Active Transport Dynamics with Wave-Based Interactions

Diverse locomoting systems disturb the environment which then can in turn affect the locomotor. Inspired by the dynamics of small bouncing droplets interacting with obstacles via complex surface fluid waves, we study an 11.7 cm diameter circular robot fan boat in a 9 cm deep pool of water. We augment these dynamics with a vibration motor mounted on the boat which generates outwardly propagating waves at the boat-water interface with frequency range 10-45 Hz. We study the boat’s interaction with a triangular lattice of fixed circular obstacles of diameter ~9 cm and edge-edge separation distance ~17 cm. In most (14/16) trials without vibration, the boat is pinned indefinitely to the first or second lattice site it encounters. With vibration, the boat traverses the lattice via spontaneous reorientations and subsequent escapes at lattice sites due to complex interactions from generated and reflected waves. Higher frequency enables greater traversal; the mean number of times the boat contacts a lattice site before becoming trapped at the edge of the container was 1.2 ± 0.5 without waves and 5.1 ± 1.8, 5.8 ± 2.0 for vibration frequencies of 14.2 ± 1.1 Hz, 35.5 ± 0.6 Hz.