Design and Modeling of a Pinwheel‐Base‐Inspired Foldable Mechanism Capable of Helical Motion

Helical motion, characterized by coupled rotation and translation along an axis, plays a crucial role in many robotic and mechanical systems. However, existing soft torsional actuators often exhibit parasitic deformation, whereas conventional rigid‐body parallel mechanisms usually have limited rotational ranges and poor serial extensibility. To address these limitations, this paper draws inspiration from the pinwheel base and proposes a novel n‐limb revolute‐spherical‐revolute ( n ‐RSR, n ≥ 3) foldable mechanism capable of helical motion. The structural design, kinematic characteristics, design‐parameter effects, force transmission characteristics, serial extension, and experimental evaluation of the proposed mechanism are systematically investigated. Theoretical analysis shows that the proposed mechanism possesses three degrees of freedom in its general configuration and can generate symmetric helical motion under identical input angles for all limbs. The rotational range of a single module can approach 180° under appropriate design parameters, and the rotational output can be accumulated by connecting multiple modules in series without additional actuation inputs. Prototype experiments validate the feasibility of the proposed mechanism and show reasonable agreement with theoretical predictions. The proposed mechanism provides a compact and extensible solution for robotic systems requiring controllable coupled rotational‐translational motion.