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A numerical study is presented on the upper limit of power extraction by a dense cross-stream array of wind turbines, using 3D Reynolds-averaged Navier–Stokes simulations of flow over porous discs. The main objectives are: (i) to investigate the effect of ‘local blockage’ due to neighbouring turbines on the limit of power extraction; and (ii) to clarify how this effect compares with the effect of ‘local flow acceleration’ obtained by staggering the array in the streamwise direction. Some unconventional array configurations with vertical turbine arrangements, following the so-called ‘multi-rotor’ concept, are also investigated. Results show that the limit of power extraction by a non-staggered array increases moderately with the number of turbines arrayed (about 5% increase in the power coefficient compared to the Betz limit when 9 turbines are arrayed side-by-side). This power increase due to the local blockage can be enhanced further, but only slightly for the case of 9 turbines, by arranging turbines vertically as well as horizontally. Staggering the array in the streamwise direction may increase the power of downstream turbines due to the effect of local flow acceleration but reduce the power of upstream turbines as the local blockage effect diminishes, resulting in a total power reduction. [ABSTRACT FROM AUTHOR]

The movement and deposition of the droplets sprayed by agricultural unmanned aerial vehicle (UAV) are influenced by the complex downwash flow field of the rotors. Instead of conducting field experiment, a high speed particle image velocimetry (PIV) method was used to measure the movement and deposition of the droplets at different rotating speeds of rotors (1000-3000 r/min) or at different transverse injecting points (20-50 cm away from its nearby rotors) in the downwash flow field of an agricultural UAV with eight rotors and conical nozzles. The maximum speed and size of the high speed zone of the droplets were found greatly influenced by the downwash velocity. The initial spray angle of the nozzle declined with the increase of downwash flow speed. It was found that the downwash velocity could not only change the deposition zone of the droplets, but also influence their distribution. The increase of the downwash velocity would increase the deposition uniformity of the droplets. The nozzle position in the downwash flow field could also influence the deposition of the droplets. When the transverse distance between the nozzle and its nearby rotors increased, the relative deposition near the downwash flow of the rotors increased simultaneously. However, the distance between the deposition peak and the nozzle stayed constant. The initial spray angle of the nozzle was not influenced by the transverse distance between the nozzle and its nearby rotors. The research results could provide a theoretical basis and reference for the optimization of the spray application of multi-rotor UAV to minimize droplets deposition uncertainty. [ABSTRACT FROM AUTHOR]

Attitude measure is the basis of multi-rotors flight control. An attitude measure system was constructed based on MEMS gyroscope, accelerometer and magnetometer to realize three-axis attitude measure of multi-rotors. The system included STM32F103 as controller, integrated accelerometer and gyroscope MPU6050, magnetometer HMC5883 as measure sensors. A sensor fusion quaternion-based extended Kalman filter compliant with this system was proposed. The attitude quaternion and the gyroscope bias were introduced as state vector, the acceleration and the magnetic measured by accelerometer and magnetometer were introduced as observation vector. Extended Kalman filter combined the nice performance of gyroscope in dynamic with accelerometer and magnetometer in static. The optimized covariance value combination can improve the accuracy of attitude estimation and had excellent tracking performance in dynamic. The measure system based on extended Kalman filter was testified and analyzed by static and dynamic tests. Experiment results illustrated that the system can obtain the information of each sensor. The attitude measure system based on extended Kalman filter realized precision attitude measure for multi-rotors in dynamic circumstances. It may lay foundation for UAV remote control. [ABSTRACT FROM AUTHOR]

