TTC pacejka modeling help

[crzycav86]

Hi. I have tire data from the TTC from 2005. I'm looking at the pacejka coefficients provided by Stackpole.

I've entered the coefficients and equations for the Hoosier 18x6-10 43101 @12psi tire into matlab and plotted. I'm having trouble getting my lat force vs Slip angle plot to match their plot. I'm getting a plot that has a similar shape curve, but the lateral forces are about 5 times greater on my plot than on the one provided in the documentation.

They define slip angle in radians and forces in Newtons. But they also have a dFz term in the equations that isn't defined anywhere that I can see. What is dFz supposed to be? Actual wheel load minus Nominal wheel load? That's what I've got and it's not working.. http://fsae.com/groupee_common/emoticons/icon_frown.gif

edit: this thread (http://fsae.com/eve/forums/a/tpc/f/125607348/m/25810075531?r=34210085531#34210085531) refers to dfz = (Fz-Fzo)/Fzo. I did that and it made the plot even worse.. http://fsae.com/groupee_common/emoticons/icon_frown.gif

Also does anyone know if there a way to convert their coefficients into the more common a0, a1... coefficients?

Thanks in advance.

[crzycav86]

Hi. I have tire data from the TTC from 2005. I'm looking at the pacejka coefficients provided by Stackpole.

I've entered the coefficients and equations for the Hoosier 18x6-10 43101 @12psi tire into matlab and plotted. I'm having trouble getting my lat force vs Slip angle plot to match their plot. I'm getting a plot that has a similar shape curve, but the lateral forces are about 5 times greater on my plot than on the one provided in the documentation.

They define slip angle in radians and forces in Newtons. But they also have a dFz term in the equations that isn't defined anywhere that I can see. What is dFz supposed to be? Actual wheel load minus Nominal wheel load? That's what I've got and it's not working.. http://fsae.com/groupee_common/emoticons/icon_frown.gif

edit: this thread (http://fsae.com/eve/forums/a/tpc/f/125607348/m/25810075531?r=34210085531#34210085531) refers to dfz = (Fz-Fzo)/Fzo. I did that and it made the plot even worse.. http://fsae.com/groupee_common/emoticons/icon_frown.gif

Also does anyone know if there a way to convert their coefficients into the more common a0, a1... coefficients?

Thanks in advance.

[exFSAE]

Lateral forces about 5 times greater than your plot? Perhaps.. 4.448 times greater? If so I can think of a reason why.

In any event, the place to ask these questions is..

http://sae.wsu.edu/ttc/

By the way, the SES coefficients ARE in the "common" a0, a1... etc format.

[crzycav86]

I'm still not sure where that number comes from, but I scaled it by 4.448 and it still doesn't match the sample plot.

The SES coefficients (in the order that they're listed) do not work with the equations that I am using.

The equations I used came from Dr. Woods' SAE paper 2004-01-3528 - "Normalization of the Pacejka Tire Model". My model was working fine with these equations and some "default" coefficients. It started screwing up with real tire data.

Does anyone know the units of the coefficients listed in the SES pdf file? I know this is a tire for that forum, but access is private, and I haven't received registration confirmation.(I registered with my university e-mail)

Thanks for your help so far.

[crzycav86]

I may have gotten to the bottom of this:

The I'm using the wrong version....

[exFSAE]

The SES document includes the equations to use. Don't bother with anything else.

[crzycav86]

I finally got it to work.

The equations are correct, and I was using the correct version - I just fat-fingered * where it should have been a +. I guess that's what I get for doing it at 2 in the morning.

Another thing is on the plot, the legend shows 6 normal loads(which are in lbs, when everything else is in Newtons - and never says so), but 5 plotted lines. There was a little error in that, but I've got it matched up and working now.

Thanks for your help.

[crzycav86]

Eq 1.31 in the '05 data has an error.

You need to multiply that by normal force Fz. Otherwise you will not get the correct aligning torque figure.