Flapping-wing Robot Research Articles

Avian-inspired embodied perception in biohybrid flapping-wing robotics

Avian feather intricate adaptable architecture to wing deformations has catalyzed interest in feathered flapping-wing aircraft with high maneuverability, agility, and stealth. Yet, to mimic avian integrated somatic sensation within stringent weight constraints, remains challenging. Here, we propose an avian-inspired embodied perception approach for biohybrid flapping-wing robots. Our feather-piezoelectric mechanoreceptor leverages feather-based vibration structures and flexible piezoelectric materials to refine and augment mechanoreception via coupled oscillator interactions and robust microstructure adhesion. Utilizing convolutional neural networks with the grey wolf optimizer, we develop tactile perception of airflow velocity and wing flapping frequency proprioception. This method also senses pitch angle via airflow direction and detects wing morphology through feather collisions. Our low-weight, accurate perception of flapping-wing robot flight states is validated by motion capture. This investigation constructs a biomechanically integrated embodied perception system in flapping-wing robots, which holds significant promise in reflex-based control of complex flight maneuvers and natural bird flight surveillance.

CFD Analysis of Takeoff from a Water Surface for an Insect-Scale Aerial/Aquatic Robot

To develop an insect-scale aerial/aquatic robot, we analyzed takeoff mechanisms to counteract surface tension, such as paddling, slapping, and clap-and-fling. Because a diving beetle, Eretes griseus, takes off directly from the water surface, a flapping-wing robot is promising as an alternative to a drone with multiple rotary wings. In this study, we first investigated diving beetle flight with a three-dimensional high-speed camera system and analyzed the motion characteristics. Subsequently, we developed a computational fluid dynamics method that tracked the water surface using a volume of fluid method, reproduced the motion with a multibody model, treated the deformation of the elastic membrane wing with the phase delay of the joint angle functions, and simulated takeoff, that is, the transition from water to air, and hovering near the water surface. The simulation result showed that during the transition, the slapping motion exerted the maximum and average lift per unit of body weight of 18 and 9.2, respectively, while those of paddling produced 0.46 and 0.23, respectively. The water surface effect improved the lift by 25% at the normalized height of less than 0.44 and disappeared at a height greater than 0.7. During hovering, while the clap-and-fling motion improved lift by 2.6% and the water surface effect was 9.8%, the synergy effect was 22%. In addition, the former enhanced it significantly after the fling, while the latter was remarkable during the wing acceleration phase. In contrast to ground effects, flapping reduced the water level and caused the ripples, dynamically changing the water surface effect.

Performance Evaluation and Wing Deformation Analysis of Flapping-Wing Aerial Vehicles with Varying Flapping Parameters and Patterns

There has been significant interest in the field of bio-inspired robotics, particularly in the development of flapping-wing robots from micro to bird size. Most flapping robots use lever-crank mechanisms or servomotors as wing flapping mechanisms. Servomotor-based flapping has the advantage of being able to generate various flapping patterns according to amplitude, offset, frequency, waveform, and other factors. However, it is not clear how these factors affect thrust generation. Therefore, this study focuses on the force generation and power consumption in different flapping patterns as well as the wing deformation during the flapping motion to provide some insights into the performance improvement. The results showed that the response characteristics of the actuators caused the thrust to saturate at high frequencies, and that sinusoidal pattern could generally achieve good performance and efficiency.

Gliding Performance of an Insect-Inspired Flapping-Wing Robot

Flying animals such as insects and birds use wing flapping for flight, occasionally pausing wing motion and transitioning into gliding to conserve energy for propulsion and achieve high flying efficiency. In this study, we have investigated the gliding performance of a gliding model based on a flapping-wing robot developed in a previous study, with the aim of developing a highly efficient flying robot that utilizes bio-inspired intermittent flight. Wind tunnel experiments with a gliding model have shown that the attitude of the wings has a strong influence on gliding performance and that a tail is effective in improving gliding performance. The results of this study provide important insights into the development of flying robots that can travel long distances with high efficiency.

A novel GEA-PSO method for optimizing the parameters of a bird-like flapping wing robot

A novel GEA-PSO method for optimizing the parameters of a bird-like flapping wing robot

Retraction: Dynamic performances of a bird-like flapping wing robot under randomly uncertain disturbances.

Retraction: Dynamic performances of a bird-like flapping wing robot under randomly uncertain disturbances.

