Chattering free tracking control of a fully actuated multirotor with passively tilted rotors

In this paper, a control allocation scheme is presented for a multirotor type of an Unmanned Aerial Vehicle (UAV). The control allocation scheme depends on the multirotor configuration and rotor system parameters, and it enables analysis of dynamics of different multirotor designs depending on the purpose and the task which the multirotor has to carry out. The analysis of force and moment distribution in space shows that the non-flat design with passively tilted rotors can overcome an inherent underactuated condition of flat multirotor configurations. By increasing the tilt angle, the multirotor is able to achieve full controllability over its six degrees of freedom (6 DOFs). A robust chattering-free sliding mode asymptotic tracking control design of a fully actuated multirotor is presented. The simulation results show satisfying tracking performance of the proposed controller

Development and Flight of a Robust Optical-Inertial Navigation System Using Low-Cost Sensors

This research develops and tests a precision navigation algorithm fusing optical and inertial measurements of unknown objects at unknown locations. It provides an alternative to the Global Positioning System (GPS) as a precision navigation source, enabling passive and low-cost navigation in situations where GPS is denied/unavailable. This paper describes two new contributions. First, a rigorous study of the fundamental nature of optical/inertial navigation is accomplished by examining the observability grammian of the underlying measurement equations. This analysis yields a set of design principles guiding the development of optical/inertial navigation algorithms. The second contribution of this research is the development and flight test of an optical-inertial navigation system using low-cost and passive sensors (including an inexpensive commercial-grade inertial sensor, which is unsuitable for navigation by itself). This prototype system was built and flight tested at the U.S. Air Force Test Pilot School. The algorithm that was implemented leveraged the design principles described above, and used images from a single camera. It was shown (and explained by the observability analysis) that the system gained significant performance by aiding it with a barometric altimeter and magnetic compass, and by using a digital terrain database (DTED). The (still) low-cost and passive system demonstrated performance comparable to high quality navigation-grade inertial navigation systems, which cost an order of magnitude more than this optical-inertial prototype. The resultant performance of the system tested provides a robust and practical navigation solution for Air Force aircraft

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

WindBots: A Concept for Persistent In-Situ Science Explorers for Gas Giants

This report summarizes the study of a mission concept to Jupiter with one or multiple Wind Robots able to operate in the Jovian atmosphere, above and below the clouds - down to 10 bar, for long durations and using energy obtained from local sources. This concept would be a step towards persistent exploration of gas giants by robots performing in-situ atmospheric science, powered by locally harvested energy. The Wind Robots, referred in this report as WindBots (WBs), would ride the planetary winds and transform aeolian energy into kinetic energy of flight, and electrical energy for on-board equipment. Small shape adjustments modify the aerodynamic characteristics of their surfaces, allowing for changes in direction and a high movement autonomy. Specifically, we sought solutions to increase survivability to strong/turbulent winds, and mobility and autonomy compared to passive balloons

Advances and Trends in Mathematical Modelling, Control and Identification of Vibrating Systems

This book introduces novel results on mathematical modelling, parameter identification, and automatic control for a wide range of applications of mechanical, electric, and mechatronic systems, where undesirable oscillations or vibrations are manifested. The six chapters of the book written by experts from international scientific community cover a wide range of interesting research topics related to: algebraic identification of rotordynamic parameters in rotor-bearing system using finite element models; model predictive control for active automotive suspension systems by means of hydraulic actuators; model-free data-driven-based control for a Voltage Source Converter-based Static Synchronous Compensator to improve the dynamic power grid performance under transient scenarios; an exact elasto-dynamics theory for bending vibrations for a class of flexible structures; motion profile tracking control and vibrating disturbance suppression for quadrotor aerial vehicles using artificial neural networks and particle swarm optimization; and multiple adaptive controllers based on B-Spline artificial neural networks for regulation and attenuation of low frequency oscillations for large-scale power systems. The book is addressed for both academic and industrial researchers and practitioners, as well as for postgraduate and undergraduate engineering students and other experts in a wide variety of disciplines seeking to know more about the advances and trends in mathematical modelling, control and identification of engineering systems in which undesirable oscillations or vibrations could be presented during their operation

Aeronautical engineering: A continuing bibliography with indexes (supplement 282)

This bibliography lists 623 reports, articles, and other documents introduced into the NASA scientific and technical information system in Aug. 1992. The coverage includes documents on the engineering and theoretical aspects of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems. It also includes research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles

Design and Implementation of a Novel Multicopter Unmanned Aircraft System for Quantitative Studies of the Atmosphere

The call for creating new innovative meteorological instruments to help fulfill observational gaps in the atmospheric sciences has been gaining strength in the past few years. This comes along with the urgent need to increase the understanding of fast-evolving atmospheric processes to subsequently provide accurate and reliable weather forecasts in a timely manner. The increased interest in obtaining atmospheric observations with higher spatio-temporal resolution pushed scientists to begin exploring and harnessing new leading-edge engineering technology. For instance, affordable and accessible Unmanned Aircraft Systems (UASs) technology emerged within this timeframe and has since evolved rapidly. Many researchers and institutions have agreed that UASs are promising technology candidates for targeted in situ weather sampling, which has the potential to meet the stringent meteorological measurement requirements. However, the current market has shifted and shaped UASs for other applications that may be unsuitable or suboptimal for weather sampling. Special considerations were examined in this study to conceptualize a specialized weather UAS (WxUAS) capable of collecting reliable thermodynamic and kinematic measurements. While also performing similarly to conventional weather instruments, such as radiosondes, Doppler wind lidars, and meteorological towers, as well as providing a complementary role whenever measurement limitations arise. Therefore, given that the exploration of integrating weather instrumentation into UAS is rare, it is hypothesized that atmospheric measurements of a modified multicopter UAS that minimizes platform-induced errors can fill the thermodynamic and kinematic data gap in the planetary boundary layer (PBL). The proposed solution is a UAS-based in situ vertical profiler system, dubbed the CopterSonde, with necessary weather instrumentation, adequate sensor placement, and useful flight functions for optimal sampling of undisturbed air. This solution attempts to provide a holistic WxUAS design where the UAS itself was adapted to become not just a payload carrier but also part of the weather instrumentation system. Flow simulation studies backed with observations in the field were used to address sensor siting and mitigate sources of thermodynamic errors. Moreover, techniques for thermodynamic measurement correction, adaptable flight behavior, and 3D wind estimation were implemented using the experimental CopterSonde concept with results comparable to widely accepted conventional weather instruments. Additionally, the platform reliability was successfully demonstrated in different challenging environments, from freezing temperatures in Hailuoto, Finland, to high elevations in Colorado, USA. A robust concept of operation and decision-making algorithms were established to ensure safe flights during demanding field campaigns. As a result, the National Oceanic and Atmospheric Administration (NOAA) in the USA has recognized the CopterSonde as part of the approved UAS fleet for NOAA-related missions. Overall, the engineering advances shown in this work helped to produce an optimized UAS capable of collecting targeted and reliable weather observations. Even though the CopterSonde is an experimental design, this work can be used as a guideline to define future standards for WxUAS development and deployment