Thin, flexible, and scalable mobile robot driven by electrostatic zipping actuators

Small-scale soft mobile robots are an attractive solution to gain access to hard-to-reach places. We demonstrate a thin (similar to 4 mm) and flexible mobile robot, 8 cm x 9 cm, mass 4 g, that uses 6 electrostatic zipping actuators with hydraulic coupling, to generate stepwise linear motion. The device is made from laminated films of polymer materials including a high-permittivity layer of a PVDF-HFP/BaTiO3 composite. Typical operating voltages are around 2 kV, and actuation frequencies range from 1 to 10 steps per second. The HAXELs in the demonstrated device have a side length of 20 mm. Each one is segmented into 4 quadrants that can be independently actuated. This enables each of the robot's 6 feet to move both front-to-back and side-to-side, allowing for sophisticated motion of the robot (i.e., forward/backward, steering, and sideways movement). We vary several design parameters and investigate different gaits, exploring parts of the large parameter space of possible designs and motion sequences. Locomotion speed up to 2.4 mm/s and a maximum payload capacity of 80 g (20x its own weight) are demonstrated for certain configurations. The actuator scale and other design parameters could be easily adjusted to optimize for movement speed or payload capacity, depending on the intended application.