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In Japan today, aging infrastructures such as dams and bridges are becoming an issue. We considered that the use of a hydrofoil multicopter would be an effective method for inspecting and surveying such facilities. When using a hydrofoil multicopter, it is possible to take off from the shore, land on the water, and dive without using a ship. The aircraft developed in this study has the capability to communicate with the land. The aircraft developed in this study is equipped with a communication buoy, and after landing on the water, a communication cable is extended from the buoy to enable underwater maneuvering via wired communication. We report on the development of a precise control system for flight and diving of this aircraft. [ABSTRACT FROM AUTHOR]

The usage of multicopter unmanned aerial vehicles (UAVs) has increased for various military and civilian purposes. The choice of propulsion system of such a vehicle is crucial to fulfill the intended mission requirements. The present study focuses on evaluating the efficiency of propulsion system by experimenting with different motor, propeller and battery combinations. The connection between the electronic speed controller (ESC) signal, current, power, thrust and torque in relation to propeller size is determined. It is observed that regardless of battery capacity or motor type, the thrust and torque produced for a given motor speed (RPM) for a specified propeller are similar. The higher capacity battery with 6000 mAh, denoted as B2 battery, consumes less current and can attain higher motor speed to produce the required thrust force than a lower capacity battery with 3300 mAh, denoted as B1 battery. The most efficient propeller, 12 inches in diameter (P4 propeller), is observed to achieve efficiency levels of 12.9 % for the B1 battery and 11.4 % for the B2 battery. Similarly, the most efficient motor, 700 KV motor (M1), is determined to exhibit efficiency of 64.29 % when coupled with the B1 battery and 62.01 % when coupled with the B2 battery. It is identified that using the B2 battery results in an increased payload capacity of 5.82 N, compared to 2.02 N with the B1 battery. Furthermore, when considering both scenarios with and without payload, greater endurance is observed when B2 battery is used as opposed to the B1 battery.

An innovative machine-learning-based probabilistic framework for online rotor fault diagnosis in multicopters is presented. The proposed scheme employs in-flight out-of-plane strain measurements at each of the multicopter booms to detect, identify, and quantify rotor faults while distinguishing them from the aircraft response to random gusts. Its robust performance is demonstrated with application to a 2-foot-diam hexacopter flying under varying forward velocity and gross weight configurations, as well as atmospheric disturbances and uncertainty. The rotor fault diagnosis takes place in two steps. First, a simple perceptron classifies the aircraft's health condition. If a rotor fault is detected it is simultaneously identified and the fault magnitude estimation step initiates. Here, linear regression models are used to predict the respective rotor degradation values with their 95% confidence intervals. The generalization capability of the method is established with several test data under unmodeled operating conditions (not used in the training phase). The proposed framework can accurately diagnose even minor rotor faults of 8% degradation while distinguishing them from aggressive gusts of up to 10 m/s magnitude. The maximum fault detection time is less than 0.3 s. The health state classification and the rotor fault magnitude quantification accuracy are over 99%. [ABSTRACT FROM AUTHOR]

The work addresses the allometric scaling of unmanned rotorcraft. Compound unmanned rotorcraft are not considered in this study. A population of 93 unmanned rotorcraft are compiled into a single dataset comprising size and performance parameters, including the maximum takeoff weight, maximum payload weight, battery mass, battery capacity, rotor diameter, endurance, range, maximum speed, and operational ceiling. Rotorcraft are grouped based on rotor configuration, propulsion type, and perceived application to study the clustering of the data points. An apparent performance limit for unmanned electric rotorcraft is found at 120 min of endurance and in the 70 km range; a higher range and endurance are currently only achievable using thermal propulsion systems. Furthermore, the regression analysis links size and performance parameters in easy-to-use expressions for the preliminary design of unmanned rotorcraft. It is determined that size parameters have a stronger correlation with the maximum takeoff weight than performance parameters. Comparative analysis suggests that unmanned rotorcraft cannot be treated as a subclass of conventional helicopters due to distinct scaling behaviors. A comparison with theoretical models based on first-order physics principles highlights the major role of low-Reynolds-number aerodynamic effects in rotorcraft scaling. [ABSTRACT FROM AUTHOR]

