Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Trajectory tracking and configuration stabilization for the vertical takeoff and landing (VTOL) aircraft has been so far considered in the literature only in the presence of a slight (or zero) input coupling (i.e., for a small /spl epsi/). In this paper, our main contribution is to address global configuration stabilization for the VTOL aircraft with a strong input coupling using a smooth static state feedback. In addition, the differentially flat outputs for the VTOL aircraft are automatically obtained as a by-product of applying a decoupling change of coordinates. <s> BIB001 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Since the original publication of Helicopter Dynamics by A.R.S. Bramwell in 1976, this book has become the definitive text on helicopter dynamics. As such it is an essential aid to those studying the behavior of helicopters. The second edition builds on the strengths of the original, and hence the approach of the first edition is retained. The authors provide a detailed summary of helicopter aerodynamics, stability, control, structural dynamics, vibration, and aeroelastic and aeromechanical stability. <s> BIB002 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this paper a Lyapunov control algorithm for a tandem rotor helicopter is obtained using backstepping techniques. A simple model dynamics for a behavior of a helicopter close to hover is obtained. Some simulation results are presented to illustrate the performance of such controller. <s> BIB003 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> We propose a global stabilizing control design for the planar vertical takeoff and landing (PVTOL) aircraft, with bounded inputs. The approach is based on the use of non-linear combinations of linear saturation functions bounding the thrust input and the rolling moment to arbitrary saturation limits. We provide global convergence of the state to the origin, using a relatively simple algorithm. <s> BIB004 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> This paper considers two-input, two-output nonlinear adaptive model following control of a 3-DOF (degree-of-freedom) tandem rotor model helicopter. The control performance is studied by real time implementation of the control algorithms in an actual helicopter testbed. Since the decoupling matrix of the model helicopter is singular, the system is not decouplable by static state feedback, and it is challenging to design a feedback control system. Dynamic state feedback is applied. The controller is designed using a nonlinear structure algorithm. Furthermore, a parameter identification scheme is introduced in the closed-loop system to improve the control performance. Three identification methods are discussed. <s> BIB005 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <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> BIB006 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> 1 Introduction.- 1.1 Background Information.- 1.2 The Mathematical Problem ..- 1.3 Controller Designs.- 1.3.1 Linear Controller Design.- 1.3.2 Nonlinear Controller Design.- 1.4 Outline of the Book.- 2 Review of Linear and Nonlinear Controller Designs.- 2.1 Linear Controller Designs.- 2.2 Nonlinear Controller Design.- 2.3 Remarks.- 3 Helicopter Basic Equations of Motion.- 3.1 Helicopter Equations of Motion.- 3.2 Position and Orientation of the Helicopter.- 3.2.1 Helicopter Position Dynamics.- 3.2.2 Helicopter Orientation Dynamics.- 3.3 Complete Helicopter Dynamics.- 3.4 Remarks.- 4 Simplified Rotor Dynamics.- 4.1 Introduction.- 4.2 Blade Motion.- 4.3 Swashplate Mechanism.- 4.4 Fundamental Rotor Aerodynamics.- 4.5 Flapping Equations of Motion.- 4.6 Rotor Tip-Path-Plane Equation.- 4.7 First Order Tip-Path-Plane Equations.- 4.8 Main Rotor Forces and Moments.- 4.9 Remarks.- 5 Frequency Domain System Identification.- 5.1 Mathematical Modeling.- 5.1.1 First Principles Modeling.- 5.1.2 System Identification Modeling.- 5.2 Frequency Domain System Identification.- 5.3 Advantages of the Frequency Domain Identification.- 5.4 Helicopter Identification Challenges.- 5.5 Frequency Response and the Coherence Function.- 5.6 The CIFER c Package.- 5.7 Time History Data and Excitation Inputs.- 5.8 Linearization of the Equations of Motion.- 5.9 Stability and Control Derivatives.- 5.10 Model Identification.- 5.10.1 Experimental Platform.- 5.10.2 Parametrized State Space Model.- 5.10.3 Identification Setup.- 5.10.4 Time Domain Validation.- 5.11 Remarks.- 6 Linear Tracking Controller Design for Small-Scale Unmanned Helicopters.- 6.1 Helicopter Linear Model.- 6.2 Linear Controller Design Outline.- 6.3 Decomposing the System.- 6.4 Velocity and Heading Tracking Controller Design.- 6.4.1 Lateral-Longitudinal Dynamics.- 6.4.2 Yaw-Heave Dynamics.- 6.4.3 Stability of the Complete System Error Dynamics.- 6.5 Position and Heading Tracking.- 6.6 PID Controller Design.- 6.7 Experimental Results.- 6.8 Remarks.- 7 Nonlinear Tracking Controller Design for Unmanned Helicopters.