(section: 3 / paragraph: b / line: 1)
Yes, as long as you design the part to be constructed as stated in rule 3.b. You may not have a predesigned part constructed on a 3D printer and used in your construction. General rule #1 applies (https://www.soinc.org/ethics_rules), as long as the designs were not commercially acquired. Competitors should be prepared to demonstrate to the local event supervisor this fact.