Differential Drive Kinematics from a Microscopic Robot*

Wheeled differential drives are one of the most widely used approaches in robotics thanks to easily controllable kinematics.  Here, we present a robot three times smaller than a period of print that obeys the same kinematics, allowing us to import well developed control laws to the microscale. Each 300 micron robot has two photovoltaic-powered electrokinetic engines that enable it to locomote at ~1 body length per second. Using a closed-loop optical setup to track robots and pattern laser light, we can modulate the power on each engine to turn the robot and obtain controlled locomotion. We find the relationship between engine power and robot dynamics is identical to differential drive systems. Further, we implement standard control laws to autonomously pilot devices and obtain coordinated motion over multiple agents. Finally, we discuss ongoing work to expand this kinematic framework to include robot-to-robot interactions and collective behavior.