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bmarci

Member Since 05 Jul 2002
Offline Last Active Today, 03:30 PM

Posts I've Made

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.

In Topic: [Car Physics] Turbochargers and friends

19 January 2015 - 05:19 AM

I'm doing what rFactor did


I don't mean to be awkward but you must know something I don't :)
Did you find/get info on rFactor's stuffs or just checking RF car settings to get inspired?

In Topic: [Car Physics] Turbochargers and friends

19 January 2015 - 03:59 AM

If driveTorque>0 then it was power locking and otherwise it was coast locking.

I'd think of (drivetorque+roadtorque)>0 ;)

Also about pacejka combining, Beckman's method is the best. And SAE low peed friction model at 400hz or 1000hz works perfectly well,


The Beckman's method is vey good indeed, but only second best.
For me, it becomes very slippery when the car starts skidding.
I let the slip ratio go over 1 thus the scaling factor cuts back the lateral forces (no donuts), and with locked wheels the sideway resistive forces "disappear". Maybe this is the reality, I never tried handbraking at 160km/h :))
I found some interesting in the RCVD: "tire data nondimensionalization". I might play around with that too.

Regarding low speed, is it SAE950311? I bought that paper too, but the lateral relaxation didn't work. Also the longitudinal was "sliding" when stopped on a hill, so I ended up with my own approach.

I'll try the drifting setup and get back to you.

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