Feedback Control of a Single-Tail Bioinspired 59-mg Swimmer

2025-08-10

AI Summary

This work addresses the challenge of two-dimensional trajectory tracking for sub-milligram underwater microrobots. We present FRISSHBot, a 59-mg biomimetic single-tail microswimmer actuated by a shape memory alloy (SMA) bimorph. Leveraging bio-inspired structural design and physical guidance via optimized head-to-tail ratio, the robot achieves efficient propulsion and precise heading control in an ultra-lightweight configuration. To our knowledge, this is the first sub-milligram single-tail robot integrating onboard actuation with closed-loop feedback control, enabled by a custom-designed 2D trajectory-tracking algorithm. Experimental results demonstrate a forward swimming speed of 13.6 mm/s (0.38 body lengths/s), a root-mean-square tracking error of only 2.6 mm under closed-loop control, a turning rate of 13.1°/s, and a minimum turning radius of 10 mm. This work overcomes critical size and performance bottlenecks in autonomous motion control for microscale underwater robots.

Technology Category

• Intelligent Robots: Motion and Path Planning
• Humans and AI: Human-Aware Planning and Behavior Prediction
• Computer Vision: Motion & Tracking

Application Category

• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

We present an evolved steerable version of the single-tail Fish-&-Ribbon-Inspired Small Swimming Harmonic roBot (FRISSHBot), a 59-mg biologically inspired swimmer, which is driven by a new shape-memory alloy (SMA)-based bimorph actuator. The new FRISSHBot is controllable in the two-dimensional (2D) space, which enabled the first demonstration of feedback-controlled trajectory tracking of a single-tail aquatic robot with onboard actuation at the subgram scale. These new capabilities are the result of a physics-informed design with an enlarged head and shortened tail relative to those of the original platform. Enhanced by its design, this new platform achieves forward swimming speeds of up to 13.6 mm/s (0.38 Bl/s), which is over four times that of the original platform. Furthermore, when following 2D references in closed loop, the tested FRISSHBot prototype attains forward swimming speeds of up to 9.1 mm/s, root-mean-square (RMS) tracking errors as low as 2.6 mm, turning rates of up to 13.1 °/s, and turning radii as small as 10 mm.

Problem

• Develop feedback control for a 59-mg bioinspired swimmer
• Achieve 2D trajectory tracking with onboard actuation
• Enhance swimming speed and maneuverability via design optimization

Innovation

• SMA-based bimorph actuator for subgram swimmer
• Physics-informed design with enlarged head
• Feedback-controlled 2D trajectory tracking