Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <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> BIB001 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> The small rotor sizes of quadrotors and multirotors makes them intrinsically less energy efficient than a traditional helicopter with a large single rotor. However, the quadrotor configuration's innate simplicity and inexpensive construction recommends its use in many aerial robotics applications. We present a four-rotor configuration that merges the simplicity of a quadrotor with the energy efficiency of a helicopter, while improving manoeuvering rotor bandwidth. This class of aircraft, called a `Y4' or `triangular quadrotor', consists of a single fixed-pitch main rotor with three smaller rotors on booms that provide both counter-torque and manoeuvering control. Our analysis indicates that a Y4 may provide a 20 per cent reduction in hovering power required, compared with a similarly sized conventional quadrotor. Using a matched pair of quadrotor/triangular quadrotor aircraft, our preliminary experiments show that the test-bed Y4 used 15 per cent less power, without optimisation. We present a dynamic model and demonstrate experimentally that the aircraft can be stabilised in flight with PID control. <s> BIB002 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> We present a modular and extensible approach to integrate noisy measurements from multiple heterogeneous sensors that yield either absolute or relative observations at different and varying time intervals, and to provide smooth and globally consistent estimates of position in real time for autonomous flight. We describe the development of algorithms and software architecture for a new 1.9kg MAV platform equipped with an IMU, laser scanner, stereo cameras, pressure altimeter, magnetometer, and a GPS receiver, in which the state estimation and control are performed onboard on an Intel NUC 3rd generation i3 processor. We illustrate the robustness of our framework in large-scale, indoor-outdoor autonomous aerial navigation experiments involving traversals of over 440 meters at average speeds of 1.5 m/s with winds around 10 mph while entering and exiting buildings. <s> BIB003 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> This paper proposes a methodology for visual tracking of a dynamic generalized subject within an unknown map, by relying on its perception as a separate entity which can be distinguished spatially and visually from its environment. To this purpose, a 3D-representation of the visible scenery is examined, and the subject is spatially identified by its externally viewed hull via a mesh-connection algorithm aided by visual cues, and visually identified by distinct feature tracking based on an incrementally built list of key-aspects. These two processes operate in closed-loop, and employing a set of assumptions regarding the subject's structural/temporal invariance the tracking health state can be determined. This work additionally presents the framework for the deployment of this scheme for autonomous aerial robotic subject tracking, employing the dynamic subject/environment distinction to obtain knowledge of the environment structure, and collision-free trajectory generation algorithms to achieve mobile tracking. <s> BIB004 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> This paper details an autonomous perching and take-off method for a quadrotor micro air vehicle (MAV) using a novel dry adhesive gripper on smooth vertical walls. The gripper mechanism uses three directional dry adhesive pads in a triangular configuration. Each pad is equipped with a force sensor that can detect the pad's loading condition. A servo motor is used to actuate the attachment and detachment of the gripper, which is mounted in the front of a quadrotor MAV. This makes perching possible by simply flying toward and hitting the target surface. Autonomous control is made possible using a Microsoft Kinect to localize the MAV and a PID controller to control the perching maneuver. Experiments show that a minimum speed of 0.4m/s is required to guarantee a successful perch. Also, in 93% of the experiments in which the MAV hits the target at a speed higher than 0.4m/s, the perching maneuver is successful. To initiate a take-off procedure, a release signal is sent to the servo and the gripper is detached from the wall by pulling the adhesive away from the surface. Once the gripper is detached, the MAV becomes airborne again and the control system stabilizes the flight. <s> BIB005 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> Unmanned multirotor helicopters have been expected for various critical tasks such as rescue missions, and it is important to sense the environment to achieve those tasks. In order to realize such sensor systems, this paper considers acoustic information recognition from a hovering helicopter which a microphone array system. As the noise of rotors distorts the acoustic information, noise reduction is necessary. Since the rotor noise varies even at the hovering flight, an acoustic model of the rotor noise is derived taking the dynamics of the helicopter into account, and the model is utilized to evaluate the performance of the microphone array. The proposed approach was verified by evaluating the optimality of a real device that was empirically tuned in authors previous work, and the computed configuration of the microphone array and the developed one coincide well, which ensures the validity of the approach. As the validation through a practical application, the signal was processed by Delay-and-Sum Beam Former to localize the sound source. The system was able to find peaks of the power that corresponded to the sound source. <s> BIB006 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> Scaling down the