Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> We aim at developing autonomous micro-flyers capable of navigating within houses or small built environments. The severe weight and energy constraints of indoor flying platforms led us to take inspiration from flying insects for the selection of sensors, signal processing, and behaviors. This paper presents the control strategies enabling obstacle avoidance and altitude control using only optic flow and gyroscopic information. For experimental convenience, the control strategies are first implemented and tested separately on a small wheeled robot featuring the same hardware as the targeted aircraft. The obstacle avoidance system is then transferred to a 30-gram aircraft, which demonstrates autonomous steering within a square textured arena. <s> BIB001 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This paper describes a control strategy to stabilize the position of a vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) in wind gusts. The proposed approach takes advantage of the cascade structure of the system to design a hierarchical controller. The idea is to separate the controller in a high level controller devoted to position control and a low level controller devoted to stabilization and attitude control. Both controllers are designed by means of backstepping techniques that allow the stabilization of the vehicle's position while on-line estimation of the unknown aerodynamic forces. The global stability of the connected system is proven, and simulations as well as experimental results are presented <s> BIB002 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <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> BIB003 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This paper presents and compares two different approaches to integrating sensor information from an Inertial Measuring Unit (IMU), Global Positioning System (GPS) receiver and monocular vision camera mounted to a low-flying Unmanned Aerial Vehicle (UAV) for building large-scale 3D terrain reconstructions. Both approaches utilise a statistically optimal bundle adjustment formulation that incorporates Vision, IMU and GPS observations into the map and pose optimisation process. Our first approach employs a novel pose-only formulation that optimises relative camera poses based on vision feature matches between frames, while incorporating IMU and GPS information. Our approach is related to, but differs from existing pose-graph techniques by formulating a set of 1D epipolar constraints for features matched between two camera frames, rather than minimising 4D feature re-projection errors, or marginalising feature states. We compare results of the method to a second approach which estimates both 3D features and poses together, using airborne vision, IMU and GPS data collected in an ecology mapping application. The results demonstrate a reduction in the computational complexity during optimisation for the pose-only approach, while producing equivalent accuracy in the reconstructed 3D terrain map. <s> BIB004 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This paper demonstrates the feasibility of accomplishing real-world inspection tasks beyond visual range with an autonomous helicopter using simple but effective methods. We propose a LIDAR-based perception and guidance system that enables a helicopter to perform obstacle detection and avoidance, terrain following, and close-range inspection. The system has been implemented on board the CSIRO unmanned helicopter and flight tested in a number of different mission scenarios in unknown environments. We have successfully completed 37 missions and recorded more than 14 hours of autonomous flight time. Missions beyond visual range were executed without a backup pilot. The system has achieved a high success rate and has proven to be dependable. <s> BIB005 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <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> BIB006 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <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> BIB007 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> We describe the design of an aerial robot inspired by birds and the underlying theoretical developments leading to novel control and closed-loop guidance algorithms for a perching maneuver. A unique feature of this robot is that it uses wing articulation to control the flight path angle as well as the heading angle. It lacks a vertical tail for improved agility, which results in unstable lateral-directional dynamics. New closed-loop motion planning algorithms with guaranteed stability are obtained by rewriting the flight dynamic equations in the spatial domain rather than as functions of time, after which dynamic inversion is employed. It is shown that nonlinear dynamic inversion naturally leads to proportional-integral-derivative controllers, thereby providing an exact method for tuning the gains. The capabilities of the proposed bioinspired robot design and its novel closed-loop perching controller have been successfully demonstrated with perched landings on a human hand. <s> BIB008 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> Autonomous navigation in obstacle-dense indoor environments is very challenging for flying robots due to the high risk of collisions, which may lead to mechanical damage of the platform and eventual failure of the mission. While conventional approaches in autonomous navigation favor obstacle avoidance strategies, recent work showed that collision-robust flying robots could hit obstacles without breaking and even self-recover after a crash to the ground. This approach is particularly interesting for autonomous navigation in complex environments where collisions are unavoidable, or for reducing the sensing and control complexity involved in obstacle avoidance. This paper aims at showing that collision-robust platforms can go a step further and exploit contacts with the environment to achieve useful navigation tasks based on the sense of touch. This approach is typically useful