Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Abstract : During this grant period, we have enhanced robustness of our designs and thus increased their ability to accommodate disturbances and unmodeled dynamics. We have also broadened the class of systems to which these methods are applicable. In a different direction, we have developed structure specific methods to analyze boundedness properties of systems with "stiffening" nonlinearities, as in micro-electromechanical probes. A major advance has been made on difficult output feedback problem with a novel nonlinear observer design, achieving robustness to modeling errors. Explicit necessary and sufficient conditions have been derived for coordinated passivation designs. A new maneuvering design has been developed. Further progress was made in MIMO adaptive control. We now briefly summarize our main results. <s> BIB001 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> The steering system on a micro helicopter is the key element for control and navigation. For a sufficient control authority the steering has to be fast, precise, reliable and lightweight. While on full scale helicopters the choice of the steering mechanism is limited, there exist many possibilities to steer a helicopter in small scale. In this paper a survey on different concepts is given followed by a realization on the coaxial micro helicopter muFly. The mechanism uses piezoelectric actuation and a simplified swash plate to apply cyclic pitch and thus maneuver the Micro Air Vehicle. <s> BIB002 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> In this paper a complete system is designed and implemented, in which the motion of a quadcopter is stably controlled based on visual feedback and measurements of inertial sensors. We focus on developing a cost effective and easy-to-setup vision system. Active markers were finely designed to improve visibility under various perspectives as well as robustness towards disturbances in the image-based pose estimation. Moreover, position- and heading controllers for the quadcopter were implemented to show the system's capabilities. The performance of the controllers was further improved by the use of inertial sensors of the quadcopter. A closed-loop control system is successfully conducted. <s> BIB003 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Preface 1 History of Aviation 1.1 Introduction 1.2 Early history and the invention of ballooning 1.3 The period between 1799 and 1870 1.4 The decades between 1870 and 1890 1.5 From 1890 until the Wright Flyer III 1.6 European aviation between 1906 and 1918 1.7 Aviation between the world wars 1.8 Development after 1940 Bibliography 2 Introduction to Atmospheric Flight 2.1 Flying - How is that possible? 2.2 Static and dynamic aviation 2.3 Forces on the aeroplane 2.4 Lift, drag and thrust 2.5 Properties of air 2.6 The earth's atmosphere 2.7 The standard atmosphere 2.8 Atmospheric flight Bibliography 3 Low-Speed Aerodynamics 3.1 Speed domains and compressibility 3.2 Basic concepts 3.3 Equations for steady flow 3.4 Viscous flows 3.5 The boundary layer 3.6 Flow separation and drag 3.7 Shape and scale effects on drag Bibliography 4 Lift and Drag at Low Speeds 4.1 Function and shape of aeroplane wings 4.2 Aerofoil sections 4.3 Circulation and lift 4.4 Aerofoil section properties 4.5 Wing geometry 4.6 High-aspect ratio straight wings 4.7 Low-aspect ratio wings 4.8 The whole aircraft Bibliography 5 Aircraft Engines and Propulsion 5.1 History of engine development 5.2 Fundamentals of reaction propulsion 5.3 Engine efficiency and fuel consumption 5.4 Piston engines in aviation 5.5 Gas turbine engine components 5.6 Non-reheated turbojet and turbofan engines 5.7 Turboprop and turboshaft engines 5.8 Gas turbine engine operation 5.9 Propeller performance Bibliography 6 Aeroplane Performance 6.1 Introduction 6.2 Airspeed and altitude 6.3 Equations of motion for symmetric flight 6.4 Steady straight and level flight 6.5 Climb and descent 6.6 Gliding flight 6.7 Cruising flight 6.8 Take-off and landing 6.9 Horizontal steady turn 6.10 Manoeuvre and gust loads Bibliography 7 Stability and Control 7.1 Flying qualities 7.2 Elementary concepts and definitions 7.3 Tail surfaces and flight control 7.4 Pitchingmoment of aerofoils 7.5 Static longitudinal stability 7.6 Dynamic longitudinal stability 7.7 Longitudinal control 7.8 Static lateral stability 7.9 Dynamic lateral stability 7.10 Lateral control 7.11 Stalling and spinning Bibliography 8 Helicopter Flight Mechanics 8.1 Helicopter general arrangements 8.2 Hovering flight 8.3 The rotor in level flight 8.4 Flight performance 8.5 Stability and control Bibliography 9 High-Speed Flight 9.1 Complications due to the compressibility of air 9.2 Compressible flow relationships 9.3 Speed of sound and Mach number 9.4 Flow in a channel 9.5 Shock waves and expansion flows 9.6 High-subsonic speed 9.7 Transonic speed 9.8 Supersonic speed 9.9 Supersonic propulsion 9.10 Performance and operation Bibliography A Units and Dimensions B Principles of Aerostatics Index <s> BIB004 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> The practice of robotics and computer vision both involve the application of computational algorithms to data. Over the fairly recent history of the fields of robotics and computer vision a very large body of algorithms has been developed. However this body of knowledge is something of a barrier for anybody entering the field, or even looking to see if they want to enter the field What is the right algorithm for a particular problem?, and importantly, How can I try it out without spending days coding and debugging it from the