Abstract-Recent biological studies on water strider insects revealed the detailed mechanism of their staying and walking on water. While macro scale bodies use buoyancy to stay on water, these very light and small insects balance their weight using repulsive surface tension forces where the insect legs are covered with hydrophobic micro-hairs. Utilizing the unique scaling advantage of these insects, this paper proposes a biologically inspired miniature micro-robot walking on water with a similar principle. The paper focuses on understanding physical characteristics of the insect and designing a robot that mimics the insect's movement. Highly hydrophobic Teflon ® coated wires are used for the legs to take advantage of surface tension force, and the robot body is made of carbon fibers for minimal weight. A T-shaped actuation mechanism with three PZT-5H based unimorph actuators is utilized to move the side legs of the robot independently for controlled locomotion. Kinematics and dynamic properties of the robot prototype are analyzed and compared with the experimental results. The tethered robot can successfully move forward, backward and can also make turns. Maximum speed of the robot in forward motion is 2.3 cm/s. In the future, environmental monitoring applications on dams, lakes, sea, etc. would become possible using a network of these robots with miniature sensors, an on-board power source and electronics.

Recent studies on the insect water strider showed that the insect heavily relies on surface tension force to stay afloat. Inspired by this insect, water strider robots have been developed using the same locomotive principles as the insect. This paper focuses on numerically modeling the supporting legs of the insect and the robots. The rigid-leg model as well as the compliantleg model is developed using numerical approaches, under an assumption made on the water surface breaking condition. The effect of different leg material and geometry are discussed. It is shown through simulations that four 7 cm-long Teflon R coated compliant supporting legs with optimized shapes can lift up to 4.3 grams (0.15 g/cm), while an actual prototype carried 3.7 grams. Another prototype using twelve of these legs successfully lifted 9.3 grams. Experiments show that the analyses capture the important features of the supporting legs. The design rules proposed in this paper will be useful in understanding the insect statics and also the robotic water strider supporting leg design. This study will allow a heavier robot to be used for education, entertainment or environment monitoring purposes.