Directional Motion on Water Surface with Keel Extruded Footpads Propelled by Marangoni Effect

Abstract

Marangoni propulsion is well-known aquatic locomotion exhibited by some aquatic insects. After secreting chemicals to reduce the surface tension nearby, they are rapidly propelled by the force originated from the surface tension gradient. Inspired by their locomotion, a water surface skimming device was implemented in this work. It could obtain thrust by periodically dripping alcohol behind to utilize Marangoni effect. In particular, this work firstly proposed a passively triggerable vessel to explore a new way of initiating Marangoni propulsion, which does not require electric power to store and release alcohol fuel. From the experimental analysis, it was found that using a Teflon tube not only facilitated periodic dripping, but it also caused the dripping period and the number of droplets become less sensible to the tilting angle of the vessel. In addition, a new model to calculate the supporting force of a footpad was proposed, and the modeling error of a circular and an elliptical footpad was 3.54% and 4.36%, respectively. Those footpads were also extruded with keel to demonstrate passive directional motion without an active controller, which exhibited 30.9 mm of lateral deviation per 1 m of forward movement. The entire device weight was 11 g, and the estimated maximum moving distance was 9 m.