentment de la formació de vol adoptada, i fins i tot en presència d'un canal de comunicació amb moltes pèrdues, aconseguint retards en la sincronització insignificants i desfasaments mínims en la posició respecte al cas ideal. Actualment hi ha altres escenaris, com les operacions de cerca i rescat, on el desplegament d'eixams de VANTs guiats manualment pot ser necessari. En aquests casos, les ordres del pilot són desconegudes a priori (impredictibles), el que significa que els VANTs han de respondre pràcticament en temps real als moviments del VANT líder per a mantindre la consistència de l'eixam. Per això, en aquesta tesi proposem el protocol FollowMe per a la coordinació de VANTs en un eixam on el líder és controlat per un pilot, i la resta de VANTs ho segueixen en temps real per a mantindre la cohesió de l'eixam. Les simulacions mostren la validesa del protocol de coordinació d'eixams proposat, detallant els límits de la solució, i definint la distància mínima entre VANTs per a evitar col·lisions.Fabra Collado, FJ. (2020). Flight coordination solutions for multirotor unmanned aerial vehicles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/147857TESI

A Distributed Approach for Collision Avoidance between Multirotor UAVs Following Planned Missions

[EN] As the number of potential applications for Unmanned Aerial Vehicles (UAVs) keeps rising steadily, the chances that these devices get close to each other during their flights also increases, causing concerns regarding potential collisions. This paper proposed the Mission Based Collision Avoidance Protocol (MBCAP), a novel UAV collision avoidance protocol applicable to all types of multicopters flying autonomously. It relies on wireless communications in order to detect nearby UAVs, and to negotiate the procedure to avoid any potential collision. Experimental and simulation results demonstrated the validity and effectiveness of the proposed solution, which typically introduces a small overhead in the range of 15 to 42 s for each risky situation successfully handled.This work was partially supported by the "Ministerio de Ciencia, Innovacion y Universidades, Programa Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad, Proyectos I+D+I 2018", Spain, under Grant RTI2018-096384-B-I00, and the Universitat Politecnica de Valencia (UPV) under grant number FPI-2017-S1 for the training of PhD researchers.Fabra Collado, FJ.; Zamora-Mero, WJ.; Sangüesa-Escorihuela, JA.; Tavares De Araujo Cesariny Calafate, CM.; Cano, J.; Manzoni, P. (2019). A Distributed Approach for Collision Avoidance between Multirotor UAVs Following Planned Missions. Sensors. 19(10):1-25. https://doi.org/10.3390/s19102404S1251910Mohamed, N., Al-Jaroodi, J., Jawhar, I., Idries, A., & Mohammed, F. (2020). Unmanned aerial vehicles applications in future smart cities. Technological Forecasting and Social Change, 153, 119293. doi:10.1016/j.techfore.2018.05.004SESAR Joint Undertakinghttps://www.sesarju.eu/Fabra, F., T. Calafate, C., Cano, J.