Collectives of Spinning Mobile Microrobots for Navigation and Object Manipulation at the Air-Water Interface

We use multiple spinning micro-rafts at the air-water interface as mobile microrobot collectives and present here their collective behaviors, including navigating around anchored obstacles, and trapping and transporting floating objects. The 3D-printed micro-rafts are circular disKS of 100 μm in diameter and have parametrically defined undulating edge profile. The study of their local interactions, manifested by the pairwise interactions between micro-rafts, reveals competing magnetic and capillary interactions that keep the collectives in their dynamic state. Using collectives of 7, 19, and 36 micro-rafts and micro-channels between millimeter-sized posts, we demonstrate the effects of the size of the collectives, the size of the obstacles, and maneuver strategies on the collective navigation. Employing methods from information theory, we show that the pairwise mutual information of the collectives increases significantly during the channel-crossing as a result of the additional constraints of the channel walls on the collectives. Finally, we demonstrate the trapping of 1-mm-diameter polystyrene bead and the trapping and transporting of 600~μm-wide pm.