How To: 3Step as Wheel Speed Differential Traction Control | AEM
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Kurt
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How To: 3Step as Wheel Speed Differential Traction Control

Below is the setup procedure I use to tune the 3Step function to act as wheel speed differential traction control in the Series 2.  This won't be as advanced as what you can do in the Infinity, but it gives us V2 guys something that works pretty well.  Unfortunately, I think it will only really work as TC for manual transmission cars.  It's fairly customizable for slip target and torque reduction aggressiveness.  It won't allow any in-cab adjustment for slip target like the Infinity does.

Most cars will have the VSS in the transmission.  It's important to have a sensor that reads the transmission tailshaft speed in order for the AEM to accurately calculate gear position.  Usually what the AEM computes for Vehicle Speed comes from this sensor, but we want to change this so it's looking at an undriven wheel instead.  You will have to determine what signal you are working with from your ABS sensors.  Usually, they'll be variable reluctor and the signal is a zero volt crossing sine wave.  On different V2 applications, T4 will be hardware configured to accept either VR or Hall (square wave) signal.  It voids your warranty to open the box, but often times there is a jumper selector that lets you choose which signal T4 is looking for.  It's up to you to figure this out for your setup, but the goal is to get a front wheel speed sensor going to T4 input so the AEM can use this for Vehicle Speed.  Set your VSS input to T4 and tune VSS Calibration so the AEM is showing correct Vehicle Speed.  Begin with VSS Cal*8 = OFF and only turn it on if needed.

In addition to this pin, you may want to add a switch to turn 3Step on/off.  One leg of the switch goes to chassis ground and the other goes to a spare switch input.  You may want to add a few switches while you're at it for other things like internal logging, nitrous, etc..  The switch isn't absolutely necessary since you can define the cut tables for a maximum rev which will effectively take the place of your main rev limiter options.

For calculating gear, you'll need to set your GearCal Spd 1/2 options to Crank (T1) and T3.  I think most applications use T3 as the input for the VSS in the transmission.  Watch the channel Gear Ratio for each gear to set the GearCal M option.  In my case, I set it to the maximum value of 10 and I see Gear Ratio at about 42 in 6th.  The important thing is to set this so you're getting a maximum value less than 255.  To set your Gear Ratio table, look at what your Gear Ratio is for each gear.  There will likely be some jitter, so note the highest and lowest value you see.  I saw a low of about 8 and a high of about 9 for 1st gear.  I added a small buffer above and below these and set the 1.0 cell to 7.5 and 1.5 cell to 9.5.  The AEM will show 1st gear when Gear Ratio is between these values.  Do this for all gears and don't make the buffer too large.

Below are the settings I use for a 6spd Supra.  The VSS Smooth/Filter/Allowed Diff/ Diff Reset Count options are set that way to give the fastest responding Vehicle Speed channel.  This is important for the 3Step funciton to work well.  The T4 options are what I use for my ABS VR sensor.  If using Hall, you'll set these to zero.  Fuel/Ign Cut C/M options are explained below.  Since I use fuel cut % for torque reduction, O2 feedback is not active in boost.  You will also likely want to adjust your VSS breakpoints.

What will be unique to each car will be the values in the 3Step cut tables.  These tables define the target slip for each gear.  In order to set these you will have to gather some clean data for each gear of Vehicle Speed and Engine Speed.  I recommend you get this data from an internal log at the highest speed for best accuracy.  At low speed there may be a few errors due to low voltage from a VR sensor, so you'll want to only use a data range that's clean.

To set your target slip, you must first determin what zero slip is for each gear.  First, log data for about a 2000rpm range for each of the lower gears under light acceleration.  You may not be able to get that range for overdrive, but that's ok.  The complete range of data must be under some acceleration so no play in the driveline is a factor in the calculation.  Engine braking will change the slope of the data slightly and, of course, full throttle with wheel slip will give you useless data.

Open the log in AEMData and open an XY Plot.  Set Vehicle Speed to X and Engine Speed to Y and check the "Plot Regression Line" box.

Highlight a range for 1st gear and multiply the slope by the VSS MPH that will be around redline. This will be your zero slip data for your particular wheel/tire combo.  Make sure the regression line goes very close to 0:0 when you get the slope for each gear.  If you change wheels or tire size, you may have to get this data again.