-C., & Manzoni, P. (2018). MBCAP: Mission Based Collision Avoidance Protocol for UAVs. 2018 IEEE 32nd International Conference on Advanced Information Networking and Applications (AINA). doi:10.1109/aina.2018.00090Drone Collision Avoidancehttps://create.arduino.cc/projecthub/anshulsingh163/drone-collision-avoidance-system-0b6002Liu, Z., & Foina, A. G. (2016). Feature article: an autonomous quadrotor avoiding a helicopter in low-altitude flights. IEEE Aerospace and Electronic Systems Magazine, 31(9), 30-39. doi:10.1109/maes.2016.150131Xiang, J., Liu, Y., & Luo, Z. (2016). Flight safety measurements of UAVs in congested airspace. Chinese Journal of Aeronautics, 29(5), 1355-1366. doi:10.1016/j.cja.2016.08.017Lin, Q., Wang, X., & Wang, Y. (2018). Cooperative Formation and Obstacle Avoidance Algorithm for Multi-UAV System in 3D Environment. 2018 37th Chinese Control Conference (CCC). doi:10.23919/chicc.2018.8483113Zhou, X., Yu, X., & Peng, X. (2019). UAV Collision Avoidance Based on Varying Cells Strategy. IEEE Transactions on Aerospace and Electronic Systems, 55(4), 1743-1755. doi:10.1109/taes.2018.2875556Kim, H., & Ben-Othman, J. (2018). A Collision-Free Surveillance System Using Smart UAVs in Multi Domain IoT. IEEE Communications Letters, 22(12), 2587-2590. doi:10.1109/lcomm.2018.2875477Wang, M., Voos, H., & Su, D. (2018). Robust Online Obstacle Detection and Tracking for Collision-Free Navigation of Multirotor UAVs in Complex Environments. 2018 15th International Conference on Control, Automation, Robotics and Vision (ICARCV). doi:10.1109/icarcv.2018.8581330Ma, L. (2018). Cooperative Target Tracking using a Fleet of UAVs with Collision and Obstacle Avoidance. 2018 22nd International Conference on System Theory, Control and Computing (ICSTCC). doi:10.1109/icstcc.2018.8540717Chen, P.-H., & Lee, C.-Y. (2018). UAVNet: An Efficient Obstacel Detection Model for UAV with Autonomous Flight. 2018 International Conference on Intelligent Autonomous Systems (ICoIAS). doi:10.1109/icoias.2018.8494201Fabra, F., Calafate, C. T., Cano, J. C., & Manzoni, P. (2018). ArduSim: Accurate and real-time multicopter simulation. Simulation Modelling Practice and Theory, 87, 170-190. doi:10.1016/j.simpat.2018.06.009Accurate and real-time multi-UAV simulationhttps://bitbucket.org/frafabco/ardusim/src/master/MAVLink Micro Air Vehicle Communication Protocolhttp://qgroundcontrol.org/mavlink/startGorelick, N., Hancher, M., Dixon, M., Ilyushchenko, S., Thau, D., & Moore, R. (2017). Google Earth Engine: Planetary-scale geospatial analysis for everyone. Remote Sensing of Environment, 202, 18-27. doi:10.1016/j.rse.2017.06.031NS-2 The Network Simulatorhttp://nsnam.sourceforge.net/wiki/index.php/Main_PageOMNeT++ Discrete Event Simulatorhttps://omnetpp.org/Quaternium, Home of the Longest Flight Time Hybrid Dronehttp://www.quaternium.com/Gauss-Markov Mobilityhttps://doc.omnetpp.org/inet/api-current/neddoc/inet.mobility.single.GaussMarkovMobility.htmlFerrera, E., Alcántara, A., Capitán, J., Castaño, A., Marrón, P., & Ollero, A. (2018). Decentralized 3D Collision Avoidance for Multiple UAVs in Outdoor Environments. Sensors, 18(12), 4101. doi:10.3390/s1812410