The flow field induced by multirotor drones is of high interest for atmospheric research, as it locally influences the atmosphere and therefore may have an impact on the sensors installed for atmospheric measurements. Further, on-board vibrations can cause significant interference with the measurement equipment. To investigate the near flow field, an approach combining measurements of pressure and temperature distribution in-flight and in a laboratory setup together with numerical simulations was applied. Existing high-frequency measurement equipment was piggybacked during the initial flight tests with a newly developed 25 kg quadcopter system in a low-cost early-stage-error approach to obtain initial data and experience. During the flights, high resolution sensors for measuring pressure, temperature, acceleration, and deformation were applied with different setups at different locations below one of the rotor planes, respectively, at one rotor arm, to determine the multicopter's influence on pressure and temperature measurements, to investigate rotor arm deformations, and to obtain data to compare with numerical simulations of this rotor setup. An external Schlieren-type measurement technique was tested to visualise the rotor vortices. The applied measurement techniques proved to be suitable for acquiring the state of the rotor-induced flow, but with some limitations. The comparison of measurements and simulations showed basic agreement and allowed for the identification of necessary adaptations for subsequent studies. The interaction of the rotor wakes with the rotor arms could be identified as the main source of the measured structural vibrations. The need for necessary improvements in the measurement setup, flight operation, and simulation setup is presented in detail. [ABSTRACT FROM AUTHOR]

Currently, most of the studies on unmanned aerial vehicle (UAV) automatic landing systems mainly depend on image information to determine the landing location. However, the system requires a camera, a gimbal system and a separate image-processing device, which increases the weight and power consumption of the UAV, resulting in a shorter flight time. In addition, a large amount of computation and slow reaction speed can cause the camera to miss a proper landing moment. To solve these problems, in this study, the moving direction and relative distance between an object and the automatic landing system were measured using a receive signal strength indicator of the radio-frequency (RF) signal. To improve the movement direction and relative distance estimation accuracy, the noise in the RF signal was minimised using a low pass filter and moving average filter. Based on the filtered RF signal, the acceleration of the multicopter to reach the object was estimated by adopting the proportional navigation algorithm. The performance of the proposed algorithm for precise landing on a moving vehicle was demonstrated through experiments. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive neurofuzzy inference system (ANFIS) for field oriented control (FOC) of a permanent magnet synchronous motor (PMSM) for multicopter applications. FOC is the most widely used speed control method for PMSMs. The utilization of linear control algorithms may not be sufficient for this type of systems due to the nonlinear characteristic of the PMSM and the presence of uncertainties such as parameter variations and external disturbances. In particular, in high power and agility applications, conventional PI controllers alone may cause undesired speed overshoot which degrade the performance of the multicopter. This paper proposes more comprehensive speed control of a PMSM drive employing an ANFIS, which offers improved tracking performance in terms of settling time and overshoot under various operating conditions. The proposed ANFIS controller implements the adaptive approach using offline training data over a PI controller that is tuned to the nominal operation of the PMSM, specifically targeting the speed error and the rate of change of error in speed. The training data is obtained from a dynamic model of the PMSM operating with a conventional PI controller. The performance analysis of both controllers under different operating conditions is simulated, and experimentally verified. By using the ANFIS controller, the overshoot is reduced from 6.17% to 1.57% at no load condition, from 36.3% to 6.23% at load, and the settling time is almost halved in both cases compared to a conventional PI controller. [ABSTRACT FROM AUTHOR]

Abstract The need for a perching robot is increasing in the field of rescue and transportation. Accordingly studies on perching an object by attaching a robot arm to a perching robot have been conducted. However, almost all the studies related to perching have been conducted using an actuated or electric device. However, perching by using an electric device has several disadvantages, such as additional power consumption and an increase in the mass of the multicopter used to load the electric source. Instead of using an electric device, perching by using an underactuated gripper can effectively avoid these disadvantages. Accordingly, we developed an underactuated passive gripper that has the advantage of nonconsumption of electric power for perching. A method to confirm the available range for stable perching is one of the problems of using an underactuated passive gripper. Therefore, in this study, we analyze a multicopter carrying an underactuated parallel-link passive gripper for available plane perching. To enable perching on planes with different thicknesses and being embedded at different depths, we summarize the available perching range and limitations based on the friction cone theory. Our conclusion is supported by both theoretical and experimental results.

