Ornithopter Research Articles

RoboFinch: A versatile audio‐visual synchronised robotic bird model for laboratory and field research on songbirds

Abstract Singing in birds is accompanied by beak, head and throat movements. The role of these visual cues has long been hypothesised to be an important facilitator in vocal communication, including social interactions and song acquisition, but has seen little experimental study. To address whether audio‐visual cues are relevant for birdsong we used high‐speed video recording, 3D scanning, 3D printing technology and colour‐realistic painting to create RoboFinch, an open source adult‐mimicking robot which matches temporal and chromatic properties of songbird vision. We exposed several groups of juvenile zebra finches during their song developmental phase to one of six singing robots that moved their beaks synchronised to their song and compared them with birds in a non‐synchronised and two control treatments. Juveniles in the synchronised treatment approached the robot setup from the start of the experiment and progressively increased the time they spent singing, contra to the other treatment groups. Interestingly, birds in the synchronised group seemed to actively listen during tutor song playback, as they sung less during the actual song playback compared to the birds in the asynchronous and audio‐only control treatments. Our open source RoboFinch setup thus provides an unprecedented tool for systematic study of the functionality and integration of audio‐visual cues associated with song behaviour. Realistic head and beak movements aligned to specific song elements may allow future studies to assess the importance of multisensory cues during song development, sexual signalling and social behaviour. All software and assembly instructions are open source, and the robot can be easily adapted to other species. Experimental manipulations of stimulus combinations and synchronisation can further elucidate how audio‐visual cues are integrated by receivers and how they may enhance signal detection, recognition, learning and memory.

Macromolecule conformational shaping for extreme mechanical programming of polymorphic hydrogel fibers

Mechanical properties of hydrogels are crucial to emerging devices and machines for wearables, robotics and energy harvesters. Various polymer network architectures and interactions have been explored for achieving specific mechanical characteristics, however, extreme mechanical property tuning of single-composition hydrogel material and deployment in integrated devices remain challenging. Here, we introduce a macromolecule conformational shaping strategy that enables mechanical programming of polymorphic hydrogel fiber based devices. Conformation of the single-composition polyelectrolyte macromolecule is controlled to evolve from coiling to extending states via a pH-dependent antisolvent phase separation process. The resulting structured hydrogel microfibers reveal extreme mechanical integrity, including modulus spanning four orders of magnitude, brittleness to ultrastretchability, and plasticity to anelasticity and elasticity. Our approach yields hydrogel microfibers of varied macromolecule conformations that can be built-in layered formats, enabling the translation of extraordinary, realistic hydrogel electronic applications, i.e., large strain (1000%) and ultrafast responsive (~30 ms) fiber sensors in a robotic bird, large deformations (6000%) and antifreezing helical electronic conductors, and large strain (700%) capable Janus springs energy harvesters in wearables.

HIT-Hawk and HIT-Phoenix: Two kinds of flapping-wing flying robotic birds with wingspans beyond 2 meters

Inspired by large and medium-sized birds, two kinds of flapping-wing flying robots with wingspans beyond 2 meters were developed. They have the appearance of a hawk and a phoenix respectively, so they are called HIT-Hawk and HIT-Phoenix. In this paper, the bionic concept, theoretical analysis, design and manufacturing are introduced in detail. Firstly, the flight principle and characteristics of large and medium-sized birds were summarized. Then, the aerodynamics was modeled based on the thin airfoil theory, and the main design basis was established. Secondly, the mechanical structures of HIT-Hawk and HIT-Phoenix were designed to ensure the lateral and longitudinal stability and have optimized flight performance. Moreover, an autonomous flight control method was proposed and realized in highly integrated on-onboard controller; it satisfies the strict restrictions on mass, size, power and shape. Finally, the prototypes were fabricated and verified through practical flight experiments. The wingspans of these two flapping wing aircrafts are 2.0 m and 2.3 m respectively, the take-off weights are 1.15 kg and 0.86 kg, and the maximum stable endurance is 65 min (with battery of 3S LiPo, 4300 mAh) and 8 min (with battery of 3S LiPo, 800 mAh). Their wind resistance can both reach level 4. Compared with the small and micro flapping-wing aerial vehicles that mimic insects or small birds, they both have strong load capacity, strong wind resistance and long endurance.

