This news release is available in Japanese.
By studying how water striders jump on water, Je-Sung Koh and colleagues have created a robot that can successfully launch itself from the surface of water. As the team watched the water strider jump on water surfaces using high-speed cameras, they noticed that the long legs accelerate gradually, so that the water surface doesn't retreat too quickly and lose contact with the legs. Using a theoretical model of a flexible cylinder floating on liquid, the authors found that the maximum force of the water striders' legs is always just below the maximum force that water surface tension can withstand. To recreate this controlled acceleration in their robot, the researchers used a torque reversal catapult (TRC) mechanism that generates a small initial torque and gradually increases - but that never exceeds the surface tension force of water. As well, the high-speed cameras reveal that the water strider sweeps its legs inward in order to maximize the time the legs can push against the surface of the water, thus maximizing the overall force; this additional concept was also applied to the robots to help them achieve lift off. With sufficiently light weight, long limbs, and the proper physical mechanisms, these robots effectively mimic their inspirational counterparts in nature. This paper is accompanied by an explanatory video that includes footage of the robots jumping, as well as a Perspective by Dominic Vella.
Article #21: "Jumping on water: Surface tension-dominated jumping of water striders and robotic insects," by J.-S. Koh; E. Yang; G.-P. Jung; S.-P. Jung; J.H. Son; S.-I. Lee; P.G. Jablonski; H.-Y. Kim; K.-J. Cho at Seoul National University in Seoul, Korea; J.-S. Koh; R.J. Wood at Wyss Institute for Biologically Inspired Engineering in Cambridge, MA; J.-S. Koh; R.J. Wood at Harvard University in Cambridge, MA; P.G. Jablonski at Polish Academy of Sciences in Warsaw, Poland.