The flow field induced by multirotor drones is of high interest for atmospheric research, as it locally influences the atmosphere and therefore may have an impact on the sensors installed for atmospheric measurements. Further, on-board vibrations can cause significant interference with the measurement equipment. To investigate the near flow field, an approach combining measurements of pressure and temperature distribution in-flight and in a laboratory setup together with numerical simulations was applied. Existing high-frequency measurement equipment was piggybacked during the initial flight tests with a newly developed 25 kg quadcopter system in a low-cost early-stage-error approach to obtain initial data and experience. During the flights, high resolution sensors for measuring pressure, temperature, acceleration, and deformation were applied with different setups at different locations below one of the rotor planes, respectively, at one rotor arm, to determine the multicopter’s influence on pressure and temperature measurements, to investigate rotor arm deformations, and to obtain data to compare with numerical simulations of this rotor setup. An external Schlieren-type measurement technique was tested to visualise the rotor vortices. The applied measurement techniques proved to be suitable for acquiring the state of the rotor-induced flow, but with some limitations. The comparison of measurements and simulations showed basic agreement and allowed for the identification of necessary adaptations for subsequent studies. The interaction of the rotor wakes with the rotor arms could be identified as the main source of the measured structural vibrations. The need for necessary improvements in the measurement setup, flight operation, and simulation setup is presented in detail.

The authors considered the use of unmanned aerial vehicles as one of the promising innovative directions for the development of economic and social sectors. The authors touched upon the prospects for their use in agriculture, especially for pesticide and agrochemical application, where accuracy, quality and timeliness are important. The relevance of multicopter performance assessment was noted. (Research purpose) The authors aim to develop and test a methodology for the evaluation of multicopters’ performance indicators for pesticide and agrochemical application in the agricultural industry. (Materials and methods) The authors used scientific and technical information and experimental materials, applied methods of system, statistical and functional-cost analysis, mathematical modeling, object and process parameter optimization, as well as previously developed methodological approaches to studying the aerial distribution of substances. (Results and discussion) The authors presented a general description and content of the developed methodology and means for assessing multicopter performance when applying working solutions that provide for an estimation error of up to 7 percent.The typical options for field plots and their treatment were specified. The authors analyzed the results of testing the methodology and software for a typical hexacopter with the payload of up to 10 kilograms. The authors analyzed the impact of working speed of up to 10 meters per second, application rates of 2-30 liters per hectare, the size and characteristics of the field plot up to 200 hectares, traffic patterns and other factors on productivity and multicopter treatment cost. (Conclusions) The authors confirmed the efficiency of implementing complex multi-factor assessment of multicopter performance indicators for working fluids application in agricultural production. The authors determined the appropriate area of applying multicopters with a payload of up to 10 kilograms in the field plots up to 50-60 hectares with a rut length of up to 800-900 meters with different treatment performance: flight – up to 10.5 hectares per flight hour, working – up to 7.5 hectares per hour, daytime – up to 55 hectares. Proposals and recommendations for the provision, organization and implementation of this work were formulated.

Unmanned Aerial Vehicle (UAV) is exposed to various types of stress during flight. One of the most significant negative influences is the vibrations produced by the rotating parts. If we assume a UAV of the multicopter type, it is a stress of the whole structure by vibrations produced by propulsion units, which are placed on symmetrically distributed arms. The propulsion unit consists of an electric-propeller assembly, with the propeller being the largest source of vibration. This is due to the uneven distribution of the mass with respect to its axis of rotation. In addition to the propeller, the rotating part is also the electric motor itself, although the electric motor contributes much less to the total vibrations than the propeller. For this reason, it is necessary to balance the propeller first statically and then dynamically balance the entire drive unit (engine + propeller). Our work is focused on vibration diagnostics of an experimental tricopter in order to optimize the power units - to produce the smallest possible vibrations.

