Scalable Jet Swimmer Driven by Pulsatile Artificial Muscles and Soft Chamber Buckling

Cephalopods, such as squid and nautilus, achieve fast swimming by jetting water swiftly from their chambers, offering benefits in swimming speed, energy efficiency, and silent operation. Inspired by these animals, a scalable soft robotic jet swimmer that utilizes soft chamber buckling to enable rapid water jetting is proposed. The design incorporates three main components: the knotted artificial muscle (KAM), an origami-inspired soft chamber, and a custom control module. The KAM generates significant force and stroke with minimal self-weight, but its actuation speed is insufficient for propelling water. To address this limit, an origami-inspired soft chamber that buckles instantly when the KAM's pulling force reaches a critical threshold is designed, thereby amplifying actuation speed and enabling rapid water jetting. The control module periodically activates the KAM to tighten and release, facilitating effective pulsatile propulsion. Similar to Cephalopods, this design is scalable and robust. Effective swimming of two robots is demonstrated with drastically different sizes, achieving a top speed of 0.62 body length per second. We also show that the propulsion is minimally compromised even when the KAM is significantly damaged. To further enable guided locomotion, a shape memory alloy rudder is incorporated for steering via infrared stimulation. This work demonstrates successful pulsatile jet swimming through the integration of smart materials and smart structures, laying the groundwork for future innovations in underwater soft robotics.