Catapult - Science-Project-a-pult

My son and I designed this catapult (patterned after an onager or mangonel) for his 6th grade science project. It is designed to go together without any glue, and only requires a length of 1/4" rod for the main axle, and two 1/8" pins for the bucket.

The bucket can be positioned along the length of the arm to explore how the length of the arm changes throwing mechanics. The bucket could also theoretically be turned one of two ways to see how the different inner profiles affect the release t