Despite the breakthroughs in the locomotion of robots at the macroscale, there is not a counterpart at the miniature scale. A recent review [1] pointed out the limitations of sub-gram systems. Locomotion based on legs is already well established for robotic platforms. Assuming a back and forth motion of the legs, a net displacement can be attained when the forward slip is not equal to the backward slip. The use of inclined legs is a common approach to achieve such an asymmetric slip. Reference [2] provides an excellent review of this approach.

Here we propose a sub-gram system based on flexible materials. The body of the robot was a 3 cm long thin film of piezoelectric polyvinylidene fluoride (PVDF) polymer. The actuation mechanism was an in-plane extensional vibration mode of the PVDF film. Two U-shaped 3D printed nylon legs were fabricated, each attached to the edges of the PVDF support. The total mass of the PVDF/legs combination was below 20 mg for all the cases under study. Unidirectional locomotion was achieved, with a maximum speed of 47 mm/s, equivalent to 1.5 body lengths/s, at a voltage of 15 V, with 2 mm long legs at an angle of 60º to the PVDF film.

[1] Ryan St. Pierre, Sarah Bergbreiter, “Toward Autonomy in Sub-Gram Terrestrial Robots”. Annual Review of Control, Robotics, and Autonomous Systems 2, 16.1-16.22, 2019.

[2] Walter Driesen, “Concept, Modeling and experimental characterization of the modulated friction inertial drive (MFID) locomotion principle: Application to mobile microrobots”. PhD thesis, École polytecnique fédérale de Lausanne, 2008.