Enter this data in your 3Step Fuel Limit table.  Then interpolate to zero MPH for each gear.  From there you choose how much slip you want.  For 1st gear, I chose 20% at 20MPH and 10% at 50MPH.  Then interpolate between 20 and 50.  For 2nd, I do 15-20% at 30MPH and 10% at 80MPH and interpolate between these two cells.  Similar for the next gears.  I'll pick the MPH cell that's around 3000rpm at zero slip for each gear and raise that by 10-20% and set the cells below that MPH to 5000rpm to avoid any action during gear changes for normal driving.  Then I set the rest of the cells to my main rev limit level.  So, 1st gear at 50MPH will be 9000rpm after I increase it 10% from 8200.  I'll set that cell and all the ones above it to 7600.  Same for each gear, find the MPH cell that is just below your main rev limit RPM and set the next cells to your main rev limit.  This way, you can leave 3Step to Always ON and you will still have your main limiter.  You may want to play with the lower VSS breakpoints and set some different levels for 1st gear to fine tune launch control.  These values work well for a turbo car that doesn't make much power below 3000rpm.  With a big V8, you may want some different settings.

 

In the 3Step Ign Limit table, set the whole table to 100rpm higher than the max limit in your 3Step Fuel Limit table.  The Fuel Cut C and Fuel Cut M options will serve as your TC torque reduction level and the Ign Cut C and Ign Cut M options will be your hard limiter.  If you want, you can also play with the 3Step Rtd Limit table.  A lot of ignition retard is very hard on exhaust valves and turbochargers, so I personally don't like to use this.  It may be appropriate on a small displacement n/a motor, though.  I set this retard table to all 10,000 and set the 3Step Max Retard option to zero.

I also highly recommend you set your boost target by throttle% and gear.  There's not much point pushing 30psi in 1st on street tires.  Set boost to just a little over what will spin the tires for each gear.  The Fuel Cut C/M options above are a good starting point.  Log the channels Engine Speed, Rev Fuel Limit, and Rev Limit Fuel Duty to see how close actual rpm is being kept to the current rpm limit.  If you don't have enough fuel cut, up the Cut M option a click, 3.1 to 3.5.  

 

 

AEM_NS
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Awesome.  Thanks for taking

Awesome.  Thanks for taking the time to write this up Kurt.

Kurt
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Sharing is caring.   

Sharing is caring.   

evil93evo
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Will this work with EMS-4, or

Will this work with EMS-4, or just series 2 boxes....?

Kurt
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Only S2 with the latest

Only S2 with the latest firmware.

AEM_NS
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Well the EMS-4 does have a 3

Well the EMS-4 does have a 3 step limiter but it doesn't reference gear like the Series 2 does.  You'd get similar functionality but not the per gear adjustment.

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Awesome post Kurt!

Awesome post Kurt!

Side note, when developing the AEM Infinity traction control system, engineering did quite a bit of research on OEM traction control methods.They tend to use a MPH-based slip measurement vs a percent-based measurement. It seems that tires want a certain amount of slip that can be measured in MPH, not necessarily a fixed percentage, for maximum traction, regardless of vehicle speed. If you were to apply that logic to a 3-step table, you would apply a fixed speed offset to all cells, above your base zero-slip values (RPM in this case) rather than a percentage above base (i.e. add 400RPM everywhere in 1st gear vs. adding 10%).

Dense147
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This can only be done if you

This can only be done if you have an abs sensor? Cant work just based off the vss? 

AEM_NS
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You don't need to use an ABS

You don't need to use an ABS sensor specifically.  Any wheel speed sensor will work (Hall Effect, VR, ABS, etc).  You can't use VSS for "ground speed" because VSS will go up when the tires slip and it'll maintain the same ratio of rpm to vehicle speed so you won't ever have indicated wheel slip.  You need to reference a non-driven wheel speed input in order to use 3-Step as TC.  The VSS input will be used to calculate gear - just as Kurt explains very thoroughly in his first post. 

DraginX
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Is there a reason you use the

Thanks for this write up!!

omarjmedina
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Excellent write up!

Excellent write up!

I have an EMS-4 and as far as I know it only accept Hall signal on VSS input pin. Which input pin may I use for the ABS VR sensor? May I use a free GPIO pin for this purpose?

