From the data in Figure \ref{402200}C-D, we also observe that after 40 steps, all trials between ya = 10 to 14 cm converge within a span of da (denoted da*). We hypothesize that robots stopped traveling within da* because the time-average field strength of the actuator magnet near the mean of da* was unable to overcome the forces (e.g., friction) impeding locomotion. Further, the mean of the data within da* decreased with increased MR-LF mass (e.g., 2.55 g: 14.37 cm, 4.43 g: 13.22 cm) suggesting that a heavier robot requires a higher magnetic field strength to move. The ya = 9 cm trials for the heaviest MR-LF (4.43 g) also converge within da* because its increased mass enabled it to move at the higher magnetic field strength at ya = 9 cm.