size and mass of micro aerial vehicles (MAVs) increases their agility and their ability to operate in tight formations. In addition, smaller robots are safer and, as we will show in this paper, more robust to collisions. This paper addresses the development of a pico quadrotor measuring 11 cm from tip to tip, with a mass of 25g. To increase the robustness of the robot to collisions, the vehicle is equipped with a 2 gram carbon fiber cage that protects it from impact velocities in excess of 4 m/s and also permits recovery after collisions. We present the design of the electrical, mechanical and computational elements, as well as experimental results demonstrating trajectory following with feedback from an external motion camera system, recovery from collisions with walls and other robots, and formation flight. <s> BIB007 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> Quad tilt rotor Unmanned Aerial Vehicle (UAV) solves the problem of underacuated system in general quadrotor UAV. The quad tilt rotor UAV can control position and attitude independently by tilting directions of propellers. However, the flight control system in a wide range of attitudes has not been discussed yet, e.g. a UAV flying and hovering with a 90 [°] pitch angle and can flip over when the range of the tilting motor rotates wide enough. In this paper, we present the attitude transition flight control system for pitch angles ranging 0 [°] to 90 [°] since flight condition with a 90 [°] pitch angle significantly differs from that in a conventional quadrotor UAV flight, and then adequate control system and sufficient experimental validation are necessary for stable flight in a wide range of attitude conditions. <s> BIB008 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> This paper presents a real-time image restoration method for aerial inspection images that are degraded by the appearance of a passive rotating shell of an unmanned aerial vehicle (UAV). <s> BIB009 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> A. Quadcopters <s> The main contribution of this paper is a high frequency, low-complexity, on-board visual-inertial odometry system for quadrotor micro air vehicles. The system consists of an extended Kalman filter (EKF) based state estimation algorithm that fuses information from a low cost MEMS inertial measurement unit acquired at 200Hz and VGA resolution images from a monocular camera at 50Hz. The dynamic model describing the quadrotor motion is employed in the estimation algorithm as a third source of information. Visual information is incorporated into the EKF by enforcing the epipolar constraint on features tracked between image pairs, avoiding the need to explicitly estimate the location of the tracked environmental features. Combined use of the dynamic model and epipolar constraints makes it possible to obtain drift free velocity and attitude estimates in the presence of both accelerometer and gyroscope biases. A strategy to deal with the unobservability that arises when the quadrotor is in hover is also provided. Experimental data from a real-time implementation of the system on a 50 gram embedded computer are presented in addition to the simulations to demonstrate the efficacy of the proposed system. <s> BIB010
A quadcopter (Fig. 7 (a)-(l) )  , BIB001 , BIB004 - BIB002 is a UAV with four rotors. Papachristos et al. BIB004 first present an autonomous quadcopter (Fig. 7 (a) ) with do-it-yourself (DIY) stereo perception unit that could track a moving target and perform collision-free navigation. With the goal of reducing quadcopter energy consumption, Kalantari et al. BIB005 build a quadcopter ( Fig. 7 (b) ) that uses a novel adhesive gripper to autonomously perch and take-off on smooth vertical walls. Kalantari and Spenko BIB001 build one of the first hybrid quadcopters (Fig. 7 (c) ) that is capable of both aerial and ground locomotion. While this quadcopter can only rotate in one direction, Okada et al. BIB009 present a quadcopter with a gimbal mechanism (Fig. 7 (d) ) that enables the quadcopter to rotate freely in the 3D space. The developed quadcopter is good for inspection applications as the gimbal-like rotating shell helps the quadcopter fly safely in a confined environment with many obstacles. To the best of our knowledge, Shen et al. BIB003 is first to present an autonomous quadcopter (Fig. 7 (e) ) that could fly robustly indoors and outdoors by integrating information from a stereo camera, a 2D lidar sensor, an IMU, a magnetometer, a pressure altimeter, and a GPS sensor. Aiming for application in search and rescue missions, Ishiki and Kumon BIB006 present a quadcopter (Fig. 7 (f) ) that is equipped with a microphone array to perform sound localization. While the hybrid quadcopter shown in Fig. 7 (c) ) BIB001 is designed to roll on flat ground, Latscha et al.  combine a quadcopter with two snake-like mobile robots (Fig. 7 (g) ), which make the resulting hybrid robot able to move effectively in disaster scenarios. To increase the safety and robustness of a swarm of quadcopter, Mulgaonkar et al. BIB007 design a small quadcopter with a mass of merely twenty-five grams (Fig. 7 (h) ). Aiming for higher performance, Oosedo et al. BIB008 develop an unique quadcopter (Fig. 7 (i) ) that could hover stably at various pitch angles with four tiltable propellers. Abeywardena et al. BIB010 present a quadcopter (Fig. 7 (j) ) that uses an extended Kalman filter (EKF) to produce high-frequency odometry by fusing information from an IMU sensor and a monocular camera. Darivianakis et al.  build a quadcopter (Fig. 7 (k) ) that can physically interact with the infrastructures that are being inspected. Driessens and Pounds BIB002 present a "Y4" quadcopter ( Fig. 7 (l) ) that combines the simplicity of a conventional quadcopter and the energy efficiency of a helicopter.