- 7.1 Introduction.- 7.2 Helicopter Nonlinear Model.- 7.2.1 Rigid Body Dynamics.- 7.2.2 ExternalWrench Model.- 7.2.3 Complete Rigid Body Dynamics.- 7.3 Translational Error Dynamics.- 7.4 Attitude Error Dynamics.- 7.4.1 Yaw Error Dynamics.- 7.4.2 Orientation Error Dynamics.- 7.4.3 Angular Velocity Error Dynamics.- 7.5 Stability of the Attitude Error Dynamics.- 7.6 Stability of the Translational Error Dynamics.- 7.7 Numeric Simulation Results.- 7.8 Remarks.- 8 Time Domain Parameter Estimation and Applied Discrete Nonlinear Control for Small-Scale Unmanned Helicopters.- 8.1 Introduction.- 8.2 Discrete System Dynamics.- 8.3 Discrete Backstepping Algorithm.- 8.3.1 Angular Velocity Dynamics.- 8.3.2 Translational Dynamics.- 8.3.3 Yaw Dynamics.- 8.4 Parameter Estimation Using Recursive Least Squares.- 8.5 Parametric Model.- 8.6 Experimental Results.- 8.6.1 Time History Data and Excitation Inputs.- 8.6.2 Validation.- 8.6.3 Control Design.- 8.7 Remarks.- 9 Time Domain System Identification for Small-Scale Unmanned Helicopters Using Fuzzy Models.- 9.1 Introduction.- 9.2 Takagi-Sugeno Fuzzy Models.- 9.3 Proposed Takagi-Sugeno System for Helicopters.- 9.4 Experimental Results.- 9.4.1 Tunning of the Membership Function Parameters.- 9.4.2 Validation.- 10 Comparison Studies.- 10.1 Summary of the Controller Designs.- 10.2 Experimental Results.- 10.3 First Maneuver: Forward Flight.- 10.4 Second Maneuver: Aggressive Forward Flight.- 10.5 Third Maneuver: 8 Shaped Trajectory.- 10.6 Fourth Maneuver: Pirouette Trajectory.- 10.7 Remarks.- 11 Epilogue.- 11.1 Introduction.- 11.2 Advantages and Novelties of the Designs.- 11.3 Testing and Implementation.- 11.4 Remarks.- A Fundamentals of Backstepping Control.- A.1 Integrator Backstepping.- A.2 Example of a Recursive Backstepping Design.- References. <s> BIB007 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Tri-rotor UAVs are more efficient compared to quadrotors in regard to the size and power requirement, yet, tri-rotor UAVs are more challenging in terms of control and stability. In this paper, we propose the design and control of a novel tri-rotor UAV. The proposed platform is designed to achieve six degree of freedom using a thrust vectoring technique with the highest level of flexibility, manoeuvrability and minimum requirement of power. The proposed tri-rotor has a triangular shape of three arms where at the end of each arm, a fixed pitch propeller is driven by a DC motor. A tilting mechanism is employed to tilt the motor-propeller assembly and produce thrust in the desired direction. The three propellers can be tilted independently to achieve full authority of torque and force vectoring. A feedback linearization associated with ℋ ∞ loop shaping design is used to synthesize a controller for the system. The results are verified via simulation. <s> BIB008 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <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> BIB009 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <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> BIB010 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <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> BIB011 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> This paper proposes a novel strategy to improve the performance and fault tolerance of multi-rotor vehicles. The proposed strategy uses dual axis tilting propellers and thus enables three different actuation mechanisms, namely, gyroscopic torques, thrust vectoring and differential thrusting. Unlike the conventional quadrotor, the proposed strategy offers a wider range of control torques by combining the three actuation mechanisms. Conventional quadrotors cannot be reconfigured if one of rotors fails. However, the proposed strategy is still able to reconfigure the vehicle with complete failure of one rotor and a pair of adverse motors. In order to prove this concept, a dual axis tilting UAV is first designed and prototyped. Next, a mathematical representation of the prototyped vehicle is modelled and verified using experiments. Then, a control system is developed based on a PD controller and pseudoinverse control allocator and validated through tests on a rig and flight tests. The tests show that the vehicle is faster than a conventional counterpart and that it can resist the failure of two rotors. Finally, this paper suggests how to lead further substantial improvements in performance. <s> BIB012 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> We derive a control-oriented model for a helicopter UAV whose complexity is sufficiently low to be usable for model-based control design yet which accurately reflects the dominant physics. The model consists of rigid-body dynamics coupled with simplified models of its subsystems: main rotor, Bell-Hiller system and tail rotor. The Bell-Hiller system is shown to provide a derivative feedback action in flight. The physical parameters of the resulting model are directly identified through a series of measurements