Servo - October 2011

by David Geer Contact the author at geercom@windstream.net

Kilobot Swarm Robots

A Swarm You Can Program, Power Up, and Charge Collectively

The idea behind swarms of robots is that they can accomplish more together than they could individually. This only works if the number of robots that can be programmed and managed in a swarm collectively (rather than individually) scales up easily to hundreds and thousands of robots that can accomplish massive tasks.

Until now, swarms have not been up to the task due to the cost of multiple robots, assembly time, and the simple lack of a way to program them, start them up, and recharge them as a group (rather than one by one). Kilobots bring us a step closer with affordable robots ($14 each) that can be assembled in five minutes each and which can scale up (for now) to a collective of 25 robots working together.

Design

The roboticists in the Computer Science Group at Harvard University designed Kilobots so each could move in an environment, run a “user defined” program, communicate with neighboring Kilobots, measure the distance to its neighbors, display something about its internal state to assist with debugging, and allow for scalable operations, according to the paper, “Kilobot: A Low Cost Scalable Robot System for Collective Behaviors” by Michael Rubenstein, Nicholas Hoff, and Radhika Nagpal.

Bottom of a Kilobot with three legs and circuitry.

To enable these capabilities, the designers endowed the robots with vibration motors, lithium-ion batteries, rigid supporting legs, infrared transmitter/receivers, and three-color RGB LEDs. The robot test environment included 25 Kilobots, a laptop-based control station, an overhead controller unit, and a charging station on a flat, smooth, level reflective table.

The simple means of movement for these robots is not wheeled motion — as popular as that design option may be — because it was simply too expensive. Instead, the robots each have two “sealed coin-shaped vibration motors.” When one of these motors is activated, the centripetal forces generated by the vibrating motor are converted to a forward force on the Kilobot located at the motor’s mounting location. The vibration of one motor [causes] a rotation of the Kilobot about its vertical axis in one direction, while the other motor rotates the robot in the other direction. This is an application of differential drive where the robot can move forward, and in clockwise and counterclockwise rotations, according to the Kilobot paper.