I'll rear my ugly head in here for a second. Flip to chapter 14 for the Radt
nondimensional method. BTW, I still have the Pacejka coefficient data you
supplied, and will have a look shortly. Thanks!
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://www.racesimcentral.net/
Much appreciated - I am still reading and learning :). I am having a break
for a couple of months to finish off my old Radio Controlled car timing
system ( http://www.race-timing.com ) if anyone is interested (*plug plug*).
But it will be great to lay back and do some reading without the urge to
code all the time - might help get a bit of structure to it all! :)
I am still a bit confused about why I am getting a massive sideways force at
zero slip angle and camber angle. I have visions of my car sitting sliding
to one side off the start line ;) - I am not sure how to calculate the
counter friction force (or more specifically the Coeff of Friction) when the
car is in the "Friction Zone" as Doug puts it, I know it must be linked to
some pacekja values, but I dunno how. The product BCD yields the cornering
stiffness and the maximum sideforce coefficient is also defined as (a1 x Fz
+ a2). Perhaps the max coefficient of friction is just a1?
Trying to work things out while typing a post is probably a bad idea,
especially at work ;)
I better go and earn my keep :)
Thanks for the help
Ash
| >I was a little disappointed in the level of detail in the tyre
| >section (I am only on chapter 5 at the minute), but it may be only a
simple
| >model to be expanded later.
|
| I'll rear my ugly head in here for a second. Flip to chapter 14 for the
Radt
| nondimensional method. BTW, I still have the Pacejka coefficient data you
| supplied, and will have a look shortly. Thanks!
|
| Todd Wasson
| ---
| Performance Simulations
| Drag Racing and Top Speed Prediction
| Software
| http://PerformanceSimulations.Com
Very cool program! I've saved it and will check in occasionally to see
what's new :0)
>I am still a bit confused about why I am getting a massive sideways force at
I still haven't run your #'s to see what results you're getting, but I think
the numbers might be correct. As others have pointed out, conicity and
plysteer can cause a lateral force, even at 0 camber and slip angle.
I wouldn't worry about that too much. Right now, I have a seperate low speed
tire model for the rotational direction, but use the same high speed version
(slip angle based) for lateral forces. The car usually oscillates slightly
when sitting still, with +/-90 degree slip angle. However, since the main
frequency is about 300Hz usually, it's barely noticable.
>Perhaps the max coefficient of friction is just a1?
From the info you posted a couple weeks ago, I'd say that a0 is probably peak
lateral coefficient of friction, while b0 is peak longitudinal. I still
haven't tried it though :-)
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
Ash, I'm playing with these now and have a couple questions for you, if you
don't mind :0). Where is BCD used? Also, where is B defined? Sideslip is in
degrees or radians? Will these coefficients only work in the metric system?
It's tricky figuring out where to put 180*PI, and PI/180 in the fy equation!!
lol
Thanks,
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
...
Hi Ash,
I've emailed you as well since you might otherwise miss this post from
something you wrote a long time ago. :)
I've started using Pacejka numbers from Genta's book, and it is
working fine here. Now side slipping. I'm using the Ferrari numbers
btw.
The weird thing was the units; Fz in kN, slipAngle in degrees, and
slipRatio in percentage (what on Earth was he thinking! ;-)).
But anyway, the car works better than before, although it generates a
lot of longitudinal forces, so I have the flipflop effect with the
tires again a bit (the wheel spinning up too fast, then the
slipratio->Fx force stops the wheel from rotating, then SR=0 and the
wheels spins up again; all until you get a bit of speed, and even then
I can hear the RPM beating as velGround and velFreeRollingWheel pass
eachother. Not to worry too much; I'm going to add RPM inertia, which
probably damps the RPM sweeps quite a bit).
As Fz is in kN and a2 is something like 1668, I'd say the friction
coeff. is 1.668 in this case. 'a1' must be the loading sensitivity. So
a1*Fz+a2 in total makes the maximum available force for your friction
circle. Well, that's what I use since yesterday, so testing should be
done still. I still can't do forward driving donuts though. :(
Was just wondering, I think you got it to work because of the
percentage thing or something, but in any case, those are my findings
upto now.
Cheers,
Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Car simulation: http://www.marketgraph.nl/gallery/racer/
