Tortoise-Inspired Magnetically Actuated Soft Robot Enabled by Segmented Legs with Programmable Bending

Inspired by the natural curvature and jointed configuration of tortoise limbs, this paper presents a magnetically controlled soft robot based on a "programmable intrinsic curvature" design paradigm. When corrugated flexural notches are introduced into a single-material elastomeric leg, localized stress concentration enables each leg to acquire a predefined curved shape during fabrication. Combined with corrugated-straw-based sacrificial molding and magnetic-field-assisted curing, the strategy allows independent tuning of bending angle and leg length. Four legs are radially integrated onto a soft torso. Experimental results show that the stepping-pushing asymmetry of a single leg is governed by the predefined curvature, with the snap-through state corresponding to the equilibrium between magnetic attraction and paramagnetic deflection. The robot achieves speeds of 1.1 mm/s on dry ground, 9.5 mm/s in semi-submerged water, and 56 mm/s in fully submerged water (at 0.8 Hz, 340 mT), a ~50-fold increase in swimming speed compared with its terrestrial locomotion speed. It also demonstrates sharp turning, payload transport, rough surface traversal, and self-righting. This work elevates intrinsic curvature from passive geometry to an active design variable for soft robots in complex multi-environment scenarios.