An optimum structural design method for a torque sensor measuring the control moment of the micro flapping-wing robot

Abstract This paper presents an optimum structural design method for a sensor capable of measuring the control torque of the micro flapping-wing robot. Torque measurement in flapping-wing robots has special demands on the sensor bandwidth. The method in this paper focuses on the development of a multi-objective optimization method based on the surrogate model to solve the sensor indicator design issues, for example, increasing sensitivity while meeting bandwidth requirements. Initially, Latin hypercube sampling was applied to the choice of the characteristic parameters of the sensor. Based on finite element techniques, the surrogate models describing displacement and eigenfrequency were established to characterize the sensor indicators, and a multi-objective optimization was conducted. According to the optimization results, the sensor structure was manufactured, and a torque measurement platform was set up. Calibration experiments and frequency response experiments demonstrated a high level of consistency between the surrogate model and the experimental data. With the assistance of the eddy current displacement sensor, the actual displacement sensitivity coefficient of the torque sensor is determined to be 0.4325 mm mNm−1, consistent with the calculation of the surrogate model. The characteristic frequency is 488.5 Hz, with a relative error of 7.47% compared to the surrogate model. This indicates that the optimum structural design method can be utilized for the rapid design of torque sensors for special requirements, thus laying the foundation for the control torque measurement of micro flapping-wing robots.

An experimental study on attitude control of a tailless hummingbird-mimetic flapping-wing robot with defective wings

Hummingbirds demonstrate remarkable robustness to wing defects by maintaining stable hovering during the molting process. However, mimicking these capabilities in flapping-wing robots presents significant challenges. To investigate the effectiveness of various controllers in maintaining the attitude of a hummingbird-mimetic flapping-wing robot against external disturbances under different wing defects, this study implemented a PD controller, a PID controller, and a three-loop feedback controller with a disturbance observer (3L-DOB controller). The flapping-wing robot features a pair of wings and controls its body’s yaw, pitch, and roll rotations by modulating the tension of wing membranes and the neutral positions of wing torsion. The performance of these controllers was evaluated through semi-tethered experiments on a gimbal, employing three Wing Sets: intact wings, one wing was defective, and both wings were defective. The defective wing emulated hummingbird wing during molting, in which the wing area was cropped by 14.1%. As a result, the 3L-DOB controller showed the best performance in terms of responsiveness and accuracy across all Wing Sets, while the PID controller also achieved comparable performance.

Analysis of hovering flight stability of an insect-like flapping-wing robot in Martian condition

In efforts to search for life-form on a planet other than Earth, many projects have been launched to measure and analyze the surface and atmospheric conditions on Mars. To extend the exploration of Mars, scientists have attempted to perform flight in the extremely thin air environment of Mars. Inspired by the successful controlled flight of NASA's Helicopter on Mars, in this work, we investigate the six-degrees-of-freedom hovering flight dynamics of an insect-like flapping-wing robot, called KUBeetle. To hover the KUBeetle on Mars, using the scaling ratios of air density and gravity on Earth and Mars, we have found that the flapping frequency should be about 113.48 Hz, which is 4.93 times faster than that on Earth, and the required lift on Mars is about 38% of that on Earth. The computational fluid dynamics (CFD) analysis suggests that the lift produced by the flapping wings at the frequency on Mars is close to that predicted by the scaling ratios. A series of simulations are used to compute the stability derivatives to complete the equations of motion. The eigenvalue and eigenvector analyses have identified one fast subsidence mode, one slow subsidence mode, and one divergence oscillation mode in the longitudinal and lateral motions on Mars, which are identical to those on Earth. The dynamic responses of the robot under three initial disturbances in the translational speeds indicate that due to the 94% smaller real part of the complex roots in the divergence oscillation modes of the longitudinal and lateral motions on Mars, the growth of flight disturbances is much slower than on Earth. Therefore, the KUBeetle is capable of hovering flight on Mars, since it has enough time to use the feedback controls to stabilize the system. This work can be used to support the studies of the flight control of flapping wing robots in the Martian atmospheric condition, and to generalize such flight control for other non-terrestrial applications in the atmospheres of other planets and/or their moons.

Vector field path following for a micro flapping-wing robot

Vector field path following for a micro flapping-wing robot

A Multi-Modal Tailless Flapping-Wing Robot Capable of Flying, Crawling, Self-Righting and Horizontal Take-Off

A Multi-Modal Tailless Flapping-Wing Robot Capable of Flying, Crawling, Self-Righting and Horizontal Take-Off

Digital Video Stabilization Method Based on Periodic Jitters of Airborne Vision of Large Flapping Wing Robots

Digital Video Stabilization Method Based on Periodic Jitters of Airborne Vision of Large Flapping Wing Robots

Numerical comparison between symmetric and asymmetric flapping wing in tandem configuration

Dragonflies show impressive flight performance due to their unique tandem flapping wing configuration. While previous studies focused on forewing-hindwing interference in dragonfly-like flapping wings, few have explored the role of asymmetric pitching angle in tandem flapping wings. This paper compares the aerodynamic performance of asymmetric dragonfly-like wings with symmetric hummingbird-like wings, both arranged in tandem. Using a three-dimensional numerical model, we analyzed wing configurations with single/tandem wings, advance ratios (J) from 0 to 0.45, and forewing-hindwing phase differences (ϕ) from 0° to 180° at a Reynolds number of 7000. Results show that asymmetric flapping wings exhibit higher vertical force and flight efficiency in both single and tandem wing configurations. Increasing the phase difference (ϕ) improves flight efficiency with minimal loss of vertical force in the asymmetric flapping mode, while the symmetrical flapping mode significantly reduces vertical force at a 180° phase difference. Additionally, symmetric tandem flapping wings unexpectedly gain extra vertical force during in-phase flapping. This study uncovers the flow characteristics of dragonfly-like tandem flapping wings, providing a theoretical basis for the design of tandem flapping wing robots.

