Omnidirectional motion of an untethered tripodal microrobot using radial piezoelectric actuators.

Miniature robots require minimal operational space for confined environments. Here, we propose an untethered tripodal piezoelectric robot to achieve omnidirectional locomotion and narrowing its required turning space exactly to its compact size (Φ3.10 × 2.75 cm3, 12.2 g). Three radial piezoelectric actuators synthesize six circumferential driving forces, while a trajectory interpolation algorithm enables omnidirectional locomotion without attitude turning. By switching between high-frequency continuous and intermittent excitation modes, the robot achieves a wide dynamic range, spanning from a 3 cm/s macroscopic speed to a 0.56 μm microscopic step resolution, thereby enabling both rapid maze navigation and precise cross-scale microscopic observation. Integrating actuation, control, communication, five onboard sensors, and power, the robot execute various inspection tasks with the capability of autonomous navigation and multi-robot coordination. These results validate key performance attributes in achieving both high integration and omnidirectional motion to enhance the ability for inspection and exploration missions.