Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> When disasters and crises arise visual information needs to be rapidly gathered and assessed in order to assist rescue workers and emergency personnel. Often such situations are life-threatening and people cannot safely obtain such information. Disasters in urban areas are particularly taxing. Structural collapse, damaged staircases and the loss communication infrastructures aggravate rescue efforts. Robots, equipped with camera, can be employed to visually capture situational awareness. As such, the focus of our work is designing a backpackable aerial robot that can hover-and-stare. Such a robot would ascend, peer through windows, and transmits video to an operator. This paper presents a backpackable tandem-rotor prototype that can carry a wireless camera <s> BIB001 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents the design and preliminary control of an indoor coaxial helicopter "CoaX" based on a concept of hybrid active and passive control. The robot is capable of passive roll and pitch stabilization against small disturbances while actively stabilizing the yaw and the altitude. We achieve omnidirectional horizontal motion by shifting the center of gravity. The structure is made out of lightweight polyurethane and carbon fiber. Preliminary tests show that "CoaX" is able to hover for short moments and the lateral control is effective. <s> BIB002 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents autonomous control for Micro-Flying Robot (?FR) and small helicopter X.R.B. In case of natural disaster like earthquake, a MAV will be very effective for surveying the site and environment in dangerous area or narrow space, where human cannot access safely. In addition, it will be a help to prevent secondary disaster. This paper is concerned with autonomous hovering control, guidance control of ?FR, and automatic takeoff and landing control of X.R.B. <s> BIB003 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> An original configuration of a small aerial vehicle having eight rotors is presented. Four rotors are devoted to the stabilization of the orientation of the helicopter, and the other four are used to drive the lateral displacements. A precompensation on the roll and pitch angles has been introduced so that the attitude dynamics is practically independent of the translational dynamics. This compensation is directly related to the velocity of the lateral motors. The dynamical model is obtained using the Euler-Lagrange approach. The proposed configuration is particularly useful for image processing since the the camera orientation is held constant. The eight-rotor rotorcraft is simpler to pilot than other rotorcrafts. A control strategy is proposed that uses the optical flow measurements to achieve a hover flight that is robust with respect to perturbations like wind. The new aerial configuration and control strategy have been tested in real-time experiments. <s> BIB004 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents a new paradigm in the design of indoor flying robots that replaces collision avoidance with collision robustness. Indoor flying robots must operate within constrained and cluttered environments where even nature's most sophisticated flyers such as insects cannot avoid all obstacles and should thus be able to withstand collisions and recover from them autonomously. A prototype platform specifically designed to withstand collisions and recover without human intervention is presented. Its dimensions are optimized to fulfill the varying constraints of aerodynamics, robustness and self-recovery, and new construction techniques focusing on shock absorption are presented. Finally, the platform is tested both in-flight and during collisions to characterize its collision robustness and self-recovery capability. <s> BIB005 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We present the implementation and demonstration of a team of two fixed-wing Unmanned Aerial Vehicles whose task is to improve the localization accuracy of a number of ground-based features. The underlying algorithmic paradigm is based on over a decade’s worth of work on Decentralized Data Fusion and Control. We present the components of the architecture, including vehicle localization, feature tracking, path planning and cooperative control. The algorithms described are implemented on a complete Unmanned Aerial System. Three demonstrations were performed, with varying levels of cooperation between team members. We present the results of these demonstrations and compare the performance of the team in completing the mission along with a quantitative understanding of the benefits achieved. <s> BIB006 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We extend the classic control problem of the inverted pendulum by placing the pendulum on top of a quadrotor aerial vehicle. Both static and dynamic equilibria of the system are investigated to find nominal states of the system at standstill and on circular trajectories. Control laws are designed around these nominal trajectories. A yaw-independent description of quadrotor dynamics is introduced, using a ‘Virtual Body Frame’. This allows for the time-invariant description of curved trajectories. The balancing performance of the controller is demonstrated in the ETH Zurich Flying Machine Arena testbed. Development potential for the future is highlighted, with a focus on applying learning methodology to increase performance by eliminating systematic errors that were seen in experiments. <s> BIB007 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> BOLT is a lightweight bipedal ornithopter capable of high-speed dynamic running and effecting transitions between aerial and terrestrial locomotion modes. The gait dynamics of both quasi-static and dynamic locomotion are examined through the use of an on-board accelerometer, part of a one gram electronics package also containing a processor and radio. We discuss the accelerations in the context of the traditional spring-loaded inverted pendulum model seen in nearly all legged locomotion in organisms. Flapping wings are shown to provide damping along with propulsive force. The aerodynamic forces of the flapping wings also impart passive stability to the robot, enabling it to run bipedally with only a single actuator. BOLT transitions from ground running to aerial hovering in as little as one meter of