Controlled Flight of a Microrobot Powered by Soft Artificial Muscles

Abstract

Flying insects capable of navigating in highly cluttered natural environments can withstand in-flight collisions because of the combination of their low inertia1 and the resilience of their wings2, exoskeletons1, and muscles. Current insect-scale (<10 cm, <5 g) aerial robots3-6 use rigid microscale actuators, which are typically fragile under external impact. Biomimetic artificial muscles7-10 capable of large deformation offer a promising alternative for actuation because they can endure the stresses caused by such impacts. However, existing soft actuators11-13 have not yet demonstrated sufficient power density for liftoff, and their actuation nonlinearity and limited bandwidth further create challenges for achieving closed-loop flight control. Here we develop the first heavier-than-air aerial robots powered by soft artificial muscles that demonstrate open-loop, passively stable ascending flight as well as closed-loop, hovering flight. The robots are driven by 100 mg, multi-layered dielectric elastomer actuators (DEA) that have a resonant frequency and power density of 500 Hz and 600 W/kg, respectively. To increase actuator output mechanical power and to demonstrate flight control, we present strategies to overcome challenges unique to soft actuators, such as nonlinear transduction and dynamic buckling. These robots can sense, and withstand, collisions with surrounding obstacles, and can recover from in-flight collisions by exploiting material robustness and vehicle passive stability. We further perform a simultaneous flight with two micro-aerial-vehicles (MAV) in cluttered environments. These robots rely on offboard amplifiers and an external motion capture system to provide power to the DEAs and control flights. Our work demonstrates how soft actuators can achieve sufficient power density and bandwidth to enable controlled flight, illustrating the vast potential of developing next-generation agile soft robots.