A Marangoni propulsion is exhibited by some aquatic insects such as rove beetles as a means of rapid escaping by secreting surfactant that lowers the surface tension behind them. Inspired by their locomotion, we proposed a non-tethered miniature robot that can skim and steer on the water surface without employing oscillatory movements of limbs. To make a robot afloat on water surface using the surface tension while attaining higher support force, a circular footpad with an equilateral triangular cross section was used. Other types of cross section shapes such as a circle and a square were also considered; however, their maximal support force obtained from numerical solution was less than an equilateral triangle. The robot had four circular footpads, which coated with superhydrophobic spray, and weighed 18.5 gram including on-board electronics, a battery, and two servo motors. During the experiment, the robot could successfully skim over the water surface by dripping methanol behind and change its moving direction by lowering a small oar either left or right side.
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