Battery Box Designs
I made the most intrusive modification of the 320i yet - cutting big rectangular holes in the rear seat platform to make room for battery boxes. The old duel gas tanks were located under the rear seat and the area left after their removal is an ideal place for battery placement. It is low and near the rear axle. I cut two 9.5"x20" holes in each side of the rear seat platform that will make room for 24 batteries on each side. Cutting the metal proved to be challenging. I used a saber saw that has a 1/4" blade. It is very controllable and precise, but the blades for cutting this thickness of metal just do not last. I think I went through 5 or 6 blades cutting the two areas. I also used a saws-all that I have and that cut through the metal like butter, but it was very hard to make a precise cut. I wanted to make the rectangular holes for the boxes to be cut precisely so I would have less material to fill in later. The joint between the boxes and the rear seat platform will have to be sealed on the inside. I also had to be careful with the cutting because the rear brake lines run around the inside of the gas tank space. Unfortunately the batteries are so tall that the battery box extends 1 inch in the front and 4 inches in the back, because the rear seat platform slopes to the back of the car. The battery box has to stick out of the rear seat platform because the bottom of the boxes cannot extend beyond the level of the rear cross-member. The boxes will have to be supported below and I am thinking of putting a thick aluminum plate under each box to protect it. The rear seat cushion will have to be modified to fit over the battery boxes. From the thickness of the seat cushion it will be possible to cut the springs out of the cushion and the seat should fit over the battery boxes with that modification.
I also made progress on the drive train. As noted in my last blog, when spinning the rear wheels there was considerable vibration in the drive train. My friend Tim Catellier emailed me and said from the video of the driveshaft installation he could see that I installed the carrier bearing upside down. Tim has converted a BMW Z3 (http://evz3.blogspot.com/) and knows all about this two piece BMW driveshaft. I flipped the carrier bearing over and voila the drive train has no vibration!! I tested up to 65MPH. The only detectable vibration was right around 25MPH. It is possible the car always had that vibration - it would not be noticed as that is right around the shift point of 1st gear. I spun the wheels up in 4th gear. The video of this progress can be seen here.
Images of the drawings for the battery boxes are here.