explained throughout. <s> BIB013 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> This paper presents design and development of an experimental testbed for nonlinear geometric controls of a rigid body. We develop a fully actuated hexrotor UAV that uses six variable pitch propellers to control six degrees of freedom maneuvers, namely three position and three attitude variables, independently. In contrast to the popular quadrotor UAVs that can hover at a single attitude, the hexrotor presented in this paper is capable of hovering at any attitude provided that thrust is sufficiently large. A geometric controller is also developed on the special Euclidean group to track given desired position and attitude trajectories under the effects of unknown disturbances. These are particularly useful for ground tests for large angle rotational dynamics of spacecraft that are combined with arbitrary translational motions. A numerical example that involves a nontrivial maneuver and preliminary experimental tests are also presented. <s> BIB014 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> We propose a new aerial tool operation system consisting of multiple quadrotors connected to a tool by spherical joints to perform tool operation tasks. We model the system and show that the attitude dynamics of each quadrotor is decoupled from the tool dynamics, so that we can consider the quadrotors as thrusters and control the tool by adjusting the orientation and magnitude of these thrusters. We also show that the 6-DOF tool dynamics could be under-actuated or fullyactuated, depending on the number of quadrotors attached to the tool and the geometric configuration of their attachments. We then design control laws for the tool-tip position/orientation tracking of the (under-actuated) tool system with two quadrotors and the (fully-actuated) tool system with three quadrotors. We use Lyapunov approach to find the desired thrust command for each quadrotor while also taking into account the spherical joint limits in a form of constrained optimization. Simulation and implementation results are performed to support the theory. <s> BIB015 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> A tilt-quad rotor is a fusion of the quad rotor and tiltrotor concepts. A tilt-quad rotor is able to move itself in all six degrees of freedom while maintaining its central core leveled, result of adding two tilting motions to two opposed rotors while the other two rotors remain fixed. Condensing the main information required to build a simulator, this paper presents the tilt-quad rotor original concept, its implementation in the ALIV3 prototype, and its modeling. The procedures and results of a thorough experimental identification of the structural, actuators and sensors parameters are also provided. <s> BIB016 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <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> BIB017 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> We have developed a robot with a new control mechanism in order to collect information on flying robots in multiple fields. We aimed for a function that could rotate the tilt angle continuously and without limit and a function for flying maintaining any desired tilt angle with a structure that could efficiently use the thrust generated by the propellers. We devised a mechanism that connected two bicopter modules, each of which combines two of the four propellers into one set and named this mechanism the “Bi2 Copter”. This mechanism provided movements including landing, take-off, and flying with any desired tilt angle. This ability of this mechanism to fly walls with continuously changing surface angles and full 360° spherical coverage makes possible applications in investigation, measurement, etc. This report covers the design concepts of this flying robot, the structure design, basic control and operations verification. <s> BIB018 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> The design, modeling, and control of a new class of modular aerial robots, obtained by rigidly interconnecting a number of ducted-fan aircraft, are presented in this paper. A remarkable feature of the proposed class of vehicles is the fact that different dynamical behaviors, ranging from underactuated to fully actuated, can be obtained by adopting a suitable interconnection topology. To exploit this variety of actuation scenarios, a combination of control allocation and feedback control algorithms is proposed. The control allocation module exploits actuator redundancy by identifying the directions in the input space that affect the vehicle dynamics, whereas the feedback controller provides stabilization of the actuated degrees of freedom over desired attitude and position trajectories. A physical prototype, realized by interconnecting two ducted-fan vehicles, is employed to experimentally demonstrate the effectiveness of the proposed methodology. <s> BIB019 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this study, we