Jump to content

  • Log In with Google      Sign In   
  • Create Account

Banner advertising on our site currently available from just $5!


1. Learn about the promo. 2. Sign up for GDNet+. 3. Set up your advert!


bmarci

Member Since 05 Jul 2002
Offline Last Active Apr 20 2015 08:48 AM

Posts I've Made

In Topic: [Car Physics] Turbochargers and friends

28 January 2015 - 02:13 PM

So, I made a plot of my Beckman's pacejka, and looks quite ... so as expected :)

 

generated_pacejka_beckman.jpg

 

No fancy 3d plots, just a heightmap made of sqrt(fx^2 + fy^2)

The upper area is for the negative slip ratio

 

The interesting thing is that my better working method looks pretty unexpected (at the left-right sides):

 

generated_pacejka_slip.jpg

 

I'll keep experimenting...


In Topic: [Car Physics] Turbochargers and friends

27 January 2015 - 10:19 AM

Hi Edy, your graphs look interesting, I didn'd know earlier why I had to use a "random" factor, usualy 1.2 to scale Fy after combining, to have better result, but that also affcted the not-over-the-peak values too.

If I wanted to make a 3d combined graph plot function like yours, are the heights (z) the sum of Fx & Fy ?

In Topic: [Car Physics] Turbochargers and friends

23 January 2015 - 03:52 PM

There are a couple of things I managed to figure out;

Watching Edy's video I realized my car is making too much wheelspin, 570Nm and a gear ratio that spins the wheel at 120Km/h in first gear. (Thanks Edy :) )

I tried with "less powerful" setup and voila got much better.

My keyboard control was also too slow for drifting and took too much time to countersteer, that also didn't help get things better.

Yet, my pacejka combiner is still weird, I doublechecked the original Beckman's paper and everything seems ok, the situation is the following;

Starting the "drift maneuver" the rear end gets some angular momentum, and when it start skidding (still spinning tires) because the slip ratio is high the lateral force "disappears" and I'm unable to stop spinning out, and while the engine is revving at max it takes about a second to get back the traction.

 

Edy, would you like to discuss your pacejka combining method? ;)

Here is what I use:

 

Normalized slip parameters

s=slip_ratio/optimal_sr

a=slip_angle/optimal_sa

 

Normalized slip functions

Fx(optimal_sr) = Ox(1)

Fy(optimal_sa) = Oy(1)

 

p=sqrt(s^2 + a^2)

 

Combined forces:

Fx(s,a)=(s/p)*Ox(p)

Fy(s,a)=(a/p)*Oy(p)

 

With taking care of original and cimbined slip signs, it should be the famous Beckman's model :)


In Topic: [Car Physics] Turbochargers and friends

20 January 2015 - 08:41 AM

WhateverMan:

I was playing yesterday with tire settings and managed to get quite good results with Beckman's method, but far not as good as yours. A small amount of TCS (20-30%) helped a lot and managed to drift with the F40, but without it it was a complete disaster...

Shifting the weight to front made it even worse, the grip increased on the front tires and during the drift when the rear end regained some traction the car instantly went off the track.

Maybe my tire curve is too "responsive" or the general settings are more racing than drifting. I have very stiff 200-250kN tire and 70kN suspension and 30kN antirollbar.

Also the front/rear doesn't differ too much, the rear is a bit softer (maybe 5-10%).


In Topic: [Car Physics] Turbochargers and friends

19 January 2015 - 06:00 AM

As we came together so nicely, I'd come up with one more question which is more visual than physical. That is backfire.
Does it happen with some random chance when rpm drops or more scientific than that?
And the same question applies to exhaust splutter.

PARTNERS