Fig. 3.

Sequential and directional propulsion. (A) A schematic of a robot with two bistable element–muscle pairs. A thinner muscle with faster actuation time is placed at the rear (i.e., $t_1<t_2$). (B) Three distinct phases of the actuation. Activation sequence. (I) Initial state with both muscles programed. (II) The thinner muscle activates, triggering the first bistable element and pushing the second muscle to touch the second bistable element. (III) The second (thicker) muscle triggers the second bistable element. (C–E) Snapshots from deploying three configurations of the multistroke swimmer that show three different directional motions at each of three phases.