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Full vehicle model help

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SilverSurfer on 3 May 2016
Edited: SilverSurfer on 3 May 2016
I'm trying to model a full vehicle with 8 dof:
  • surge
  • sway
  • yaw
  • roll
  • rotation of wheels
I'm using a SAE coordinate system:
  • x forward
  • y to the right of the driver
  • z down
I use Pacejka's formula for the calculation of longitudinal and lateral forces. These are the basics equations:
As regards notation
  • AS is front left
  • AD is front right
  • PS is rear left
  • PD is rear right
Can anyone help me to find out if I made modeling errors and to tune the model?
It seems to me the main problem is longitudinal slip. I do not understand which convention should I use. Inside Pacejka's book I found this:
I also found different formulas for driving condition where at denominator there is r*omega.
I find strange behaviours in the model, for example if I try to plot longitudinal rear force vs longitudinal slip. If I make a simulation without steering I get non zero values for roll angle, yaw rate, lateral velocity.
Now I'm using a step size of 0.001. Before I was using 0.01 and the graphics look like they came from experimental data.


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