In this paper, the dynamics modeling of coaxial octorotor UAVs is described taking into account the majority of uncertain factors such as actuator faults, parametric deviations, and external disturbances. Then, a robust and fault-tolerant controller is designed for both position and attitude dynamics using a higher-order integral dynamic sliding mode controller (I-DSMC). The robustness and fault-tolerant capabilities of the proposed I-DSMC are further improved by using a nonlinear finite time disturbance observer (FTDO). The adaptive I-DSMC provides correction terms for unknown lumped uncertainty in real-time by use of FTDO estimates. Lyapunov stability is provided for the closed-loop system. The efficacy of the proposed controller is supported by simulation studies. The results reveal that multiple actuator failures are accommodated in the octorotor UAV without loss of controllability in any channel. Further, the simulation results show that the selected multirotor configuration along with the proposed controller combination provides an effective solution for multiple actuator failures in presence of other uncertainties. [ABSTRACT FROM AUTHOR]

Unmanned air vehicles are intrinsically non-linear, unstable, uncertain, and prone to a variety of faults, most commonly the motor faults. The main objective of this paper is to develop a fault-tolerant control algorithm for the quadrotors with the motor faults. Accordingly, a novel adaptive modified incremental nonlinear dynamic inversion (MINDI) control is proposed to stabilize and control the quad-rotor with partial motor faults. The controller consists of a MINDI controller augmented with a discrete-time nonlinear adaptive algorithm. Since the incremental nonlinear dynamic inversion (INDI) algorithm is essentially based on the sensor measurements, it necessitates the angular rates differentiation and therefore amplifies the high-frequency noises produced by the gyroscopes. The application of derivative filters causes unavoidable internal state delays in the INDI structure. Henceforth, the performance of the controller developed for the unstable and uncertain quadrotors degrades considerably. To address this drawback, this paper proposes the MINDI controller which basically derives the angular accelerations from the angular moment estimations. Furthermore, to increase the robustness of the MINDI against motor faults, a discrete-time adaptive controller has been incorporated. The performance of the proposed controllers is verified both through the nonlinear simulations and testbed experiments. The results are compared with a recent efficient algorithm, which had been implemented on a quad-rotor model. [ABSTRACT FROM AUTHOR]

The present paper shows an innovative multirotor Unmanned Aerial Vehicle (UAV) which is able to easily and quickly change its configuration. In order to satisfy this feature, the principal structure is made of an universal plate, combined with a circular ring, to create a rail guide able to host the arms, in a variable number from 3 to 8, and the legs. The arms are adjustable and contain all the avionic and motor drivers to connect the main structure with each electric motor. The unique arm design, defined as all-in-one, allows classical single rotor configurations, double rotor configurations and amphibious configurations including inflatable elements positioned at the bottom of the arms. The proposed multi-rotor system is inexpensive because of the few universal pieces needed to compose the platform which allows the creation of a kit. This modular kit allows to have a modular drone with different configurations. Such configurations are distinguished among them for the number of arms, number of legs, number of rotors and motors, and landing capability. Another innovation feature is the introduction of the 3D printing technology to produce all the structural elements. In this manner, all the pieces are designed to be produced via the Fused Deposition Modelling (FDM) technology using desktop 3D printers. Therefore, an universal, dynamic and economic multi-rotor UAV has been developed.

For unmanned helicopters to be used in industrial applications, autonomous flight control is necessary. This study aims to shorten the time required to tune a controller and design a stable control system for model variation of unmanned multi-rotor helicopters. Designing model based controllers requires a significant amount of time and effort for model identification and the tuning of controller parameters. Additionally, changes in the dynamics of the plant lead to deterioration of control performance. In this paper, we propose adaptive I-PD control having on-line system identification mechanism for change-of-altitude direction of a helicopter to solve the problems that have been presented. First, the calculation of the altitude model and system identification mechanism are described. In order to guarantee the minimum phase property of the altitude model, we use the delta operator for system identification. We show the accuracy of the altitude model and the validity of the proposed system identification algorithm using flight data. Next, we design an adaptive I-PD controller based on the identified parameters. I-PD gains are adjusted sequentially by a partial model matching method. Finally, we demonstrate the validity of the proposed control system by way of a flight experiment. The experimental result shows we were able to design a highly precise altitude controller in about 10 seconds.

