Fig. 6: Morphing a robot’s leg enables untethered and unconstrained amphibious locomotion.

a The amphibious robot has four 2D bending SMMs as the legs. It swims in the water using the rear two legs in a straight shape as flippers. It morphs the flippers into curved limbs for walking on the ground. b The mechanical design of each leg’s power train. The robot body was cut for a better view. The gray surfaces indicate the cutting cross section of the robot body’s wall. c The schematic of the robot’s electrical circuit. d The robot swims, morphs, and walks inside a tank. The inset shows the morphing process: first the legs are rotated up vertically, and then the spines are softened, and the legs become curved after the TCAs are actuated. Finally, the legs are rotated to dip into the water to speed up the stiffening of the spine. e The robot walks, morphs, and swims in a natural outdoor environment.