original research papers? The author has maintained two open-source MATLAB Toolboxes for more than 10 years: one forrobotics and one for vision. The key strength of the Toolboxes provide a set of tools that allow the user to work with real problems, not trivial examples. For the student the book makes the algorithms accessible, the Toolbox code can be read to gain understanding, and the examples illustrate how it can be used instant gratification in just a couple of lines of MATLAB code. The code can also be the starting point for new work, for researchers or students, by writing programs based on Toolbox functions, or modifying the Toolbox code itself. The purpose of this book is to expand on the tutorial material provided with the toolboxes, add many more examples, and to weave this into a narrative that covers robotics and computer vision separately and together. The author shows how complex problems can be decomposed and solved using just a few simple lines of code, and hopefully to inspire up and coming researchers. The topics covered are guided by the real problems observed over many years as a practitioner of both robotics and computer vision. It is written in a light but informative style, it is easy to read and absorb, and includes a lot of Matlab examples and figures. The book is a real walk through the fundamentals of robot kinematics, dynamics and joint level control, then camera models, image processing, feature extraction and epipolar geometry, and bring it all together in avisual servo system. Additional material is provided athttp://www.petercorke.com/RVC <s> BIB005 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> We provide a novel hardware and software system for micro air vehicles (MAV) that allows high-speed, low-latency onboard image processing. It uses up to four cameras in parallel on a miniature rotary wing platform. The MAV navigates based on onboard processed computer vision in GPS-denied in- and outdoor environments. It can process in parallel images and inertial measurement information from multiple cameras for multiple purposes (localization, pattern recognition, obstacle avoidance) by distributing the images on a central, low-latency image hub. Furthermore the system can utilize low-bandwith radio links for communication and is designed and optimized to scale to swarm use. Experimental results show successful flight with a range of onboard computer vision algorithms, including localization, obstacle avoidance and pattern recognition. <s> BIB006 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Quad Rotorcraft Control develops original control methods for the navigation and hovering flight of an autonomous mini-quad-rotor robotic helicopter. These methods use an imaging system and a combination of inertial and altitude sensors to localize and guide the movement of the unmanned aerial vehicle relative to its immediate environment. The history, classification and applications of UAVs are introduced, followed by a description of modelling techniques for quad-rotor's and the experimental platform itself. A control strategy for the improvement of attitude stabilization in quad-rotor's is then proposed and tested in real-time experiments. The strategy, based on the use low-cost components and with experimentally-established robustness, avoids drift in the UAV's angular position by the addition of an internal control loop to each electronic speed controller ensuring that, during hovering flight, all four motors turn at almost the same speed. The quad-rotor's Euler angles being very close to the origin, other sensors like GPS or image-sensing equipment can be incorporated to perform autonomous positioning or trajectory-tracking tasks. Two vision-based strategies, each designed to deal with a specific kind of mission, are introduced and separately tested. The first stabilizes the quad-rotor over a landing pad on the ground; it extracts the 3-dimensional position using homography estimation and derives translational velocity by optical flow calculation. The second combines colour-extraction and line-detection algorithms to control the quad-rotor's 3-dimensional position and achieves forward velocity regulation during a road-following task. In order to estimate the translational-dynamical characteristics of the quad-rotor (relative position and translational velocity) as they evolve within a building or other unstructured, GPS-deprived environment, imaging, inertial and altitude sensors are combined in a state observer. The text give the reader a current view of the problems encountered in UAV control, specifically those relating to quad-rotor flying machines and it will interest researchers and graduate students working in that field. The vision-based control strategies presented help the reader to a better understanding of how an imaging system can be used to obtain the information required for performance of the hovering and navigation tasks ubiquitous in rotored UAV operation. <s> BIB007 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> In this article we present a flatness-based controller that solves the trajectory tracking problem for an unmanned four-rotor aircraft. A simple version of the dynamical system obtained from a suitable coordinate transformation of the Euler–Lagrange model of the system is used. This model, combined with a suitable input saturation nonlinearity, also avoids the inconvenient system singularities. The corresponding tracking error is shown to be globally asymptotically stable but only locally exponentially stable, while the controller maintains the four-rotor system motions inside a feasible region. Numerical