This paper proposes a cascaded control structure and a method of practical application for attitude control of a multi-rotor Unmanned aerial vehicle (UAV). The cascade control, which has tighter control capability than a single-loop control, is rarely used in attitude control of a multi-rotor UAV due to the input-output relation, which is no longer simply a set-point to Euler angle response transfer function of a single-loop PID control, but there are multiply measured signals and interactive control loops that increase the complexity of evaluation in conventional way of design. However, it is proposed in this research a method that can optimize a cascade control with a primary and secondary loops and a PID controller for each loop. An investigation of currently available PID-tuning methods lead to selection of the Simple internal model control (SIMC) method, which is based on the Internal model control (IMC) and direct-synthesis method. Through the analysis and experiments, this research proposes a systematic procedure to implement a cascaded attitude controller, which includes the flight test, system identification and SIMC-based PID-tuning. The proposed method was validated successfully from multiple applications where the application to roll axis lead to a PID-PID cascade control, but the application to yaw axis lead to that of PID-PI. [ABSTRACT FROM AUTHOR]

A multi-rotor system (MRS), in which multiple wind turbines are placed on one tower, is a promising concept for super-large wind turbines at over 10 MW due to the cost and weight advantages. The coherence effects on an MRS were investigated in this study. Although a wide range of coherences were measured so far, a decay constant of C = 12 is recommended in the IEC61400-1 standard. Dynamic simulations were performed for a 14-MW MRS, which consists of seven 2-MW turbines and includes wind models with three different coherences. Although the results show that a larger coherence increases the output power and the collective loads due to tower base fore-aft bending, it reduces the differential loads due to tower-base torque and tower-top nodding. The most significant case is the fatigue damage due to tower base fore-aft bending, which was more than doubled between the decay constants of C = 6 and C = 12. The present results indicate that the coherence should be defined carefully in the design of large-scale MRSs because its effect on them is not straightforward. [ABSTRACT FROM AUTHOR]

Multi-rotor floating offshore wind turbines have been recently proposed as an innovative technology to further reduce the cost of offshore wind energy. Even though examples of commercial prototypes are present, the literature lacks studies on the dynamic performance of such systems. This work presents a comparative analysis of a two-rotor wind turbine concept mounted on spar-type, semi-submersible, and tension-leg platforms. Their short-term performance is assessed by considering six different load cases considering directionally congruent turbulent wind profiles and irregular sea states. The analysis is carried out through an in-house fully-coupled code developed in Modelica. AeroDyn v15 within FAST v8 by NREL is coupled to the Modelica code to achieve blade-element momentum capabilities. Results indicate that platform yaw motion is an important dynamic mode of the systems, particularly for the spar configuration. Stiffer station-keeping lines and longer fairlead distance to the platform centerline reduce significantly yaw motion, as in the case of the semi-submersible and tension-leg configurations. Large tower base bending moment standard deviations and the associated concentration of energy at the platform heave and pitch motion frequencies indicate an increased risk for fatigue damage for the TLP configuration, especially at above-rated wind speeds. Moreover, large tendon loads can pose concerns in terms of fatigue and limit state performance. Large mean platform pitch angle and yaw standard deviation contribute to the reduction of electric power output quality. Extreme storm conditions greatly increase the response standard deviation, especially for the semi-submersible configuration. • Dynamic analysis of two-rotor wind turbine mounted on spar, semi-submersible, and TLP floating platforms. • Platform yaw motion significant dynamic mode for each system. • Platform yaw motion is particularly high for spar-type floating platforms given lower yaw stiffness and shorter fairlead distance from the centerline. • For TLP platform, large tendon loads and tower base bending moment STD indicate an increased risk for fatigue damage. • Extreme storm conditions increase the response STD, especially for the semi-submersible platform. [ABSTRACT FROM AUTHOR]

