Several animal species demonstrate remarkable locomotive capabilities on land, on water, and under water. A hybrid terrestrial-aquatic robot with similar capabilities requires multimodal locomotive strategies that reconcile the constraints imposed by the different environments. Here we report the development of a 1.6 g quadrupedal microrobot that can walk on land, swim on water, and transition between the two. This robot utilizes a combination of surface tension and buoyancy to support its weight and generates differential drag using passive flaps to swim forward and turn. Electrowetting is used to break the water surface and transition into water by reducing the contact angle, and subsequently inducing spontaneous wetting. Finally, several design modifications help the robot overcome surface tension and climb a modest incline to transition back onto land. Our results show that microrobots can demonstrate unique locomotive capabilities by leveraging their small size, mesoscale fabrication methods, and surface effects.

Flapping-wing flight is ubiquitous among natural flyers. Flying insects can perform incredible acrobatic maneuvers, such as rapid turning, somersault, and collision avoidance in cluttered environments. Unlike fixed wing aircrafts or rotorcrafts, these tiny creatures utilize highly unsteady aerodynamic phenomena to achieve extraordinary locomotive abilities.
Taking inspiration from biological flappers, we develop a robot capable of insect-like flight, and then go beyond biological capabilities by demonstrating multi-phase locomotion and impulsive water-air transition. In this dissertation, we conduct experimental and computational studies of flapping wing aerodynamics that aim to quantify fluid-wing interactions and ultimately distill scaling rules for robotic design. Comparative studies of fluid-wing interactions in air and water reveal remarkable similarities, which lead to the development of the first hybrid aerial-aquatic flapping wing robot. Further, we show that microrobots face unique challenges and opportunities due to the dominance of surface tension at the millimeter scale. By developing an impulsive mechanism that utilizes an electrochemical reaction, we demonstrate the first-ever water to air takeoff in a microrobot.