A Cephalopod-Inspired Soft-Robotic Siphon for Thrust Vectoring and Flow Rate Regulation.

Cephalopods could simultaneously achieve both accurate positioning and agile bodily maneuvers by coordinating the mantle and the funnel, which is ideal for underwater robotic applications toward a compact propulsor with combined thrust vectoring and regulation. For a wide range of underwater applications from videography to manipulation, this novel approach would offer a compact and integrated alternative to the state-of-the-art with multiple vectoring thrusters. This article presents a biomimetic soft-robotic siphon (BSRS) as the propulsor unit, consisting of a novel central flow-regulative duct (CFRD) encircled by three circumferential siphon actuation muscles (SAMs). Hydraulic pressurization of the SAMs could enable both thrust vectoring by deflecting the BSRS and flow regulation by proportionally alternating the orifice of the CFRD. The design, modeling, and fabrication of the BSRS are presented in detail. Experiments using a prototype BSRS were conducted for validating the performances of deflection deformation and flow regulation, showing bending range of over 180° and flow-restricting capability of up to 100%. A burst effect was achieved with the ability of exceeding the constant flow rate by up to 50%, enabling tremendous thrust increase in very short time. This work proves the feasibility of combining omnidirectional deflection with flow regulation within a soft-robotic mechanism, paving the way to compact water-jetting propulsion for underwater robots.