Our tentative battery rack plan failed on several levels. He'd like to see more welding and less screws; screws can work loose and pull through metal, particularly aluminium. In fact, where screws go through aluminium, there should be a small steel plate around it to resist tear through.
There should be no aluminium on the bottom of the vehicle where it can be ripped by scrapes and stones. Battery boxes should be attached to box sections by bolts that go through all the way. The bolt should go through a "crush bush" 2 mm thick welded on both sides. The idea is that you can torque up the bolt without crushing the box section. That's way more than the Tek screws we we envisioning
!We can move the front sway bar from its current position where it's somewhat in the way, but it needs to be bolted to something substantial; it's not just torsion that the bar experiences, as we thought, it also gets some vertical force. We should use the existing bracket as a guide for the new one.
We are planning two long racks of cells right behind the passenger's seats, about head height. Somehow we didn't think of what would be needed to restrain those racks of cells in the event of a sudden stop like a head-on accident. Fortunately this where seat belts and roll bars are attached, so something strong can be attached there. He will calculate how strong it needs to be offline.
We are allowed to bend up or down the spot welded seams around the boot and fuel tank areas, but he likes to see "stitches" of welds a few centimetres long, especially near corners. Apparently stitches are better than continuous welds, since a crack won't keep propagating past the end of the stitch.
Special attention is needed at reinforced corners like this:
We are to retain the reinforcing, but we can cut the seam nearby, e.g. where the yellow lines are. (There is an overlap of seems right near the reinforcing, hence the gap from the end of the reinforcing to the cut). The cuts should be curved as shown and stitch welded at the edges where the yellow lines are.
He made us aware that we are likely increasing the centre of gravity of the vehicle. Our original plan had more battery cells under the boot, but we put the controller there for better front to back weight ratio, but in the process raised the centre of gravity quite a bit. We have now modified our front to back spreadsheet to calculate the new centre of gravity. We believe it will go up 33 mm (from 403 mm), or about 8.5%. There isn't much that can be done about it, but it may make a 100 km/h lane change test more difficult. (We may or may not be made to take that test).
The new NCOP regulations should make it much easier for the engineer signing off. At present, there are no hard and fast rules, so it's all left to judgement and subject to controversy. With the new regulations, they can just "mark to the regs" and there is little room for argument.
In case you're wondering: that was the only photo I could find quickly with the reinforced corners.