A multi-disciplinary design optimization framework is proposed to improve the noise emissions of a quadcopter in forward flight with only a small penalty in aerodynamic performance. The design parameters are the spanwise distribution of the sweep angle and chord length of the propeller blades. The intention is to minimize the aerodynamic interactions between the propellers, as well as with the airframe, as they are associated with the tonal noise emissions that are known to dominate the radiated acoustic field in such applications. The noise prediction is obtained following the principles of the aeroacoustic analogy, using in this work a URANS CFD solver for the calculation of the unsteady blade loading, and an in-house aeroacoustic solver for the resulting acoustic radiation. The results demonstrate that the aerodynamic and acoustic performance cannot be improved simultaneously if the noise level is estimated using an unweighted sound metric, but that significant noise reduction can be achieved with a minor degradation of the mean thrust when the A-weighted noise emissions are taken as objective function. • High thrust and low-noise emissions are competing objectives in optimization. • The tonal noise emitted at the first BPF cannot be reduced without reducing thrust. • The higher BPF harmonics become dominant when the spectrum is A-weighted. • Around 3.5 dB noise reduction can be achieved for the A-weighted dominant tone. • The corresponding aerodynamic penalty is about 8%. [ABSTRACT FROM AUTHOR]

Most types of Unmanned Aerial Vehicle (UAV, drone) missions requiring Vertical-Take-Off-and-Landing (VTOL) capability could benefit if a drone's effective range could be extended. Example missions include Search-And-Rescue (SAR) operations, a remote inspection of distant objects, or parcel delivery. There are numerous research works on multi-rotor drones (e.g., quadcopters), fixed-wing drones, VTOL quadplanes, or tilt-motor/tilt-wing VTOLs. We propose a unique compact VTOL UAV optimized for long hover and long-range missions with great lifting capacity and manoeuvrability: a tandem-wing quadplane with fixed motors only. To the best of our knowledge, such a drone has not yet been researched. The drone was designed, built, and tested in flight. Construction details, its advantages, and issues are discussed in this research. [ABSTRACT FROM AUTHOR]

The traditional multicopter design method usually requires a long iterative process to find the optimal design based on given performance requirements. The method is uneconomical and inefficient. In this article, a practical method is proposed to automatically calculate the optimal multicopter design according to the given design requirements including flight time, altitude, payload capacity, and maneuverability. The proposed method contains two algorithms, including an off-line algorithm and an online algorithm. The off-line algorithm finds the optimal components (propeller and electronic speed controller) for each motor to establish its component combination, and subsequently, these component combinations and their key performance parameters are stored in a combination database. The online algorithm obtains the multicopter design results that satisfy the given requirements by searching through the component combinations in the database and calculating the optimal parameters for the battery and airframe. Subsequently, these requirement-satisfied multicopter design results are obtained and sorted according to an objective function that contains evaluation indexes, including size, weight, performance, and practicability. The proposed method has the advantages of high precision and quick calculating speed because parameter calibrations and time-consuming calculations are completed offline. Experiments are performed to validate the effectiveness and practicality of the proposed method. Comparisons with the brutal search method and other design methods demonstrate the efficiency of the proposed method. Note to Practitioners—The proposed method is fast and practical to obtain an optimal solution by only using a low-performance web server, and the algorithm has been published online at http://www.flyeval.com/recalc.html to provide an online optimization design service for users. To make it convenient to apply the proposed method to multicopter designs, the propulsion system combination database obtained by our off-line algorithm is released along with the article. This database includes more than 1500 experimentally calibrated propulsion combinations, which are adequate for readers to use the proposed optimization algorithms to design multicopters with weights (sizes) ranging from 0.2 to 50 kg. [ABSTRACT FROM AUTHOR]

Air quality measurements usually consist of ground-based instrumentation at fixed locations. However, vertical profiles of pollutants are of interest for understanding processes, distribution, dilution and concentration. Therefore, a multicopter system has been developed to investigate the vertical distribution of the concentration of aerosol particles, black carbon, ozone, nitrogen oxides (NOx) and carbon monoxide and the meteorological parameters of temperature and humidity. This article presents the requirements by different users, the setup of the quadrocopter system, the instrumentation and the results of first applications. The vertical distribution of particulate matter next to a highway was strongly related to atmospheric stratification, with different concentrations below and above the temperature inversion present in the morning. After the qualification phase described in this article, two identically equipped multicopters will be used upwind and downwind of line or diffuse sources such as highways or urban areas to quantify the influence of their emissions on the local air quality. [ABSTRACT FROM AUTHOR]