runway. Overall, the advantages provided by wings in terrestrial locomotion, coupled with aerial capabilities, allow BOLT to navigate complex three dimensional environments, switching between locomotion modes when necessary. <s> BIB008 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this article we present a mathematical model of a spincopter - an inherently stable and easy to control unmanned aerial vehicle (UAV). Although the devised model represents only the first approximation of spincopter's physics, it captures basic phenomena that are sufficient for derivation and testing of a simple control algorithm. Results obtained by simulations in Simulink®, presented herein, demonstrate efficient performance of the proposed simple controller structure. Further tests, including investigation of complex aerodynamics effects and hardware-specified limitations, have been done using X-Plane® software package. Finally, the proposed controller has been tested experimentally. Both, X-Plane® and experimental results confirmed the outcome from Simulink®. <s> BIB009 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This article presents a survey on publicly available open-source projects (OSPs) on quadrotor unmanned aerial vehicles (UAVs). Recently, there has been increasing interest in quadrotor UAVs. Exciting videos have been published on the Internet by many research groups and have attracted much attention from the public [1][7]. Relatively simple structures of quadrotors has promoted interest from academia, UAV industries, and radio-control (RC) hobbyists alike. Unlike conventional helicopters, swashplates, which are prone to failure without constant maintenance, are not required. Furthermore, the diameter of individual rotors can be reduced as a result of the presence of four actuators [8]. <s> BIB010 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Recently, there has been increased interest in the development of autonomous flying vehicles. However, as most of the proposed approaches are suitable for outdoor operation, only a few techniques have been designed for indoor environments, where the systems cannot rely on the Global Positioning System (GPS) and, therefore, have to use their exteroceptive sensors for navigation. In this paper, we present a general navigation system that enables a small-sized quadrotor system to autonomously operate in indoor environments. To achieve this, we systematically extend and adapt techniques that have been successfully applied on ground robots. We describe all algorithms and present a broad set of experiments, which illustrate that they enable a quadrotor robot to reliably and autonomously navigate in indoor environments. <s> BIB011 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We study the problem of designing dynamically feasible trajectories and controllers that drive a quadrotor to a desired state in state space. We focus on the development of a family of trajectories defined as a sequence of segments, each with a controller parameterized by a goal state or region in state space. Each controller is developed from the dynamic model of the robot and then iteratively refined through successive experimental trials in an automated fashion to account for errors in the dynamic model and noise in the actuators and sensors. We show that this approach permits the development of trajectories and controllers enabling such aggressive maneuvers as flying through narrow, vertical gaps and perching on inverted surfaces with high precision and repeatability. <s> BIB012 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this work we consider the problem of controlling a team of micro-aerial vehicles moving quickly through a three-dimensional environment while maintaining a tight formation. The formation is specified by shape vectors which prescribe the relative separations and bearings between the robots. To maintain the desired shape, each robot plans its trajectory independently based on its local information of other robot plans and estimates of states of other robots in the team. We explore the interaction between nonlinear decentralized controllers, the fourth-order dynamics of the individual robots, time delays in the network, and the effects of communication failures on system performance. Simulations as well as an experimental evaluation of our approach on a team of quadrotors suggests that suitable performance is maintained as the formation motions become increasingly aggressive and as communication degrades. <s> BIB013 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents a method for enabling a fleet of circularly arranged quadrocopters to throw and catch balls with a net. Based on a first-principles model of the net forces, nominal inputs for all involved vehicles are derived for arbitrary target trajectories of the net. Two algorithms that generate open-loop trajectories for throwing and catching a ball are also introduced. A set of throws and catches is demonstrated in the ETH Zurich Flying Machine Arena testbed. <s> BIB014 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> A full-state feedback controller is proposed to ful ll the requirements for ying an indoor holonomic airship. The airship is a custom-design spherical blimp actuated by 6 propellers in a symmetric arrangement. It is capable of general translational and rotational motion. A continuous tracker is designed to follow an arbitrary reference trajectory by employing the continuous version of the linear quadratic regulator (CLQR) in nite time. The controller is implemented and tested on the airship for tracking a rectangular trajectory in a laboratory setting. With little computation cost, the CLQR controller achieves signi cant improvement in terms of overshoot and attitude tracking error when compared to a standard proportional-derivative controller. To provide state information to the controller, an unscented Kalman lter is used to fuse information from a Vicon motion capture system and an on-board inertial measurement unit. The lter design is combined with the CLQR and this dynamic feedback controller is tested on the airship for the same rectangular trajectory. The use of sensor fusion and ltering leads to a signi cant reduction in actuator e ort. <s> BIB015 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper, we describe a system that enables a low-cost quadrocopter coupled with a ground-based laptop to navigate