Test drive and weight distribution

Post date: Oct 4, 2014 7:28:49 PM

After we succeeded in fitting all 64 battery cells in the car and finally getting the BMS to operate the contactors of the two separate battery packs, we were looking forward to be able to test the car on the street. This meant bringing it down carefully from the side of the house to street level...

But, one should remember that this particular car has low Koni shocks, which did not leave for a lot of ground clearance. Today, with all the batteries, weight has increased a little bit and the car has maybe 7cm of clearance in the front. So it scrapes one of the ramps when driving down. Clearly, new springs will be required to make this car road-legal...

Eventually we were able to test it in the street and play a bit with some motor controller settings:

It runs really nice, pulls well. Braking with the Hella UP30 vacuum pump works flawlessly. However, steering at low speed is hampered by the fact that it is now a manual rack, and there is a lot of weight on the front wheels, which are 215 wide.

Some days later we started to fear that the car might be too heavily loaded in the front to ever pass technical inspection. Mind you that Mazda has left very little room for actually "loading" this car. The '94 1.8 MX-5 weighs, depending on the options installed, around 1080~1100kg. The maximum load specified on the chassis plate is 1230kg. This means a useful capacity of less than 150kg. So a heavy driver and passenger and the MX-5 is at its maximum capacity?!

For the technical inspection, we cannot deviate too much from this weight. This is going to be a real challenge, since 64 LiFePO4 100Ah batteries weigh around 210kg, and the AC motor is about 72kg...

Related to this problem is the weight distribution. The maximum weight of 1245kg is specified to be 620kg at the front and 640kg at the rear (that adds up to 1260, but hey, that's what it says on the chassis plate).

So, since we have 10 battery cells hanging over the front axle, we suspect that we will not meet this specification. Since corner scales are very expensive, we decided to buy some cheap bathroom scales rated up to 180kg and weigh each corner separately:

The scales may not be super accurate, but the results were at least repeatable.

This result is without bumpers, dashboard, and some other accessories... So we will need to keep a close eye on the total weight, and are considering to move some of the 10 "overhang"-batteries in the front to a more central position to aid in the weight distribution. The question is... where?

To be continued :)