This study focuses on vibration reduction for quadcopters and octocopters with elastic, two-bladed, fixed-speed, variable-pitch rotors through the use of relative rotor phasing. The study defines phase modes such as a pitch phase mode with relative phasing between the front and aft rotors, a roll phase mode with relative phasing between the left and right rotors, and a differential phase mode with relative phasing between the clockwise and counter-clockwise spinning rotors for both the quadcopter and the octocopter, as well as additional higher harmonic phase modes for the octocopter. Parametric studies on individual phase modes indicate that, for the quadcopter in forward flight, the pitch and roll phase modes can almost entirely eliminate the 2/rev vibratory forces (at the aircraft level), but the 2/rev vibratory moments cannot be minimised at the same time. By simultaneously using multiple phase modes, a Pareto front can be generated and a solution selected based on the relative emphasis on force or moment vibration reduction. For the octocopter, it was observed that individual higher harmonic modes (specifically the 2 c or 2 s modes) could almost entirely eliminate both the 2/rev vibratory forces and moments, simultaneously. Compared with vibration levels in forward flight that might, on average, be expected if the rotors were randomly phased, a 62% reduction of a composite vibration index can be achieved on a quadcopter, and complete elimination of vibration was achievable on an octocopter, with appropriate rotor phasing. [ABSTRACT FROM AUTHOR]

The need for a perching robot is increasing in the field of rescue and transportation. Accordingly studies on perching an object by attaching a robot arm to a perching robot have been conducted. However, almost all the studies related to perching have been conducted using an actuated or electric device. However, perching by using an electric device has several disadvantages, such as additional power consumption and an increase in the mass of the multicopter used to load the electric source. Instead of using an electric device, perching by using an underactuated gripper can effectively avoid these disadvantages. Accordingly, we developed an underactuated passive gripper that has the advantage of nonconsumption of electric power for perching. A method to confirm the available range for stable perching is one of the problems of using an underactuated passive gripper. Therefore, in this study, we analyze a multicopter carrying an underactuated parallel-link passive gripper for available plane perching. To enable perching on planes with different thicknesses and being embedded at different depths, we summarize the available perching range and limitations based on the friction cone theory. Our conclusion is supported by both theoretical and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the introduction, investigation, and critical assessment of three data-driven methods for rotor failure detection and identification in a multicopter. These methods are based on aircraft attitude signals obtained from forward flight under turbulence and uncertainty. The knowledge-based method exploits the system rigid-body dynamics insight under the different rotor failures to construct a decision tree that detects and identifies the rotor failure simultaneously by how the roll, pitch, and yaw signals violate the statistical confidence limits immediately after failure. For the statistical time-series method, the development of stochastic time-series models and residual-based statistical hypothesis tests are discussed. Here, fault detection in the transient response is followed by identification after the signals reach a stationary state, after controller compensation, with the healthy and the different faulty models, respectively, in a two-step manner. The third method employs the healthy time-series model to extract a useful feature, which is the residual cross correlation, as an input to a neural network trained to achieve simultaneous rotor failure detection and identification. The time-series assisted neural network is capable of making decisions throughout the entire flight with an accuracy of 98.8%, with minimum computation time (less than 0.03 s) making it the best alternative for real-time monitoring. [ABSTRACT FROM AUTHOR]

The motion of an arm installed to a multicopter can possibly disturb its orientation. To realize an aerial manipulation by using a multicopter with a robot arm, a control of its center of gravity (COG) is required. In previous study, we proposed a design method for the mechanism of a robotic arm suitable for a multicopter. In the proposed design method, the arm can adjust its COG due to redundancy degrees of freedom. For safe flight, however, it is necessary to obtain its parameters utilized for multicopter control before take-off. In this research, we propose a method to estimate parameters to adjust COG with simple experiment before take-off. Moreover, to suppress the number of times of measurements and parameters variation, we obtain appropriate calibration orientations by simulation and confirm the effectiveness by calibration experiment using the obtained orientations. Finally, we fly a multicopter with the developed arm and observe a rotational speed of the propeller using a high-speed camera and evaluate the effect of the arm movement on the multicopter.

Pose estimation is an important issue for the visual servoing of multicopters. With a process model customized for multicopters and a generic camera model, an extended Kalman filter (EKF) method is proposed in this paper to estimate the pose of multicopters based on off-board multiple cameras. In consideration of EKF implementation, a general point correspondence method that can deal with any number of feature points and cameras is further designed. The proposed EKF method is applicable to not only a single fish-eye (or conventional) camera but also multiple fish-eye (or conventional) cameras. Observability analysis and experiment results show the proposed EKF method is more robust against noise and marker missing than existing filtering methods.

