2,123 research outputs found
Autonomous Flight Control for Multi-Rotor UAVs Flying at Low Altitude
Unmanned aerial vehicles (UAVs) at low altitude flight may significantly degrade their performance and the safety under wind disturbances and incorrect operations. This paper presents a robust control strategy for UAVs to achieve good performance of low altitude flight and disturbance rejection. First, a novel second-order hexacopter dynamics is established and the position tracking is translated to the altitude and the rotational angle tracking problem. An integrated control scheme is created to deal with the challenges faced by hexacopter at low altitude flight, in which the influence of near-ground threshold distance and the desired roll, pitch, and yaw are analyzed. Moreover, an improved flying altitude planner and an attitude planner for low altitude conditions are designed respectively to avoid the overturning risk due to the big reaction torque and external disturbances. Second, a sliding-mode-based altitude tracking controller and an attitude tracking controller are designed to reduce the tracking errors and improve the robustness of the system. Finally, the proposed control scheme is tested on simulation and experiment platforms of multi-rotor UAV to show the feasibility and accurate trajectory tracking at low altitude flight
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Mitigating ground effect on mini quadcopters with model reference adaptive control
Mitigating ground effect becomes a big challenge for autonomous aerial vehicles when they are flying in close proximity to the ground. This paper aims to develop a precise model of ground effect on mini quadcopters, provide an advanced control algorithm to counter the model uncertainty and, as a result, improves the command tracking performance when the vehicle is in the ground effect region. The mathematical model of ground effect has been established through a series of experiments and validated by a flight test. The experiments show that the total thrust generated by rotors increases linearly as the vehicle gets closer to the ground, which is different from the commonly-used ground effect model for a single rotor vehicle. In addition, the model switches from a piecewise linear to a quadratic function when the rotor to rotor distance is increased. A control architecture that utilizes the model reference adaptive controller (MRAC) has also been designed, where MRAC is added to the altitude loop. The performance of the proposed control algorithm has been evaluated through a set of flight tests on a mini quadcopter platform and compared with a traditional proportional–integral–derivative (PID) controller. The results demonstrate that MRAC dramatically improves the tracking performance of altitude command and can reduce the rise time by 80 % under the ground effect
Autonomous Obstacle Collision Avoidance System for UAVs in rescue operations
The Unmanned Aerial Vehicles (UAV) and its applications are growing for both civilian and
military purposes. The operability of an UAV proved that some tasks and operations can be
done easily and at a good cost-efficiency ratio.
Nowadays, an UAV can perform autonomous tasks, by using waypoint mission navigation
using a GPS sensor. These autonomous tasks are also called missions. It is very useful to certain
UAV applications, such as meteorology, vigilance systems, agriculture, environment mapping
and search and rescue operations.
One of the biggest problems that an UAV faces is the possibility of collision with other objects
in the flight area. This can cause damage to surrounding area structures, humans or the UAV
itself. To avoid this, an algorithm was developed and implemented in order to prevent UAV
collision with other objects.
“Sense and Avoid” algorithm was developed as a system for UAVs to avoid objects in collision
course. This algorithm uses a laser distance sensor called LiDAR (Light Detection and
Ranging), to detect objects facing the UAV in mid-flights. This light sensor is connected to an
on-board hardware, Pixhawk’s flight controller, which interfaces its communications with
another hardware: Raspberry Pi. Communications between Ground Control Station or RC
controller are made via Wi-Fi telemetry or Radio telemetry.
“Sense and Avoid” algorithm has two different modes: “Brake” and “Avoid and Continue”.
These modes operate in different controlling methods. “Brake” mode is used to prevent UAV
collisions with objects when controlled by a human operator that is using a RC controller.
“Avoid and Continue” mode works on UAV’s autonomous modes, avoiding collision with
objects in sight and proceeding with the ongoing mission.
In this dissertation, some tests were made in order to evaluate the “Sense and Avoid”
algorithm’s overall performance. These tests were done in two different environments: A 3D
simulated environment and a real outdoor environment. Both modes worked successfully on a
simulated 3D environment, and “Brake” mode on a real outdoor, proving its concepts.Os veículos aéreos não tripulados (UAV) e as suas aplicações estão cada vez mais a ser
utilizadas para fins civis e militares. A operacionalidade de um UAV provou que algumas
tarefas e operações podem ser feitas facilmente e com uma boa relação de custo-benefício. Hoje
em dia, um UAV pode executar tarefas autonomamente, usando navegação por waypoints e um
sensor de GPS. Essas tarefas autónomas também são designadas de missões. As missões
autónomas poderão ser usadas para diversos propósitos, tais como na meteorologia, sistemas
de vigilância, agricultura, mapeamento de áreas e operações de busca e salvamento. Um dos
maiores problemas que um UAV enfrenta é a possibilidade de colisão com outros objetos na
área, podendo causar danos às estruturas envolventes, aos seres humanos ou ao próprio UAV.