investigated a novel type of the multirotor aerial vehicle with two-dimensional multilinks to demonstrate stable aerial transformation for high mobility in three-dimensional environments. Our goal was to tackle the challenge of traversing narrow spaces or gaps, which is one of the difficulties for existing structure of multirotors, especially in the cluttered indoor environment of disaster sites. The research involved three steps. First, we developed the modeling of the link modules that compose a multirotor with two-dimensional multilinks and conducted a quadrotor prototype. Second, we derived a stable flight control method for aerial transformation on the basis of linear-quadratic-integral optimal control. Third, we investigated the motion planning for the aerial transformation using a state validation method and path optimization in the joint space to maintain the stability during transformation. Successful aerial transformation and the ability of the prototype to negotiate narrow gap... <s> BIB020 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> We propose a novel multi-rotor flying platform, ODAR (omni-directional aerial robot), which is fully-actuated (i.e., can assume arbitrary motion in SE(3) or generate arbitrary control wrench in se(3)) by six opportunistically distributed rotors, each driven by reversible ESC (electronic speed controller) for bi-directional thrust generation. Due to this omni-directional wrench generation, the ODAR system can realize such powerful behaviors impossible with conventional multi-rotor flying platforms as: 360° photo/video shooting while holding its position for VR scene generation; or resisting sideway gust while keeping its attitude and exerting downward pushing force larger than its own weight for aerial manipulation applications. This paper presents optimal mechanical design, modeling and control, hardware and software implementation, and experimental verification of the ability of the ODAR system to attain those behaviors impossible with the conventional drones as stated above. <s> BIB021 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this article, a novel Vertical Take-Off and Landing (VTOL) Single Rotor Unmanned Aerial Vehicle (SR-UAV) will be presented. The SRUAV's design properties will be analysed in detail, with respect to technical novelties outlining the merits of such a conceptual approach. The system's model will be mathematically formulated, while a cascaded P-PI and PID-based control structure will be utilized in extensive simulation trials for the preliminary evaluation of the SR-UAV's attitude and translational performance. <s> BIB022 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Quadrotors have recently been drawing greater research and commercial attention to the point that they have become one of the most popular types of unmanned aerial vehicles. Their applications vary from entertainment to transportation, commercial and even military applications. In this paper, a novel quadrotor design is proposed. The design decouples all motions by allowing each rotor to tilt in two directions about the quadrotor fixed frame. This modification improves the stability and safety of the quadrotor and gives it more manoeuvrability and robustness. The mathematical model of the proposed system is carried out using Newton-Euler technique. Several flight scenarios are also simulated under a simple PID controller to illustrate the superiority over conventional quadrotor designs. <s> BIB023 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Quadrotor helicopters are among one of the most interested topics in the robotics field in the last decade. Regularly, a simple quadrotor has four fixed motors, giving the availability of controlling 4 independent inputs for a 6 degrees-of-freedom (DOF) system. In the recent studies, there is a tendency on changing the controlled system from fixed actuators to the ones that can have dynamic rotations around their axes or planes. This approach is progressing nowadays in order to build more robust versions of quadrotors. The design and control system of a tilt-roll rotor quadrotor has been studied and simulated in this paper. Each of the rotor speeds and their particular angle with respect to the earth frame is adaptively controlled using various control algorithms including cascaded PID. Design implementation of the tiltable geometry is also presented as well as the tilting mechanism’s electronic and CAD design. The mathematical model of the tiltable geometry is given and compared with the previous designs by the help of simulations held on Matlab. The simulations prove that the proposed design is more robust and stable than the regular quadrotor especially when environmental limitations are taken into account. <s> BIB024 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this article a Tilt-Wing Unmanned Aerial Vehicle (TW-UAV) and the preliminary evaluation of its hovering characteristics in extended simulation studies are presented. In the