Unmanned Aerial Vehicle (UAV) is exposed to various types of stress during flight. One of the most significant negative influences is the vibrations produced by the rotating parts. If we assume a UAV of the multicopter type, it is a stress of the whole structure by vibrations produced by propulsion units, which are placed on symmetrically distributed arms. The propulsion unit consists of an electric-propeller assembly, with the propeller being the largest source of vibration. This is due to the uneven distribution of the mass with respect to its axis of rotation. In addition to the propeller, the rotating part is also the electric motor itself, although the electric motor contributes much less to the total vibrations than the propeller. For this reason, it is necessary to balance the propeller first statically and then dynamically balance the entire drive unit (engine + propeller). Our work is focused on vibration diagnostics of an experimental tricopter in order to optimize the power units - to produce the smallest possible vibrations. [ABSTRACT FROM AUTHOR]

This paper presents a preflight diagnosis method for detecting multicopter's motor abnormalities using jig equipment data. While operating multicopters on a regular basis, determining whether it can perform the flight or not is important. For this, we use disturbance observer's output as a feature for detecting degree of the abnormality by Gaussian process regression. During the ground inspection test where most of the disturbances are under control, motor degradation and disturbances are significantly correlated. Then, motor degradation can be estimated using the Gaussian process regression. To create multivariate output models against different degrees of motor abnormalities, we use multitask a Gaussian process regression model. To verify the performance of the proposed approach, actual preflight tests on a ground jig device developed in-house were performed with an actual quadcopter drone. [ABSTRACT FROM AUTHOR]

Most types of Unmanned Aerial Vehicle (UAV, drone) missions requiring Vertical-Take-Off-and-Landing (VTOL) capability could benefit if a drone’s effective range could be extended. Example missions include Search-And-Rescue (SAR) operations, a remote inspection of distant objects, or parcel delivery. There are numerous research works on multi-rotor drones (e.g., quadcopters), fixed-wing drones, VTOL quadplanes, or tilt-motor/tilt-wing VTOLs. We propose a unique compact VTOL UAV optimized for long hover and long-range missions with great lifting capacity and manoeuvrability: a tandem-wing quadplane with fixed motors only. To the best of our knowledge, such a drone has not yet been researched. The drone was designed, built, and tested in flight. Construction details, its advantages, and issues are discussed in this research.

In drone photography of vast natural terrain, it is difficult to know in advance the exact location and shape of an object. In addition, there are many time and location constraints in such environments; therefore, it is desirable to capture images quickly by automatic flight. The authors had previously proposed a method to determine the safety of such an automatic flight photography plan in advance and capture photographs quickly. The method was designed to model an object from the safety zone using multiple drones and determine a safe path in advance. However, further improvement in the efficiency was necessary when photographing the object over a large area. In contrast, in this study, to improve the efficiency of the safe flight path determination method for large-scale subjects, we developed a new method to model each number of photographs using structure from motion (SfM) and verify the accuracy of the model obtained for each number of photographs in advance. In addition, by determining the appropriate number of shots based on the results obtained and reducing the loss of time and battery during shooting, we verified the extent to which the total flight time could be reduced for a flight path of shooting a large-scale object in the Esan Prefectural Natural Park. In the case of the Esan Prefectural Natural Park, we demonstrate that the difference in the small-object shooting time was not a problem, but the difference was significant for shooting large objects. The effectiveness of determining and applying, in advance, the number of shots that provides appropriate accuracy is demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a rebound reduction mechanism for landing multicopter. Multicopter applications in the logistics industry are expected to increase owing to the aging of logistics drivers and the decline in their numbers. Currently, most multicopters land on their designated landing pads. However, these pads are not always available at the destination, and landing on rough terrain is needed in such cases. This paper describes the development of a mechanism to reduce rebound during landing, which can easily cause tipping over. The mechanism should be lightweight to ensure that battery power is conserved and that payload transport capability is increased. Simultaneously, the mechanism should be robust against environmental variations because multicopters are used outdoors and under various temperature conditions. A mechanism consisting of a spring and a magnetic damper is proposed and is modeled using multibody dynamics. It is known that the magnetic damper possesses robustness against temperature variations. Moreover, this paper presents the design parameter optimization for the proposed mechanism considering both the rebound reduction effect and weight reduction. The spring constant and viscous damping coefficient of the proposed mechanism are determined via numerical simulations with the electromagnetic simulator JMAG. The effectiveness of the proposed mechanism is verified via vertical freefall simulations. A simple experimental system is used to evaluate the mechanism, and the experimental results indicate that the mechanism is effective. [ABSTRACT FROM AUTHOR]

