For a 10-mm-long robot, as shown in fig. S9 (A and B), we observed noticeable motion even under an AC drive voltage as low as 8 V peak to peak (movie S6), which is a relatively low voltage requirement among insect-scale piezoelectric actuators (45).
The attached video demonstrates the locomotion of a 10 mm-long prototype in the controlled transparent quartz tube environment. Specifically, the relatively low voltage requirement is demonstrated by the noticeable motion at 8V.