Flight control of a large-scale flapping-wing flying robotic bird: System development and flight experiment

Large-scale flapping-wing flying robotic birds have huge application potential in outdoor tasks, such as military reconnaissance, environment exploring, disaster rescue and so on. In this paper, a multiple modes flight control method and system are proposed for a large-scale robotic bird which has 2.3 m wingspan and 650 g mass. Different from small flapping wing aerial vehicle, the mass of its wings cannot be neglected and the flapping frequency are much lower. Therefore, the influence of transient aerodynamics instead of only mean value are considered in attitude estimation and controller design. Moreover, flight attitude and trajectory are highly coupled, and the robot has only three actuators----one for wings flapping and two for tail adjustment, it is very difficult to simultaneously control the attitude and position. Hence, a fuzzy control strategy is addressed to determine the command of each actuator by considering the priority of attitude stabilization, trajectory tracking and the flight safety. Then, the on-board controller is designed based on FreeRTOS. It not only satisfies the strict restrictions on mass, size, power and space but also meets the autonomous, semi-autonomous and manual flight control requirements. Finally, the developed control system was integrated to the robotic prototype, HIT-phoenix. Flight experiments under different environment conditions such as sunny and windy weather were completed to verify the control method and system.

Development of Vision Stabilizing System for a Large-Scale Flapping-Wing Robotic Bird

Bio-inspired flapping-wing flying robots have huge application potential in military reconnaissance, environment exploring, disaster rescue and so on. Vision sensors are usually mounted to provide image information of targets. However, the position and attitude of this kind of robot changes drastically during flapping flight, resulting in more challenges for stable imaging. In this paper, a vision stabilizing system (also called stabilizer or camera gimble) is developed to supply stable imaging condition for a large-scale flapping wing robotic bird with 2.3m wingspan and 650g weight. Based on theoretical analyses and experiments, flight characteristics of the robot are first obtained. Then a 3-DOF stabilizer is designed to supply 2-DOF rotation and 1-DOF translation movement. The kinematics and dynamics equations are then derived to analyze the disturbance on the fuselage caused by the stabilizer. Furthermore, the key parameters of the stabilizer are determined according to the constraints on the flight capability. To deal with the interaction between the stabilizer and the fuselage, a coordinated control strategy is proposed and the onboard controller is developed to control the compounded system. Finally, the prototype of the stabilizer is assembled and integrated to a real robotic bird. Practical flight experiments are carried out and the results show that the developed stabilizer has good working performance.

Design, Fabrication, and Analysis of Flapping and Folding Wing Mechanism for a Robotic Bird

Emulating periodic main wing movement of a bird for generating lift and thrust remains a significant challenge in developing a robotic bird. The sequences of main wing motion are comprised of flapping, folding, bending, and twisting. In this paper, we concentrate on the flapping and folding motion, and design two wing mechanisms based on a 4-bar linkage structure: one is only for Flapping Motion (FM) and the other is for simultaneous Flapping and Folding Motion (FFM) during a wing stroke. We derive relationships between length and angle of links to analyze kinematic characteristics of the mechanisms and conduct an optimization to select the length parameters of links that allow maximization of the flapping angle. We run a simulation to confirm the performance of the optimized parameters by examining physical properties, and fabricate two wing mechanisms accordingly. In particular, the folding motion is achieved without using an additional actuator. Force measurements to investigate a lift profile of each mechanism and their quantitative comparison of the performance of both types confirm the benefits of the folding motion in the perspectives of wing frequency and lift. We expect that our kinematic formulation, design procedures, and comparative measurement results can help develop a wing mechanism to create a truly biomimetic robotic bird.

