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Fish locomotion emerges from diverse interactions among deformable structures, surrounding fluids and neuromuscular activations, i.e. fluid–structure interactions (FSI) controlled by fish's motor systems. Previous studies suggested that such motor-controlled FSI may possess embodied traits. However, their implications in motor learning, neuromuscular control, gait generation, and swimming performance remain to be uncovered. Using robot models, we studied the embodied traits in fish-inspired swimming. We developed modular robots with various designs and used central pattern generators (CPGs) to control the torque acting on robot body. We used reinforcement learning to learn CPG parameters for maximizing the swimming speed. The results showed that motor frequency converged faster than other parameters, and the emergent swimming gaits were robust against disruptions applied to motor control. For all robots and frequencies tested, swimming speed was proportional to the mean undulation velocity of body and caudal-fin combined, yielding an invariant, undulation-based Strouhal number. The Strouhal number also revealed two fundamental classes of undulatory swimming in both biological and robotic fishes. The robot actuators were also demonstrated to function as motors, virtual springs and virtual masses. These results provide novel insights in understanding fish-inspired locomotion.
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Development of a Stingray-inspired High-Frequency Propulsion Platform with Variable Wavelength
Undulatory fin motions in fish-like robots are typically created using intricate arrays of servo motors. Motor arrays offer impressive versatility in terms of kinematics, but their complexity leads to constraints on size, hydrodynamic force production, and power consumption, particularly when studying propulsive performance at high-frequencies. Here we present an alternative design that uses a single motor and a tunable rotary cam-train system to achieve a spectrum of fin motions running from oscillation (wavenumber < 1) to undulation (wavenumber > 1). Our platform enables thrust, lift, power, and wake measurements at prescribed pitch amplitudes, frequencies, and wavenumbers. We demonstrated the platform’s oscillating and undulating capabilities via force and wake measurements in a water tank. Studies of fin wavenumber offer design insights for fish-like underwater robots, particularly those with stingray-inspired designs.
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- PAR ID:
- 10385469
- Date Published:
- Journal Name:
- 2022 IEEE/RSJ International Conference on Intelligent Robots and Systems
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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