simulations are presented to assesses the effectiveness of the proposed control strategy. <s> BIB008 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Abstract Over the last decade, considerable interest has been shown from industry, government and academia to the design of Vertical Take-Off and Landing (VTOL) autonomous aerial vehicles. This paper uses the recently developed sliding mode control driven by sliding mode disturbance observer (SMC-SMDO) approach to design a robust flight controller for a small quadrotor vehicle. This technique allows for a continuous control robust to external disturbance and model uncertainties to be computed without the use of high control gain or extensive computational power. The robustness of the control to unknown external disturbances also leads to a reduction of the design cost as less pre-flight analyses are required. The multiple-loop, multiple time-scale SMC-SMDO flight controller is designed to provide robust position and attitude control of the vehicle while relying only on knowledge of the limits of the disturbances. Extensive simulations of a 6 DOF computer model demonstrate the robustness of the control when faced with external disturbances (including wind, collision and actuator failure) as well as model uncertainties. <s> BIB009 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> This paper deals with the design and implementation of a nonlinear control algorithm for the attitude tracking of a four-rotor helicopter known as quadrotor. This algorithm is based on the second order sliding mode technique known as Super-Twisting Algorithm (STA) which is able to ensure robustness with respect to bounded external disturbances. In order to show the effectiveness of the proposed controller, experimental tests were carried out on a real quadrotor. The obtained results show the good performance of the proposed controller in terms of stabilization, tracking and robustness with respect to external disturbances. <s> BIB010 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Standard quadrotor UAVs possess a limited mobility because of their inherent underactuation, i.e., availability of 4 independent control inputs (the 4 propeller spinning velocities) vs. the 6 dofs parameterizing the quadrotor position/ orientation in space. As a consequence, the quadrotor pose cannot track an arbitrary trajectory over time (e.g., it can hover on the spot only when horizontal). In this paper, we propose a novel actuation concept in which the quadrotor propellers are allowed to tilt about their axes w.r.t. the main quadrotor body. This introduces an additional set of 4 control inputs which provides full actuation to the quadrotor position/orientation. After deriving the dynamical model of the proposed quadrotor, we formally discuss its controllability properties and propose a nonlinear trajectory tracking controller based on dynamic feedback linearization techniques. The soundness of our approach is validated by means of simulation results. <s> BIB011 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Cooperative Control of Multi-Agent Systems extends optimal control and adaptive control design methods to multi-agent systems on communication graphs. It develops Riccati design techniques for general linear dynamics for cooperative state feedback design, cooperative observer design, and cooperative dynamic output feedback design. Both continuous-time and discrete-time dynamical multi-agent systems are treated. Optimal cooperative control is introduced and neural adaptive design techniques for multi-agent nonlinear systems with unknown dynamics, which are rarely treated in literature are developed. Results spanning systems with first-, second- and on up to general high-order nonlinear dynamics are presented. Each control methodology proposed is developed by rigorous proofs. All algorithms are justified by simulation examples. The text is self-contained and will serve as an excellent comprehensive source of information for researchers and graduate students working with multi-agent systems. <s> BIB012 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> The advantages associated to Vertical Short-Take-Off and Landing (V/STOL) have been demonstrated since the early days of aviation, with the initial technolology being based on airships and later on helicopters and planes. Its operational advantages are enormous, being it in the field of military, humanitarian and rescue operations, or even in general aviation. Helicopters have limits in their maximum horizontal speed and classic V/STOL airplanes have problems associated with their large weight, due to the implementation of moving elements, when based on tilting rotors or turbojet vector mechanical oriented nozzles. A new alternative is proposed within the European Union Project ACHEON (Aerial Coanda High Efficiency Orienting-jet Nozzle). The project introduces a novel scheme to orient the jet that is free of moving elements. This is based on a Coanda effect nozzle supported in two fluid streams, also incorporating boundary layer plasma actuators to achieve larger deflection angles. Herein we introduce a state-of-the-art review of the concepts that have been proposed in the framework of jet orienting propulsion systems. This review allows to demonstrate the advantages of the new concept in comparison to competing technologies in use at present day, or of competing technologies under development worldwide. <s> BIB013 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> An unmanned aerial vehicle (UAV) stabilization strategy based on computer vision and switching controllers is proposed. The main goal