Hello Electrified Miata Fans! Last weeks goals were:
1. make more BMS boards,
2. finish up the mid-sized Miata battery pack
3. continue constructing the bell housing adapter for the Leaf motor/Miata transmission.
4. Debug why 12 BMS boards didn't work as a string.
There were certainly some changes in status through out the week. Join us on the journey to make the Electrified Miata prototype and see what we've learned along the way.
As you may remember from last week, only 7 of the 12 BMS boards responded when I connected them in a string. If we used 6 BMS boards in one string, everything worked, but not so with 12. We thought 12 should work, so I asked Joe to help with this problem. He brought a nice tool that both functioned as a oscilloscope and a logic analyzer. The tool (https://www.saleae.com/) , plugs into Joe's computer via USB and understands serial data logic, that is, it can translate the ones and zeros into hex bytes for the humans. Quickly, the tool helped us see that the dreaded signal degradation was the cause. This was Saturday night, and for fun, because I wanted to find any other problems with the system, we decided to try the system at 1200 baud. Since it was known the system didn't work with 12 boards, we went back to 6 boards in a string. Joe made a new firmware image and tried to install it using the boot loader function. That didn't work and we spent a fair amount of Saturday night eating pizza and debugging.
Joe left scratching his head. Sometimes things are clearer the next day. In this case, Joe couldn't reproduce the problem at his house. Joe was persistent and kept changing things and was able to reproduce, understand, and fix the problem. Our boot loader now works even better.
After all of that, Joe showed off the newest revision with the signal degradation problem fixed in an 8 stack working at 9600 baud. Yay!!!
The older revision BMS boards had a 14 microsecond delay per board where as the newest revision has ~700 nanosecond delay per board. We still have one more revision after this one, but we are zeroing in on having a very usable and cheap and clean BMS system. The BMS is coming, the BMS is coming!
The rest of the the week went by quickly and car night was here again. Bruce and Brian worked on forming the bell housing adapter. They had chosen the hardest parts first, so this time, everything was a little easier. In fact, so much easier that all the parts were cut, drilled and fitted.
Now we'll have to weld them together. We need a motor to hold the pieces in place while Bruce welds, so I'll take apart motor number 3, which has a broken coolant port and some snapped engine mounts. With the motor separated from the inverter, we aren't welding with sensitive electronics attached.
Ed made progress on the coupler, straightening out the problem I created on the clutch end of the coupler. (see last weeks blog).
He then started on the opposite end, which holds the Leaf motor coupler. Of course we lost another screw that holds the lathe cutter. I'm thinking loc-tite blue may help with this problem, as loosing this screw does slow us down.
I wasn't the most productive this week, but I did get the mid sized Miata battery nearly finished, installing pig-tails and electrically joining the test packs into a mid-size Miata pack. I also installed the protective bottom plastic, leaving only the plastic top and last electrical link to finish this week. Between the three Miata batteries, and the 2 test packs, we'll be able to spin the motor to complete the alignment process between motor and transmission. Once that is finished, we'll be installing the motor in the car! I better get the big Miata battery finished too and the engine bay cleaned up. Yikes, there is a lot to do!
I won't be writing to y'all next week as I'll be enjoying the weekend at COTA watching Broch Evans drive his formula Mazda and taking a little time off to celebrate my birthday. We'll be staying on the straightaway at the behest of my wife in her RV that needs a little work. That was some pretty clever thinking on her part to get me working on her RV!
The goals for next two weeks are:
1. finish and weigh mid-size Miata battery
2. weld bell-housing adapter.
3. finish and weld clutch/Leaf coupler.
4. spin our test motor with low torque using the laptop
5. Test 20 BMS boards in a string.
This will put us in a position to finish mounting the transmission and
start working on making motor mounts for car installation! We are
getting so close now.
Thanks for reading! Hope everyone is healthy and having fun.
See y'all in two weeks.