Knowledge of position in the context of its surrounding is necessary for robots to build maps and develop path plans. Limitations in odometry and the lack of a priori knowledge reduce the effectiveness of a single robot to retain a sense of position for any extended duration. The problem is only compounded when the scale of the robot is reduced. However, by employing multiple robots we can exploit their distributed nature to provide an external context in which to evaluate sensor readings for mapping and localization. We have designed a team of centimeter-sized robots that coordinate sensing and action to establish and maintain position as they move throughout space. By utilizing low-cost ultrasonic sensors, the team is able to measure the range between each robot pair. We pose these measurements in terms of a position likelihood and combine them to find a global solution that best maximizes the position likelihood of each robot. We also address a unique multipath interference mode that arises as a direct result of the reduced scale of the robot team. We present our experiences with localization and control of a small robot team.
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