autonomously in previously unknown and GPS-denied environments. Our system consists of three components: a monocular SLAM system, an extended Kalman filter for data fusion and state estimation and a PID controller to generate steering commands. Next to a working system, the main contribution of this paper is a novel, closed-form solution to estimate the absolute scale of the generated visual map from inertial and altitude measurements. In an extensive set of experiments, we demonstrate that our system is able to navigate in previously unknown environments at absolute scale without requiring artificial markers or external sensors. Furthermore, we show (1) its robustness to temporary loss of visual tracking and significant delays in the communication process, (2) the elimination of odometry drift as a result of the visual SLAM system and (3) accurate, scale-aware pose estimation and navigation. <s> BIB016 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Exertion activities, such as jogging, provide many health benefits, but exercising on your own can be considered disengaging. We present our system 'Joggobot', a flying robot accompanying joggers. Our design process revealed preliminary insights into how to design robots for exertion and how to address emerging design challenges. We summarize these insights into the four themes: 'embodiment', 'control', 'personality' and 'communication', which mark initial starting points towards understanding how to design robots for exertion activities. We hope our work guides and inspires designers when facilitating the benefits of exertion through robots. <s> BIB017 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This research constitutes an initial investigation into key issues which arise in designing a flying humanoid robot (FHR), with a focus on human-robot interaction (HRI). The humanoid form offers an interface for natural communication; flight offers excellent mobility. Combining both will yield companion robots capable of approaching, accompanying, and communicating naturally with humans in difficult environments. Problematic is how such a robot should best fly around humans, and what effect a robot's flight will have on a person in terms of non-verbal communicative cues. To answer these questions, we propose an extension to existing proxemics theory (“z-proxemics”) and predict how typical humanoid flight motions will be perceived (“z-kinesics”). Data obtained from participants watching animated sequences are analyzed to check our predictions. The paper also reports on the building of a flying humanoid robot, which we will use in interactions. <s> BIB018 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents Skye, a novel blimp design. Skye is a helium-filled sphere of diameter 2.7m with a strong inelastic outer hull and an impermeable elastic inner hull. Four tetrahedrally-arranged actuation units (AU) are mounted on the hull for locomotion, with each AU having a thruster which can be rotated around a radial axis through the sphere center. This design provides redundant control in the six degrees of freedom of motion, and Skye is able to move omnidirectionally and to rotate around any axis. A multi-camera module is also mounted on the hull for capture of aerial imagery or live video stream according to an `eyeball' concept - the camera module is not itself actuated, but the whole blimp is rotated in order to obtain a desired camera view. Skye is safe for use near people - the double hull minimizes the likelihood of rupture on an unwanted collision; the propellers are covered by grills to prevent accidental contact; and the blimp is near neutral buoyancy so that it makes only a light impact on contact and can be readily nudged away. The system is portable and deployable by a single operator - the electronics, AUs, and camera unit are mounted externally and are detachable from the hull during transport; operator control is via an intuitive touchpad interface. The motivating application is in entertainment robotics. Skye has a varied motion vocabulary such as swooping and bobbing, plus internal LEDs for visual effect. Computer vision enables interaction with an audience. Experimental results show dexterous maneuvers in indoor and outdoor environments, and non-dangerous impacts between the blimp and humans. <s> BIB019 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Quadrocopters exhibit complex high-speed fight dynamics, and the accurate modeling of these dynamics has proven diffcult. Due to the use of simplifed models in the design of feedback control algorithms, the execution of highperformance fight maneuvers under pure feedback control typically leads to large tracking errors. This paper investigates an iterative learning scheme aimed at the non-causal compensation of repeatable trajectory tracking errors over the course of multiple executions of periodic maneuvers. The learning is carried out in the frequency domain and uses a simplifed model of the closed-loop dynamics of quadrocopter and feedback controller. The resulting algorithm requires little computational power and memory, and its convergence is shown for the nominal model. This paper further introduces a time-scaling method that allows the initial learning to occur at reduced speeds, thus extending the applicability of the algorithm for high performance maneuvers. The presented algorithms are validated in experiments, with a quadrocopter fying a fgure-eight maneuver at high speed. <s> BIB020 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We present the design of a system that allows quadrocopters to balance an inverted pendulum, throw it into the air, and catch and balance it again on a second vehicle. Based on first principles models, a launch condition for the pole is derived and used to design an optimal trajectory to throw the pole towards a second quadrocopter. An optimal catching instant is derived and the corresponding position is predicted by simulating the current position and velocity estimates forward in time. An algorithm is introduced that generates a trajectory for moving the catching vehicle to the predicted catching point in real time. By evaluating the pole state after the impact, an adaptation strategy adapts the catch maneuver such that the pole rotates into the upright equilibrium by itself. Experimental results demonstrate the performance of the system. <s> BIB021 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper introduces a method for carrying a flexible payload with multiple attached flying vehicles. A model for a particular class of flexible structures is presented, and an estimator is derived that observes the pose of the structure in space as well as the magnitude of some characteristic deformation modes. A control strategy that controls the flexible payload to a desired pose while also controlling the deformations to zero is introduced. The presented methods are validated in the ETH Zurich Flying Machine Arena by flying with a thin, flexible ring that is carried by six quadrocopters. <s> BIB022 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents a multi-field universal vehicle that is able to work at land, sea and air. The vehicle consists of a quad-copter with variable-pitch propellers that enable the vehicle to stand on the ground at a given tilt angle, roll on the ground like a wheel, and float and move on the water, in addition to flying like a conventional quad-copter. This article clarifies the behavioral objectives, structural design, basic control mechanism of the ring-shaped robot, and examples of 3D measurements. <s> BIB023 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper details the design, modeling, and experimental validation of a novel mobile robot capable of both aerial and terrestrial locomotion. Flight is achieved through a quadrotor configuration; four actuators provide the required thrust. Adding a rolling cage to the quadrotor makes terrestrial locomotion possible using the same actuator set and control system. Thus, neither the mass nor the system complexity is increased by inclusion of separate actuators for terrestrial and aerial locomotion. An analysis of the system's energy consumption demonstrates that during terrestrial locomotion, the robot only needs to overcome rolling resistance and consumes much less energy compared to the aerial mode. This solves one of the most vexing problems of quadrotors and rotorcraft in general - their short operation time. Experimental results show that the hybrid robot can travel a distance four times greater and operate almost six times longer than an aerial only system. It also solves one of the most challenging problems in terrestrial robot design - obstacle avoidance. When an obstacle is encountered, the system simply flies over it. <s> BIB024 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper describes an integrated navigation sensor module, including a camera, a laser scanner, and an inertial sensor, for unmanned aerial vehicles (UAVs) to fly both indoors and outdoors. The camera and the gimbaled laser sensor work in a complementary manner to extract feature points from the environment around the vehicle. The features are processed using an online extended Kalman filter (EKF) in simultaneous localization and mapping (SLAM) algorithm to estimate the navigational states of the vehicle. In this paper, a new method is proposed for calibrating a camera and a gimbaled laser sensor. This calibration method uses a simple visual marker to calibrate the camera and the laser scanner with each other. We also propose a real-time navigation algorithm based on the EKF SLAM algorithm, which is suitable for our camera-laser sensor package. The algorithm merges image features with laser range data for state estimation. Finally, these sensors and algorithms are implemented on our octo-rotor UAV platform and the result shows that our onboard navigation module can provide a real-time three-dimensional navigation solution without any assumptions or prior information on the surroundings. <s> BIB025 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Most existing robots are designed to exploit only one single locomotion mode, such as rolling, walking, flying, swimming, or jumping, which limits their flexibility and adaptability to different environments where specific and different locomotion capabilities could be more effective. Here we introduce the concept and the design of a flying robot with Adaptive Morphology for Multi-Modal Locomotion. We present a prototype that can use its wings to walk on the ground and fly forward. The wings are used as whegs to move on rough terrains. This solution allows to minimize the structural mass of the robot by reusing the same structure (here the wings) for different modes of locomotion. Furthermore, the morphology of the robot is analysed and optimized for ground speed. <s> BIB026 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents a novel approach for constructing light-weight, low-cost air-deployable sensor modules and miniature unmanned aerial vehicles which consist of printed circuit boards as integrated electronic, structural and aerodynamic lift-producing devices. In this way, each aircraft can be a single-piece, single-manufacturing step assembly, reducing materials, processing and labour costs. This approach allows the fabrication of devices that are sufficiently inexpensive so as to be economic for single-use or disposable applications, such as long-range sensor deployment for environmental monitoring. We present two example low-cost, proof-of-concept aircraft employing electro-aeromechanical structures - rotary-wing and fixed-wing - and demonstrate their flight performance. <s> BIB027 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents an open-source indoor navigation system for quadrotor micro aerial vehicles (MAVs), implemented in the ROS framework. The system requires a minimal set of sensors including a planar laser range-finder and an inertial measurement unit. We address the issues of autonomous control, state estimation, path-planning, and teleoperation, and provide interfaces that allow the system to seamlessly integrate with existing ROS navigation tools for 2D SLAM and 3D mapping. All components run in real time onboard the MAV, with state estimation and control operating at 1 kHz. A major focus in our work is modularity and abstraction, allowing the system to be both flexible and hardware-independent. All the software and hardware components which we have developed, as well as documentation and test data, are available online. <s> BIB028 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Autonomous navigation for large Unmanned Aerial Vehicles (UAVs) is fairly straight-forward, as expensive sensors and monitoring devices can be employed. In contrast, obstacle avoidance remains a challenging task