Br,

Omar Medina.-

Omar medina .-

AEM_NS
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You're correct - the EMS-4

You're correct - the EMS-4 can only accept digital speed inputs.  You'd have to modify the VR signal to be digital in order to input it into the EMS-4 without damaging it (VR signals can have 50+ volts of amplitude).

JohnBradley
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I recently set all of this up

I recently set all of this up on my J32 powered Civic and noticed that while I had awesome feedback in 1st gear I had no gear detection being outputted to the 3 step table (or boost table for that matter) other than 1st.  I went back to the Gear table and verified that I had gear detection in all forward gears.  On our linked AWD dyno I can see the rear VSS is calibrated to dyno speed and sees the VSS output to the dash.  However I am still "stuck in 1st".  Is there additional setup that I missed?

Thanks

 

Aaron

Kurt
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Make sure the options A/T

Make sure the options A/T Gear Control and TC Gear From Selector are OFF.  

JohnBradley
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Both are set to off, I had

Both are set to off, I had wondered if one was supposed to be enabled.  I am also not seeing gear output to the boost target gear table, ignition trim per gear, or anything gear based really.

Thanks

Aaron

AEM_NS
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Did you properly setup the

Did you properly setup the Gear channel like is described in the first post?  Do you see a different Gear Ratio value when in each gear?  You can't have Gear without Gear Ratio working correctly.

JohnBradley
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I did not do it exactly as

I did not do it exactly as detailed in the first post, I just used the gear calc wizard in Setup.  It shows calculated gear correctly though so I thought I was golden.  I will redo it tonight and see what I get.

thanks

Aaron

JohnBradley
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So I had TC from Gear

So I had TC from Gear selector off but somehow had turned TC Gear off as well.  Once I turned that on, Bob's your Uncle.

Thanks

Aaron

AWD260R
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If it needs ABS sensor can it

If it needs ABS sensor can it be just one wheel in the front?   I'm a R32 gtr drive train AWD and what pin out will I be needing to pin in the ABS wheel sensor?  Thanks for the posting it will definitely me in the future.

JohnBradley
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So after having used this

So after having used this over the last year I have seen that the timing retard when used is not progressive at all? It seems to follow the cut formula for the percentage and then apply that to the max retard limit?  I did the rough math of my overshoot and as it is pretty constant based on the target slip I end up with 7*-7.9* retard from the formula and in practice on a 15* limit.  It doesnt hold it out and bring it back slowly nor introduce it like the 2 step multiplier that I can tell.  I am just checking to make sure there isnt something I am missing in the setup?

Thanks

Aaron

Kurt
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I just tested 3 Step ign/fuel

I just tested 3 Step ign/fuel cut and ign retard on the bench.  Ignition and fuel cut both follow the stated formula: Cut Duty = Cut C + ((overshoot/50)*Cut M)  The Cut Duty% channels are actually slightly misleading.  A displayed value of 0 - 5.86% will actually give no cut.  6.25 - 18.36% give an actual injector/ign cut duty of 19%.  There are seven steps in actual cut duty from 0-100%.  You wouldn't feel this as everything happens so fast.  Just FYI if you're interested to know how it actually works. 

Ign retard is handled slightly differently.  C and M work the same but the overshoot is divided by 57 instead of 50 for 3Step Ign Retard.  3Step Max Retard is not a factor in the calculation, it just sets a ceiling so the retard level can only be at or below that level.  

JohnBradley
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Thank you for taking the time

Thank you for taking the time to see what it was doing Kurt and give me some math to use.  I have decided to run an Arduino circuit to calc wheel speed differential as a 0-5v and then plumb that into the knock control and user defined boost control (normally for the potentiometer gag).  I will just move the 0-5v knock reference to a different channel to continue to use it as a reference since I am not using the actual knock control anyway.  From the real world testing I have done the reinstate on the ignition retard is too much too fast and it seasaws the timing in and out, in my case 7* at a time.

