Fig. 4: Experimental setup and synchronization of the motors in confined balls with transparent half-spheres.

a The schematic representation of the experimental setup using 4 balls with transparent half-spheres in a circular confinement (D = 0.4 m). We attached fluorescent tape to the internal motors and illuminated the setup with UV light to visualize the motion of the internal motor. b We show the space-time representation of a disordered and ordered period in the comoving reference frame with respect to the leading ball. The red oscillations of the fluorescent tape correspond to the oscillation of the internal motors. During periods of order, the oscillations synchronize their frequencies and phases. c The corresponding power spectrum density shows this change in the frequency distribution of the internal motors’ oscillation. d The oscillations of the internal motors become independent of the balls’ motion by stabilizing it with respect to the velocity corresponding to the individual ball’s center of mass. Plotting the frequency maxima of these oscillations shows that the frequencies lock during synchronized movement.