Re: [Jsbsim-devel] Real-time friction change: side force

[Михаил С. <soi...@gm...>]

What a fast response! Thank you!


By the way, where theese Pacejka coefficients was taken from? I was working
hard with Pacejka coeffs in Racer car simulator in far 2002-2004, and I
remember, that it's almost impossible to find real data. Also I remember,
that there was no 4 coefficients for describing force, but something around
11-13 for longitudal and side forces.


2013/11/10 Bertrand Coconnier <bco...@gm...>

> Hi Michael,
>
> I think you are reading correctly the source code. The side force is
> computed using the so-called "Pacejka's magic formula" and the parameters
> are all hard coded except one : 'Peak' which is set equal to 'staticFCoeff'
> during the object 'FGLGear' construction. Since 'Peak' is not updated when
> 'staticFCoeff' is changed, it keeps the same value for the whole object
> life. Hence the result you are observing.
>
> I committed a fix in CVS so that 'Peak' and 'staticFCoeff' are always kept
> in synchronisation. If you are running FlightGear I attached the patch to
> this e-mail. You can apply it in FlightGear source directory and then
> recompile FlightGear. Under Linux, the commands should look like the
> following
>
> $ cd path_to_fightgear_source/src/FDM/JSBSim
> $ patch -p1 < path_to_the_patch/SideCoeff.diff
> $ cd ../../..
> $ make
>
> Feedback is welcome.
>
> Bertrand.
>
>
>
> 2013/11/10 Михаил Сойтанен <soi...@gm...>
>
>> Good day!
>> Tomash Brechko has realesed his module for FlightGear, which can change
>> friction coefficients for every gear in real-time, depending on underlaying
>> surface and it's condition. (Letter and link can be seen in FG-devel
>> mailing list).
>> In this case I found one interesting thing, possibly a bug. FGLGear.cpp
>> have computation for side_friction_coefficient - FCoeff.
>> As I can uderstand, FCoeff is multiplied by the vertical strut force and
>> it is resulting side force. I tried to turn steered nosewheel at 80 degrees
>> and start move forward. Due to very big slip_angle FCoeff didn't change .
>> And when I moved out of concrete to surface with less friction and
>> static_friction coefficient changes, FCoeff didn't change. Is this normal
>> behaviour or I'm reading source code wrong?
>>
>> Best regards, Michael
>>
>>
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>
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