Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB001 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> We consider the planning and control of multiple aerial robots manipulating and transporting a payload in three dimensions via cables. Individual robot control laws and motion plans enable the control of the payload (position and orientation) along a desired trajectory. We address the fact that robot configurations may admit multiple payload equilibrium solutions by developing constraints for the robot configuration that guarantee the existence of a unique payload pose. Further, we formulate individual robot control laws that enforce these constraints and enable the design of non-trivial payload motion plans. Finally, we propose two quality measures for motion plan design that minimize individual robot motion and maximize payload stability along the trajectory. The methods proposed in the work are evaluated through simulation and experimentation with a team of three quadrotors. <s> BIB002 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In the past few decades, unmanned aerial vehicles (UAVs) have become promising mobile platforms capable of navigating semiautonomously or autonomously in uncertain environments. The level of autonomy and the flexible technology of these flying robots have rapidly evolved, making it possible to coordinate teams of UAVs in a wide spectrum of tasks. These applications include search and rescue missions; disaster relief operations, such as forest fires [1]; and environmental monitoring and surveillance. In some of these tasks, UAVs work in coordination with other robots, as in robot-assisted inspection at sea [2]. Recently, radio-controlled UAVs carrying radiation sensors and video cameras were used to monitor, diagnose, and evaluate the situation at Japans Fukushima Daiichi nuclear plant facility [3]. <s> BIB003 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This work presents the design of flight control algorithms for set-point stabilization of a class of modular aerial vehicles obtained by rigidly interconnecting a number of single ducted-fan aircraft. Interestingly enough, for such a modular configuration, certain types of interconnection structure between the different modules may lead to redundancy both in term of the overall number of actuators available onboard and in the number of degrees of freedom that can be actually governed simultaneously. The design of the control policy for such a complex dynamical behavior is handled by defining specific control allocation algorithms for each possible case (for which a taxonomy is given in the paper) and by deriving an overall control structure capable to switch among these policies according to the properties of the selected configuration. This approach results in an architecture that combines classical control schemes for under-actuated air vehicles - such as those employed in most Vertical Take-Off and Landing (VTOL) aircraft - with control strategies for fully-actuated vehicles. <s> BIB004 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> We address the problem of cooperative transportation of a cable-suspended payload by multiple quadrotors. In previous work, quasi-static models have been used to study this problem. However, these approaches are severely limited because they ignore the payload dynamics, and do not explicitly model the underactuation in the control problem. Thus, there are no guarantees on the payload trajectory or the cable tensions, which must be non negative. In this paper, we develop a complete dynamic model for the case when payload is a point load and for the case when the payload is a rigid body. We show in both cases the resulting system is differentially flat when the cable tensions are strictly positive. We also consider the case where the tensions are non negative (including the case with zero tensions) and establish that these systems are differentially flat hybrid systems by considering the switching dynamics induced by the unilateral tension constraints. We use the differential flatness property to find dynamically feasible trajectories for the payload+quadrotors system. We show using numerical and experimental methods that these trajectories are superior to those obtained by quasi-static models. <s> BIB005 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> Performing aerial 6-dimensional manipulation using flying robots is a challenging problem, to which only little work has been devoted. This paper proposes a motion planning approach for the reliable 6-dimensional quasi-static manipulation with an aerial towed-cable system. The novelty of this approach lies in the use of a cost-based motion-planning algorithm together with some results deriving from the static analysis of cable-driven manipulators. Based on the so-called wrench-feasibility constraints applied to the cable tensions, as well as thrust constraints applied to the flying robots, we formally characterize the set of feasible configurations of the system. Besides, the expression of these constraints leads to a criterion to evaluate the quality of a configuration. This allows us to define a cost function over the configuration space, which we exploit to compute good-quality paths using the T-RRT algorithm. As part of our approach, we also propose an aerial towed-cable system that we name the FlyCrane. It consists of a platform attached to three flying robots using six fixed-length cables. We validate the proposed approach on two simulated 6-D quasi-static manipulation problems involving such a system, and show the benefit of taking the cost function into account for such motion planning tasks. <s> BIB006 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> Abstract This work focuses on the modeling and the control design for a class of multi-propeller aerial vehicles. The idea is to consider the aircraft as a modular system obtained by interconnecting a number of actuator modules, each one given by a fixed-pitch propeller driven