when weight restrictions prevent the use of heavier sensors, or as a low-level detection mechanism supplementing other sensing modalities. In this paper, a solution based on force and inertial sensors used to detect obstacles all around the robot is presented. Eight miniature force sensors, weighting 0.9g each, are integrated in the structure of a collision-robust flying platform without affecting its robustness. A proof-of-concept experiment demonstrates the use of contact sensing for exploring autonomously a room in 3D, showing significant advantages compared to a previous strategy. To our knowledge this is the first fully autonomous flying robot using touch sensors as only exteroceptive sensors. <s> BIB009 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> Developing models of flapping-winged fliers in free flight is vital for accurate control. The aerodynamics associated with flapping-winged flight are complex. Hence, a look-up table flight force model from wind tunnel data is a practical approach. In this work, we compare the flight of an ornithopter micro aerial vehicle (MAV), using free flight data collected from a Vicon motion capture system, to measured wind tunnel force and moment values. We compare the two data sets at equilibrium as a metric to determine the quality of the wind tunnel flight force estimation. To compare the two data sets, we find the predicted equilibrium angle of attack and velocity for the ornithopter in free flight. For a given flapping frequency and pitch control elevator deflection angle at free flight equilibrium, we compute the level sets at zero for pitch moment, net horizontal force, and net vertical force from the wind tunnel data. We then use the point on the zero moment level set that minimizes the vertical and horizontal force. The angle of attack and velocity at this minimal point are the wind tunnel predicted equilibrium point and are compared to the analogous free flight equilibrium point. We determined that the wind tunnel underestimates the angle of attack of the equilibrium point observed in free flight by 15 degrees, while the equilibrium velocity has an error of 0.1 m/s between the two sets at an average flight speed of 2 m/s. <s> BIB010 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This study describes the design and implementation of several bioinspired algorithms for providing guidance to an ultra-lightweight micro-aerial vehicle (MAV) using a 2.6 g omnidirectional vision sensor. Using this visual guidance system we demonstrate autonomous speed control, centring, and heading stabilisation on board a 30 g MAV flying in a corridorlike environment. In addition to the computation of wide-field optic flow, the comparatively high-resolution omnidirectional imagery provided by this sensor also offers the potential for image-based algorithms such as landmark recognition to be implemented in the future. <s> BIB011 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> In this work, we develop a cooperative launching system for a 13.2 gram ornithopter micro-aerial vehicle (MAV), the H2Bird, by carrying it on the back of a 32 gram hexapedal millirobot, the VelociRoACH. We determine the necessary initial velocity and pitch angle for take off using force data collected in a wind tunnel and use the VelociRoACH to reach these initial conditions for successful launch. In the wind tunnel predicted success region, we were able to complete a successful launch for 75 percent of the 12 trials in that region. Although carrying the H2Bird on top of the VelociRoACH at a stride frequency of 17 Hz increases our average power consumption by about 24.5 percent over solo running, the H2Bird, in turn, provides stability advantages to the VelociRoACH. We observed that the variance in pitch and roll velocity with the H2Bird is about 90 percent less than without. Additionally, with the H2Bird flapping at 5 Hz during transport, we observed an increase of 12.7 percent of the steady state velocity. Lastly, we found that the costs of transport for carrying the H2Bird flapping and without (6.6 and 6.8) are lower than the solo costs of transport for the VelociRoACH and for the H2Bird (8.1 and 10.1). <s> BIB012 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <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> BIB013 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> Without sufficient payload capacity to carry necessary electronic components, flying robots at the scale of insects cannot fly autonomously. Using a simple scaling heuristic to determine a few salient vehicle properties, we develop a vehicle design that possesses the requisite payload capacity for the full suite of required components for control autonomy. We construct the vehicle using state-of-the-art methods, producing a 380 mg vehicle with a 115 mg payload capacity, and demonstrate controlled hovering of the fully-loaded vehicle. The payload-capable vehicle demonstrated here establishes a scalable vehicle design and validates current fabrication methods, laying a foundation for an eventual, fully-integrated robotic system. <s> BIB014 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> We present the control design, system integration, and free flight evaluation of a novel 227 g swashplateless coaxial helicopter. This micro aerial vehicle (MAV) achieves authority over roll, pitch, and yaw orientation as well as maneuvering thrust using only two propellers directly affixed to two motors. No additional aerodynamic control surfaces or actuators are introduced. Instead, cyclic control is obtained through the underactuated dynamic response of the main rotor itself to a modulated drive torque. Comparisons are drawn to conventional four-motor quadrotors and four-actuator fixed pitch coaxial helicopters in terms of mechanical complexity and actuator mass fraction. Trim power consumption in hover is reported across a range of symmetric and asymmetric loading states. Closed loop trajectory tracking maneuvers are demonstrated in a motion capture environment. <s> BIB015 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This