beginning, an overview of the TW-UAV's design properties are established, highlighting the novelties of the proposed structure and the overall merits. The TW-UAV's design and structural properties are mathematically modeled and utilized for the synthesis of a cascaded P-PI and PID based control structure for the regulation of its hovering performance. In addition, extensive simulation trials are performed in order to evaluate the structure's efficiency in controlling the TW-UAV's attitude and position under various noise and disturbance scenarios. <s> BIB025 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Traditional quadcopter suffers terribly from its underactuation which implies the coupling between the rotational and the translational motion. In this paper, we present a quadcopter with dynamic rotor tilting capability in which the four propellers are allowed to tilt together around their arm axis. The proposed model provides leveled forward/backward horizontal motion and therefore, ensures a correct view of the onboard camera, and increases the vehicle speed by reducing the air drag. The rotor tilt mechanism also provides an instant high speed in the forward or reverse direction and offers a quick and solid air brake to restrain that fast moving speed. The nonlinear dynamical model for the quadcopter under consideration is derived using Newton-Euler formalization. A control strategy is then proposed aimed to control the altitude, attitude, and the forward speed of the obtained model. Finally, a numerical simulation is used to integrate the system model with the controller and to test the system performance. Simulation results are reported to demonstrate the advantages of the proposed novel configuration. <s> BIB026 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this letter, we introduce a novel transformable aerial robot called DRAGON, which is a dual-rotor-embedded multilink robot with the ability of multi-degree-of-freedom (DoF) aerial transformation. The new aerial robot can control the full pose in $\mathsf {SE}(3)$ regarding the center of gravity (CoG) of multilinks and can render the multi-DoF aerial transformation, which is accomplished by the original two-DoF force vectoring mechanism on each link called the dual-rotor gimbal module. The dynamics is derived on the basis of the special definition of CoG orientation, followed by a control method decoupled into thrust force control and rotor gimbal control. In the thrust force control, the minimum force norm is considered to avoid force saturation, and the rotor gimbal control method is developed to enhance both translational and rotational stabilities during hovering and large-scale aerial transformation. The prototype composed of four links is constructed, and associated preliminary experiments are performed. The feasibility of the novel mechanical design and the proposed control method for the aerial transformation is demonstrated. <s> BIB027 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Abstract We present a novel aerial manipulator concept composed of a fully actuated hexarotor aerial vehicle and an n degree of freedom manipulator. Aiming at interaction tasks, we present a trajectory following control framework for the end-effector of the manipulator. The system is modeled in Euler-Lagrangian formalism and in Denavit-Hartenberg form. Benefiting from the redundancy of the system, we present several cost function strategies based on the projected gradient method to optimize the aerial manipulator behavior. The control framework is based on exact feedback linearization. In an advanced simulation section, we thoroughly present the robustness of the system and its limits in two typical configuration constituted by an 8 and a 10 degrees of freedom redundant aerial manipulator. <s> BIB028 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In recent years, unmanned aerial vehicles (UAVs) have acquired an increasing interest due to their wide range of applications in military, scientific, and civilian fields. One of the quadcopter limitations is its lack of full actuation property which limits its mobility and trajectory tracking capabilities. In this work, an overactuated quadcopter design and control, which allows independent tilting of the rotors around their arm axis, is presented. Quadcopter with this added tilting mechanism makes it possible to overcome the aforementioned mobility limitation by achieving full authority on torque and force vectoring. The tilting property increases the control inputs to 8 (the 4 propeller rotation speed plus the 4 rotor tilting angles) which gives a full control on the quadcopter states. Extensive mathematical model for the tilt rotor quadcopter is derived based on the Newton-Euler method. Furthermore, the feedback linearization method is used to linearize the model and a mixed sensitivity H∞ optimal controller is then designed and synthesized to achieve the required performance and stability. The controlled system is simulated to assure