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.

This letter presents the design, fabrication, and performance test of a fish-like underwater miniature robot directly driven by two piezoelectric actuators. Considering the different medium conditions and the ever-present challenge of waterproofing in underwater motion, the miniaturization of underwater robots is regarded as an innovative task. In this letter, by mimicking the swing of fish caudal fins to generate thrust, a piezoelectric actuator is used to directly drive the artificial fins. This robot merely consists of six components, including two PZT actuators, a pair of caudal fins, and two glass fiber fixtures. Such a design serves to streamline the process of assembly. The total mass of prototype miniature robot is only 0.8 g and has a body length (BL) of 4 cm. The robot has demonstrated its capacity for flexible and swift underwater movement. It can perform straight and turning movements underwater, with a maximum forward speed of 8.01 BL/s (32.05 cm/s) at a driving voltage of 180 V. It has a maximum payload of 0.84 g and minimum turning radius of 7.9 cm.

To improve the torque performance of the axial-flux permanent-magnet motor (AFPMM), differential evolution (DE) and cuckoo search (CS) are proposed for optimizing the motor’s structural parameters. The object of this research is an AFPMM with a single-rotor and double-stator configuration. Firstly, finite element analysis (FEA) and BP neural network machine learning (ML) were combined to obtain an ML calculator. This calculator is about the relationships between five input structural parameters of the motor and two output torque parameters (i.e., average torque and cogging torque). Then, an optimization objective function was designed to reduce the cogging torque while increasing the average output torque. And motor structural parameters were optimized using the DE and CS algorithms, respectively. Finally, air-gap flux density, average torque, cogging torque, and ripple torque before and after the optimization of the motor structure parameters are compared by FEA. The results show that both algorithms achieved almost the same optimized structural parameters. And the optimized motor has reduced cogging torque while increasing the average output torque and reducing the ripple torque. Compared with the CS, the DE is more advantageous in terms of faster iteration speed, shorter time to obtain the optimal solution, and less resource consumption.

Due to its excellent adaptability to the environment and flexibility in narrow spaces, amphibious microrobots have become an important research direction recently. This study proposes an amphibious microrobot driven by piezoelectric actuators with a body length of 4.5 cm and a mass of 1.4 g. The microrobot consists of two active front legs, two passive rear legs, two caudal fins, and a support frame. Each front leg and each caudal fin are designed as structures integrated with their respective piezoelectric actuators. The microrobot has a tilted body, and the ground exerts an oblique upward impact force that makes it jump forward when its front legs swing backwards. The opposite swing of the two caudal fins generates propulsion for swimming. The components of the microrobot are manufactured based on the monolithic laminate process. The monolithic front actuator-leg and monolithic actuator-fin both emerge from a multi-layer material laminate. The support frame is designed and fabricated as a monolithic structure to improve assembly accuracy and reduce redundant assembly steps. The manufactured microrobot demonstrates its flexible and fast amphibious movements. Its maximum land walking speed reaches 15.3 cm s⁻¹ and its turning speed reaches 48.2 degrees per second. The microrobot has a maximum payload capacity of 5 g moving on land. When the front legs and caudal fins work simultaneously, its underwater swimming speed reaches 9.1 cm s⁻¹, and the maximum turning speed is 20.5 degrees per second. The microrobot also confirms a maximum payload of 3 g during its underwater movement.

This study aimed to enhance the stability and response speed of a passive stabilized double-wing flapping micro air vehicle (FMAV) by implementing a feedback-controlled biomimetic tail. A model for flapping wings accurately calculated the lift force with only a 2.4% error compared to the experimental data. Experimental tests established the relationship between control torque and tail area, swing angle, and wing–tail spacing. A stability model for the double-wing FMAV was developed, incorporating stabilizing sails. Linearization of the hovering state facilitated the design of a simulation controller to improve response speed. By adjusting the feedback loops of velocity, angle, and angular velocity, the tail controller reduced the angle simulation response time from 4 s to 0.1 s and the velocity response time from 5.64 s to 0.1 s. In take-off experiments, a passive stabilized prototype with an adjustable tail angle exhibited enhanced flight stability compared to fixed tails, reducing standard deviation by 72.96% at a 0° take-off angle and 56.85% at a 5° take-off angle. The control axis standard deviation decreased by 38.06% compared to the passive stability axis, confirming the effectiveness of the designed tail angle controller in reducing angular deflection and improving flight stability.