Evaluation of Planar Inkjet-Printed Antennas on a Low-Cost Origami Flapping Robot

An investigation on antenna solutions for expendable origami paper flapping robots is presented. An origami flapping robotic bird that can be produced using standard A4 paper is employed. Antennas resonating at the two commonly used frequency bands, 2.4 GHz and 5.2 GHz, are designed for the limited space available on the folded origami structure. Two developments of the same dual-band monopole antenna are discussed. The first antenna is located on the robot's spine and the second on its tail. A space diversity configuration is also studied. The antennas are printed directly onto a photo paper substrate and then folded into an origami robotic crane's body structure. An ordinary desktop inkjet printer fitted with silver nanoparticle conductive ink cartridges has been employed. CST Microwave Studio TM has been used to design the antennas. A good agreement between the measured and simulated S11 results is achieved with a reasonable -10dB impedance bandwidth realized in the three cases studied. The radiation patterns are omnidirectional in the XZ plane which is desirable for the specific application. The diversity configuration has a mutual coupling of <; -23dB and a gain of 1.4 dB and 2.8 dB at 2.4 GHz and 5.2 GHz respectively. The aim is to provide a new vision for antennas embedded into expandable flying robots based on traditional origami structures.

Review on Bio-Mimitic Robotic Bird

Review on Bio-Mimitic Robotic Bird

Robocygne: Dancing Life into an Animal-Human-Machine

Robocygne is an artistic project that revolves around the development of a custom-built robotic bird, dancing to a remix of Tchaikovsky’s Swan Lake. The artists created the choreography through a process in which movements were danced into the robot by the choreographer’s manipulation of the bird’s limbs, by hand, to the music. To enable this multitracking procedure, the artists, in collaboration with the engineers, developed novel software that allowed overlying recording of motions in synchronization with an audio track. From an artistic perspective, the authors discuss the search for choreographic and musical qualities and emphasize how material aspects of body and technology interrelate with emotional expression in Robocygne.

Design, fabrication, and characterization of multifunctional wings to harvest solar energy in flapping wing air vehicles

Currently, flapping wing unmanned aerial vehicles (a.k.a., ornithopters or robotic birds) sustain very short duration flight due to limited on-board energy storage capacity. Therefore, energy harvesting elements, such as flexible solar cells, need to be used as materials in critical components, such as wing structures, to increase operational performance. In this paper, we describe a layered fabrication method that was developed for realizing multifunctional composite wings for a unique robotic bird we developed, known as Robo Raven, by creating compliant wing structure from flexible solar cells. The deformed wing shape and aerodynamic lift/thrust loads were characterized throughout the flapping cycle to understand wing mechanics. A multifunctional performance analysis was developed to understand how integration of solar cells into the wings influences flight performance under two different operating conditions: (1) directly powering wings to increase operation time, and (2) recharging batteries to eliminate need for external charging sources. The experimental data is then used in the analysis to identify a performance index for assessing benefits of multifunctional compliant wing structures. The resulting platform, Robo Raven III, was the first demonstration of a robotic bird that flew using energy harvested from solar cells. We developed three different versions of the wing design to validate the multifunctional performance analysis. It was also determined that residual thrust correlated to shear deformation of the wing induced by torsional twist, while biaxial strain related to change in aerodynamic shape correlated to lift. It was also found that shear deformation of the solar cells induced changes in power output directly correlating to thrust generation associated with torsional deformation. Thus, it was determined that multifunctional solar cell wings may be capable of three functions: (1) lightweight and flexible structure to generate aerodynamic forces, (2) energy harvesting to extend operational time and autonomy, and (3) sensing of an aerodynamic force associated with wing deformation.

Wireless power transfer and fault diagnosis of high-voltage power line via robotic bird

This paper presents a new idea of wireless power transfer (WPT) and fault diagnosis (FD) of high-voltage power line via robotic bird. The key is to present the conceptual robotic bird with WPT coupling coil for detecting and capturing the energy from the high-voltage power line. If the power line works in normal condition, the robotic bird is able to stand on the power line and extract energy from it. If fault occurs on the power line, the corresponding magnetic field distribution will become different from that in the normal situation. By analyzing the magnetic field distribution of the power line, the WPT to the robotic bird and the FD by the robotic bird are performed and verified.