the validity of the proposed controller and the quadcopter design. The controller is tested for its effectiveness in rejecting disturbances, attenuating sensor noise, and coping with the model uncertainties. Moreover, a complicated trajectory is examined in which the tilt rotor quadcopter has been successfully followed. The test results show the supremacy of the overactuated quadcopter over the traditional one. <s> BIB029 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> Omnidirectional MAVs are a growing field, with demonstrated advantages for aerial interaction and uninhibited observation. While systems with complete pose omnidirectionality and high hover efficiency have been developed independently, a robust system that combines the two has not been demonstrated to date. This paper presents VoliroX: a novel omnidirectional vehicle that can exert a wrench in any orientation while maintaining efficient flight configurations. The system design is presented, and a 6 DOF geometric control that is robust to singularities. Flight experiments further demonstrate and verify its capabilities. <s> BIB030 </s> Snake Aerial Manipulators: A Review <s> E. DESIGN CONSIDERATIONS OF THRUST VECTORING AND PROPULSION <s> In this article, a novel Thrust Vectoring Vortex Climbing Robot (TVV-CR) will be presented from a design development and experimental evaluation perspective. To the goal of providing an efficient and robust climbing robot design, with minimized weight and high permissible payload, a novel Electric Ducted Fan (EDF)-based actuation design is proposed for achieving simultaneous locomotion and adhesion via a controllable tilt mechanism, while excluding the need for active motorized wheels. Towards the development of the TVV-CR, the design and development stages will be presented in detail, while proposing a P-PI-based cascaded control structure for evaluating its overall properties. The efficiency of the suggested scheme will be evaluated by multiple experimental results indicating the robot's ability to follow randomly generated paths, while maintaining its adhesion under different surface inclinations. <s> BIB031
The following considerations are concerned to the degree of mobility of the entire aerial-structure Table. 5, which is highly dependent on various thrust-vectoring methodologies (e.g by pneumatic, vacuum or hydraulic main-flow deviation, by main rotor full-body tilting, by propeller tilting with a kind of swashplate, by ailerons, by center of gravity alteration with a mobile-mass, by coordination of multiple propellers among others Fig. 13 ) BIB015 ,  , BIB011 . Planar operation this is the basic mode of snake aerial manipulation. The execution of three-dimensional angular movement, falls exclusively into the gripper or final effector. The full structure roll and pitch angles tend to zero, or depend on the trajectories in X and Y for its later stabilization to zero once the trajectories have been achieved  , BIB015 , BIB020 . The only feasible independent movements are three-dimensional translations and yaw rotations  , BIB020 , like in a quadcopter Fig. 2,5 . Omnidirectional operation: in this case, the aerial manipulator has total mobility or beyond the planar configuration Fig. 7,8,11 , the three-dimensional angular movement is independent of the translational and is achieved by one or several techniques of thrust-vectoring applied to each of the propellers or vehicles BIB027 , BIB021 , BIB014 ,  BIB008 BIB026   BIB028 BIB029 BIB030 BIB012 BIB022 BIB016 BIB009 BIB023 BIB024 BIB017  . This concept also applies to both parallel and serial aerial manipulators, it is worth to mention that control strategies also change their paradigm. While the objective of the planar configurations is to keep the pitch and roll angles around zero or path-dependant of X and Y movements BIB020 , BIB010 , the goal of omnidirectional configurations is to achieve independence between translational and rotational modes of flight. In this way a remarkable school of control, is the one developed by Taeyoung Lee which is based on geometrical approaches     , and the method applicable to aerial manipulators through a kino-dynamic decoupling of the orientational and translational controllers developed by Choi  and Lee []94. Convertible operation: It is convenient to separate the tasks of an snake aerial manipulator into two steps  , BIB020 , BIB025 : transport to the workspace (long distance flight) and in situ aerial manipulation (short distance operations). In this way during the transport to the work area, it is desirable to keep the entire structure as some type of long-distance aircraft (airplane, helicopter), and once it arrives to the work area, transform the vehicle into an snake aerial manipulator, shutting down on the way unnecessary engines, reducing with this the power consumption and storing this power for the manipulation phase. In order to exemplify the previous paragraphs, an aircraft called helibot based on coaxial vehicles, and currently in