Design and development of a novel soft valve and energy-storage mechanism for high-power underwater robotic pulse-jet propulsion

Soft robots have many unique qualities such as adaptability and robustness which make them attractive for applications in delicate environments including those that may impact natural ecosystems. Underwater soft robots are a growing area of research that aims to exploit these qualities for certain applications such as environmental monitoring or inspection in places like coral reefs or natural settings with both flora and fauna present. In the interest of expanding this area of study and developing opportunities within aquatic environments, this paper describes the design, development, and testing of a novel soft valve system with an energy-storage membrane to enable high-power jet propulsion for locomotion. The presented system aims to impose minimal impact or risk to these settings through the development of this propulsion system which offers a novel alternative to spinning propellors most often used in underwater vehicles. The valve operates based on buckling principles, applying force via a rack and pinion mechanism to achieve a controlled opening. Additionally, the Poisson effect plays a significant role in the valve’s opening behavior. Experimental testing was conducted to evaluate three different thicknesses for two different materials Ecoflex 00-30 and Elastosil M4601. Results demonstrated the maximum holding pressure was up to 56 kPa. Additional testing was conducted assessing the swimming distance and speed of the prototype in a water tank. The robot demonstrated a maximum swimming speed of up to 4 cm/s (0.29 BL/s) and a maximum distance traveled of over 24 cm. The valve design and the energy-storage membrane hold promise to be implemented into a single small robust unit used in multi-directional robots in the future.