Spring toy-inspired soft robots with electrohydraulic actuators

Toys are useful resources for structural inspiration in science and engineering. Their fascinating structures provide new strategies for robotics, particularly in overcoming challenging obstacles and increasing adaptability to unstructured environments. Recent advances in actuators made of soft materials have enabled robots to exhibit safer and more adaptive behaviors during locomotion. However, it is still difficult to descend quickly without falling off at the drop point. In the same context, we recall playing with spring toys descending on stairs. In this paper, we introduce an electrohydraulic-based soft robot inspired by the structure of spring toys. The robot demonstrated a novel and previously unreported ability to descend a series of stairs. Specifically, the soft robot consisted of a helical structure and multiple electrohydraulic actuators. A helical structure was used to accommodate the expansion of the electrohydraulic actuators and to operate a wider range of bending motions. This design prevents unpredictable falls and achieves operation while maintaining a sufficient level of flexibility. We also experimentally investigated the actuation characteristics of the soft robot in terms of motion and force. Additionally, we demonstrated a soft gripper using the spring toy-inspired robot as another potential application.