MoTeC Global Forum

Hey guys,

I have a 2009 Porsche GT3 Cup race car with the factory ADL2 dash. I've been trying to get an identifier of (pending) wheel lockup under braking working for the last month or so, with out much luck. I could get it working with hardcoded minimum speed values for each wheel, but that's not optimal for tracks with a wide range of corner speeds.

I currently have it setup as:

1 User Math Channel (Lockup Threshold): value 1 is Ground Speed, multiply then divide by scale factor of 1000 the second value, which is the % minimum wheel speed I want to trigger the alert ('90' for 90% of ground speed).

2 Alarms setup, 1 for the front and 1 for the rear. Each alarm simply checks if Brake Status > 0, Ground Speed > 15 km/h, and Ground Speed <= Lockup Threshold, for each wheel.

When I save the Alarms I get a warning that the channels being compared are of different data types. 'Ground Speed' is km/h, and 'Lockup Threshold' is unitless. I was hoping it'd Just Work out in the real world, but after testing it, it definitely does not trigger the alarm.

If I graph the values (individual wheel speeds and the Lockup Threshold channel), I can definitely see the wheel speeds drop below the Lockup Threshold but no alarm is triggered. Is there a trick to set the data type of the Lockup Threshold channel to km/h so the comparison works properly in the dash config? Or should I create additional channels for each wheel that simply take the wheel speed and multiply by 1 and return the whole number of unitless type, and compare that to Lockup Threshold?



Thanks for any tips/advice you guys may have!

-mike

...not much to add, but I like what you are doing.,, So keenly interested.

If the S/W says that the units are not compatible that to me is good news, as that means that the s/w looks at the unit as well as the numbers.

You lockup speed is unitless - so that looks off.
Can you copy the exact math lines you are using?

I am thinking that maybe LUS (Lock up speed) = 0.90*speed
Lockup(n) = speed-wheel(n)/lockup-speed
Then the RHS of the above equation is now unitless.

Is that the left front locking up?

How are the rear wheels breaking loose after the front wheel lockup? You are barely turning right...

How are you getting the yaw rate measurements?

I did it with a 3d table.
YAxis - Ground speeds
XAxis - Drive speed
Result = GP SPeed channel, renamed to whatever suits.

Resultant channel = a Percentage of the the ground and drive speed. So the 3d Table has 4 cells.
0 to 100
to
100

If I want 20% slip to be the threshold to classify it as a lockup I fill in the cells next to the 100's with 80, or less if I want a bigger slip value to be a lockup. Then I set up 4 conditions, for each wheel, to be true momentarily when the its speed is less than the lockup threshold. You can add features to make it turn of after 5 seconds, a timeout if a speed sensor fails.

Holmz wrote:Can you copy the exact math lines you are using?

I'm not sure how to copy the exact math formulas since it's all point and click GUI. But here's a couple screen shots of the config and warning I get when saving the alarms.

Holmz wrote:Is that the left front locking up?

How are the rear wheels breaking loose after the front wheel lockup? You are barely turning right...

How are you getting the yaw rate measurements?

Ya left front is locking up in that earlier graph screenshot. It's a tight 90 degree left turn followed immediately by an 'open' S that I take flat out while jumping the curbs (cause of the rear wheel spin). Yaw rate was already preconfigured in the car when it came from Porsche so I've never looked at how it worked.

Martin, you lost me with the 3d table. Maybe it's because I'm still learning my way around the Motec software, but what you described looked like it'd work for traction control but not wheel lockup caused my braking?

I just created 4 new User Math channels that simply take the Wheel Speed for each wheel, multiply it by 1 and return it into a Unitless Channel. I'm going to try using those Unitless channels in the Alarms section and see if that works... pretty ghetto but I'm getting frustrated.

-mike

Mike,

A few things first off- it may help us diagnose your problem if you logged each input you use for the alarm and you logged the alarm status itself, then posted a log capture showing all these together (just to ensure that all the inputs work as expected). Also, the channel you choose as your Maths output has predefined units, so choose a channel which has the units you need. In this case, you can rename a "GP SPEED (Lge)" channel, which has the same resolution as your Ground Speed channel (0.1 km/h). If viewing the inputs directly and changing the output channel type doesn't solve the problem, then we'll have to explore other avenues. Try and "Simulate" your alarm inputs first in ADL2 Manager; if it doesn't work there, it won't work on track.

In the Cup Cars that I have worked on, I have seen the lockups set as speed differences. For example, "FL Lockup" would be active when "Wheel Speed FL" is X mph slower than "Ground Speed." If you wanted a "Front Lockup" channel, you would use the speed differences between the front corners and ground speed and the speed difference between ground speed and drive speed. If you lock up all 4, none of these will work without a GPS reference, but I think you'd know anyways.

As for the Yaw Rate, I've worked with a few Cup Cars that had this where it had come over CAN and was the unit used by the ABS system. They were in that year range so I'm guessing its the same for you, but your dash configuration will tell you whether or not this is the case.