for Micro Aerial Vehicles (MAVs) which operate at low altitude in cluttered environments. Unlike large vehicles, MAVs can only carry very light sensors, such as cameras, making autonomous navigation through obstacles much more challenging. In this paper, we describe a system that navigates a small quadrotor helicopter autonomously at low altitude through natural forest environments. Using only a single cheap camera to perceive the environment, we are able to maintain a constant velocity of up to 1.5m/s. Given a small set of human pilot demonstrations, we use recent state-of-the-art imitation learning techniques to train a controller that can avoid trees by adapting the MAVs heading. We demonstrate the performance of our system in a more controlled environment indoors, and in real natural forest environments outdoors. <s> BIB029 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We present a vision based control strategy for tracking and following objects using an Unmanned Aerial Vehicle. We have developed an image based visual servoing method that uses only a forward looking camera for tracking and following objects from a multi-rotor UAV, without any dependence on GPS systems. Our proposed method tracks a user specified object continuously while maintaining a fixed distance from the object and also simultaneously keeping it in the center of the image plane. The algorithm is validated using a Parrot AR Drone 2.0 in outdoor conditions while tracking and following people, occlusions and also fast moving objects; showing the robustness of the proposed systems against perturbations and illumination changes. Our experiments show that the system is able to track a great variety of objects present in suburban areas, among others: people, windows, AC machines, cars and plants. <s> BIB030 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper, we present an approach that allows a quadrocopter to follow a person and to recognize simple gestures using an onboard depth camera. This enables novel applications such as hands-free filming and picture taking. The problem of tracking a person with an onboard camera however is highly challenging due to the self-motion of the platform. To overcome this problem, we stabilize the depth image by warping it to a virtual-static camera, using the estimated pose of the quadrocopter obtained from vision and inertial sensors using an Extended Kalman filter. We show that such a stabilized depth video is well suited to use with existing person trackers such as the OpenNI tracker. Using this approach, the quadrocopter not only obtains the position and orientation of the tracked person, but also the full body pose - which can then for example be used to recognize hand gestures to control the quadrocopter's behaviour. We implemented a small set of example commands (“follow me”, “take picture”, “land”), and generate corresponding motion commands. We demonstrate the practical performance of our approach in an extensive set of experiments with a quadrocopter. Although our current system is limited to indoor environments and small motions due to the restrictions of the used depth sensor, it indicates that there is large potential for such applications in the near future. <s> BIB031 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents the design and control of a multirotor-based aerial manipulator developed for outdoor operation. The multi-rotor has eight rotors and large payload to integrate a 7-degrees of freedom arm and to carry sensors and processing hardware needed for outdoor positioning. The arm can also carry an end-effector and sensors to perform different missions. The paper focuses on the control design and implementation aspects. A stable backstepping-based controller for the multirotor that uses the coupled full dynamic model is proposed, and an admittance controller for the manipulator arm is outlined. Several experimental tests with the aerial manipulator are also presented. In one of the experiments, the performance of the pitch attitude controller is compared to a PID controller. Other experiments of the arm controller following an object with the camera are also presented. <s> BIB032 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper, we address the attitude and vertical stabilization problem for small-scale helicopters. An emergency controller that would successfully stabilize the helicopter in a safe flight mode when a pilot/autopilot fails to control it, owing to unexpected reasons, is of outmost importance in flight control systems. In this direction, we propose a low complexity nonlinear control scheme that drives the angles and the vertical speed to zero with prescribed transient and steady state response, without incorporating any knowledge of the dynamic model parameters in the control design. The stereographic coordinates were employed to model the attitude state of the helicopter in an attempt to guarantee the safe stabilization for every possible initial orientation without introducing any representation singularities as in the Euler angles representation or increasing complexity as in conventional four element quaternions. Moreover, the transient and steady state performance of the proposed scheme is a priori determined even in the presence of external disturbances. Furthermore, the overall control scheme can be easily implemented on embedded flight systems equipped with low-cost sensors. Finally, simulation and experimental results on a realistic platform verify the efficacy of the proposed method. <s> BIB033 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We describe an algorithm and hardware system of a 3D self-localization method for very cost effective hovering robots. The hardware system consists of very compact calculation and sensor units, instead of using a high performance calculation unit like a laptop PC. In the experiment, the comparison with the ground truth sensor is discussed and implementation of the system on a palm-sized quad-copter is studied to realize a very compact, on-board, fully autonomous quad-copter. <s> BIB034 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In navigation tasks, mobile robots often have to deal with substantial uncertainty due to imperfect actuators and noisy sensor measurements. In this paper, we consider the problem of online trajectory generation for safe navigation in the presence of state uncertainty and the resulting deviations