Emergence of run-and-tumble-like motion in active robots connected together with a rigid rod.

Motility is one of the most remarkable features of living organisms and active particles. Its emergence is a complex interplay of various components that are often also active. Even though there are numerous examples of living and artificial active particles, there is a lack of detailed understanding of how individual active components, in conjunction, give rise to such complex motility characteristics. Here, we perform experiments on a "compound robot" composed of two motile robots connected with a rigid rod. The robots are centimeters-long disk-shaped programmable active particles with off-centered pivot points around which the rod can freely rotate. A pivot located at the left/right side of the robot's orientation introduces right/left-handed chirality in the robot dynamics. We show that when individual robots are programmed to follow active Brownian motion, the left-right chiral compound robot can display run-and-tumble-like dynamics. We find that the spontaneously evolving run and tumble events correspond to the states where the velocities of the two robots are aligned and misaligned, respectively. We also discover a systematic dependence of run-time statistics on the rotational noise of the individual robots. Overall, we demonstrate how complex motility behaviour arises in an active particle composed of multiple active components and possible strategies to tune such a motion.