theoretical development and patenting, will be described. The helibot is an UAS like-PVTOL or bicopter aircraft BIB004 BIB001 BIB018 with thrust-vectoring mountings, composed of at least two modules, one is the shoulder and the other the elbow where is mounted a gripper, these modules are coaxial drones each, one with its respective steering mechanism (e.g. a swashplate). In order to allow the transition flight tasks there is an extra propeller which can rotate 90 degrees with a servo system or an outrunner motor in order to use the system as a counter rotating helicopter. Finally, for locking and releasing yaw movements each coaxial UAV has a clutch system Fig. 8 . It has 7 flight modes. Serial planar snake aerial manipulator: this mode of operation is a kind of an aircraft-propelled snake aerial manipulator but by using coaxial motors instead of multirotors Parallel planar snake aerial manipulator: in this mode of operation, the rotation of the elbow is locked by the clutch-system obtaining the coaxial aircraft version of BIB015 or BIB019 , Parallel omnidirectional snake aerial manipulator: keeping the elbow locked by means of the clutch and using the steering system of the coaxial motors, it is possible to modify the angles of the propellers and in this way they can generate omnidirectional movement as described in  . Serial omnidirectional snake aerial manipulator: the same as the previous one, but by releasing the rotation of the elbow while the clutch is disengaged Tandem helicopter BIB003 ,  , BIB005 : by keeping the clutch active in order to block the rotation of the elbow, this mode is achieved by deactivating the secondary counter-rotating propellers in both coaxial aircrafts and leaving the main ones (those that are directly linked to the steering system). This mode of flight is useful in the case of bulky or massive systems Standard helicopter or counter-rotating helicopter BIB006 , BIB002 BIB007 BIB013 : this mode is achieved by locking the elbow rotation and completely deactivating the elbow drone (gradually or instantaneously according to the scale of the aircraft and the task). After that, by activating the counter-rotating support propeller and placing it at 90 degrees with respect to the ground plane (the elbow drone could also function as a counter rotating propeller) Airplane: keeping in mind that an steering system based on servomotors for moving the full propeller body could be employed at certain vehicle scales, is also possible to transform all the system from vertical takeoff and landing and use an airplane displacement by changing the variable direction propellers to an angle with a component parallel to the ground(in this case an aerodynamic redesign of the linkages must be developed). The proposed operation will be similar to that of convertible wing UAVs as in the case of a tail-sitter. Discussion: A classification of snake aerial manipulators based on the way they can move in the space was introduced, this classification is absolutely related with several thrust-vectoring methodologies, but is limited to three categories: planar, omnidirectional and convertible, the main problem here is to select the most suitable way of thrust-vectoring technique for each kind of aerial mobility. Vectorization goes hand in hand with omnidirectionality, both are the essential elements of this type of vehicles, the first concept as the cause and the second as the effect, but their applications are limited by costs, machinability and physical constraints. It is for example unthinkable to use mechanical vectorization methods to move the full body of a propeller in large-scale vehicles (for this reason it is preferred to redirect the blades of the propellers), however it is a viable technique and also widely used in small vehicles, the reason is that moving such a large propellers turning at high rpms implies moving a large amount of inertia, which is not noticeable or negligible in small aircraft. In this way, although all current projects on snake aerial manipulators are made with mechanical vectorization, it is also convenient to analyze its possible expansion at large scales by fluidic vectorization. Conversely, fluidic vectorization for small vehicles is unfeasible because of the cost and the difficulty of manufacturing miniature pumps and valves. Another line of action is to design new methods of vectorization such as the carried out by  , where harmonic pulsation is applied in the rotation frequency of an under-actuated propeller, another example is by using the known effects of shape memory of certain materials by electrification or magnetization. Finally, it should be remembered that these concepts can be extended in application to other work environments such as underwater or viscous places and all the elements or techniques that can be explained or discussed here should be analyzed under operating conditions such that it could be feasible to use them there. It is even possible to design aerial-powered land vehicles BIB031 .