from the desired trajectory. Our approach combines probabilistic estimation of the a priori collision risk with efficient trajectory generation, exploiting the differential flatness of many robotic systems in an explicitly constrained polynomial trajectory representation. Through trajectory optimization, our approach allows to flexibly trade off risk against, for example, the duration of the trajectory. It is computationally efficient because each optimization step has polynomial complexity. In contrast to other approaches, our method can also optimize the trajectory duration and supports cost functions that facilitate higher-order smoothness of the trajectory. Our experiments demonstrate the performance of the approach and show that our trajectories result in substantially lower collisions probabilities compared to minimum-snap trajectories in a quadrotor landing task. <s> BIB035 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Balls are the most popular equipment for sports. To play with balls, certain physical methods, or "vocabularies," such as throwing, hitting, spinning, or kicking have been developed by reflecting the fact that balls obey physical dynamics. This feature forms the foundation of ball-based sports; however, we consider that it limits the possibility of such sports. For instance, the speed of balls could be considerably fast for small children, senior people, or people with physical disabilities. In this paper, we propose a flying ball based on quadcopter technology. This ball has the ability hover and to change its location and behavior based on the context of the sport or game. With this technology, the physical dynamics of a ball can be re-programmed by sports designers, and new ball-playing vocabularies, such as hovering, anti-gravity, proximity, or remote manipulation, can be introduced to extend the method in which people interact with balls. In this paper, we introduce this concept as a method of augmenting sports, and present our initial flying ball system that consists of a grid shell that comprises a micro quadcopter, and demonstrates new sports interactions with the ball. <s> BIB036 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents an aerial manipulator consisting of a multirotor equipped with a robotic multi-link arm attached to the top of the multirotor body. This setup has strong potentialities for inspection of structures, since the arm is able to safely touching the structure surface with a sensor while flying, taking measurements from the underside for example in bridges. The paper presents the dynamic model of the system and the derivation of a nonlinear controller, which is tested in simulation. First flight experiments with prototype of the system are also presented. <s> BIB037 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> This paper presents a trajectory tracking control strategy based on the subspace stabilization approach to accurately manipulate an under-actuated flying robot from a known initial state to the desired terminal state. To facilitate the development of this tracking strategy, the dynamical model of the quadrotor is firstly proposed. Subsequently, an optimal trajectory generation algorithm is adopted to generate dynamically consistent trajectories regarding the initial and terminal state constraints in specific missions. Then, a trajectory tracking control strategy based on the subspace stabilization approach is developed considering the lumped disturbances and time delays. The developed control strategy is applied for ball juggling of a highly under-actuated quadrotor, which is a popular flying robot in recent years. Real-time experimental results show that the quadrotor can be accurately manipulated from a known initial state to the desired terminal state within a given time horizon. In the consecutive juggling tasks, the quadrotor with a racket of radius 0.065 m can consecutively juggle the ball for averagely 4 hits in each rally, and a longest rally achieved by the developed control strategy is 14 hits. The feasibility of the developed control strategy is also preliminarily verified through the cooperative juggling between two quadrotors. All of these results demonstrate the effectiveness of the developed control strategy. <s> BIB038 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Autonomous, vision-based quadrotor flight is widely regarded as a challenging perception and control problem since the accuracy of a flight maneuver is strongly influenced by the quality of the on-board state estimate. In addition, any vision-based state estimator can fail due to the lack of visual information in the scene or due to the loss of feature tracking after an aggressive maneuver. When this happens, the robot should automatically re-initialize the state estimate to maintain its autonomy and, thus, guarantee the safety for itself and the environment. In this paper, we present a system that enables a monocular-vision-based quadrotor to automatically recover from any unknown, initial attitude with significant velocity, such as after loss of visual tracking due to an aggressive maneuver. The recovery procedure consists of multiple stages, in which the quadrotor, first, stabilizes its attitude and altitude, then, re-initializes its visual state-estimation pipeline before stabilizing fully autonomously. To experimentally demonstrate the performance of our system, we aggressively throw the quadrotor in the air by hand and have it recover and stabilize all by itself. We chose this example as it simulates conditions similar to failure recovery during aggressive flight. Our system was able to recover successfully in several hundred throws in both indoor and outdoor environments. <s> BIB039 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Unmanned aerial vehicles (UAVs) such as multicopters are expected to be used for inspection of aged infrastructure or for searching damaged buildings in the event of a disaster. However, in a confined space in such environments, UAVs suffer a high risk of falling as a result of contact with an obstacle. <s> BIB040 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Building a high-end aerial robot for research is a challenging task. Our aim in this paper is to design a compact hexacopter capable of high payload and has flexible gimbal and powerful onboard computer with $ 500. This hexacopter serves as a flying platform with great customizability, where