Quick engineering checks. kind='beam' {length_mm, load_N, width_mm, height_mm, support:'cantilever'|'simple', material}; 'torsion' {torque_Nm, diameter_mm, material}; 'bolt' {diameter_mm, load_N, bolts, grade, mode:'tension'|'shear'}; 'motor' {force_N, radius_mm, speed_rpm, efficiency}; 'spring' {wire_mm, coil_mm, active_coils, deflection_mm}; 'belt' {drive_diameter_mm, driven_diameter_mm, drive_rpm, center_distance_mm}. Materials: steel, stainless, aluminum, titanium, brass, abs, pla, nylon. Cost: 1 credit per call.