http://www.sciencemag.org/news/2019/09/watch-robot-made-robots-move-around

Good news for small, helpless robots who long to be a part of something bigger: Researchers have found a way to create “robots made of robots” that can move around, even though the individual parts can’t travel on their own.

To create this robot horde, researchers designed several roughly iPhone-size machines called “smarticles”—short for smart particles—that could flap their small arms up and down but could not move from place to place by themselves. They then put five of the smarticles in a plastic ring. This group of robots—which the researchers call a “supersmarticle”—could move by itself in random directions as the individual smarticles collided with each other.