This article presents a monocular vision-based algorithm for detecting obstacles and identifying obstacle-aware regions, developed to be used for collision avoidance by a multicopter. The first step of our algorithm is to predict a disparity image from a single-view image via implementing a deep encoder-decoder network. All pixels in this disparity prediction are then categorized as one of three classes, obstacle, road, or obstacle-free, by combining V-disparity analysis and a fuzzy inference system. For pixels belonging to obstacle objects, obstacle-aware regions are generated within the field of visual perception. To accommodate the safety margins of a multicopter, intermediate waypoints are then added to obtain a new flyable path that passes through an unknown environment safely. Experimental results verified the effectiveness of the detection of obstacles and the identification of obstacle-aware regions. The accuracy of disparity prediction and monocular depth estimation were quantitatively compared to support the feasibility of monocular vision in obstacle avoidance. Furthermore, the entire algorithm was successfully tested on a robotic platform, autonomously flying a hexacopter in an outdoor space with obstacles. In conclusion, the proposed monocular algorithm performs well for obstacle detection and depth estimation and is potentially an alternative to a binocular solution.

Air quality measurements usually consist of ground-based instrumentation at fixed locations. However, vertical profiles of pollutants are of interest for understanding processes, distribution, dilution and concentration. Therefore, a multicopter system has been developed to investigate the vertical distribution of the concentration of aerosol particles, black carbon, ozone, nitrogen oxides (NOx) and carbon monoxide and the meteorological parameters of temperature and humidity. This article presents the requirements by different users, the setup of the quadrocopter system, the instrumentation and the results of first applications. The vertical distribution of particulate matter next to a highway was strongly related to atmospheric stratification, with different concentrations below and above the temperature inversion present in the morning. After the qualification phase described in this article, two identically equipped multicopters will be used upwind and downwind of line or diffuse sources such as highways or urban areas to quantify the influence of their emissions on the local air quality.

The paper presents the results of the numerical calculation of the flow around hybrid unmanned aircraft with X-tail stabilizers. This aircraft design is an innovative combination of a gyroplane and a multirotor. The aerodynamic properties of the two-part X-tail stabilizer were analysed. The aerodynamic forces and moments on this element of the aircraft were specified from the CFD simulation calculations for the defined values of the angle of attack and the slip angle, and particular attention was paid to the differences between the upper and lower parts of the stabilizer. In addition, the turbulence kinetic energy on the surface of the vortex core region were analysed to conduct a qualitative and quantitative analysis of energy losses in flow, resulting from local separation and vortices. The obtained results allow for conducting further aerodynamic comparative analyses on other types of stabilizers. [ABSTRACT FROM AUTHOR]

Multicopter is relatively easy to control and is used in various fields. Typical multicopter drones use batteries as a power source, but it has limitations in flight time. The aim of this study is to contribute to the increase of flight time through the use of hydrogen fuel cells and weight reduction of drones. In this study, the weight of hydrogen storage vessel is optimized using a genetic algorithm and a numerical analysis based on the Tsai-Wu failure theory. As a result, the vessel weight was reduced by more than 23.79% compared to the initial weight in the algorithm iteration. To confirm that the weight optimization and using hydrogen fuel cell improved flight time, the hovering times are calculated. Consequently, the hovering time when using the hydrogen fuel cell is increased by 37.85% than using the batteries. And the hovering time increased by 17.73% with optimized vessel weight. • The weights of hydrogen storage vessels are optimized using genetic algorithms. • The hydrogen storage vessels analyze with Tsai-Wu failure theory. • Hovering times of UAVs applied the optimized vessels are predicted and compared. [ABSTRACT FROM AUTHOR]