Aaron@EnglishRacing

Kurt
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Before the 02v02 update, I

Before the 02v02 update, I had thought of using the Hondata TC device and tie it to the Alt function but the price kept me from going beyond thinking about it. lol  Your idea of the Arduino is interesting, but I doubt you'll be able to tie it to the knock control function.  There are no options to assign different inputs for knock control so you're stuck with those specific ones.  There is a chip between those pins and the cpu that processes the knock sensor signal.  The output of that chip is a 0-5v dc level after each ignition event that goes to the cpu.  The signal on those pins go through a capacitor, so they won't work with a 0-5v dc signal.  You could probably open the box and remove those chips and just run a jumper from the input to the output pads and bypass the capacitors.  I don't think you should do this!

You might consider using a mixture of all the 3 step retard and ign/fuel cut components and playing with the slip level.  You can assign a different proportional level for each one.  All the cars I've set up work really well with just fuel cut!  Also, setting up an appropriate boost target for each gear/rpm/tps% will certainly make the 3 step function more effectively!  No point in running full boost in lower gears.  Pulling 50° of timing to reduce power with 30lbs of boost doesn't make sense to me either.  Adjusting boost target based on slip level might also be a challenge to tune as the response will take ages compared to ign/fuel cut.  I think you may see that seesaw effect taken to a new level with a proportional gain applied to boost target.

JohnBradley
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I am currently running boost

I am currently running boost by gear and boost by rpm. I can try boost by TPS, but pedalling the car in the past hasnt helped.  I had the 3 step slip set to 10% in 1st 2nd, 8% in 3rd, 6% in 4th and above for retard and +2% for fuel cut and +2% ignition cut on top of each gear setting.  With the fuel cut active the "see saw" follow AFR which might be an illusion but I am curious if it cuts individual cylinders or if its a global cut and maybe why I am seeing a drastic AFR change in the log?  Boost by gear has been pretty sedate on a good surface, we are on unprepped airstrips but some are definitely cleaner, and I thought was going to work fine on less clean surfaces.  I was like 12/20/28/31/31 at a race in colorado in June with 7.5% max slip observed.  I run 275/50-15 M&H drag radials so the grip is decent especially with 940 lbs on each of the drive tires.  In Oregon in Sept those boost levels had me all over the 3 step and was creating the aforementioned see saw feel.

The other option I will explore is running timing per gear in ignition trims to help soften the amount of work that the 3 step has to do.  Based on some testing on smaller tires earlier in the year it seems I can keep the car from misfiring with as much as 8* extra pulled out of the main map.  It seems I am fast running out of the Series 2 capabilities in this regard as a high torque V6 in a FWD isnt easy to hook up.  One reason I chose it to test my theories on TCS though, worst case scenario :)

EDIT: The other idea I just had (since KC seems to be a no go) was to feed it into the air temp circuit so I can at least get linear timing retard vs voltage.  I can scale it to 0*=0%, 40*=4%, etc to match the output of the arduino and get a quick glance at the level of slip based on the logged "temp".  I will run the air temp off a spare temp input.  I will parrot the 0-5 over to the Boost User Trim to drop boost the same way as I had outlined before.

Aaron

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Thanks for an awesome write

Thanks for an awesome write up.   I have a couple of questions:

I am running a Honda S2000 plug in V2 unit.  (Model 30-6032) This lists T4 as a spare speed input.  How do i find out if this is configured for hall effect or VR.   Happy to open the box but need to know what jumper I need tocheck or change to do this (if it is required).  I am worried about connecting a VR tranducer to one configured for hall effect as I understsnad this can damange the EMS.

Also, what is the difference between fuel or ignition  cut M and Fuel or ignition cut C 

 

Kurt
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I don't have info on the

I don't have info on the input configuration for other V2 models, that would have to come from AEM.

If you look in the EMS4 Install and Tuning Guide, you'll find a lot of info on the program.  Also, the help window on the right side of the screen in AEMTuner shows info on most of the channels, options, and tables.  The formula is Cut Duty = Cut C + ((overshoot/50)*Cut M)

Racecar100
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Thanks Kurt,  I am a bit of a

Thanks Kurt,  I am a bit of a nube with the AEM as I am based in New Zealand where Link is the most popular aftermarket EMS.  Appreciate your support and help with this.  Cheers Paddy

AEM_NS
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If you check the instructions

If you check the instructions you'll see that T4 is physically pinned to the TDC2 input which is a 2 wire VR input.

menmi
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The options for the 3step

The options for the 3step ignition retard table are they the same like the main limiter? Ignition retard C and Ignition retard M?