V2 lower-leg candidates: PETG structure and stiffness

Three lower-link concepts for a Mini Cheetah-size V2 now include a common knee test flange, metal compression sleeves and a replaceable foot cup. Fusion CAD and a separate linear solid-FEM study compare a tapered I-section, a split box and diagonal ribs. The actuator interface is provisional; printing and physical stiffness measurements are still pending.

• Same 195 mm knee-to-ball reference length: A tapered web, B split box with shear registers and bolts, C diagonal ribs. The 195 mm length is a Mini Cheetah reference, not a finalized V2 requirement
• 20 N virtual-load comparison, A / B / C: in-plane stiffness 26.98 / 27.20 / 26.80 N/mm; lateral stiffness 5.47 / 11.44 / 8.36 N/mm. The reported displacement is a work-conjugate virtual coordinate, not measured foot-tip motion
• Three candidates, two mesh sizes and two load directions: all 12 FEM cases passed equilibrium and energy checks; maximum stiffness change between meshes 0.73%. CAD: 85 solids, no positive-volume overlaps
• B uses a continuous PETG reference without seam slip or metal reinforcement; its value is not the stiffness of the bolted assembly. All three omit contact clearance, print anisotropy, creep, impact and fatigue
• First physical comparison proposed: C against A. In this model C adds 10.3% link mass and 52.8% lateral stiffness, with similar in-plane stiffness. The tongue needs print support; no prototype has yet been printed or load-tested