Carbon Fiber Layups
We considered multiple materials for fabricating our enclosures. Aluminum would be too heavy, and we didn't have the equipment and experience to create clean, watertight welds. We evaluated multiple COTS plastic enclosures too, but it would have been hard to find one for our exact dimensions, and the seals would not have performed as well as we would've liked them to.
Carbon fiber could be molded to virtually any shape and size we needed while still being lightweight. Although it was the most expensive option, we decided that the benefits outweigh the costs, and learning how to perform carbon layups would be a skill that would greatly benefit the team.
Carbon Fiber Cutlists
We decided on a wet layup, as it was cheaper than pre-preg and would not require an autoclave. All the enclosures consist of a combination of two fabrics: a 19.75 oz 2x2 twill for providing structure on the faces, and a 5.7 oz 2x2 twill to overlap the gaps between the thick fabrics and to act as a finishing layer as well.
We carefully designed the layouts, then traced onto the fabric before cutting them out.
Cutting fabric
We shaped the molds from polystyrene, using a hotwire cutter and sanding. The hotwiring templates were laser-cut hobby plywood. The dimensions of the enclosures' openings were critical, as the allowance between the carbon fiber enclosure and the aluminum lip was between 0.08"-0.13".
Hotwiring the battery enclosure mold.
We used 60-minute epoxy, which was more than enough time for our four smaller enclosures but was just enough time for our large part. For our first part, we had problems with the mold sticking to the carbon, so we wrapped the remaining molds with clear packing tape. The remaining parts did not have any trouble coming off of the packing tape.
Final Completed Part!
Working with carbon fiber was easier than I expected, but still difficult nonetheless. The whole process was a lot of work, and there were many unexpected challenges. However, the entire experience was very rewarding, from design to sanding, and I'm glad to now have basic experience with composite design and fabrication.