A Solution for the Efficient Takeoff and Flight Coordination of UAV Swarms

[ES] En la última década, hemos asistido a un gran aumento del uso de los VANTs, debido principalmente a los avances en tecnología y materiales. Hoy en día, los VANTs ya no son solo juguetes para el entretenimiento, sino también importantes activos para muchas empresas. Los VANTs son muy versátiles y, por ello, existen muchas y variadas aplicaciones: misiones de búsqueda y rescate, vigilancia de fronteras, inspección térmica de tuberías, cinematografía y agricultura de precisión, solo por nombrar algunas. En estos momentos en que las industrias están incorporando soluciones basadas en VANTs, es crucial que la investigación avance. El cambio más destacado (con respecto a los VANTs) que presenciaremos en esta década, es el despliegue de grupos de VANTs trabajando en colaboración para cumplir un objetivo superior. Estos grupos, también llamados enjambres de drones, permiten realizar tareas más complejas, de forma más eficiente, o con mayor redundancia. Sin embargo, existen retos inherentes al funcionamiento de un enjambre de VANTs. Debe existir una buena comunicación entre los VANTs, deben evitarse las colisiones y los VANTs individuales deben utilizarse de forma inteligente para aumentar la eficiencia global. En este trabajo fin de master se da solución a algunos de los principales problemas relativos a los enjambres de vehículos aéreos no tripulados. En primer lugar, diseñamos varios patrones de formación de enjambres ´útiles. A continuación, incorporamos esas formaciones en dos procedimientos de despegue - una heurística y un algoritmo ya existente (KMA) - los cuales se prueban ampliamente para decidir cual es el más adecuado para despegar un enjambre de VANTs de la manera más eficiente. Una vez que somos capaces de despegar de forma sincronizada y segura un enjambre completo, continuamos nuestra investigación proporcionando una solución para mantener ese enjambre organizado, y estable durante una misión pre-planificada. Nuestra solución incorpora mecanismos para proporcionar resiliencia al enjambre, de tal manera que todos y cada uno de los VANTs pueden abandonar el enjambre (en pleno vuelo), sin perturbar a los demás en su misión.[EN] In the last decade, we have seen a great increase in the use of Unmanned Aerial Vehicles (UAVs). This is mainly due to advances in technology and materials. Nowadays, UAVs are no longer only toys for entertainment, but also important assets for many enterprises. UAVs are versatile, and thus many diverse applications exist: search and rescue missions, border surveillance, thermal pipeline inspection, cinematography, and precision agriculture, just to name a few. Now that the industry is incorporating UAVs based solutions, it is crucial that research advances. The most prominent change (with respect to UAVs) that we will witness in this decade, is the deployment of groups of UAVs working collaboratively to fulfill a higher goal. Those groups, also called swarms, allow us to perform more complex tasks, more efficiently, or with more redundancy. However, there are inherent challenges while operating a swarm of UAVs: there must be a good communication channel between the UAVs, collisions must be avoided, and the individual UAVs should be used intelligently in order to increase the overall efficiency. In this master thesis, a solution is given for some of the main problems concerning Unmanned Aerial Vehicle (UAV) swarms. First, we lay out various useful swarm formation patterns. Then we incorporate those formations in two takeoff procedures - an heuristic and an existing algorithm (KuhnMunkres algorithm (KMA)) - which are extensively tested to decide which one is the most appropriate for the takeoff of a swarm of UAVs in the most efficient manner. Once we are able to take off an entire swarm, we continue our research by providing a solution to keep that swarm organized and stable during a pre-planned mission. Such solution incorporates mechanisms to provide resilience to the swarm in such a manner that any number of UAVs can be removed from the swarm (mid-flight) without disturbing the others in their mission.Wubben, J. (2021). A Solution for the Efficient Takeoff and Flight Coordination of UAV Swarms. Universitat Politècnica de València. http://hdl.handle.net/10251/172620TFG

Generalized software application for operation of a 3D vehicle in air, water and land

