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Author Topic: Drive by Wire Throttle (DBW) & Left Foot Braking (LFB)  (Read 333 times)
LGMCCARTHY
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« on: August 04, 2017, 05:47:15 PM »

I have a question for the autocross group about LFB a newer auto with a Drive By Wire throttle.

I RFB when I autox my 2012 Miata, and I have never experienced what my co-driver did at the recent Champ Tour  @ Toledo.

My co-driver, Tom Corron of NWOR, is a LFBraker, he has never driven my Miata before but has prior experience in a 2009 Miata.  On his TnT runs on Friday he experienced power loss (DBW throttle position to idle.) every time he LFB while maintaining partial throttle when he went to back to full throttle.

1.   Traction Control and Stability Control turned off before every run. 
2.   We disconnected the battery and did a reset of the Stability Control system and the steering wheel angle sensor.
3.   We checked full level with the Torque App and it was 25%, added fuel to bring it up to 30% (about 4 gals.).
 
Made another run, same result.

1.   We disconnected the battery and did another reset of the Stability Control system and the steering wheel angle sensor.

Made another run, same result.  Tom's TnT runs were about 0.5 sec slower than my runs, definitely not normal for Tom's abilities, even taking into account his first time in my car.

Since TnT runs were over we devised a plan of action for Saturday's runs.  Since I was running first, I would make a normal (slower than molasses run) using my normal RFB style and report back.  Based on my feedback Tom would try modifying his LFB style first before going to RFB.

My first run was a normal (slower than molasses run), but I did not experience any issues with the car's power, there were a couple points during my run where I could have spun the car if I used more throttle.  So, from my viewpoint my car was making good power.

We had a smaller run group and Tom's first run was about 10 minutes after my first run.  He started the run using his normal LFB style, experienced power loss at three points during his first run, neither the first two instances being as bad as what it was doing on Friday's runs, he started to have the power loss a third time, but he completely lifted off the throttle quickly before going back to full throttle and the power loss stopped as soon as the throttle was lifted.

So it appeared to us that the car didn't want the throttle and brake applied at the same time for a extended period (2-3 seconds), and if you did this it would reduce power because it detected some kind of emergency situation.  Maybe related to the Toyota unintended acceleration issue in early 2000's.  I have done some research and found that a number of automakers have programmed the ECU's with what they call a BOS (Brake Override System).  This system sends the output to the DBW throttle to idle in the event both the throttle and brake are both depressed for longer than 1-2 seconds.

Has anyone experienced this BOS while autocrossing a newer DBW car?

Does anyone know of a legal, temporary override of this system, so that one can LFB with aggressive throttle application for autox?

Comments greatly appreciated, thanks ............. Larry   Smiley
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Larry McCarthy
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« Reply #1 on: August 05, 2017, 02:50:29 AM »

I have left-footed for about 27 years now, and yes, there are cars that reduce or cut the throttle when the brake is applied at the same time. For example, pretty much the entire Nissan lineup. Took me a while to readjust myself driving Pete's SE-R or Ryan's 370Z. Nissans cut the throttle to 25% when the brake is applied.

A good solution is to temporarily disconnect the switch at the brake pedal that activates the brake light circuit. This is how the helicopter mom ECU knows when the brake is on. Of course, this can have adverse effects with regard to the ABS, so test. Thoroughly.
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dps214
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« Reply #2 on: August 05, 2017, 09:46:15 AM »

Sounds right. To my knowledge most newer things do that. I'm not a left foot braker but I've screwed around with the fiesta enough to know that it has that feature. Disconnecting the brake switch may work but I think it's not technically street class legal. In my experience there's ways to override it at least for a few more seconds, but not that I'd want to try on an autocross course. ( throttle -> brake -> quickly lift off and reapply throttle)
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Dan Shea
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LGMCCARTHY
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« Reply #3 on: August 05, 2017, 09:18:10 PM »

Dan,

That's exactly how my co-driver was able to LFB to some extent.  Throttle -> LFBrake -> Quickly lift off and reapply Throttle.  He improved as he got more runs, but he still was struggling with getting the right timing, and he wasn't able to balance the car's transitions the way he was used to doing in his non-DBW NA Miata.
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Larry McCarthy
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« Reply #4 on: August 07, 2017, 08:34:42 AM »

The Corvette does not like the brake and throttle to be depressed at the same time.  After years of LFB, we've gone back to RFB and use the dead pedal to keep us planted in the seat.

While admittedly I do not have cat-like reflexes (unless it's an old, fat, half-blind cat), I think to get the timing just right to not engage the the system and do effective LFB in a modern car is going to be a challenge, and I think you are better off just doing RFB.  It's too easy to leave one of your feet hovering over the pedal and inadvertently engage the system at an inopportunity time.
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I have two big heavy 'Murican race cars. Must be an old guy thing.
LGMCCARTHY
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« Reply #5 on: August 07, 2017, 09:31:46 AM »

Rich,

I agree totally with you.   Roll Eyes

I am just trying to understand how the system works so that when I get the opportunity for a LFB co-driver to wring out my car, I can maybe do something so the he will not have to completely go against his long developed style.  I would like to find a legal, safe way (doesn't affect ABS) to disable or minimize the intrusion of the BOS.

I have never LFB and more than likely never will, and as such was completely caught off guard when my Champ Tour co-driver reported almost complete power loss during his first TnT runs in my car.

My research continues...............  Smiley
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Larry McCarthy
2001 Miata - STR - Semi-Retired
2012 Miata - CS
frsbaum
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« Reply #6 on: August 08, 2017, 10:20:30 AM »

On some manufactures (like Honda), you can over ride the BOS by increasing the amount of throttle after applying the brakes.  So even if you are at 100% throttle going into your braking zone, after applying the brakes quickly reduce throttle to ~50% and then back to 100%.
If you are going into the breaking zone at less than wide open, its a little easier because you can then just add more gas while breaking and then pull back again before releasing the brake.  The Honda logic also gives you about 1000ms before cutting the throttle so in very short braking zones its not even as much of an issue.

Not that Honda makes a RWD fun car anymore, but this might help out CTR drivers.
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Steven Schairbaum
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« Reply #7 on: August 09, 2017, 11:20:47 AM »

Just tell the fool to RFB and their problem will be solved.
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Banshee
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« Reply #8 on: August 09, 2017, 11:49:09 PM »

On some manufactures (like Honda), you can over ride the BOS by increasing the amount of throttle after applying the brakes.  So even if you are at 100% throttle going into your braking zone, after applying the brakes quickly reduce throttle to ~50% and then back to 100%.
If you are going into the breaking zone at less than wide open, its a little easier because you can then just add more gas while breaking and then pull back again before releasing the brake.  The Honda logic also gives you about 1000ms before cutting the throttle so in very short braking zones its not even as much of an issue.

Not that Honda makes a RWD fun car anymore, but this might help out CTR drivers.

I heard that awhile ago. They were doing some tests during the promo phase of the CTR rollout, and the CTR is the only vehicle that didn't give them some kind of error on the dash/and or reduced power.
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