by a motor, and of payload modules, representing the equipment and all the other passive components installed onboard. A control strategy based on control allocation is then proposed so as to govern a generic multi-propeller aerial vehicle by means of a unique globally stabilizing controller. The effectiveness of the proposed results are then demonstrated by considering the problem of controlling the dynamical model of quad-rotor aerial vehicle. <s> BIB007 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB008 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB009 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In this paper, the dynamic model of a tilting rotor quadcopter, i.e., a quad-rotor aerial vehicle with rotors that can tilt along one of its axes, is presented. The tilting rotor quadcopter provides the added advantage in terms of additional stable configurations, made possible by additional actuated controls, as compared to a traditional quadcopter without titling rotors. The tilting rotor quadcopter design is accomplished by using an additional motor for each rotor that enables the rotor to rotate along the axis of the quadcopter arm. This turns the traditional quadcopter into an over-actuated flying vehicle allowing us to have complete control over its position and the orientation. In this paper, a dynamic model of the tilting rotor quadcopter vehicle is derived for flying and hovering modes. The model includes the relationship between vehicle orientation angle and rotor tilt-angle. Furthermore, a PD controller is designed to achieve the hovering and navigation capability at any desired pitch or roll angle. The dynamic model and the control design is verified with the help of numerical studies. <s> BIB010 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB011 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> Given the tethered aerial robot problem, in this paper we investigate a multi-agent extension considering a chain of two underactuated flying robots. Our goal is to independently control the elevations (angles) of the two links (or, equivalently, the Cartesian position of the last robot) and their internal stress. For this purpose we theoretically prove the dynamic feedback linearizability of the system and we exploit this property to design a nonlinear controller that exactly linearizes the system. The controller is able to steer the outputs of interest along any trajectory s.t. the desired elevations and stresses are functions of time of class C3 and C1, respectively. The controller is able to track independently both positive and negative stresses, i.e., both tension and compression. Resorting to an equivalence argument we then also show the differential flatness of the system. Finally we also demonstrate some of the abilities of the proposed method through numerical examples. <s> BIB012 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> We consider the problem of state-observation and control for a bi-tethered aerial system composed by a physical chain of two underactuated aerial robots, also called UAVs. The controlled outputs are the Cartesian position of the last robot and the internal forces along the links. We aim at a minimal use of sensors in order to retrieve the full state. For this goal we propose an output transformation method whose applicability implies the system observability. When this is the case we prove that it is possible to design a nonlinear state estimator based on the high gain- and Luenberger- observers that is able to retrieve the state from any dynamic condition. We also demonstrate how this estimator can be employed with a nonlinear controller for the Cartesian position and the link stresses while ensuring the stability in closed-loop. We show the validity of the method for sensorial configurations composed only by two accelerometers (no gyros) and just two encoders, or two accelerometers (no gyros) and just two inclinometers. A realistic simulative validation concludes the paper. <s> BIB013 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This paper presents the full dynamics and control of arbitrary number of quadrotor unmanned aerial vehicles (UAV) transporting a rigid body. The rigid body is connected to the quadrotors via flexible cables where each flexible cable is modeled as a system of arbitrary number of serially connected links. It is shown that a coordinate-free form of equations of motion can be derived for the complete model without any simplicity assumptions that commonly appear in other literature, according to Lagrangian mechanics on a manifold. A geometric nonlinear controller is presented to transport the rigid body to a fixed desired position while aligning all of the links along the vertical direction. A rigorous mathematical stability proof is given and the desirable features of the proposed controller are illustrated by numerical examples and experimental results. <s> BIB014 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This paper deals with the dynamics and controls of a quadrotor unmanned aerial vehicle that is connected to a fixed point on the ground via a tether. Tethered quadrotors have been envisaged for long-term aerial surveillance with high-speed communications. This paper presents an intrinsic form of the dynamic model of a tethered quadrotor including the coupling between deformations of the tether and the motion of the quadrotor, and it constructs geometric control systems to asymptotically stabilize the coupled dynamics of the quadrotor and the tether. The proposed global formulation of dynamics and control also avoids complexities and singularities associated with local coordinates. These are illustrated by numerical examples. <s> BIB015 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB016 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In this paper a novel aerial manipulation system is proposed. The mechanical structure of the system, the number of thrusters and their geometry will be derived from technical optimization problems. The aforementioned problems are defined by taking into consideration the desired actuation forces and torques applied to the end-effector of the system. The framework of the proposed system is designed in a CAD Package in order to evaluate the system parameter values. Following this, the kinematic and dynamic models are developed and an adaptive backstepping controller is designed aiming to control the exact position and orientation of the end-effector in the Cartesian space. Finally, the performance of the system is demonstrated through a simulation study, where a manipulation task scenario is investigated. <s> BIB017 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> Welcome.