The unmanned vehicles (UV) and its applications are growing exponentially. Using the radio control is the most common way to control these types of vehicles for being a simple and cheap method to control an UV. However, it doesn’t have a visual interface that allows the user to see the vehicle’s information such as battery status, speed, distance, geolocation, etc. To deal with this problem, some mobile and desktop applications have been developed. To communicate between the control device and the vehicle, dongles are commonly used to establish the connection using radio, Bluetooth or Wi-Fi. In most cases, these technologies don’t allow the user to control at long distances, Beyond Line Of-Sight (BLOS), and these applications are focused to use mostly on multi-copters, and most of the times, they only allow to connect a vehicle at a time. The purpose of this dissertation is to study the reliability of an application able to control multiple types of vehicles, such as aerial, land and water vehicles. This application allows the user to connect multiple vehicles at the same time using a single device, easily change the vehicle assigned to control, by using mobile networks to perform the communication between the developed application and the vehicle. In this way, it will be possible to connect a 3D – hybrid vehicle, which is a vehicle capable of moving in water, land and air environments, allowing the user to control the vehicle at long distances with video feedback. To achieve the purpose of this dissertation, it was developed an Android application to allow controlling the vehicle by using mobile networks to communicate. In the vehicle, besides the common electronics used in an unmanned vehicle (ESC’s, motors, batteries, controller board, etc.), it will be used a Raspberry Pi 2 model B with a 3rd Generation (3G) and 4th Generation (4G) dongle that will connect the vehicle to the internet, routing the messages coming from the controller board placed in the vehicle to the mobile application. It was also developed a server application to do the user management and exchange the messages coming from both platforms: vehicle and application.Os veículos não tripulados e as suas aplicações estão em forte crescimento. O uso de rádio controlo é a maneira mais comum de controlar estes tipos de veículos, sendo o método mais barato e simples de controlar um veículo não tripulado. Contudo, não têm uma interface visual que permita ao utilizador ver as informações do veículo, tais como o nível da bateria, a velocidade, distância, geolocalização, entre outros. Para ajudar com este problema, têm sido desenvolvidas algumas aplicações para dispositivos móveis e computadores, que permitem controlar e monitorizar este tipo de veículos. Para estabelecer a comunicação entre o dispositivo de controlo e o veículo, são frequentemente usados dongles para comunicar por rádio, Bluetooth ou Wi-Fi. Na maioria dos casos, estas tecnologias não possibilitam ao utilizador o controlo a longas distâncias, para além da linha de vista, e costumam ser focadas para o uso em multicopteros, possibilitando, na maioria dos casos, a ligação de um único veículo. O âmbito desta dissertação pretende estudar e desenvolver uma aplicação com elevada fiabilidade, capaz de controlar vários tipos de veículos, nomeadamente, veículos aéreos, terrestres e aquáticos. Esta aplicação irá permitir a ligação a vários veículos ao mesmo tempo, trocar facilmente o veiculo a controlar, recorrendo aos sistemas de comunicação móveis celulares, 3ª geração (3G ) e 4ª geração (4G) para garantir a comunicação entre a aplicação desenvolvida e o veículo não tripulado. Seguindo estes princípios, é possível controlar um veículo 3D hibrido (em modo de ar, terra e mar). Esta permite ao utilizador controlar o veículo a longas distâncias com o uso de uma transmissão de vídeo. Para alcançar o objetivo desta dissertação foi desenvolvida uma aplicação Android para possibilitar o controlo recorrendo às redes móveis celulares. No veículo, além da eletrónica habitual, para um veículo não tripulado (motores, ESC’s, baterias, etc.), será também utilizado um Raspberry Pi 2 modelo B com um dongle 3G/4G que liga o veículo, redirecionando as mensagens vindas da placa de controlo para a aplicação móvel. Para a comunicação entre a aplicação e o veículo foi também desenvolvida uma aplicação instalada no servidor que é responsável pela gestão de utilizadores e pela troca de mensagens vindas de ambas as plataformas: veículo e aplicação

Concept and Feasibility Evaluation of Distributed Sensor-Based Measurement Systems Using Formation Flying Multicopters

Unmanned aerial vehicles (UAVs) have been used for increasing research applications in atmospheric measurements. However, most current solutions for these applications are based on a single UAV with limited payload capacity. In order to address the limitations of the single UAV-based approach, this paper proposes a new concept of measurements using tandem flying multicopters as a distributed sensor platform. Key challenges of the proposed concept are identified including the relative position estimation and control in wind-perturbed outdoor environment and the precise alignment of payloads. In the proposed concept, sliding mode control is chosen as the relative position controller and a gimbal stabilization system is introduced to achieve fine payload alignment. The characterization of the position estimation sensors (including global navigation satellite system and real-time kinematics) and flight controller is carried out using different UAVs (a DJI Matrice M600 Pro Hexacopter and Tarot X4 frame based Quadcopter) under different wind levels. Based on the experimental data, the performance of the sliding mode controller and the performance of the gimbal stabilization system are evaluated in a hardware-in-the-loop simulation environment (called ELISSA). Preliminary achievable control accuracies of the relative position and attitude of subsystems in the proposed concept are estimated based on experimental result