different sensors can be mounted easily onto the hexacopter for new applications. We discuss our implementation details and preliminary insights during the development process. In addition, we also present our approach on designing a compact gimbal for two cameras, a lidar, and an ultrasonic sensor. Our latest design of gimbal is easy to customize and replicate. <s> BIB041 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <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> BIB042 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> We present the design and implementation of a small Vertical-Take-Off-and-Landing (VTOL) aircraft. The vehicle requires minimal additional components to achieve the hover capability and is thus very efficient in forward flight. We improve over the state of the art by using a single controller in all flight modes without using blending between hover condition and fixed wing controllers or gain scheduling. We present a compact airflow estimation model for VTOL airframes which rely on the slipstream across control surfaces for hover attitude control. Furthermore we show attitude and position control results in simulation. Finally we show outdoor flight experiments validating our simulation results. <s> BIB043 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this work, we examine two design modifications to a tethered motor-driven flapping-wing system. Previously, we had demonstrated a simple mechanism utilizing a linear transmission for resonant operation and direct drive of the wing flapping angle for control. The initial two-wing system had a weight of 2.7 grams and a maximum lift-to-weight ratio of 1.4. While capable of vertical takeoff, in open-loop flight it demonstrated instability and pitch oscillations at the wing flapping frequency, leading to flight times of only a few wing strokes. Here the effect of vertical wing offset as well as an alternative multi-wing layout is investigated and experimentally tested with newly constructed prototypes. With only a change in vertical wing offset, stable open-loop flight of the two-wing flapping system is shown to be theoretically possible, but difficult to achieve with our current design and operating parameters. Both of the new two and four-wing systems, however, prove capable of flying to the end of the tether, with the four-wing system prototype eliminating disruptive wing beat oscillations. <s> BIB044 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper, we present a monocular visual-inertial odometry algorithm which, by directly using pixel intensity errors of image patches, achieves accurate tracking performance while exhibiting a very high level of robustness. After detection, the tracking of the multilevel patch features is closely coupled to the underlying extended Kalman filter (EKF) by directly using the intensity errors as innovation term during the update step. We follow a purely robocentric approach where the location of 3D landmarks are always estimated with respect to the current camera pose. Furthermore, we decompose landmark positions into a bearing vector and a distance parametrization whereby we employ a minimal representation of differences on a corresponding σ-Algebra in order to achieve better consistency and to improve the computational performance. Due to the robocentric, inverse-distance landmark parametrization, the framework does not require any initialization procedure, leading to a truly power-up-and-go state estimation system. The presented approach is successfully evaluated in a set of highly dynamic hand-held experiments as well as directly employed in the control loop of a multirotor unmanned aerial vehicle (UAV). <s> BIB045 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper we present a new real-time image-based localization method for scenes that have been reconstructed offline using structure from motion. From input video, our method continuously computes six-degree-of-freedom camera pose estimates by efficiently tracking natural features and matching them to 3D points reconstructed by structure from motion. Our main contribution lies in efficiently interleaving a fast keypoint tracker that uses inexpensive binary feature descriptors with a new approach for direct 2D-to-3D matching. Our 2D-to-3D matching scheme avoids the need for online extraction of scale-invariant features. Instead, offline we construct an indexed database containing multiple DAISY descriptors per 3D point extracted at multiple scales. The key to the efficiency of our method is invoking DAISY descriptor extraction and matching sparingly during localization, and in distributing this computation over a temporal window of successive frames. This enables the system to run in real-time and achieve low per-frame latency over long durations. Our algorithm runs at over 30 Hz on a laptop and at 12 Hz on a low-power computer suitable for onboard computation on a mobile robot such as a micro-aerial vehicle. We have evaluated our method using ground truth and present results on several challenging indoor and outdoor sequences. <s> BIB046 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> The fusion of IMU and RGB-D sensors presents an interesting combination of information to achieve autonomous localization and mapping using robotic platforms such as ground robots and flying vehicles. In this paper, we present a software framework for cooperative localization and mapping while simultaneously using multiple aerial platforms. We employ a monocular visual odometry algorithm to solve the localization task, where the depth data flow associated to the RGB image is used to estimate the scale factor associated with the visual information. The current framework enables autonomous onboard control of each vehicle with cooperative localization and mapping. We present a methodology that provides both a sparse map generated by the monocular SLAM and a multiple resolution dense map generated by the associated depth. The localization algorithm and both 3D mapping algorithms work in parallel improving the system real-time reliability. We present experimental results to show the effectiveness of the proposed approach using two quadrotors platforms. <s> BIB047 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> In this paper, we describe trajectory planning and state estimation algorithms for aggressive flight of micro aerial vehicles in known, obstacle-dense