- Motion Planning.- Force Distribution.- Application and Protoypes.- Design and Components.- Kinematics and Interval Methods.- Calibration und Identification.- Control.- Dynamics Modelling. <s> BIB018 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> We introduce a new aerial manipulator system that consists of an airborne base actuated by multiple spherically-connected quadrotors and a manipulator rigidly connected to that base. We first model the dynamics of the system and show that attitude dynamics of each quadrotor is decoupled from the base-manipulator dynamics. Therefore, we can consider the quadrotors as thrusters to control the base-manipulator dynamics. We then use Lyapunov approach to design a pose-tracking control for the end-effector of the manipulator and optimally distribute that control to each quadrotor on the base and each joint rotor on the manipulator. The simulation of a system of three quadrotors and a 2 degree-of-freedom (DOF) manipulator is presented to support the theory. <s> BIB020 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In this paper, we consider the problem of controlling an aerial robot connected to the ground by a passive cable or a passive rigid link. We provide a thorough characterization of this nonlinear dynamical robotic system in terms of fundamental properties such as differential flatness, controllability, and observability. We prove that the robotic system is differentially flat with respect to two output pairs: elevation of the link and attitude of the vehicle; elevation of the link and longitudinal link force (e.g., cable tension, or bar compression). We show the design of an almost globally convergent nonlinear observer of the full state that resorts only to an onboard accelerometer and a gyroscope. We also design two almost globally convergent nonlinear controllers to track any sufficiently smooth time-varying trajectory of the two output pairs. Finally, we numerically test the robustness of the proposed method in several far-from-nominal conditions: nonlinear cross-coupling effects, parameter deviations, measurements noise, and nonideal actuators. <s> BIB021 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This paper addresses the problem of cooperative aerial transportation of an object using a team of quadrotors. The approach presented to solve this problem accounts for the full dynamics of the system and it is inspired by the literature on reconfigurable cable-driven parallel robots (RCDPR). Using the modelling convention of RCDPR it is derived a direct relation between the motion of the quadrotors and the motion of the payload. This relation makes explicit the available internal motion of the system, which can be used to automatically achieve additional tasks. The proposed method does not require to specify a priory the forces in the cables and uses a tension distribution algorithm to optimally distribute them among the robots. The presented framework is also suitable for online teleoperation. Physical simulations with a human-in-the-loop validate the proposed approach. <s> BIB022 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In this paper, we propose a bilateral tele-operation scheme for cooperative aerial manipulation in which a human operator drives a team of Vertical Take-Off and Landing (VTOL) aerial vehicles, that grasped an object beforehand, and receives a force feedback depending on the states of the system. For application scenarios in which dexterous manipulation by each robot is not necessary, we propose using a rigid tool attached to the vehicle through a passive spherical joint, equipped with a simple adhesive mechanism at the tool-tip that can stick to the grasped object. Having more than two robots, we use the extra degrees of freedom to find the optimal force allocation in term of minimum power and forces smoothness. The human operator commands a desired trajectory for the robot team through a haptic interface to a pose controller, and the output of the pose controller along with system constraints, e.g., VTOL limited forces and contact maintenance, defines the feasible set of forces. Then, an on-line optimization allocates forces by minimizing a cost function of forces and their variation. Finally, propeller thrusts are computed by a dedicated attitude and thrust controller in a decentralized fashion. Human/Hardware in the loop simulation study shows efficiency of the proposed scheme, and the importance of haptic feedback to achieve a better performance. <s> BIB023 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <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> BIB024 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> In this paper, we introduce a novel type of the multirotor aerial vehicle with two-dimensional multilinks which enables the stable aerial transformation for high mobility in three-dimensional environments. Our goal is to hold and carry object by using the whole-body manipulation in the air. 