When I was creating the ballista, I ran into some problems that took up more time than I hoped. For the head of the ballista, the nails I had put to hold the entire thing in place kept cracking the wood, so I made multiple heads with different screws and nails. The best one to use was the small silver-colored nails, and that was the one I ended up using in my final design. I also messed up the energy-storing part of the ballista. I tried using a string at first, to best mimic the photo, but then I did some tests and it kept failing to keep enough power inside. I used every type of string available to me, but they all failed. Then I thought of using the rubber band. Even though the rubber band does not look like the ballista in the photo, it works better than any type of string. I stuck with the rubber band, but I had no time to put the rubber band in place before I had to submit the project.