of this system is to perform tracking of a moving target on ground. The architecture implemented consists of a quadrotor equipped with an embedded camera which provides real-time video to a computer vision algorithm where images are processed. A vision-based estimator is proposed, which makes use of 2-dimensional images to compute the relative 3-dimensional position and translational velocity of the UAV with respect to the target. The proposed estimator provides the required states measurements to a micro-controller for stabilizing the vehicle during flight. The control strategy consists of switching controllers, which allows making decisions when the target is lost temporarily or when it is out of the camera’s field of view. Real time experiments are presented to demonstrate the performance of the target-tracking system proposed. <s> BIB014 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> We address the problem of cooperative transportation of a cable-suspended rigid-body payload by multiple quadrotors. We develop a coordinate-free dynamical model of the system by developing equations of motions directly on the unit sphere and the special orthogonal group. This model is used to design a geometric feedback control to track a reference trajectory for the load's pose (position and orientation), as well as the yaw angle of each quadrotor, and the orientation of each cable. Simulation results and formal proofs of the controller are presented to demonstrate the stability properties of the controller. <s> BIB015 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Aerial Manipulators (AMs) are a special class of underactuated mechanical systems formed by the join of Unmanned Aerial Vehicles (UAVs) and manipulators. A thorough analysis of the dynamics and a fully constructive controller design for a quadrotor plus n-link manipulator in a free-motion on an arbitrary plane is provided, via the lDA-PBC methodology. A controller is designed with the manipulator locked at any position ensuring global asymptotic stability in an open set and avoiding the AM goes upside down (autonomous). The major result of stability/robustness arises when it is proved that, additionally, the controller guarantees the boundedness of the trajectories for bounded movements of the manipulator, i.e. the robot manipulator executing planned tasks, giving rise to a non-autonomous port-controlled Hamiltonian system in closed loop. Moreover, all trajectories converge to a positive limit set, a strong result for matching-type controllers. <s> BIB016 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> The model-free sliding mode control based on fractional order sliding surface is built upon: i) An absolutely continuous control structure that does not require the exact dynamic model to induce a fractional sliding motion in finite time, and ii) A methodology to design fractional references with a clear counterpart in the frequency domain is proposed. This in order to improve the system response, in particular the transient period, and to generate a high-performance during the sliding motion. Numerical simulations support the proposal and illustrates the closed-loop system, which provides a better insight of the proposed scheme. <s> BIB017 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> The Handbook of Unmanned Aerial Vehicles is a reference text for the academic and research communities, industry, manufacturers, users, practitioners, Federal Government, Federal and State Agencies, the private sector, as well as all organizations that are and will be using unmanned aircraft in a wide spectrum of applications. The Handbook covers all aspects of UAVs, from design to logistics and ethical issues. It is also targeting the young investigator, the future inventor and entrepreneur by providing an overview and detailed information of the state-of-the-art as well as useful new concepts that may lead to innovative research. The contents of the Handbook include material that addresses the needs and know how of all of the above sectors targeting a very diverse audience.The Handbook offers a unique and comprehensive treatise of everything one needs to know about unmanned aircrafts, from conception to operation, from technologies to business activities, users, OEMs, reference sources, conferences, publications, professional societies, etc. It should serve as a Thesaurus, an indispensable part of the library for everyone involved in this area. For the first time, contributions by the worlds top experts from academia, industry, government and the private sector, are brought together to provide unique perspectives on the current state-of-the-art in UAV, as well as future directions. The Handbook is intended for the expert/practitioner who seeks specific technical/business information, for the technically-oriented scientists and engineers, but also for the novice who wants to learn more about the status of UAV and UAV-related technologies.The Handbook is arranged in a user-friendly format, divided into main parts referring to: UAV Design Principles; UAV Fundamentals; UAV Sensors and Sensing Strategies; UAV Propulsion; UAV Control; UAV Communication Issues; UAV Architectures; UAV Health Management Issues; UAV Modeling, Simulation, Estimation and Identification; MAVs and Bio-Inspired UAVs; UAV Mission and Path Planning; UAV Autonomy; UAV Sense, Detect and Avoid Systems; Networked UAVs and UAV Swarms; UAV Integration into the National Airspace; UAV-Human Interfaces and Decision Support Systems; Human Factors and Training; UAV Logistics Support; UAV Applications; Social and Ethical Implications; The Future of UAVs. Each