environments. Finding aggressive but dynamically feasible and collision-free trajectories in cluttered environments requires trajectory optimization and state estimation in the full state space of the vehicle, which is usually computationally infeasible on realistic timescales for real vehicles and sensors. We first build on previous work of van Nieuwstadt and Murray and Mellinger and Kumar, to show how a search process can be coupled with optimization in the output space of a differentially flat vehicle model to find aggressive trajectories that utilize the full maneuvering capabilities of a quadrotor. We further extend this work to vehicles with complex, Dubins-type dynamics and present a novel trajectory representation called a ?Dubins-Polynomial trajectory?, which allows us to optimize trajectories for fixed-wing vehicles. To provide accurate state estimation for aggressive flight, we show how the Gaussian particle filter can be extended to allow laser rangefinder localization to be combined with a Kalman filter. This formulation allows similar estimation accuracy to particle filtering in the full vehicle state but with an order of magnitude more efficiency. We conclude with experiments demonstrating the execution of quadrotor and fixed-wing trajectories in cluttered environments. We show results of aggressive flight at speeds of up to 8 m/s for the quadrotor and 11 m/s for the fixed-wing aircraft. <s> BIB048 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Jogging is a popular exertion activity. The abundance of jogging apps suggests to us that joggers can appreciate the opportunity for technology to support the jogging experience. We want to take this investigation a step further by exploring if, and how, robotic systems can support the jogging experience. We designed and built a flying robotic system, a quadcopter, as a jogging companion and studied its use with 13 individual joggers. By analyzing their experiences, we derived three design dimensions that describe a design space for flying robotic jogging companions: Perceived Control, Focus and Bodily Interaction. Additionally, we articulate a series of design tactics, described by these dimensions, to guide the design of future systems. With this work we hope to inspire and guide designers interested in creating robotic systems to support exertion experiences. <s> BIB049 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> C. UAV Topics Distribution <s> Visual Odometry is a key technology for robust and accurate navigation of unmanned aerial vehicles in a number of low altitude applications <120 m, particularly in environments where access to a global positioning system is possible, but not guaranteed. Navigating via vision alone reduces dependence on a global positioning system and other global navigation satellite systems, enhancing navigation robustness even in the presence of jamming, spoofing or long dropouts. To date, however, most demonstrations of visual odometry are in close proximity to the ground or other structures and are often implemented as a monocular camera combined with inertial sensing, rather than vision alone, to account for scale drift. Stereo visual odometry has received little attention for applications beyond 30 m altitude due to the generally poor performance of stereo rigs for these extremely small baseline-to-depth ratios, otherwise termed long-range stereo. This paper demonstrates stereo visual pose estimation at altitudes of up to 120 m above ground level on a small fixed-wing unmanned aerial vehicle by adapting the traditional stereo visual odometry paradigm to explicitly account for inaccurate triangulation and poorly observed scale from the stereo baseline. In addition, issues related to long-range stereo such as biased sensing are investigated to justify the approach, and a novel bundle adjustment algorithm is presented capable of handling vibration induced structural deformation between the cameras. This is achieved by continually optimizing the stereo transform within a set of inequality bounds. Results are presented demonstrating the algorithm on field-gathered data from a 2 m wingspan fixed-wing unmanned aerial vehicle flying at 30-120 m altitude over a 6.5 km trajectory. <s> BIB050
Table II summarizes the top twenty-five keywords in the surveyed UAV papers. From Table II , we note that system modeling and control papers are the most frequent keywords. This is not surprising, as most UAVs require system modeling for dynamic control. It has been shown that a simple modelfree PID controller is good enough for the basic maneuvers of a UAV BIB010 , BIB011 - BIB019 . For aggressive maneuvers BIB012 , BIB020 or more complex dynamics with onboard manipulators BIB037 , BIB032 , dynamic models are normally employed. With a precision indoor positioning system, current state-of-the-art methods have successfully demonstrated formation flights BIB013 , flying inverted pendulum BIB007 , pole acrobatics BIB021 , ball juggling BIB038 , cooperative operation BIB014 - BIB022 , and failure recovery BIB039 . From Table II , we can also observe that there are large amount of hardware development papers since 2001, including papers on quadcopters BIB010 , BIB011 , BIB023 , BIB024 , BIB040 , hexacopters BIB041 -  , octocopters BIB025 - BIB004 , coaxial helicopters BIB002 , BIB005 - BIB003 , a helicopter BIB033 , a tandem helicopter BIB001 , a bicopter BIB042 , a trirotor UAV  , fixedwing UAV BIB043 , BIB026 , flapping-wing UAV BIB044 - BIB008 , cyclocopter BIB027 , BIB009 , and blimp UAVs BIB019 , BIB015 . In recent years, researchers focus on higher level tasks such as navigation and task planning in UAVs BIB028 - BIB016 . In addition, researchers also pay attention to visual odometry BIB050 , BIB045 , localization BIB046 - BIB034 , and mapping BIB006 - BIB047 applications of UAVs. More recently, researchers work on obstacle or collision avoidance BIB048 - BIB035 , which are important topics for UAVs. Current state-of-the-art UAVs could perform robust image-based six Degrees-of-Freedom (DoF) localization BIB046 , cooperate mapping BIB006 , aggressive flight in dense indoor environment BIB048 , and flying through a forest autonomously BIB029 . More recently, researchers also focus on HRI and teleoperation of UAVs, including jogging UAVs BIB017 , BIB049 , a flying humanoid robot BIB018 , a hand-sized hovering ball BIB036 , and various human-following UAVs BIB030 - BIB031 .