Comprehensive analysis of efficient swimming using articulated legs fringed with flexible appendages inspired by a water beetle

Design and Reality-Based Modeling Optimization of a Flexible Passive Joint Paddle for Swimming Robots

Rowing motion with paired propellers is an essential actuation mechanism for swimming robots. Previous work in this field has typically employed flexible propellers to generate a net thrust or torque by using changes in the compliance values of flexible structures under the influence of a fluid. The low stiffness values of the flexible structures restrict the upper limit of the oscillation frequency and amplitude, resulting in slow swimming speeds. Furthermore, complex coupling between the fluid and the propeller reduce the accuracy of flexible propeller simulations. A design of a flexible passive joint paddle was proposed in this study, and a dynamics model and simulation of the paddle were experimentally verified. In order to optimize the straight swimming speed, a data-driven model was proposed to improve the simulation accuracy. The effects of the joint number and controller parameters on the robot's straight swimming speed were comprehensively investigated. The multi-joint paddle exhibited significantly improved thrust over the single-joint paddle in a symmetric driving mode. The data-driven model reduced the total error of the simulated data of the propulsive force in the range of control parameters to 0.51%. Swimming speed increased by 3.3 times compared to baseline. These findings demonstrate the utility of the proposed dynamics and data-driven models in the multi-objective design of swimming robots.

Experimental analysis of the sweepback angle effect on the thrust generation of a robotic penguin wing

Penguins have evolved excellent swimming skills as diving birds, benefiting from their agile wings. This paper experimentally analyzes the effects of the wing sweepback angle on thrust generation using a robotic penguin wing. A developed wing mechanism that can realize penguin-like flapping and feathering motion was used for actuating five alternative wing models, with different sweepback angles ranging from 0° to 50°. Force measurements under a steady water flow were conducted for both fixed and flapping states for all wing models. The results showed that small sweepback angles of 30° or less in the fixed state caused a steep lift curve and a moderate sweepback angle of 30° produced the largest lift-to-drag ratio. In the flapping state, the smaller sweepback wings generated a larger net thrust for the same wing motion, whereas the larger-sweepback wings produced more thrust under the same Strouhal number. The findings also revealed that larger sweepback wings more easily achieve the maximum net thrust in terms of less angle-of-attack control. In contrast, the hydrodynamic efficiency was not greatly affected by the sweepback. Regardless of the sweepback, the trend of the efficiency increasing with increasing flow speed indicates that the penguin wings can be more suitable for high-speed locomotion for higher hydrodynamic efficiency.

AquaClimber: a limbed swimming and climbing robot based on reduced order models

Many legged robots have taken insight from animals to run, jump, and climb. Very few, however, have extended the flexibility of limbs to the task of swimming. In this paper, we address the study of multi-modal limbed locomotion by extending our lateral plane reduced order dynamic model of climbing to swimming. Following this, we develop a robot, AquaClimber, which utilizes the model's locomotive style, similar to human freestyle swimming, to propel itself through fluid and to climb vertical walls, as well as transition between the two. A comparison of simulation and model results indicate that the simulation can predict how hand design, arm compliance, and driving frequency affect swimming speed and behavior. Using this reduced order model, we have successfully developed the first limbed aquatic-scansorial multi-modal robot.