The aim of this work is a complete description of the multi-rotor implementation; this description covers from selection criteria of the pieces, through their assembly to the tuning of PID controllers. The results shown in this article are derived from the experience gained from the assembly of two multi-rotors, a study on PDI controller design for a quadrotor and three scientific initiation projects dedicated to learning to tune quadrotor PID controllers. The article shows with specific examples how to perform the selection of the principal components of a multi-rotor with conditions different budget also shows the numerical results for the tuning of a quadrotor stability PID controllers. This paper presents suggestions of certain components used to assemble multi-rotors, justifying its choice moreover describes a procedure to perform the selection of motor, propeller, ESC and battery. Also covers a description of the physical installation and calibration procedures of these aircraft. In addition, it presents the structures built to make the tuning of stability PID controllers and describes in detail the process carried out to tune them. This research serves as the basis to accelerate the multi-rotors implementation process to be used to perform a specific application or being test platforms for the developments of stability controllers. [ABSTRACT FROM PUBLISHER]

One of the most outstanding problems of our technical age is the heavy aerial pollution. There are several well-known methods [6, 10-15] that exist for large-area pollution detection, but the measurement of the exact rate of pollution in smaller areas (e.g., industrial zones or disasteraffected areas of a few square kilometres), as well as the numerical expression of changes therein, remain an unsolved problem. The main feature of the developed device is that it can provide exact measurements for a small area at low altitudes (under 500m AGL (Above Ground Level)), and it is also capable of periodical measurements between 0.0001-10 Hz. With the data analysis provided by the system, we can obtain immediate information about the pollution of the given area, as well as changes in pollution levels over time. [ABSTRACT FROM AUTHOR]

The paper presents an analytical framework for addressing the hovering time prediction of rotary-wing aircraft, with a particular focus on multi-rotor platforms. By imposing the balance between required and available power, the endurance expression is derived as a function of airframe features, rotor parameters, and battery capacity. The best endurance condition is also obtained in terms of optimum capacity and hovering time, by means of two approximate closed-form solutions. The proposed methodology was validated by means of numerical simulation and flight testing. Results show the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

With recent advances in technology, personal aerial imagery acquired with unmanned aerial vehicles (UAVs) has transformed the way ecologists can map seasonal changes in wetland habitat. Here, we use a multi-rotor (consumer quad-copter, the DJI Phantom 2 Vision+) UAV to acquire a high-resolution (< 8 cm) composite photo of a coastal wetland in summer 2014. Using validation data collected in the field, we determine if a UAV image and SWOOP (Southwestern Ontario Orthoimagery Project) image (collected in spring 2010) differ in their classification of type of dominant vegetation type and percent cover of three plant classes: submerged aquatic vegetation, floating aquatic vegetation, and emergent vegetation. The UAV imagery was more accurate than available SWOOP imagery for mapping percent cover of submergent and floating vegetation categories, but both were able to accurately determine the dominant vegetation type and percent cover of emergent vegetation. Our results underscore the value and potential for affordable UAVs (complete quad-copter system < $3,000 CAD) to revolutionize the way ecologists obtain imagery and conduct field research. In Canada, new UAV regulations make this an easy and affordable way to obtain multiple high-resolution images of small (< 1.0 km2) wetlands, or portions of larger wetlands throughout a year. [ABSTRACT FROM AUTHOR]

