Battery box part 1

The bike needed a box to house the battery pack. Initially I was planning on doing something pretty rough with folded sheet metal at a local engineering shop, but my bud Jeremy offered to help, so we ended up designing and fabricating something much fancier with plywood. 

First I guesstimated the number of cells I could squeeze in the cavity between the seat tube and rear wheel with a few bits of board, and some old 18650 batteries I had lying around. I worked out I could fit 98 (14S7P).

Battery pack sizing

I then came up with a more pleasing geometry with a trusty bit of cardboard, a ruler, and a protractor.

Rough outline

The outline was fed into Solidworks, and the files given to Jeremy. He then beautified the design, and did all the important Mechanical Engineering stuff like working out wall thicknesses, hole sizes, etc. A prototype laminate was cut out of acrylic, and we sanity checked the fit.

Prototype sidewall laminate

Jeremy then made a cardboard model of the battery box on Solidworks, and then we checked the geometry on the bike. It looked good.

Test fitting the cardboard model

Next up was cutting the actual box material. We went with 18mm ply for the size walls, and 9mm for the lid and base. This was cut with a water jet cutter at Jeremy's work. That thing is seriously badass piece of kit, and made short work of the plywood.

Jeremy at the water jet cutter controls

Laying out the plywood.

Cutting plywood

The finished laminates

Jeremy didn't trust me to glue the box together (fair enough), so did it himself. I don't know how he did it (magic maybe?), but I presume he used glue and clamps.

The box all glued up.

Next up, we had to come up with a mounting solution for the bike, and surface finishing.