ArduSim: Accurate and real-time multicopter simulation

[EN] As the popularity and the number of Unmanned Aerial Vehicles (UAVs) increases, new protocols are needed to coordinate UAVs when flying autonomously, and to avoid that these UAVs collide with each other. Directly testing such novel protocols on real UAVs is a complex procedure that requires investing much time, money and research effort. Hence, it becomes necessary to have the possibility to first test different solutions using simulation. Unfortunately, existing tools present significant limitations: some of them only simulate accurately the flight behavior of one UAV, while some other simulators can manage several UAVs simultaneously, but not in real-time, thus loosing accuracy regarding the mobility pattern of the UAV. In this work we address such problem by introducing ArduSim, a novel simulator that allows controlling in soft real-time the flight and communications of multiple UAVs, being the developed protocols directly portable to real devices. The contributions of this work include: (i) the ArduSim simulation platform, which allows realistic simulation and control of multiple UAVs simultaneously, offering functionalities not provided by existing alternatives; (ii) a model for the WiFi communications link between UAVs, based on real experiments, and that is integrated into ArduSim itself; and (iii) a thorough study of the scalability performance of our simulator.This work was supported by the Ministerio de Economia y Competitividad for the "Programa Estatal de Investigacion, Desarrollo e Innovacion Orientada a Retos de la Sociedad, Proyecto I+D+I SMART@CARPHONE: Integracion del smartphone y el vehiculo para conectar conductores, sensores y entorno a traves de una arquitectura de servicios funcionales" (grant number TEC2014-52690-R), and the Universitat Politecnica de Valencia (UPV) under program "Contratos Pre-doctorales para la Formacion de Personal Investigador (FPI)" (grant number 0060100000).Fabra Collado, FJ.; Tavares De Araujo Cesariny Calafate, CM.; Cano, J.; Manzoni, P. (2018). ArduSim: Accurate and real-time multicopter simulation. Simulation Modelling Practice and Theory. 87:170-190. https://doi.org/10.1016/j.simpat.2018.06.009S1701908

Multicopter Dynamics in Small Uninhabited Aerial Systems

Quadcopters and other multicopters were one of the first considered vertical take-off and landing vehicle configurations for heavier than air transport in the early 20th century. After the success of Oehmichen’s No. 2 Quadcopter and de Bothezat Quadcopter in the 1920s, multicopter designs slowly faded until a reemergence into the small unmanned aerial systems realm as toys. With the beginning of the 21st century, quadcopters have become a mainstream object with many commercial vehicles available for personal or professional usage. However, since the reemergence, the academic work on these small multirotor UAS as remained largely separated from the academic work on larger manned vertical take off and landing systems. This thesis works to review fundamental theory from basic dynamics and rudimentary aerodynamics of helicopter flight before analyzing the current state of small multicopter modeling and control to identify weaknesses in current approaches. This work also uses flow visualization and ground effect testing to help illuminate some multicopter aeromechanic and vehicle dynamics couplings that are not currently being observed from current quadcopter models. These observations can be used in the development of future robust controllers for these multirotor platforms

Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer

In this thesis, consisting of five scientific papers, I investigate the potential of unmanned aircraft systems (UAS) in stable boundary layer (SBL) research, by developing and applying a new innovative observation strategy. In this strategy we supplement ground-based micrometeorological observations from masts and remote-sensing systems with a number of different UAS. To achieve good agreement between the different systems employed in this approach, I further investigate the quality and intercomparability of UAS-based observations of atmospheric temperature, humidity, pressure and wind, and develop and apply common, best-practice data processing methods. In Paper I we give a brief introduction to the ISOBAR project and provide an overview over the first SBL campaign at Hailuoto and the prevailing synoptic, sea-ice and micrometeorological conditions. We demonstrate the quality of our measurement approach by combining UAS profile data with observations from the wind and temperature sensing systems. Repeated UAS temperature profiles give detailed insight into the temporal evolution of the SBL, which we find was often subject to rapid temperature changes affecting the entire depth of the SBL. We further highlight the potential of the sampled data by detailed investigations of a case study, featuring rapid shifts in turbulent regimes and strong elevated thermal instabilities, which were likely to result from the instability of an elevated internal gravity wave. In Paper II we assess the quality and intercomparability of UAS-based atmospheric observations from the most extensive intercomparison experiment to date. We evaluate the precision and bias of temperature, humidity, pressure, wind speed and direction observations from 38 individual UAS with 23 unique sensor configurations based on observations next to a 18-m mast equipped with reference instruments. In addition, we investigate the influence of sensor response on the quality of temperature and humidity profiles. By grouping the different sensor–platform combinations with respect to the type of aircraft, sensor type and sensor integration (i.e., measures for aspiration and radiation shielding), we attempt to draw general conclusions from the intercomparison results. Overall, we find most observation systems in good agreement with the reference observations, however, some systems showed fairly large biases. In general, hovering multicopters showed less variability than fixed-wing systems and we attribute this finding to the difference in sampling strategies. The most consistent observations of the mean wind were achieved by multicopter-mounted sonic anemometers. Sensor response errors were smaller for fine-bed thermistors compared to temperature sensors of integrated-circuit type, and sensor aspiration proofed to be substantially relevant. We conclude, that sensor integration considerations, like radiation shielding and aspiration, are likely to be as important as the choice of the sensor type, and give a couple of recommendations for future perspectives on UAS-based atmospheric measurements. Paper III presents the ISOBAR project to a broader scientific audience, including a description of the two measurement campaigns, ISOBAR17 and ISOBAR18 and the contrasting meteorological and sea ice conditions. We further provide an overview on the micrometeorological conditions during the 13 intensive observational periods (IOPs), which resulted in detailed data sets on the SBL in unprecedented spatiotemporal resolution. Numerous cases with very-stable stratification under clear-sky and weak-wind conditions were observed, featuring a variety of different SBL processes. These processes resulted in rapid changes in the SBL’s vertical structure. Based on selected in-depth case studies, we investigate the interactions of turbulence in the very stable boundary layer (VSBL) with different processes, i.e., a shear instability, associated with a low-level jet; a rapid and strong cooling event, observed a couple of meters above the ground; and a wave-breaking event, caused by the enhancement of wind shear. In a first qualitative model validation experiment we use data from one IOP to assess the performance of three different types of numerical models. Only the turbulence resolving large-eddy simulation model is found capable of reproducing a VSBL structure similar to the one observed during the IOP. The other models, i.e., an operational weather prediction and a single-column model, substantially overestimated the depth of the SBL. Paper IV introduces a new fixed-wing UAS for turbulence observations and first results from validation experiments carried out during ISOBAR18. Airborne observations of mechanical turbulence from straight horizontal flight paths are compared to corresponding eddy-covariance measurements mounted on a 10-m mast during weakly stable conditions with moderate wind speeds. Different average and spectral turbulence quantities, as well as mean wind speed and direction were computed for both systems and compared to each other. The UAS observations of mean wind and turbulence are in good agreement with the reference observations and the turbulence spectra agree qualitatively in the onset of the inertial subrange and the turbulence production range. Minor differences are likely to be caused by a slightly elevated UAS flight level and additional small altitude variations in the presence of relatively strong vertical gradients. In a second comparison, vertical profiles of mean wind and turbulence variables, determined from straight horizontal UAS flights at several different levels are compared qualitatively to profile observations from the 10-m mast and a phased-array sodar system providing 10-min averaged wind and vertical velocity variance profiles above 35 m. Qualitatively, the results agree well for the first two out of three profiles. During the third profile, the UAS data indicate the existence of a low-level jet but not an upside-down boundary layer structure, which would be expected due to the elevated source of turbulence. This observation is, however, not supported by the other measurement systems. Instead, the sodar data indicate a strong decrease in wind speed during the time of this profile. The fact that the lower part of the UAS profile was sampled before the start of the strongest transition, resulted in a seemingly wrong shape of the vertical profiles. This finding highlights the relevance of non-stationarity and the importance of additional reference systems for the correct interpretation of UAS sampled turbulence profiles. Paper V explores the potential of a new method to estimate profiles of turbulence variables in the SBL. In this method we apply a gradient-based scaling scheme for SBL turbulence to multicopter profiles of temperature and wind, sampled during ISOBAR18. We first validate this method by scaling turbulence observations from three levels on a 10-m mast with the corresponding scaling parameters, and comparing the resulting non- dimensional parameters to the semi-empirical stability functions proposed for this scheme. The scaled data from the three levels largely collapse to the predicted curves, however, minor differences between the three levels are evident. We attribute this discrepancy to the non-ideal observation heights for the determination of vertical gradients at the upper turbulence observation level. After the successful validation we apply this method to UAS profiles, by computing profiles of the gradient Richardson number to which we then apply the stability functions to derive turbulence variables. We demonstrate this approach based on three case studies covering a broad range of SBL conditions and boundary layer heights. Since the application of this scaling scheme is only valid within the SBL, we estimate the boundary layer height from the sodar and two different methods based on UAS data. Comparisons at the lowest levels against turbulence variables from the 10-m mast and at higher levels against a Doppler wind lidar, which also provides estimates of some turbulence variables, indicate broad agreement and physical meaningful results of this method. Supplementing the findings from the five scientific papers, this thesis also provides the detailed description on the methodology and data processing procedures, I applied for the synthesis of observations from UAS, micrometeorological masts and boundary layer remote-sensing systems. Furthermore, I present results on the validation of the different wind observation methods, using lidar wind observations as the common reference. Finally, I provide an outlook on future perspectives of SBL and UAS-based boundary-layer research, and how further developments in SBL observation strategies may benefit from recent and future developments.Doktorgradsavhandlin

