As many of you know, we’ve been working on open-sourcing a drivetrain from a 2011 Smart ForTwo Electric Drive. We can control the DC-DC converter, the AC unit, the charger and make the motor turn. It was time to move from our complete drivetrain test assembly to a workbench assembly where each of the components are set up and wired both independently from, and to each other, verifying we can run each of the items successfully independent of the vehicle’s wiring harness and together as if they have been placed into a custom EV build.
After moving everything to a bench and chasing down lots of wiring issues, setting up liquid cooling and a high voltage power supply, etc., we realized that even though we had all of the components working (to some extent), we still had to:
- map the motor data streams for some semblance of speed control over the motor (all we can do now is make it spin at one speed)
- build a control board
- write software to pull everything together into a single package and make it more than less usable.
All of this would be done by trying to control the motor through the existing control board via the existing software and whatever surprises that may have in store for us.
We were batting around different ways of making all this work, noting that none of us currently working on the project are what you’d call “programmers.” After much discussion and debate, we decided to take a page out of EV West’s book and build a new board that would control both the IGBT driver board and the DC to DC converter board and bolt into the existing control board’s location inside the motor housing. Now we can take advantage of work that has already been completed, and move the project along more quickly. Our board design is patterned after Damien Maguire’s Tesla build.
The new approach is to replace the inverter’s control board and software; this will make the motor easier to control, as we have access to the software that runs it, but slightly less efficient due to the type of control strategy being used. However, the control strategy we’ll be employing will work on almost any synchronous-wound AC motor and is approximately only 1-2% less efficient – a huge advantage for the small loss in efficiency.
Ideally, after we’ve built this board and have it working, we’ll be able to use it as a template for almost any other AC synchronous motor produced (i.e. Tesla, GM, Nissan), and quickly adapt it to run any of these motors. Of course the plan is to open source everything so you can build one, too. We may also make a small run of the boards for the Smart; if we’re going to build 4 or 5 for ourselves, we may as well have 50 made.
I’d like to thank Jarrod, Damien, Collin, the Software Guy, and all the other open source folks out there making this possible. Also thanks to EVWest who’ve been instrumental in making this happen and supplying the parts we need.
Here’s a link to Damien Maquire’s Tesla Project so you can see how he does it: https://www.youtube.com/playlist?list=PLPHK4T9kKEyblTISV7u-PrSgSV6VD4YYz