We have demonstrated mm-scale untethered robots using a single axis magnetic field control to have swarm operations and independent crawling and rolling motions. There are three distinctive accomplishments as compared with the state-of-art: 1) working prototypes in the mm-scale with a moving speed of ~50 body size/s under the crawling mode operation; (2) an ultra-high moving speed of ~277 body size/s under the rolling mode operation; and 3) demonstrations of several complex swarming behaviors including chain-shape formation, crawling, and separation As such, the proposed operation schemes provides a new class of strategies to control mm-scale swarm robots for potential environmental and medical applications, such as minimally invasive surgeries