Helipad detection for accurate UAV pose estimation by means of a visual sensor

In this article, we tackle the problem of developing a visual framework to allow the autonomous landing of an unmanned aerial vehicle onto a platform using a single camera. Specifically, we propose a vision-based helipad detection algorithm in order to estimate the attitude of a drone on which the camera is fastened with respect to target. Since the algorithm should be simple and quick, we implemented a method based on curvatures in order to detect the heliport marks, that is, the corners of character H. By knowing the size of H mark and the actual location of its corners, we are able to compute the homography matrix containing the relative pose information. The effectiveness of our methodology has been proven through controlled indoor and outdoor experiments. The outcomes have shown that the method provides high accuracies in estimating the distance and the orientation of camera with respect to visual target. Specifically, small errors lower than 1% and 4% have been achieved in the computing of measurements, respectively

Autonomous, Long-Range, Sensor Emplacement Using Unmanned Aircraft Systems

Automated, in-ground sensor emplacement can significantly improve remote, terrestrial, data collection capabilities. Utilizing a multicopter, unmanned aircraft system (UAS) for this purpose allows sensor insertion with minimal disturbance to the target site or surrounding area. However, developing an emplacement mechanism for a small multicopter, autonomy to manage the target selection and implantation process, as well as long-range deployment are challenging to address. We have developed an autonomous, multicopter UAS that can implant subsurface sensor devices. We enhanced the UAS autopilot with autonomy for target and landing zone selection, as well as ensuring the sensor is implanted properly in the ground. The multicopter UAS, limited by onboard energy, can be carried by a transport aircraft to within 1 km of the desired sensor location site and deployed by a novel parachuting-canister system. Through a comprehensive set of field trials and testing, we assess the effectiveness of each subsystem. We evaluate our system on missions covering distances up to 25 km away in mountains 1 km above the takeoff location