Multi-rotor is an aircraft that can vertically takeoff, land and freely hover. It can be used as a platform to monitor field information near ground with remote sensing technology. It is a beneficial supplement to satellite remote sensing monitoring. Flight control is the core of the whole flight system and attitude detection is an important part of flight control. Therefore, real-time acquire accurate attitude information is the basis for its flight controlling. In this paper, taking multi-rotor as object, a multi-sensor attitude detection system was established. The system included STM32F103 as microprocessor, MPU6050 as three-axis gyroscope and accelerometer, HMC5883 as electronic compass. However, when vehicle accelerated horizontally, deviations among sensors would be produced because attitude angular could be measured by gyroscope timely, but accelerometer and electronic compass would lag due to the averaging. Moreover, accelerometer cannot distinguish any horizontal acceleration from gravity. In order to eliminate the measure deviations among above sensors, multi-sensor information fusion method with fuzzy-proportion integration (fuzzy-PI) deviation correction based on quaternion and its coordinate conversion was proposed. Fuzzy-proportion integration (fuzzy-PI) deviation correction method integrated precise performance of PI regulator and fast feature of fuzzy regulator. According to the vehicle at low or high speed motion, the deviations would be bigger or smaller. When the deviations and its integrations were less than the predetermined threshold value, it switched to PI regulator to obtain accurate measure. When they were greater than the predetermined threshold value, the algorithm switched to fuzzy regulator to correct the deviation as soon as possible. Attitude angle detected by fuzzy-PI deviation correction method, complementary filter algorithm and DMP program were validated by SGT320E multi-functional three-axis rotary platform. The measurement results were monitored and acquired through serial port. When roll angle ranged from -40° to 40°, static angle measurements were made. Experiment result showed that the average measure error of roll angle and pitch angle with the proposed method was 1.213° and 1.072°, less than complementary filter algorithm. It could satisfy the accuracy requirement in aircraft attitude detection. Furthermore, time consumption per attitude angle solution with above 3 methods running on the proposed multi-sensor attitude detection hardware system was recorded through timer in STM32 and their solution time consumptions were less than 1ms, which proved that the hardware system can satisfy the quick response requirement of angle measure. Solution time of fuzzy-PI deviation correction method was 2 134 μs, less than the other tow methods because the hardware system with fuzzy-PI deviation correction method had a good real-time performance and was suitable for fast calculation measure. In addition, in long static measurement, the proposed method did not generate static drift or divergence and in dynamic measurement, roll angle and pitch angle tracking maximum error was 1.969° and 3.581° with measurement accuracy reaching 1°, which results were closed to DMP solver within MPU6050. The dynamic measure experiment demonstrated that dynamic correcting deviation among multi-sensor in the fuzzy-PI deviation correction method can effectively modify the deviation among sensors, fast and accurately measure vehicle movement. Our study showed that the multi-sensor hardware system based on fuzzy-PI deviation correction method with characteristics of higher solution frequency, higher accuracy, lower cost, can implement for detecting attitude angles of wide range types of vehicles. [ABSTRACT FROM AUTHOR]

Abstract: In up-scaling conventional, single rotor wind turbines, increases in weight (volume related) tend to outstrip benefits from increase in energy capture (area related). The multi-rotor concept turns this disadvantage on its head and exploits the area to weight advantage of small rotors. Other advantages of multi-rotors include standardization of components leading to cost reduction, better distributed and generally reduced system loads, enhanced control possibilities and improved logistics for assembly and maintenance.A 20 MW multi rotor system is compared with a notional 20 MW conventional wind turbine and also 4 x 5 MW state-of-the-art offshore wind turbines. [Copyright &y& Elsevier]

During the last few years, scientists have become increasingly concerned about air quality. Particularly in large cities and industrialised areas, air quality is affected by pollution from natural and anthropogenic sources and this has a significant impact on human health. Continuous monitoring of air quality is an important step in investigating the causes and reducing pollution. In this paper, we propose a new autonomous multi-rotor aerial platform that can be used to perform real-time monitoring of air quality in large cities. The air quality monitoring system is able to cover large areas, with high spatial resolution, even above average buildings, while being relatively low cost. We evaluate the proposed system in several locations throughout a metropolitan city, during different seasons and generate fine-grained heat-maps that display the level of pollution of specific areas based on different altitudes. [ABSTRACT FROM AUTHOR]

