Insect-Inspired Marangoni Surfer Robots Tweak Surface Tension to Propel Themselves Atop Water

A team of roboticists have built a compact surfing robot, inspired by pond skaters and other water-skimming insects, which rides high through surface tension: the Marangoni surfer.

"By releasing lipid-laden excretions, certain insects can change the local surface tension — in this case, lowering it, like adding dish soap to water — causing a surface force imbalance that pulls the insect forward," two of the searchers, Hassan Massoud and Mitch Timm, write in a post for the Michigan Tech Unscripted Research Blog. "This wondrous ability is caused by Marangoni propulsion, a method of generating thrust via creating surface tension gradients."

"To our surprise, a close inspection of previous work on Marangoni surfers reveals that even though many insects use this method of propulsion, most robotic designs using it remain rudimentary."

The team decided to try their own approach, building a compact remote-control robot dubbed the Marangoni surfer. Like the pond skaters on which it is based, the robot can use surface tension to sit on top of the water — and can deploy isopropyl alcohol to alter the surface tension and propel itself forward or make a turn.

"To make this engineering challenge a reality, we developed custom-made flow control and steering mechanisms," the pair explain. "These features complement integrated power and fuel sources, a remote transmitter, a receiver and two servos, resulting in a non-tethered robotic surfer with unparalleled functionality.

"The integrated technology in our robot and its unique method of speed and directional control eliminates complicated and undesirable features such as noisy engines or propellers that can disrupt or harm sea life. This means fewer disturbances are introduced into the bulk of the liquid, reducing the drag and making the robot more like the insects it mimics, while having the additional benefit of being virtually silent in operation."

The researchers believe that the robot could be used for a range of practical applications, from monitoring wildlife to finding sources of pollution - while an upgraded autonomous version, still theoretical at this point, could self-correct and optimise its movements automatically and operate as a swarm with ease.

The team's work has been published in the journal Bioinspiration & Biomimetics under closed-access terms — but will be republished under a Creative Commons license as open-access after a 12-month embargo period that began in September this year.