Spider-inspired bidirectional robotic joints driven by electrohydraulic multiaxial strain

Compared with conventional motors and servos, soft-actuated angular-motion devices are superior in environmental adaptability and human-robot interaction, yet they can only achieve active bidirectional angular motion by integrating antagonistic actuators or restriction modules. The integration of such components introduces deformation antagonism, compromises structural simplicity, and increases control complexity. Herein, we propose a spider-inspired centimeter-scale soft bidirectional robotic joint driven by a pair of synchronously controlled electrohydraulic actuators (EHAs). Specifically, the EHAs generate multiaxial strain, enabling the joint to bidirectionally rotate depending on its physical state, without introducing additional functional components or asynchronous controllers. Furthermore, the joint demonstrates (i) high-speed (forward: 2851° per second, reverse: 1934° per second) and wide-stroke (up to 156.8°) rotational performance, (ii) multimodal motion (e.g., self-unfolding, self-folding, and reciprocating swinging), (iii) continuous response (up to 40 hertz), and (iv) payload-bearing capability. Last, three joint-integrated devices validate its feasibility as a multifunctional, high-dynamic, and single-channel-controlled actuation component in diverse robotic applications. This work establishes a viable design framework for minimalist yet versatile bioinspired robots.