Micro aerial vehicles (MAVs) usually suffer from several challenges, not least of which are unsatisfactory hover efficiency and limited fly time. This paper discusses the aerodynamic characteristics of a novel Hex-rotor MAV with a coaxial rotor capable of providing higher thrust in a compact structure. To extend the endurance during hover, flow field analysis and aerodynamic performance optimization are conducted by both experiments and numerical simulations with different rotor spacing ratios (i = 0.56, 0.59, 0.63, 0.67, 0.71, 0.77, 0.83, 0.91). The measured parameters are thrust, power, and hover efficiency during the experiments. Retip ranged from 0.7 × 105 to 1.3 × 105 is also studied by Spalart–Allmaras simulations. The test results show that the MAV has the optimum aerodynamic performance at i = 0.56 with Retip = 0.85 × 105. Compared to the MAV with i = 0.98 for Retip = 0.85 × 105, thrust is increased by 5.18% with a reduced power of 3.8%, and hover efficiency is also improved by 12.14%. The simulated results indicate a weakness in inter-rotor interference with the increased rotor spacing. Additionally, the enlarged pressure difference, reduced turbulence, and weakened vortices are responsible for the aerodynamic improvement. This provides an alternative method for increasing the MAV fly time and offers inspiration for future structural design. [ABSTRACT FROM AUTHOR]

In this work, previous studies focused on wake propagation and flow development of multi-rotor drones are consolidated and discussed. An in depth understanding of wake propagation is critical to accurately predict as it can have adverse effects on vehicle stability and can contaminate in-situ sensor measurements that are placed on the vehicle, such as those which facilitate autonomous maneuvering or atmospheric sampling. Studies that have focused on this issue or similar issues have primarily focused on proximity effects include Computational Fluid Dynamics simulations of wake propagation and multi-rotor flows, and experimental studies using flow visualization and Particle Image Velocimetry to capture multi-rotor wake and flow development. Although some preliminary investigations have been carried out, a comprehensive study has not been conducted that includes research on multi-rotors in vertical flight modes (ascending and descending) which are unique multi-rotor capabilities that are often utilized. An in-depth study of multi-rotor wake development is needed to provide insight into the design and optimization of multi-rotors for various applications, including applications in confined environments or for other applications where the wake propagation significantly impacts mission success. [ABSTRACT FROM AUTHOR]

This study investigates psychoacoustic aspects of the noise of multi-rotor type unmanned aerial vehicles (UAV). Two psychoacoustic experiments were performed for a dual purpose: to examine the difference of annoyance induced by the noise from three types of UAVs and a civil aircraft and also to identify the acoustic factors influencing the annoyance from UAV noise. In the first experiment, the annoyance of each stimulus was quantified from psychoacoustic tests and compared with each other. The psychoacoustic tests confirms that UAV noise generally causes more annoyance than civil aircraft noise at the same loudness level. The physical and psychoacoustic indices of the stimuli were analyzed statistically using principal component analysis and regression. The loudness, sharpness and fluctuation strength were derived as significant factors that affect the annoyance of UAV noise. In the second experiment, six new sound samples were created by modifying the sharpness and the fluctuation strength of one representative UAV noise to check the results of the first experiment. Regressions of the test results reaffirmed that the sharpness and fluctuation strength are significant in the annoyance of UAV noise. [ABSTRACT FROM AUTHOR]

A systematic review and analysis of the literature of diffuser-augmented horizontal-axis turbines are presented. A collection of 155 articles in the area is analyzed and classified. The work sample is divided into 16 main research branches for discussion. Performance assessment metrics are proposed based on power coefficient and tip-speed-ratio, to quantify and compare all diffuser-augmented turbines in a unified, meaningful manner. Design suggestions for the development of diffuser-augmented turbines are pointed out based on the analysis of 73 cases. A power coefficient assessment on the work sample presented that, in 58% of the cases, the diffuser-augmented turbines surpassed the power coefficient of scaled bare turbines of the same diameter. A tip-speed-ratio assessment presented that almost 90% of the diffuser-augmented turbines developed a narrower operational interval. Five high-performing diffuser-augmented turbines are discussed, highlighting their methodologies and contributions. Caution is advised when coupling a diffuser to a bare turbine with an already high power coefficient; the diffuser-augmented turbine, especially in those cases, should be designed employing a simultaneous diffuser-rotor optimization. • Systematic analysis of the current literature on diffuser-augmented horizontal-axis turbines is made. • A collection of 155 articles is dived in 16 research branches and discussed. • A diffuser-enhancement parameter is defined and used to compare the effectiveness of diffusers. • In 58% of the DAHT analyzed, the diffuser increases the C p when compared to a bare turbine scaled to the diffuser diameter. • Diffuser-augmented horizontal turbines tend to display narrower C p versus TSR curves compared to its bare version. [ABSTRACT FROM AUTHOR]

