The untapped potential of electrically-driven phase transition actuators to power innovative soft robot designs

In the quest for electrically-driven soft actuators, the focus has shifted away from liquid-gas phase transition, commonly associated with reduced strain rates and actuation delays, in favour of electrostatic and other electrothermal actuation methods. This prevented the technology from capitalizing on its unique characteristics, particularly: low voltage operation, controllability, scalability, and ease of integration into robots. Here, we introduce a phase transition electric soft actuator capable of strain rates of over 16%/s and pressurization rates of 100 kPa/s, approximately one order of magnitude higher than previous attempts. Blocked forces exceeding 50 N were achieved while operating at voltages up to 24 V. We propose a method for selecting working fluids which allows for application-specific optimization, together with a nonlinear control approach that reduces both parasitic vibrations and control lag. We demonstrate the integration of this technology in soft robotic systems, including the first quadruped robot powered by liquid-gas phase transition.