Para evitar tais ocorrências, foi desenvolvido e implementado um algoritmo para evitar a colisão
de um UAV com outros objetos.
O algoritmo "Sense and Avoid" foi desenvolvido como um sistema para UAVs de modo a evitar
objetos em rota de colisão. Este algoritmo utiliza um sensor de distância a laser chamado
LiDAR (Light Detection and Ranging), para detetar objetos que estão em frente do UAV. Este
sensor é ligado a um hardware de bordo, a controladora de voo Pixhawk, que realiza as suas
comunicações com outro hardware complementar: o Raspberry Pi. As comunicações entre a
estação de controlo ou o operador de comando RC são feitas via telemetria Wi-Fi ou telemetria
por rádio. O algoritmo "Sense and Avoid" tem dois modos diferentes: o modo "Brake" e modo
"Avoid and Continue". Estes modos operam em diferentes métodos de controlo do UAV. O
modo "Brake" é usado para evitar colisões com objetos quando controlado via controlador RC
por um operador humano. O modo "Avoid and Continue" funciona nos modos de voo
autónomos do UAV, evitando colisões com objetos à vista e prosseguindo com a missão em
curso. Nesta dissertação, alguns testes foram realizados para avaliar o desempenho geral do
algoritmo "Sense and Avoid". Estes testes foram realizados em dois ambientes diferentes: um
ambiente de simulação em 3D e um ambiente ao ar livre. Ambos os modos obtiveram
funcionaram com sucesso no ambiente de simulação 3D e o mode “Brake” no ambiente real,
provando os seus conceitos
SwarMAV: A Swarm of Miniature Aerial Vehicles
As the MAV (Micro or Miniature Aerial Vehicles) field matures, we expect to see that the platform's degree of autonomy, the information exchange, and the coordination with other manned and unmanned actors, will become at least as crucial as its aerodynamic design. The project described in this paper explores some aspects of a particularly exciting possible avenue of development: an autonomous swarm of MAVs which exploits its inherent reliability (through redundancy), and its ability to exchange information among the members, in order to cope with a dynamically changing environment and achieve its mission. We describe the successful realization of a prototype experimental platform weighing only 75g, and outline a strategy for the automatic design of a suitable controller
Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping
Acknowledgments We thank Johan Havelaar, Aeryon Labs Inc., AeronVironment Inc. and Aeronautics Inc. for kindly permitting the use of materials in Fig. 1.Peer reviewedPublisher PD
Sky-Farmers: Applications of Unmanned Aerial Vehicles (UAV) in Agriculture
Unmanned aerial vehicles (UAVs) are unpiloted flying robots. The term UAVs broadly encompasses drones, micro-, and nanoair/aerial vehicles. UAVs are largely made up of a main control unit, mounted with one or more fans or propulsion system to lift and push them through the air. Though initially developed and used by the military, UAVs are now used in surveillance, disaster management, firefighting, border-patrol, and courier services. In this chapter, applications of UAVs in agriculture are of particular interest with major focus on their uses in livestock and crop farming. This chapter discusses the different types of UAVs, their application in pest control, crop irrigation, health monitoring, animal mustering, geo-fencing, and other agriculture-related activities. Beyond applications, the advantages and potential benefits of UAVs in agriculture are also presented alongside discussions on business-related challenges and other open challenges that hinder the wide-spread adaptation of UAVs in agriculture
Model predictive altitude and velocity control in ergodic potential field directed multi-UAV search
This research addresses the challenge of executing multi-UAV survey missions
over diverse terrains characterized by varying elevations. The approach
integrates advanced two-dimensional ergodic search technique with model
predictive control of UAV altitude and velocity. Optimization of altitude and
velocity is performed along anticipated UAV ground routes, considering multiple
objectives and constraints. This yields a flight regimen tailored to the
terrain, as well as the motion and sensing characteristics of the UAVs. The
proposed UAV motion control strategy is assessed through simulations of
realistic search missions and actual terrain models. Results demonstrate the
successful integration of model predictive altitude and velocity control with a
two-dimensional potential field-guided ergodic search. Adjusting UAV altitudes
to near-ideal levels facilitates the utilization of sensing ranges, thereby
enhancing the effectiveness of the search. Furthermore, the control algorithm
is capable of real-time computation, encouraging its practical application in
real-world scenarios
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