With the advancement of helicopter stealth technology and the development of compound helicopters, dynamic electromagnetic scattering of rotor or multi-rotors has become a hot topic of research. In order to deal with the radar stealth problem of compound helicopter target non-coaxial multi-rotor, a multi-rotor dynamic scattering (MDS) calculation method based on dynamic simulation principle (DSP) and multi-axis rotation transformation (MRT) is presented. Single rotor, azimuth angle, elevation angle, rotor disc tilt and attitude angle are all calculated and analyzed in detail. The results show that the electromagnetic scattering of the rotor-like targets exhibits significant periodicity, and the disc tilt or attitude angle affects this periodic and full-machine dynamic scattering. The proposed MDS method is effective and efficient for the dynamic electromagnetic scattering of aircraft operating on individual rotor or multi-axis rotor-type targets. [ABSTRACT FROM AUTHOR]

We present a model-based approach to estimate the vertical profile of horizontal wind velocity components using motion perturbations of a multirotor unmanned aircraft system (UAS) in both hovering and steady ascending flight. The state estimation framework employed for wind estimation was adapted to a set of closed-loop rigid body models identified for an off-the-shelf quadrotor. The quadrotor models used for wind estimation were characterized for hovering and steady ascending flight conditions ranging between 0 and 2 m/s. The closed-loop models were obtained using system identification algorithms to determine model structures and estimate model parameters. The wind measurement method was validated experimentally above the Virginia Tech Kentland Experimental Aircraft Systems Laboratory by comparing quadrotor and independent sensor measurements from a sonic anemometer and two SoDAR instruments. Comparison results demonstrated quadrotor wind estimation in close agreement with the independent wind velocity measurements. However, horizontal wind velocity profiles were difficult to validate using time-synchronized SoDAR measurements. Analysis of the noise intensity and signal-to-noise ratio of the SoDARs proved that close-proximity quadrotor operations can corrupt wind measurement from SoDARs, which has not previously been reported. [ABSTRACT FROM AUTHOR]

This work presents a method for estimating the model parameters of multi-rotor unmanned aerial vehicles by means of an extended Kalman filter. Different from test-bed based identification methods, the proposed approach estimates all the model parameters of a multi-rotor aerial vehicle, using a single online estimation process that integrates measurements that can be obtained directly from onboard sensors commonly available in this kind of UAV. In order to develop the proposed method, the observability property of the system is investigated by means of a nonlinear observability analysis. First, the dynamic models of three classes of multi-rotor aerial vehicles are presented. Then, in order to carry out the observability analysis, the state vector is augmented by considering the parameters to be identified as state variables with zero dynamics. From the analysis, the sets of measurements from which the model parameters can be estimated are derived. Furthermore, the necessary conditions that must be satisfied in order to obtain the observability results are given. An extensive set of computer simulations is carried out in order to validate the proposed method. According to the simulation results, it is feasible to estimate all the model parameters of a multi-rotor aerial vehicle in a single estimation process by means of an extended Kalman filter that is updated with measurements obtained directly from the onboard sensors. Furthermore, in order to better validate the proposed method, the model parameters of a custom-built quadrotor were estimated from actual flight log data. The experimental results show that the proposed method is suitable to be practically applied. [ABSTRACT FROM AUTHOR]