Effect of robot mass and actuation distance on locomotion. (A) Initial speed of MR-LF with various masses 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 mass on speed. (B) Schematic showing total actuation distance (da), calculated as the diagonal distance from the actuator magnet center to the robot center. (C,D) Total actuation distance (da) as a function of step number for the MR-LF (C) and MR-DF (D) designs 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.