Supersmarticle: a locomoting robot made of robots

To discover principles by which simple robots can be integrated to form more complex robots, we developed a stochastic locomotor composed of simple non-motile robots. These smarticles (14 cm long) are 3D printed, three-link 2-degree-of-freedom robots with simple sensory capabilities (sound/light). The outer link positions are controlled by servo motors and can perform gaits (periodic closed trajectories in 2D configuration space) or hold a shape. Each smarticle is incapable of individually displacing or rotating. However, when confined in an unanchored 20 cm plastic ring, the smarticle ensemble (which we refer to as a supersmarticle), can displace through collisions among active smarticles and the ring. When all smarticles are identical in mass and movement procedure, the system exhibits a diffusive motion due to the collisions between the smarticles and the ring. When one of them is deactivated (via light/sound cues) and maintained a straight shape, the system diffuses and drifts towards or away from the direction of the inactive particle. A 1D model treating the active smarticles as a single fluctuating point mass captures these behaviors. The model reveals how the magnitude and direction of the drift depend on the mass ratio of the confining ring and the inactive particle.