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Old 10-21-2020, 06:27 PM   #1
kyoshi11
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Tap into ECU for brake pedal position

I know there is a TPS on the car and am wondering if there is a brake position sensor? I want to make active aero as a fun project and am wondering if there is a way to access brake and speed data?
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Old 10-21-2020, 06:42 PM   #2
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I know there is a TPS on the car and am wondering if there is a brake position sensor? I want to make active aero as a fun project and am wondering if there is a way to access brake and speed data?
What do you mean by brake position? Brake light switch? I think you can even sample real time brake line pressure. Depends on how deeply you want to dig.
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Old 10-21-2020, 07:08 PM   #3
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I want to make the wing actuate when brake pedal position is >50% and I plan to attach an arduino with other commands so the wing moves under certain conditions like if im going over 50 mph with >50% brakes and have it return to original position if I have my foot on the brake for longer than 5 seconds. Would i be looking into ECU for brake line pressure?
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Old 10-21-2020, 11:09 PM   #4
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I want to make the wing actuate when brake pedal position is >50% and I plan to attach an arduino with other commands so the wing moves under certain conditions like if im going over 50 mph with >50% brakes and have it return to original position if I have my foot on the brake for longer than 5 seconds. Would i be looking into ECU for brake line pressure?
80% sure you're looking for CAN ID 0xD1. Brake pressure is definitely available and you won't need to do anything directly with the ECU, just get the arduino listening on the CAN.

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Old 10-21-2020, 11:52 PM   #5
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I just added that parameter to my OBDLink app. It's there and works but I don't know dig it out.
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Old 10-22-2020, 04:25 AM   #6
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As folks have said already your only option is the brake pressure sensor signal, but it is probably a better solution for what your after

Iíve recently mapped some CAN ID to my AIM dash, they might be helpful for you if you going down this route, combo of TPS and Brake pressure should make for a nice active aero solution.

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Old 10-22-2020, 06:46 PM   #7
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I’ve recently mapped some CAN ID to my AIM dash,
Do you know how those values can be translated to parameter IDs for a tactrix logger? I get gain and offset but the rest is a mystery.
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Old 10-23-2020, 12:03 AM   #8
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You might find these useful:
CAN bus: https://github.com/timurrrr/RaceChro...can_db/ft86.md
OBD PIDs: https://racechrono.com/forum/discuss...r-frs-brz-gt86
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Old 10-23-2020, 12:37 AM   #9
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Ahh hey, you're the last post in that racechrono thread that I dug up looking for this! Lots of good info in these links.
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Old 10-23-2020, 09:34 PM   #10
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Why not run the active aero off a accelerometer. Car weight distribution would seem to be more relevant than brake pressure, which could change on the track.
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Old 10-23-2020, 09:52 PM   #11
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Why not run the active aero off a accelerometer. Car weight distribution would seem to be more relevant than brake pressure, which could change on the track.
Accelerometers typically produce pretty noisy data, so you need to use some filtering, which will most likely introduce some delays, making the whole system less effective (aero helps the most when you start braking).

You may also introduce a positive feedback loop, where as you progressively press on the brake pedal you first have low deceleration, and then the aero kicks in as soon as you a certain amount of deceleration. This may make the car respond non-linearly to increasing deceleration rate. The unpredictable delay will only make this effect worse, kinda similar to a turbo lag.
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Old 10-24-2020, 06:36 AM   #12
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Do you know how those values can be translated to parameter IDs for a tactrix logger? I get gain and offset but the rest is a mystery.

Hi

Been a while since I messed with the OBD PIDs and Iím not familiar with that particular logger if Iím honest. But attached are the standard PID codes for the OBD (not all will be applicable for 86) and Iím afraid I donít know how your logger takes the PID data addresses so you might have to fiddle about a little.

Anyways hope itís of some help.

86 Standard PIDs 4.pdf
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Old 10-24-2020, 02:04 PM   #13
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Hi

Been a while since I messed with the OBD PIDs and Iím not familiar with that particular logger if Iím honest. But attached are the standard PID codes for the OBD (not all will be applicable for 86) and Iím afraid I donít know how your logger takes the PID data addresses so you might have to fiddle about a little.

Anyways hope itís of some help.

Attachment 194116
He was talking about mapping CAN PIDs, not OBD PIDs. The doc you've attached doesn't mention anything about brakes.
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Old 10-29-2020, 04:36 PM   #14
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If you want active aero, best way is to have it driver controller. Add a button or switch to change wing position. Have your normal cornering position as your default, and then reduce angle (or open wing if multielement) on the straights. Dont do the other way around (increase angle during braking), air becomes turbulent as the wing moves, you dont want that to happen midcorner and you will loose the downforce as you step off the brakes and onto the gas, when you still need it a lot.
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