part is written by internationally renowned authors who are authorities in their respective fields.The contents of the Handbook supports its unique character as a thorough and comprehensive reference book directed to a diverse audience of technologists, businesses, users and potential users, managers and decision makers, novices and experts, who seek a holistic volume of information that is not only a technical treatise but also a source for answers to several questions on UAV manufacturers, users, major players in UAV research, costs, training required and logistics issues. <s> BIB018 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Mobility of a hexarotor UAV in its standard configuration is limited, since all the propeller force vectors are parallel and they achieve only 4-DoF actuation, similar, e.g., to quadrotors. As a consequence, the hexarotor pose cannot track an arbitrary trajectory while the center of mass is tracking a position trajectory. In this paper, we consider a different hexarotor architecture where propellers are tilted, without the need of any additional hardware. In this way, the hexarotor gains a 6-DoF actuation which allows to independently reach positions and orientations in free space and to be able to exert forces on the environment to resist any wrench for aerial manipulation tasks. After deriving the dynamical model of the proposed hexarotor, we discuss the controllability and the tilt angle optimization to reduce the control effort for the specific task. An exact feedback linearization and decoupling control law is proposed based on the input-output mapping, considering the Jacobian and task acceleration, for non-linear trajectory tracking. The capabilities of our approach are shown by simulation results. <s> BIB019 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> This paper presents a framework to deal with outdoor navigation using an AR.Drone Parrot quadrotor. The proposed system runs in a centralized computer, the ground station, responsible for the communication with the unmanned aerial vehicle (UAV) and for synthesizing the control signals during flight missions. The outdoor navigation is performed through using a layered control architecture, where a high-level control algorithm, designed from the kinematic differential equations describing the movement of the UAV, is used to generate reference signals for a low-level velocity controller. To feedback the controllers, the sensorial data provided by the AR.Drone onboard sensors and a GPS module are fused through a Kalman Filter, allowing getting a more reliable estimate of the UAV state. Finally, experimental results are presented, which demonstrate the effectiveness of the proposed framework. <s> BIB020 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Control of aerial robots is a popular research field as applications with different payloads lead to a variety of flight missions. Quadrotor-type unmanned systems are one such example considered in this paper. The performance in any flight experiment depends strictly on the chosen feedback control scheme, which is the core issue addressed in the paper. A number of approaches have been reported in the literature and this paper presents a survey of these schemes with an in-depth discussion of recent research outcomes. A detailed performance evaluation of the controllers, namely proportional-integral-derivative control, sliding mode control, backstepping control, feedback linearization-based control and fuzzy control schemes, are presented. Due to the popularity of the quadrotor-type aerial vehicles, the contribution of the current work is to provide an in-depth guide to the autopilot designers of quadrotor-type unmanned aerial vehicles. <s> BIB021 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> This contribution presents a modeling technique for an aerial manipulator based on a quad-rotor vehicle provided with a robotic arm. Dual quaternions, which are a little explored but powerful mathematical tool, are proposed as an alternative to the classical Euler angles approach for the kinematic and dynamic modeling. A feedback control law based on dual quaternions is used to validate the proposed model, taking into account the external effects of the robotic limb. Numerical simulations and experiments validate the proposal, opening a path for future research. <s> BIB022 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Abstract Nowadays, there is a growing need for flying drones with diverse capabilities for both civilian and military applications. There is also a significant interest in the development of novel drones which can autonomously fly in different environments and locations and can perform various missions. In the past decade, the broad spectrum of applications of these drones has received most attention which led to the invention of various types of drones with different sizes and weights. In this review paper, we identify a novel classification of flying drones that ranges from unmanned air vehicles to smart dusts at both ends of this spectrum, with their new defined applications. Design and fabrication challenges of micro drones, existing methods for increasing their endurance, and various navigation and control approaches are discussed in details. Limitations of the existing drones, proposed solutions for the next generation of drones, and recommendations are also presented and discussed. <s> BIB023 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> We present a tutorial introduction to the multi-rotor unmanned aerial vehicles, often simply referred as drones. We first explain typical configuration, components