paper presents a biologically inspired, 3.2g untethered vehicle capable of both active (flapping) and passive (gliding) flight. We discuss the overall vehicle design, as well as its validation with thrust data from benchtop testing, simulation, and flight test results. The vehicle has one pair of flapping wings for thrust generation, making it a good analogue for insects of the same scale. Flight energetics and control can be thoroughly explored through the array of simulation and testing that have been implemented. Integrated electronics provide wireless communication, sensing, and basic open-loop flight control, making flight test iteration fast and providing additional dynamics data. All of the testing setups and the physical vehicle working together have created a robust development environment for future iterations on the vehicle. The successful flight of the vehicle, including the data collection from onboard sensors and an external motion capture arena, show that this platform is ideal to study flight energetics and control schemes at an insect scale. <s> BIB016 </s> Recent Developments in Aerial Robotics: A Survey and Prototypes Overview <s> D. Flapping-wing UAVs <s> This paper is devoted to the performance optimization of an aerial manipulation system composed of a Flettner-helicopter and 7 DoF manipulator. With experiments we demonstrate that the time delays in signal propagation between perception and actuation modules play an important role for the overall performance of an aerial manipulator system using visual servoing. We present an approach for estimation of the perception-action time delay and its active compensation based on the predicted motion of the manipulator end-effector. <s> BIB017
A flapping-wing UAV (Fig. 10 (a)-(g) ) BIB003 , BIB010 - BIB016 , also known as ornithopter and usually in about a hand size, is a UAV that generate lifting and forward force by flapping its wings. Aiming for a better aerodynamic modeling, Rose and Fearing BIB010 compare the flight data collected from a wind tunnel to flight data collected from a free flight condition by using their bird-shaped flapping-wing UAV-H 2 Bird (Fig. 10 (a) ). They find atht the flight data collected from the wind tunnel is not accurate enough to predict the flight data during free flight and further experiments are required. Rose et al. BIB012 develop a coordinated launching system for H 2 Bird by mounting it onto a hexapedal robot (Fig. 10 (b) ). With the hexapedal robot's helps, H 2 Bird has a more steady launching velocity. Peterson and Fearing [59] Fig. 9 : Prototypes of fixed-wing UAVs (in alphabetical order: BIB013 ,  , BIB006 , BIB007 , BIB004 - BIB001 ) appear in the reviewed papers. See text for details. Fig. 10 : Prototypes of flapping-wing UAVs (in alphabetical order: BIB003 , BIB010 - BIB016 ) appear in the reviewed papers. See text for details. develop a flapping-wing UAV-BOLT that is capable of flying and walking on the ground like a bipedal robot (Fig. 10 (c) ). Inspired by birds, Paranjape et al. BIB008 design a flappingwing UAV that is able to perch naturally on a chair or human hand ( Fig. 10 (d) ). One of the unique features of their UAV is to control the flight path and heading angles by using wing articulation. on the other hand, Lamers et al.  develop a flapping-wing UAV that has a mini monocular camera system ( Fig. 10 (e) ). By combining the camera and a proximity sensor, their UAV can achieve obstacle detection by applying a machine learning method. Flapping-wing UAVs with insect shapes are also common. Ma et al. BIB014 fabricate an bee-shaped flapping-wing UAV that has a mass of 380 mg by using novel methods ( Fig. 10 (f) ). After detailing their design and fabrication processes, they also demonstrate a hovering flight with the developed mini UAV. Rosen et al. BIB016 develop another insect-scaled flappingwing UAV that is capable of flapping and gliding flights ( Fig. 10 (g) ). E. Single-rotor, Coaxial, and Ducted-fan UAVs A single-rotor helicopter (Fig. 11 (a)-(c) ) BIB005 - BIB017 is a UAV that relies on a main rotor and a tail rotor to generate thrust for VTOL, hovering, forward, backward, and lateral flights. By using a lidar-based perception system, Merz and Kendoul BIB011 demonstrate a helicopter that can perform obstacle avoidance and close-range infrastructure inspection. Backus et al. BIB015 focus on the aerial manipulation of an helicopter. Specifically, they design a robotic hand for their helicopter to perform grasping and perching actions effectively. Laiacker et al. BIB017 aim to optimize their visual servoing system on a helicopter that is equipped with a 7 DoF industrial manipulator. On the other hand, a coaxial helicopter ( Fig. 11 (d)-(f) ) is a UAV that uses two contra-rotating rotors mounted on the same axis to generate thrust for VTOL, hovering, forward, backward, and lateral flights. Moore et al. BIB011 implement a lightweight omnidirectional vision sensor for their mini coaxial helicopter to perform visual navigation. Conventionally, a helicopter requires additional servo motor and a mechanical device called swashplate for horizontal position control. Paulos and Yim BIB015 present a novel coaxial helicopter that requires no servo motor and mechanical device for horizontal position control. In order to perform horizontal movement, the rotors are driven by a modulated signal in order to generate both lifting and lateral forces simultaneously. Instead of avoid obstacles like a conventional UAV, Briod et al. BIB009 design a coaxial helicopter that uses force sensors around the UAV to detect obstacle and able to perform autonomous navigation safely without the high risks of collisions. A ducted-fan UAV (Fig. 11 (g) ) is a UAV that has similar rotors configuration with a coaxial helicopter but the rotors are mounted within a cylindrical duct. The duct helps to reduce thrust losses of the propellers and the ducted fans normally have rotational speeds. Pflimlin et al. BIB002 present a ductedfan UAV that can stabilize itself in wind gusts by using a two-level controller for position and attitude controls.