Scientists from MIT, Harvard University and City University of Hong Kong developed a drone with soft actuators. Each actuator takes the form of a thin rubber cylinder coated in carbon nanotubes. When voltage is applied to the device, the nanotubes produce an electrostatic force which both squeezes and elongates the cylinder. Once that voltage is shut off, the cylinder contracts back to its default state. Therefore, by rapidly switching the electrical current on and off, the actuator in turn expands and contracts, flapping the attached wings almost 500 times per second as it does so.