and construction of the drones. We then provide basic kinematic and dynamic modeling of drones and their principle of flight. Some representative motion control techniques are then presented, which take into account the issue of under-actuation of the drones. State estimation problem of the drones, that is crucial for their proper flying, yet, should be done only by using onboard sensors and their sensor fusion, is explained. Some emerging research directions requiring capability beyond typical drones are also mentioned. <s> BIB024 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> Abstract In this paper we present the design, modelling and control of an omni-directional multirotor vehicle, i.e. a fully-actuated vehicle that can hover at any attitude and accelerate in any direction. Based on a static force and torque analysis for generic rotor configurations, an octorotor configuration is derived that maximizes the vehicle’s agility while rendering its characteristics almost rotationally invariant. A prototype vehicle with the derived rotor configuration is built using reversible fixed-pitch rotors that can generate positive and negative thrust, enabling the vehicle to independently control its thrust and torque in all three dimensions. A control scheme that allows for simultaneously tracking a desired position and attitude trajectory is introduced. Experimental results demonstrate the feasibility of the vehicle design and control strategy. <s> BIB025 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> We propose a novel aerial manipulation platform, an omnidirectional aerial robot, that is capable of omnidirectional wrench generation with opportunistically distributed/aligned Sectional rotors. To circumvent the tight thrust margin and weight budget of currently available rotor and battery technologies, we propose a novel design optimization framework, which maximizes the minimum-guaranteed control force/torque for any attitude while incorporating such important and useful aspects as interrotor aerointerference, anisotropic task requirement, gravity compensation, etc. We also provide a closed-form solution of infinity-norm optimal control allocation to avoid rotor saturation with the tight thrust margin. Further, we elaborate the notion of electronic speed controller induced singularity and devise a novel selective mapping algorithm to substantially subdue its destabilizing effect. Experiments are performed to validate the theory, which demonstrate such capabilities not possible with typical aerial manipulation systems, namely, separate translation and attitude control on SE(3), hybrid pose/wrench control with downward force of 60 N much larger than its own weight (2.6 kg), and peg-in-hole teleoperation with a radial tolerance of 0.5 mm. <s> BIB026 </s> Snake Aerial Manipulators: A Review <s> Ways of collaboration, Planning methodologies and Control Techniques: <s> This paper presents a theoretical study on omni-directional aerial vehicles with body-frame fixed unidirectional thrusters. Omniplus multi-rotor designs are defined as the ones that allow to exert a total wrench in any direction using positive-only lift force and drag moment (i.e., positive rotational speed) for each rotor blade. Algebraic conditions for a design to be omniplus are derived, a simple necessary condition being the fact that at least seven propellers have to be used. An energy optimal design strategy is then defined as the one minimizing the maximum norm of the input set needed to span a certain wrench ellipsoid for the adopted input allocation strategy. Two corresponding major design criteria are then introduced: firstly, a minimum allocation-matrix condition number aims at an equal sharing of the effort needed to generate wrenches in any direction; secondly, imposing a balanced design guarantees an equal sharing of the extra effort needed to keep the input in the non-negative orthant. We propose a numerical algorithm to solve such optimal design problem and a control algorithm to control any omnidirectional platform. The work is concluded with informative simulation results in non-ideal conditions. <s> BIB027
There are two ways to control a collaborative aerial manipulator, the distributed and the centralized. In the first one is considered the independent control of each vehicle to maintain a pre-established formation by the union of the elements of transmission. To deal with that, methods denominated in the literature as consensus or formation control  , BIB012 , are used. Here each aircraft must worry about achieving its own position and orientation such that an stable common formation is maintained, similar when two or more individuals move a piece of furniture. On the other hand, at centralized interaction, the whole system is considered as a single dynamic entity and each multicopter or propeller is modeled as a thruster that generates torques and forces with a common effect in a virtual point of the system called center of gravity, center of masses, geometric center, center of flotation, etc, It is said to be virtual, because this point could or could not be physically placed over the system depending on its geometric configuration, inertial properties, as well as rotational and translational velocities and accelerations achieved. In the centralized way of flight, all aircrafts must worry about achieving a common dynamic and not just a geometrical formation  . Even more, most of the approaches are concerned with obtain propeller arrays called allocation matrices  , BIB025 . Concerning the ways of cooperation, there are also flight modes to achieve them, also known as planning