Effect of compartment rigidity on locomotion. (A) Initial speed of MR-LF (left) and MR-LF-S (right) with equal mass across ya offsets (box colors). Boxes show the 25-75% range, whiskers indicate min-max, and mean values are connected by a black line (n = 5). A comparison between plots shows the effect of compartment configuration on speed, where the MR-LF robot has a rigid compartment, and the MR-LF-S has a soft compartment. (B) Total actuation distance (da) as a function of step number for the MR-LF (left) and MR-LF-S (right) of equal mass across ya distances (line color). Trials of ya = 10 to 14 cm converge within a span of da (indicated by brackets and denoted da*) which corresponds to the minimum field strength needed for locomotion.