Hi, I'm the author of the article. Feel free to ask any questions you may have.
I have to go to bed, I have work in about 4 hours, so I'll reply when I can.
I have to go to bed, I have work in about 4 hours, so I'll reply when I can.
That being said, is there maybe somewhere a more thorough write-up about the whole thing? You know, with more in-depth technical details, gotchas, and so on? I'm sure many people would enjoy reading that!
Thanks for posting!
Sorry, no. I don't have a blog or website or anything. The closest thing I have to a devlog are some posts in a private Facebook group dedicated to the Holden Commodore.
I think this project is almost 12 months old now.
The approval I got from the engineer was due to the following points:
1. The 6 speed came out of a newer generation of the model.
2. My controller has some safety features.
3. My controller emulates factory hydraulic behaviour. Had I implemented something like a transbrake, I would have been in for a very long ride of red tape.
I contacted a VicRoads certified engineer in regards to the project and got the all clear.
Even my insurance was OK with it.
I think it's because most of the legislation is aimed at engine modifications.
Firstly, Congratulations. This is no trivial accomplishment. Here are the questions I have.
1. Normally, cars come with their own ECUs for the engine. Interfacing with them requires knowledge about the underlying firmware used afaik. Did you happen to reverse engineer the firmware so that you could interface your own electronics with the provided ECU ?
2. How did you make the car believe that your 6 speed automatic transmission was a 4 speed automatic ?
3. > "the ability to go ahead and change the way it works whenever I want." - Could you please elaborate what you mean by this ?
Again, I am amazed by what you have accomplished. My inner mechanical engineer is so keen to know how this all came together. I think everyone would definitely appreciate if you could provide a rough overview of how you achieved these things. Thank you :)
2. I'd like to introduce you to "manualisation" [0]. It's where the solenoids of the 4 speed are wired directly to the gear selector switch. The 4 speed computer is surprisingly tolerant of this, and it forms the basis of my interface.
My interface provides enough information to the 4 speed computer to stop it from erroring out or putting my car into limp mode. However, it is aware that something has changed because changes in engine RPM do not correlate with its shift commands.
3. I mean in terms of software. I can modify the behaviour of my box more than a standard tune can. I can add a 0-100KM/h tracker to my system, or shift lights, I can fundamentally change the decision making process in shifting (for the moment it's torque based), etc.
I could go out on a limb and a GPS module and a map; it'd select a gear based on the corner angle and speed or so.
Thank you for kind words :) If you have any other questions, ask away!
1. So based on my understanding, engine speed sensor readings are sent to the TCU which in turn regulates the solenoids(There might be other sensors as well but for my question, I think they aren't that important). So in order for your modification to work, you have to get these CAN frames, understand the reading, regulate your 6 speed auto gearbox and then create a CAN frame that would imitate the sensors of the 4 speed auto gearbox(to basically tell the TCU that the gearbox has been regulated correctly). You can in principle neglect the actuator commands that are sent by the TCU to the solenoids since you are regulating it on your own. However, in order to do this, you have to understand the CAN frames being used and also the protocol used(address based or message based). How did you figure this out ? Or is my understanding wrong here ?
2. Did you use FreeRTOS for your STM32F407 component ?
I really appreciate you taking the time to answer the questions :)
1. My apologies, I've confused you. CAN communications are purely internal for my system, it doesn't communicate via CAN to the car's computers.
The sensors and actuators give or accept voltage signals, and my controller inputs or outputs those accordingly. For example, the 4 speed has some pressure sensors to monitor the valve body behaviour, and I send some HI or LO voltage signals in emulation of it.
2. I do use FreeRTOS for the 407. I don't need to, since I use a super loop and all my memory is either static or allocated on the stack.
I love CAN bus (for my own designs), but I don't see the effort of attempting to reverse engineer GM's format as worth it, especially since I had no prior experience with CAN.
Thank you :) I've got another D automotive project which I hope to write about soon.
I spend a tonne of time in the reference manual for the 6 speed, and things clicked for what my next steps should be. It was really about trying to familiarise myself with the problem as much as possible.