methodologies. Using drones terminology, and the distributed way, a cooperative aerial manipulator can be programmed as this example: an aircraft or propeller must act as a waist having to maintain a fixed mode of spatial and rotational location by using loitter, guided, post hold, etc flight modes, and the multicopters or propellers that are part of the arms should operate in althold, sport, stabilize, or similar flight modes, because they must maintain their height and orientation but their planar position is variable  . On the other hand, in the centralized manner, each multicopter changes its own mode of operation continuously, adapting by itself according to the condition of mobility that is required. According to our investigation, all the flight modes are variants or combinations among the next three kinds: 1 Almost pure translational approaches: In spite of being complete dynamical approaches, they focuses on the postulate of bringing the aircraft angles and their respective angular velocities to a zero reference (except for the yaw angle). The main objective is to achieve smooth translational movements. At present, they are the most extensive methodologies for UAV controllers BIB007 ,  BIB008 BIB009 . They have application in snake aerial manipulators take-off and landing phases (see forward sections). Their basic control tools concerning with nonlinear standard control can be found at [180] , [181] . 2 Kinodynamic approaches: They are relatively new approaches  ,  . Currently they are based on backstepping techniques, and the idea is to disengage translational and rotational models, giving dynamic quality to the translational model and quasi-static character to orientation. They could find their application during the aerial manipulation phase (look at next sections). Their control foundations are related with nonlinear backstepping and the references about can be found at BIB001 ,  . 3 Geometric approaches: Those approaches are also fully dynamical, but the aircraft orientation is designed to achieve rude, complex, aggressive and acrobatical movements BIB022 , BIB015 ,  ,  . They can be really useful at the transformation phase, and long-flight to the workspace phases (see forthcoming sections). Their elementary control design concerning with nonlinear geometric control can be found at  ,  . Finally there are control techniques, each flight mode can achieve a task, through a huge variety of existing control techniques, from a simple PD to a neuro-fuzzy control. For example, a loiter mode can be achieved by using a PID control or in the same way by using intelligent algorithms or sliding modes. The effect of the control technique employed is not in the task but in the performance of the task (faster, more violent, softer, more natural with respect to a living being, optimal in energy consumption, optimal in the runtime etc) BIB008 , BIB023 BIB021 BIB010  BIB016 BIB017 . In summary, the operation of a collaborative aerial manipulator is a choice between two ways of vehicle collaboration, even their combination: centralized and distributed. Where each vehicle operates with a considerable variety of flight modes (loitter, guided, pos hold, acro, etc) and also each flight mode is achieved through a variety of control techniques (PD, sliding, intelligent, fuzzy, etc.). This way, the final result of operation has a wide range of algorithms whose selection depends on each user and the desired application. This will determine which cooperative way, flight method and control technique to use or maybe a mixed sequence of operations (as in a blender keypad or in an car gearbox) Reading of orientation, planar position and altitude sensors: The way to do this is by using IMUs, magnetometers, barometers, accelerometers and GPS units, all of them operating with different communication protocols and sampling frequencies, in some cases by design of the sensor and in others by priority of the measurement  , BIB024 . Command to the propellers and execution servomechanisms: This consist in the direct propeller control (e.g brushless motors) and also in the use of auxiliary motors (e.g servomotors) for performing secondary tasks during the flight. For example, camera stabilizers, ailerons and mechanisms of thrust vectoring BIB013 , BIB011 , BIB019 . In general, propeller action must be faster than auxiliary motors (e.g 490Hz and 50Hz respectively) Feedback control of attitude, planar position and altitude: In general, UAV control is divided into these three modes of execution, the priority is to maintain a height of operation also known as hovering, the intermediate priority range is to control the orientation or attitude of the aircraft and finally its planar position, also known as steering BIB002 , BIB004 , BIB007 ,  , BIB018 . Image Processing: This task becomes necessary in conditions where satellital positioning are not available  , BIB020 ,  ,  BIB024 BIB003 BIB014 BIB005 . Internal communication of data: This is usually performed through serial topology buses. It is the way in which the data of the sensors are shared and processed towards the main processor and at the same time, the way in which the processor decides how to write to the actuator systems. Storage data and telemetry: It is the way in which the system stores and shares the data among flying units for their use and interaction including the wireless communication among the aircraft. Reading of remote control commands: It consists in reading the remote control units, which establish the link among the aircrafts and the ground base. As can be seen, together with the telemetry, there are two different wireless modules. The