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That's weird, that car should be able to do it more, but what tire did you use?
I guess it's impossible with low powered car.
Yes, I tried. Doing donut in LFS is easy even with 140hp 1150kg car.
I tried stock S15, S15 "donut" is worse than S2000. The rear tire hardly slip.
You should try again without TCS. If the rear tire do not spin, won't the rear tire still grip?
in my opinion, GT4 unrefined tire simulation is the cause. When I try to make the rear tire spin, the rear tire do not loose grip as much as expected. Resulting in car going forward instead of pivoting front tire.
There is an interesting dicussion from doc file from racer.nl by car simulation creator. Talking about how the tire need to simulate differently at low or zero speed, "stopping on a hill" bug and "need a specialized model for slow speed anyway"
Racer forumTodd
Ruud, look into the Pacejka Magic Formula. I believe chapter 14 in Race Car
Vehicle Dynamics has a little blurb in it (relating it to non-dimensional tire
theory, something I still haven't got to match real tire data acceptably.)
Aside from that, search the net for Pacejka's work. He's figured out a snazzy
formula that lets you modify 4 coefficients to generate a realistic curve.
…
There's another little problem here that I knew was coming and now must deal
with it, so figured I'd warn you ahead of time so you can fix it before me :-).
It's called the "stopping on a hill" bug.
If the car is stopped on a hill (pointed straight towards the top or bottom,
no special angle), the slip ratio model doesn't generate any force to keep the
car in place. Oops again. Both velocities are 0 (free rolling and true
rolling) hence, 0 slip ratio and 0 force. The car slides very gently down the
hill even with the tires locked. Ponder that one for a while and let me know
what you think :-)
Dave P.
Well, we shipped Viper Racing with that same hill-sliding bug--I didn't fix
it until after we started working on our current project (NASCAR Heat), and
got a little smarter about tire modeling. (Ended up fixing by modeling the
shear-spring effect of the sidewalls) But just using slip ratios, slip
angles, and camber angles will get you pretty far for starters--the
magnitude of pneumatic trail is more of a factor in steering wheel rim force
than in the car's yawing moment.
-Dave P.
MGI
(oh here I am giving away hard-won techniques)
I figured that the empirical tire modeling formulas that I was using were
incorporating the effect of building up of tire shear, and then parts of the
tire "springing back" as the bits that were making up the patch moved off
the ground (and of course transitioning to a sliding state at the tail end
(and head, I suppose) of the contact patch--as you said, this is what a slip
angle/ratio based system is modeling. At non-zero tire rotation rates, the
"shear" is constantly being relieved, making act more like a damper than a
spring. So the trick was to continuously dissipate the stored "shear"
energy as a function of rotation, and blend between the two types of model
as the tire rotation went from zero to a small epsilon rate, and then use
just slip-based modeling above that speed. It worked out pretty well, as
you get nice effects like the "kickback" when you screech to a stop and then
they toss the car a little bit backwards, a phenomenon we all experienced
when learning how to drive...
I think that's what's going on when you drive a normal car to a stoplight,
and then pull off the brake right as you come to a stop; this lets the tire
"unwind" itself in a smooth and controlled fashion.
Since this was all for road/oval racing with no standing starts (except
for pitstops) this seemed like plenty good, especially given current CPU
speeds--I'm sure for doing high-end drag racing simulations, you'd need
fancier deformation modeling with all that crazy tire crinkling and stuff
I've seen in the shots of dragsters shooting out of the hole.
Anyways, it's nice to hear that other people care about this kind of
stuff...
-Dave P.
MGI
Matt
> The car slides very gently down the hill even with the tires locked
Yes, that's annoying.You need to include static friction in some way.
We change the equations of motion to take into account each tire being
constrained or not, but that is rather complex with one to four tires stopped
and the various redundancies. You will need a specialized model for slow
speed anyway, so try and get the slow speed and stopped modeling to
work together.
> Constrained? I don't understand what that means.
If one tire happens to be stopped, and you deicde to use that
fact, you can reformulate the equations of motion taking that into
account. Add equations that force the acceleration at that tire
contact point to be zero, along with the other usual equations.
The added constraint equation will change the results you get.
For example, if you pin one tire fixed on a hillside, you know that
all the others are forced to move only on circular paths around the
This is the other thing I mentioned earlier. The slip ratio "difference
instead of ratio" method at low speed prevented instabilies, but once you
introduce a big braking force, it starts up again. This cause for this started
(in my model anyway), by torque from the brakes acting in an opposite direction
from wheel rotation. If the wheel is turning slowly forward, a big braking
force makes it suddenly spin BACKWARD, then forward and back, forward and back,
etc.. The bigger the force, the bigger the instability/jumping.
Now I detect when the wheel's direction had changed, THEN check to see if
the torque exerted on the tire by the road exceeded the brake's torque capacity
(or % at whatever pedal position). If it didn't exceed it, the wheels could
not move so the tire rotational speed is set to 0. This cured instabilities
from braking torques. Basically, this is simply detecting when a tire CANNOT
begin rotating once it has stopped (of course, it never really stops unless
sampling rate is nearly infinite or you get REALLY lucky, so look for the
direction CHANGE instead.)
At my shop we term this friction reversal and it can occur and has to
be dealt with almost everywhere. The tires both when stopped and
in some conditions even when moving, all through the drive train,
collisions, ...
> Friction reversal? That's a good name for it. Any tips on how to handle
> it?
As was suggested in this thread, if it changes sign,
try holding it stopped for awhile. Of course, you then have to
come up with all sorts of tricky criteria for when to
stop and when to release it!
The general problem with 4 wheeled cars is difficult because
of the large number of different possible reversal situations you
can be in at any one time, and also the potential for redundancies.
(Can cause numerical problems when solving the equations of motion.)
I guess PD do not manage to sort out the low speed behaviour in GT4.
ROFL, good point 👍. You never said it has to circle front tire either.
). If you want, using the steering display will help you as well, showing how much G-Force is applied to the side. When i was doing this, you want i somewhat a bit less than the "1". if you go more, then it'll overdo it (with these settings). If you see a large fluctuation within that blue dot, you're screwing it up.You can use the view of the environment as help. If the spinning motion looks smooth then you are pretty much succeeding. But things aren't as they seem. When i did this, it looked liek i was doing it, but if you look VERY carefully, at one point the spin will turn faster than it would at another point. The Bleachers, when your in your spin, it'll look like you are spinning fast, but then when you are looking at the open spaces or anything with low details, it'll appear you're going slower. Dont let that confuse you. 
