Multi-modal flapping robots demonstrate potential capabilities to accomplish assigned missions in confined indoor and outdoor environments. In this letter, inspired by the multimodal movement of insects, we report a multimodal tailless flapping wing robot capable of flying, crawling, self-righting and horizontal take-off. The robot has two pairs of wings, and achieves flight attitude stabilization and control through wing stroke-plane modulation. Terrestrial locomotion is accomplished through a hexapod crawling mechanism driven by a set of two geared motors. Horizontal take-off is achieved by flapping wings and stroke-plane modulation, it can reduce the fuselage height of the crawling mode, so that the robot can crawl through smaller gaps. Furthermore, this mechanism enables the robot to self-right in the event of overturning. Currently, the robot weighs 35.4 g, has a wingspan of 33 cm, and it could fly at a maximum speed of about 5 m/s or crawl on the ground at a speed of up to 30 cm/s. And the robot could endure up to 8.2 minutes in flight or over 60 minutes in crawling using an onboard battery. Experiments show that the robot has demonstrated the ability to flexibly transition between flight and crawling modes, and it could fly in intricate environments and crawl through small gaps.

With the goal of designing a biologically inspired robot that can hold a stable hover under internal and external disturbances. We designed a tailless Flapping-wing Micro Aerial Vehicle (FMAV) with onboard 3D velocity perception. In this way, the wind disturbance caused by the relative motion of the FMAV can be quantified in real time based on the established altitudinal dynamics model. For the rest of the total disturbance, an active disturbance rejection controller is proposed to estimate and suppress those disturbances. In comparison with the traditional PID controller, this proposed approach has been validated. The results show that, in the hovering flight with the internal unmodeled dynamics, the root-mean-square of height controlled is only 2.53 cm. Even with the different weights of loads mounting on the FMAV, the ascending trajectory of flights remains impressively consistent. In the forward flight with the external disturbance, the root-mean-square error of height controlled is 2.78 cm. When the FMAV flies over a ladder introducing an abrupt external disturbance, the maximum overshoot is only half of that controlled by the PID controller. To our best knowledge, this is the first demonstration of FMAVs with the capability of sensing motion-generated wind disturbance onboard and handling the internal and external disturbances in hover flight.

With the complex aerodynamics, the accurate system model of the flapping-wing micro aerial vehicle required for precise control is hard to acquire, meanwhile, due to the unique control strategy, the coupling between the actuators also brings a great challenge to the control of the vehicle. In this paper, we establish a theoretical model of the vehicle. Based on this model, we propose a multiaxial adaptive controller with the reference generator for the attitude and altitude control using the backstepping design method, the stability of this controller is proved by the Lyapunov function. Moreover, a control allocation algorithm is proposed to coordinate the different actuators such that they together produce the desired virtual control efforts. In addition, we detail the lightweight design of the flapping-wing micro aerial vehicle with altitude and attitude sensing onboard. Then, the effectiveness of the proposed control scheme is verified by the simulation and the flight test with multi-axis simultaneous control conducted on this lightweight vehicle. The experimental results show that the controller can maintain hovering flight and ensure the convergence of the adaptive parameters even when the unilateral thrust of the vehicle is not enough due to manufacturing and assembly errors. This work provides an idea for us to explore how insects maintain stable flight in the face of changes in their model parameters.

Most traditional flapping-wing micro air vehicles (FMAVs) adopt a serial control mechanism, which means that one drive corresponds to one degree of freedom. However, the serial mechanism often struggles to meet FMAV requirements in terms of stiffness, size, and reliability. In order to realize a compact reliable control mechanism, we developed a two-wing insect-like FMAV with a parallel control mechanism. The prototype possesses an optimized string-based flapping wing mechanism, a 2RSS/U parallel control mechanism, and an onboard power supply and controller. The pulley’s profile of the string-based mechanism was refined to reduce the deformation and impact of the string. The parameters of the parallel mechanism were designed to enable the stroke plane to rotate a large angle to produce control torque. The prototype had a flapping frequency of 25 Hz, a full wingspan of 21 cm, and a total weight of 28 g. A PID controller with a decoupler based on the kinetics solution of parallel mechanism was designed to control the FMAV. A force and torque (F/T) experiment was carried out to obtain the lift and control torque of the prototype. The measured data showed that the flapping wing mechanism provided sufficient lift and the control mechanism generated a toque caused by the stroke plane rotation and trailing edge movement and were linear to the control input. A flight test was carried out to verify the flight stability of the prototype. The result shows that the attitude angle only fluctuates within a small range, which proved that the control mechanism and control strategy were successful.

To investigate aerodynamic performance of Flapping Wing Micro Air Vehicle (FWMAV), it is significant to design an efficient test system for measuring aerodynamic performance of FWMAV in hovering condition. In this study, a test platform with a simple trigger device, which can synchronously obtain data including forces, wing motion and power consumption under a certain flight status of uncontrolled FWMAV, was introduced. Time-resolved forces generated by wing flapping were measured by an ATI force transducer and the wing kinematics was tracked by a high-speed camera. A customed circuit was designed for power consumption. For simple experimental operation, a low- level signal was used to trigger our system for data acquisition, data processing and data storage. A flapper with 20cm wing span, which weighs 9.37g without batteries, was tested to characterize its aerodynamic performance through this platform. Test results show that the wing flapping frequency of the flapper can almost reach 13Hz at the flapping angle of 180° producing 8.1g maximum mean lift and 0.27g maximum mean thrust, which can provide valuable references for performance improvement and validation of aerodynamic modelling of FWMAV.