(a), (d) Setup, (b), (e) temporal record of rotor velocity, and (c), (f) probability distribution of averaged rotor velocity from experiments (left column, ((a)–(c)) and numerical simulations (right column, (d)–(f)). (a), (d) System composed of an asymmetric rotor and self-propelled robots. Flower-shape acrylic boards are used to prevent robots from sticking on the outside boundary. (b), (e) Temporal fluctuations around averaged rotation velocity of the rotor. (c), (f) Probability distribution functions of averaged angular velocity Ω_τ.