With 29 separate modules on CAN I've quickly realized that programming the entire vehicle logic would be a nightmare without very detailed forethought. Below is the current architecture layout with 10 separate CAN buses, 29 modules, and 3 EVCU's (Electric Vehicle Control Unit).
I decided to retain the factory location and structure for the EPS controller, 12V battery, fuse block, and engine cover.... These locations have been fully tested in production so this choice should help increase the overall quality and reliability of the build.
The one downside, or rather just an added analysis point, of using only OEM CAN components in the build is that I'll have to make sure that everything plays well together. Each component has CAN ID's that it uses for status messages and ones it listens to for commands. The complicated issue here is that these modules were designed for use on different vehicles, and different OEMs all together. If I threw everything on a single CAN bus two modules could use the same ID for status messages, or even worse, a status message from one module could be a command ID for another.
Now if I would have stayed with the arduino/EVTV hardware I'd be much further along, as I was already sending and receiving CAN messages with the arduino due & EVTV CAN shield months ago. I do truly feel though that a more reliable and safety focused board is needed when steering, throttle, and brake control is involved.
Another great aspect of this EV conversion is that I can justify to myself that I just need more tools. Ever since I learned how to MIG weld in early high school, but once I learned how to TIG weld in college I was hooked and knew that I wanted a TIG welder, but couldn't justify it.... until now.
The batteries are the most difficult to package and find the best location to mount. Both because they are a huge amount of volume, and that they’re my best lever to adjust the weight balance of the car.
The interface between the motor and the RX8 transmission is the most critical mechanical design of the entire build. I have to ensure that the shafts are aligned within thousands of an inch while rotating at 10,000 rpm and the spacing is perfect to ensure full clutch engagement and disengagement. Unfortunately there are no off-the-shelf parts that I can use for this, it all has to be custom.
Since this vehicle is supposed to be a practical daily driver in the summer, air conditioning is going to be a must. The RX8 has an AC compressor, but it is belt driven and clutch engaged. Belts don’t work with my design criteria of limited to no maintenance and engagement clutches just waist a lot of 12V power to lock the pulley to the shaft.
It was pretty unfortunate that USPS damaged my package to the point where they decided it was ‘of no value’. USPS customer support was an absolute pain to deal with through the 3 week process of finally being able to collect insurance on it, but in the end it was at least resolved.
Before I get everything installed, I need to get it all working and electrically setup the way I want. In order to do this though, I needed to get everything setup on the bench and create a control interface to take place of various signals that just aren’t on the bench (RX8 stuff like ignition, throttle, etc)
I ended up going with a stage 3 clutch and HD pressure plate. The stage 3 clutch uses a 6 puck design to increase the clamping pressure (psi) on the clutch surface. This upgrade also does away with the standard organic clutch material and replaces it with copper ceramic pucks. This is usually used exclusively in race applications because it results in a very short and aggressive clutch engagement. Luckily for me though, I could care less how harsh the clutch engagement is because I don’t need to slip the clutch at launch.
I put off purchasing a DC/DC converter for quite some time because I really wasn’t happy with any solutions that I could purchase. I just didn’t have any confidence that they would last, or really even meet my needs, until I stumbled across this perfect OEM solution.
Typical ICE engines are only about 20-30% efficient, putting the rest of the energy into heat, noise, and vibration. The high voltage AC drivetrain that I’ll be using is closer to 90-95% efficient, so there will be magnitudes less heat generation.
The challenge here is how to trick the EPS into thinking that the car is actually driving down the road when the ICE engine has been removed and the module that supplies the vehicle speed is also gone.
Step 1: Figure out what its looking for Step 2: Put those signals back on the bus
The RX8 cluster is primarily controlled through the CAN bus and listens for other modules broadcasting speed, rpm, temps, error codes, etc. Since the ECU will no longer be on the bus broadcasting these parameters (and there is no ICE engine to get sensor inputs from) I will have to send the appropriate CAN messages myself.
So I finally found what I think is the perfect car, and now its time to get it shipped up to Michigan. Now I've shipped quite a few cars across the country for work so I just assumed this would be an easy, painless process. Man was I wrong....
The motor and motor controller arrived as well! Not only did this not travel as far as the battery pack did from Israel, but since these are from the Azure Dynamics auction they're actually back home here in the Detroit area now.