Non‐Redundant Social Information Use in Avian Flocks with Multisensory Stimuli

AbstractAnimals generally live in multisensory worlds; however, our understanding of multisensory perception is rather limited, despite its relevance for explaining the mechanisms behind social interactions, such as collective detection while foraging in groups. We tested how multisensory stimuli affected the antipredator behavior of dark‐eyed juncos (Junco hyemalis) using alarm calls as an auditory signal and flushing behavior as a visual cue. We varied the degree of risk within the group by manipulating the number of group mates alarm calling and/or flushing using robotic birds. We assumed that alarm calling and flushing were redundant stimuli and predicted that they could generate one of three types of responses (enhancement, equivalence, or antagonism) depending on the mechanism of multisensory perception. We set up an artificial flock with three robotic juncos surrounding a live junco and controlled for multiple confounding factors (e.g., identity of the focal, body mass, food deprivation time). We found that the degree of alarm of live juncos increased when at least one robot flushed. However, the time it took the live individuals to react to the robots' behavior increased, rather than decreased, with at least one alarm call. This could be the result of an orienting response or sensory overload, as live juncos increased scanning behavior after being exposed solely to alarm calls. Contrary to some theoretical assumptions, alarm calling and flushing behavior elicited independent unimodal responses, suggesting that they are non‐redundant stimuli and that together they could reduce the occurrence of false alarms and facilitate flock cohesion.

Advantages of an Ornithopter versus an Airplane with a Propeller

Advantages of an Ornithopter versus an Airplane with a Propeller

Autopilots for Ultra Lightweight Robotic Birds: Automatic Altitude Control and System Integration of a Sub-10 g Weight Flapping-Wing Micro Air Vehicle

This article described a control law for stabilizing the vertical motion of a flapping-wing MAV and developed a system architecture that is potentially beneficial in realizing the autonomous flight of flapping-wing MAVs fewer than 10 g. The article began with a brief introduction to the Golden Snitch, including its development history and the development of the overall system. The vertical dynamics were given for altitude control. The use of wind tunnel tests to obtain aerodynamical parameters was described. Due to the limited payload-carrying capability, the control architecture was modified so that automatic control of flight altitude of a flapping-wing MAV fewer than 10 g is possible using current technology. Taking the hardware constraint into account, it was shown that the modified P-control can stabilize the vertical motion and track altitude commands. Numerical simulations and flight tests were presented that demonstrate the function of the developed control law and the system architecture. We believe this flapping-wing MAV to be the first under 10 g able to automatically maintain its flight altitude.

Where does a flock end from an information perspective? A comparative experiment with live and robotic birds

Predator detection is improved when individuals join groups. Theory assumes that the transfer of social information about predators among individuals is immediate and accurate. However, animals in groups space themselves at different distances. Little is known about the shape of the social information transfer function over distance, which can affect group cohesion and ultimately the costs and benefits of group living. Our goal was to study the flow of social information in 3 bird species with different visual acuity (European starling, brown-headed cowbird, and house finch). We used robotic birds to manipulate the availability of social information. In a previous study, we demonstrated that birds react to robotic birds in the same way as they do to live birds. We measured the probability of 3 linearly placed live birds reacting to the flushing behavior of 2 robotic birds of the same species. Our study species were tested independently. We found a nonlinear decrease in social information flow with increasing distance between the robots and live birds; however, this decrease was more pronounced in species with lower visual acuity. Additionally, social information apparently degraded when flowing between closely spaced individuals, which could lead to false alarms. Our findings suggest that the benefits of social information flow are restricted to small neighbor distances and that larger species, with higher visual acuity, may have a greater spatial domain of collective detection. This mechanism may explain the spatial limits of flocks based on the transfer of social information. Key words: antipredator behavior, collective detection, predator detection, social information, vigilance, visual acuity. [Behav Ecol]

Application of fractional algorithms in the control of a robotic bird

In this paper, it is studied the dynamics of the robotic bird in terms of time response and robustness. It is analyzed the wing angle of attack and the velocity of the bird, the tail influence, the gliding flight and the flapping flight. The results are positive for the construction of flying robots. The development of computational simulation based on the dynamic of the robotic bird should allow testing strategies and different algorithms of control such as integer and fractional controllers.