Biologically Inspired Miniature Water Strider Robot

Abstract

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.

The hydrodynamics of water-walking arthropods

“…This observation raises a number of interesting dynamical questions, including the role of the integument in detaching from the free surface. This class of problems is currently under consideration and is likely to inform the design of biomimetic water-walking devices (Hu et al 2003(Hu et al , 2007Suhr et al 2005; …”

Fire ants self-assemble into waterproof rafts to survive floods

“…Although denser than water, they rely upon surface tension forces in the manner of water-walking insects and certain biomimetic robots (15)(16)(17). However, surface tension is generally too weak to support objects that have the density of water and a size much larger than the capillary length ℓ c ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi σ w ∕ðρ w gÞ p ≈ 2.3 mm, where σ w is the surface tension of water.…”

Vertical force acting on partly submerged spindly cylinders

“…The robots, whose legs consist of spindly cylinders decorated with hydrophobic materials, are based on the fundamental principles of the water strider's ability to float and move on the water surface. 1,[5][6][7][8][9][10][11] It is of interest to consider how great a load these cylindrical legs can support on a water surface.…”

“…In the past decade since the advent of water strider robots, there has been substantial interest in better understanding the underlying mechanisms involved in interactions between water and partly submerged spindly cylinders. 4-7, 9, 11, 13-28 For instance, Sitti et al 5 performed a parametric study on the load capacity of a single cylindrical leg on water via a numerical method, and provided a set of rules regarding the design of the supporting legs of water strider robots. Vella et al 13 discussed how the density and radius of the cylinder affect the ability of cylinder to float on the water surface, and investigated the role of the contact angle.…”

“…In the case of water strider robots, experiments have shown that the lift force decreases with increasing distance between neighboring legs. 5 The leg distance, therefore, is set as large as possible in the design of water strider robots. 5-7, 11, 25 When the distance reaches a certain value, the problem reduces to a single-cylinder one.…”