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 whole-body aerial manipulation based on the enveloping grasping method for the four-link type which takes the additional inertial parameters and joint torque into account. Successful aerial transformation and manipulation with the quadrotor prototype were demonstrated, confirming the feasibility of our proposed transformable multirotor for aerial maneuvering. <s> BIB025 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This work focuses on the design of estimation algorithms able to identify the interconnection topology of a class of modular aerial vehicles obtained by rigidly interconnecting a number of actuator and payload modules. The idea is to obtain a composable aerial vehicle that can be easily assembled and then deployed on the selected application scenario without a priori knowledge of the exact final geometric structure. Two different scenarios are then addressed. In the first one, it is assumed that the modules can be interconnected only following a pre-defined scheme, namely the admissible geometric configurations constitute a discrete set. In the second one, no restrictions on the admissible geometric configuration are taken into account. The effectiveness of the proposed identification algorithms is finally shown by means of numerical simulations comprehensive of noises affecting the sensors' output. <s> BIB026 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> This paper addresses the exploitation of the combined potential of the directly-actuated and the underactuated control authorities of unmanned aerial vehicles with thrust-vectoring actuation. For the modeling, control synthesis and experimental evaluation a custom developed unmanned tri-tiltrotor is employed, equipped with rotor-tilting mechanisms which enable the direct actuation of its longitudinal dynamics, while retaining the standard body-pitching underactuated authority. An explicit model predictive control scheme relying on constrained multiparametric optimization is proposed for the dual-authority optimal control. The backbone of this scheme is a modeling representation that incorporates the separate internal dynamics of the two actuation principles and their interferences as they concurrently act on the free-flying vehicle body, while tractably representing their differentiated effects on the evolution of the longitudinal dynamics. This paper additionally presents the key implemented features that enable the autonomous operation of the employed tilt-rotor platform, in order to provide a reliable testbed for experimental evaluation. Finally, extensive experimental studies which conclusively validate this strategy’s increased efficiency are demonstrated. <s> BIB027 </s> Snake Aerial Manipulators: A Review <s> B. DESIGN CONSIDERATIONS OF STRUCTURAL DYNAMICS <s> Transport of objects is a major application in robotics nowadays. While ground robots can carry heavy payloads for long distances, they are limited in rugged terrains. Aerial robots can deliver objects in arbitrary terrains; however they tend to be limited in payload. It has been previously shown that, for heavy payloads, it can be beneficial to carry them using multiple flying robots. In this paper, we propose a novel collaborative transport scheme, in which two quadrotors transport a cable-suspended payload at accelerations that exceed the capabilities of previous collaborative approaches, which make quasi-static assumptions. Furthermore, this is achieved completely without explicit communication between the collaborating robots, making our system robust to communication failures and making consensus on a common reference frame unnecessary. Instead, they only rely on visual and inertial cues obtained from on-board sensors. We implement and validate the proposed method on a real system. <s> BIB028
According to BIB003 , BIB012 BIB013 BIB021 there are two main variants of snake aerial manipulators and their combinations, based on the way in which the UAVs or propellers are joined to compose a floating structure: Flexible Aerial Snakes Fig. 4 . In this case, the current technology has focused on the use of cables, however, BIB012 proposes mechanisms and controllers that can vary from the suspended cable, to the rigid union passing through different types of flexible linkages. Representative publications are: BIB014 , BIB005 , BIB009 ,  , BIB002 BIB028 BIB022 BIB006 BIB015 . Rigid Aerial Snakes the rigid case Fig. 1,2 ,3,5,6,7,8. They are UAV teams  , BIB016  BIB023 or a set of independent propellers BIB017 BIB024 BIB004 BIB025 BIB007 BIB026 , which are capable of moving the structure to which they are rigidly mounted by using various methodologies of thrust vectoring BIB008 BIB001 BIB010 BIB011 BIB027 . Also, they provide dexterity, additional degrees of mobility and capacities of an aerial like-robotic arm manipulator. A subclassification, occurs according to the kinematic chain that conform the airships or propellers [80] - BIB018 . Rigid Parallel Aerial Snakes The parallel approach. In this classification, the movement and force resulting in a specific point of the structure (where a gripper or end effector is usually placed), is determined by the coordinated operation of each individual engine-element in a closed kinematic chain (UAVs or propellers), BIB019 , BIB017 , BIB020 Fig. 5,7,8 . The fact of having a parallel structure has the advantages that the center of mass, gravity, geometric and pressure, as well as the general form of the aerial structure do not vary considerably with the execution of a task (at least not as drastically like the serial approach), this allows to focus the design on contact force assignments. Rigid Serial Aerial Snakes The serial approach. In this case, the movement and force applied to the point of interest follows an open kinematic chain, which, in addition to bring more mobility to the aerial mechanical structure, has the problem of introduce severe inertial changes. This is because the position of the center of gravity, mass, geometric and pressure, could change with the shape and trajectory variations during the execution of the entire task (such as a human arm for example). So the tasks to be performed are not only those for generating contact forces but also movement, reconfigurability and dexterity  , BIB012 , BIB025 Fig. 1,2 