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Comment by pretty_dumm_guy | Hacker News Reader

Hi,

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 :)

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1. I don't interface to my car's electronics over serial or CAN bus. Instead, I interface by emulating actuators and sensors the 4 speed gearbox computer expects.

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!

[0] https://youtu.be/H1T6vr44Zak

Thank you for your reply. That is quite enlightening. I am quite surprised that the Transmission Control Unit(TCU) is tolerant of the solenoid modification. However, I have two questions though.

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 :)

I was quite surprised, too. Maybe it was a little gift from Holden to the burnout bogans?

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.

Ah okay. This simplifies the setup a lot. I had done some testing and validation of ECUs 9 years ago. So my questions were based on the understanding I had developed back then. Thank you for clarifying it. Again, awesome work :)

If my car relied heavily on CAN (like the next generation Commodore) I probably would have sold it.

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.

Sorry for my late reply. I'm currently at work- I'll make sure to reply when I knock off. Have a great day :)

No problem at all. Take your time :)

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