Robot locomotion by fluid–fluid interaction

Abstract

This paper describes a locomotion strategy for robots based on the interaction between two fluids, through the development of an untethered mobile robot. The fundamental principle of robot locomotion is to exploit the active deformations of ferrofluid caused by internal magnetic fields, which generate reaction forces to the surrounding fluid (in this study, water). The developed robot is equipped with two permanent magnets (PMs), two electromagnets (EMs), two clusters of ferrofluid, and a control unit with batteries. It has a length, width, and mass of 107 mm, 94 mm, and 127 g, respectively. In the robot, PMs are used to hold clusters of ferrofluid. The activation of EMs by the controller achieves forward and rotational movements of the robot. Experimental results show the forward speed and rotational speed in water to be 2.7 mm/s (at a driving frequency of 9 Hz) and 1.2°/s (at a driving frequency of 7 Hz), respectively. The measured thrust force of the robot is 2 mN, further supporting the concept of robot locomotion by fluid–fluid interaction.