Trajectory Generation and Tracking Control for Flapping Wing Robot Three-Dimensional Flight

Trajectory Generation and Tracking Control for Flapping Wing Robot Three-Dimensional Flight

Aerodynamic Analysis and Flight Control of a Butterfly-Inspired Flapping-Wing Robot

Aerodynamic Analysis and Flight Control of a Butterfly-Inspired Flapping-Wing Robot

Dynamic Deformation Measurement of Bionic Flapping-Wing Robot Based on Fiber Bragg Grating Array

Dynamic Deformation Measurement of Bionic Flapping-Wing Robot Based on Fiber Bragg Grating Array

Target Detection and Localization for Flapping-Wing Robots Based on Biological Eagle-Eye Vision

Target Detection and Localization for Flapping-Wing Robots Based on Biological Eagle-Eye Vision

Thrust enhancement and degradation mechanisms due to self-induced vibrations in bio-inspired flying robots

Bio-inspired flying robots (BIFRs) which fly by flapping their wings experience continuously oscillating aerodynamic forces. These oscillations in the driving force cause vibrations in the motion of the body around the mean trajectory. In other words, a hovering BIFR does not remain fixed in space; instead, it undergoes oscillatory motion in almost all directions around the stationary point. These oscillations affect the aerodynamic performance of the flier. Assessing the effect of these oscillations, particularly on thrust generation in two-winged and four-winged BIFRs, is the main objective of this work. To achieve such a goal, two experimental setups were considered to measure the average thrust for the two BIFRs. The average thrust is measured over the flapping cycle of the BIFRs. In the first experimental setup, the BIFR is installed at the end of a pendulum rod, in place of the pendulum mass. While flapping, the model creates a thrust force that raises the model along the circular trajectory of the pendulum mass to a certain angular position, which is an equilibrium point and is also stable. Measuring the weight of the BIFR and the equilibrium angle it obtains, it is straightforward to estimate the average thrust, by moment balance about the pendulum hinge. This pendulum setup allows the BIFR model to freely oscillate back and forth along the circular trajectory about the equilibrium position. As such, the estimated average thrust includes the effects of these self-induced vibrations. In contrast, we use another setup with a load cell to measure thrust where the model is completely fixed. The thrust measurement revealed that the load cell or the fixed test leads to a higher thrust than the pendulum or the oscillatory test for the two-winged model, showing the opposite behavior for the four-winged model. That is, self-induced vibrations have different effects on the two BIFR models. We felt that this observation is worth further investigation. It is important to mention that aerodynamic mechanisms for thrust generation in the two and four-winged models are different. A two-winged BIFR generates thrust through traditional flapping mechanisms whereas a four-winged model enjoys a clapping effect, which results from wing-wing interaction. In the present work, we use a motion capture system, aerodynamic modeling, and flow visualization to study the underlying physics of the observed different behaviors of the two flapping models. The study revealed that the interaction of the vortices with the flapping wing robots may play a role in the observed aerodynamic behavior of the two BIFRs.

Experimental Analyses of Aerodynamic Force Generation and Wing Motion Associated with a Single-motor-driven Butterfly-inspired Flapping-wing Robot

Experimental Analyses of Aerodynamic Force Generation and Wing Motion Associated with a Single-motor-driven Butterfly-inspired Flapping-wing Robot

Closed-loop nonlinear optimal control design for flapping-wing flying robot (1.6 m wingspan) in indoor confined space: Prototyping, modeling, simulation, and experiment

The flapping-wing technology has emerged recently in the application of unmanned aerial robotics for autonomous flight, control, inspection, monitoring, and manipulation. Despite the advances in applications and outdoor manual flights (open-loop control), closed-loop control is yet to be investigated. This work presents a nonlinear optimal closed-loop control design via the state-dependent Riccati equation (SDRE) for a flapping-wing flying robot (FWFR). Considering that the dynamic modeling of the flapping-wing robot is complex, a proper model for the implementation of nonlinear control methods is demanded. This work proposes an alternative approach to deliver an equivalent dynamic for the translation of the system and a simplified model for orientation, to find equivalent dynamics for the whole system. The objective is to see the effect of flapping (periodic oscillation) on behavior through a simple model in simulation. Then the SDRE controller is applied to the derived model and implemented in simulations and experiments. The robot bird is a 1.6 m wingspan flapping-wing system (six-degree-of-freedom robot) with four actuators, three in the tail, and one as the flapping input. The underactuated system has been controlled successfully in position and orientation. The control loop is closed by the motion capture system in the indoor test bed where the experiments of flight have been successfully done.