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?

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.

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.

I just added that parameter to my OBDLink app. It's there and works but I don't know dig it out.

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

I’ve 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.

https://uploads.tapatalk-cdn.com/202...8a14a45398.jpg

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.

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

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.

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.

Hi

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

Anyways hope it’s 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.

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.

Speed, Brake Pressure and Yaw would be the most important things I think.

I like the idea that the default position of the system should be "max downforce", and that it should only ever be in a non-default position when the accelerator pedal was at 100% for sufficient time recently.

A somewhat tricky thing is how to ignore gear changes.

Hmm, by introducing "lag" prior adjusting wing slightly longer then it takes for upshift, so that you are w/o aero adjustment on full throttle again?
Then again, in some tracks there might be fast speed shallow turns where one can stay on full throttle throughout with stock power level and good tires/aero. Imho switching off from full throttle despite flooring it might be wrong in this case. Then maybe custom aero adjustment tuning from GPS coordinates as input? Heck .. digging into too deep. And wouldn't have confidence to rely on it while driving 10/10.
I get overall impression, that active aero that gets auto adjusted is too overcomplified and not safe enough. And even if implemented, better with more/less button control from cabin, not from sensors/canbus reading to get pedal positions and so on .. but as on-the-fly manual choice of aero specific corner preoptimized, why not. Won't differ much from brake bias/engine map/TC/ABS choice for GT3 cars adjustment while driving, depending on corner configuration, how far into race thus weight/fuel, and condition of track/temps/rain/tire wear/pace.
But brakes position .. still useful, but better left for logging/telemetry purpose, to analyze driving and find out errors, what/where to fix with driving inputs, not as input source for active aero.

Deactivate wing movement when clutch is depressed. Working by GPS coordinates would take a lot of individual track tuning.

lot of .. but potentially netting best results possible. If something like dampers can be adjusted by gps (tein's EDFC), why not wing?