challenge here is to ensure that they operate accurately at different frequencies and also with multiple channels. Reading of analog and digital ports: It consists of the habilitation, interaction, reading and writing of analog ports, and general purpose input / output digital ports. Signal filtering: The addition of noise to the UAVs is implicit with the mechanical vibration of the motors and their electrical interaction with the environment. In this way, a filtering algorithm is necessary, which is usually done by means of Kalman techniques. Sensor fusion: When the task environment changes constantly, it is necessary to use a combination of geolocation sensors. An example is between tasks where the drone passes from an external environment to an internal and a switch between an artificial vision system and a GPS must be done. Tasks planning: It is necessary to obtain velocities and acceleration data for smooth movements, and also there are authors who indicate and show that it is necessary to include the snap (the acceleration second derivative)  , as the sensors are restricted to read velocities, positions and accelerations, and in most of the cases this is done partially or inaccurately. It is necessary to include estimators that involve mathematical observers, neuronal estimation, fuzzy estimation and also algorithms of trajectory planning. All these operations implies the need for developing even better matrix optimization algorithms. Real time task priority: Given the different operating frequencies of the sensors, actuators, systems and control loops, it is necessary to prioritize the execution of tasks, those of higher priority are usually the individual motor control, the attitude control, and the altitude reading; the intermediate ones are those of planar reading, and finally in a lower range are the tasks of serial communication, reading of remote control commands and storage of flight data. On the other hand within the priorities related to control, the hierarchies are attitude, altitude, steering and three-dimensional trajectory. For our purposes is enough with the capabilities of the Pixhawk autopilot which has an RTOS system able to assign priorities and execution times. However, in the case of designing a new flight controller or task, it is necessary to establish a real time system scheduler for the correct execution of the desired events. Discussion: This section has dealt with various problems commonly found at UAV designing, with emphasis on real-time task scheduling and planning methodologies. Addressing generalities about the individual engine components of a snake aerial manipulator. In the particular case that they are composed of multicopters, the relevant difficulties have been already investigated and developed. However, it is insisted on the restrictions of a team of aircraft with morphing capabilities and interdependent physical linkages, so there are 4 priorities and subjects of research: Reduction in the weight and size of the sensors and actuators: while using just an aircraft maybe such parameters are not so relevant for the execution of a task, but as in this case an aircraft team and their components are required, the weight and volume is multiplied, reducing operating times and demanding better and huge power supplies. Reduction in their electrical consumption: this point is linked to the previous paragraph, although it could be independent, that is to say, while the motors do not consume so much power, it is possible for a system with greater size and weight to have a longer duration flight. Even, it could be feasible to reduce batteries or other power elements and just to transport the required equipment. Better real-time processing systems: it is known for example, than certain processing units, have difficulties in order to control a quadcopter, so pretending to use them with six or more engines means migrating to more expensive or not so intuitive equipment. This way, it is necessary to develop more technology in autopilots or development cards that allows at least to 10 brushless motors, a minimum of 6 servomotors, a minimum of 4 analog inputs, a set of GPIO ports for digital inputs and outputs, and wireless and wired reading and writing with at least 2 serial ports to operate at the same time, considering also to store data flight as, position and orientation while filtering at least 8 signals (orientations and altitude plus their derivatives) and carrying out multiple calculations. As already indicated, autopilots such as the Pixhawk BIB006 are quite versatile, but they could deal with a limited number of engines, and in the case of a snake aerial manipulator, they become overdemanded. Finally it is ideal to develop mixed or intelligent control schemes that determine when an action is more relevant than others for each one of the engine elements that form part of the general structure, and that are able to identify certain parameters such as the location of the gravitational center (or any other). In addition, it is also necessary to consider the execution of the global task and the effect on each individual engine element (as already said, a controller suitable for knowing how to decide between the hierarchy of manipulation, free flight, take off, transformation or landing tasks and their corresponding subprocesses). Also is ideal to develop controllers that do not require biasing or positive translation and work directly on the positive space of the actuators (which implies the use of numerical methods, and computational and optimization algorithms instead of classical fully mathematical control schemes)  , BIB026 , BIB027 .