rec.autos.simulators

by **Ruud van Ga** » Wed, 25 Jul 2001 01:36:58

Hi all,

I'm trying to get a feel for suspension and steering systems, but I
don't have a good starting point yet (mathematically).
I know what the caster angle is, have looked at the pretty pictures in
RCVD explaining the dozen or so terms that describe a steering axis
angles and such, but I can't put this into mathematics.

A concrete example, if I have a certain caster angle, what would this
do (mathematically) with the forces both in the tire itself and in the
steering feedback?
I've got the impression that caster angle should make a lot of
difference in the driving behavior at high speed (I've got
aerodynamics more or less in, so ouch I'll have to drive an F1 car
soon), but I wouldn't know how this behavior changes (also because
I've never 'felt' in real life what the difference between different
caster angles is).

Thanks for any pointers on this one,

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.racesimcentral.net/
Free car sim : http://www.racesimcentral.net/

by **Dave Henri** » Wed, 25 Jul 2001 01:49:51

from old family knowledge.
Increasing use of Castor(oil) tends to make the rear end loose and unstable,
loosing control at inopportune times can be the result of too much Castor.
dave henrie

I...(snip)

by **Art McEwe** » Wed, 25 Jul 2001 02:08:15

If it's not answered in this series, I'm sure the author knows....

http://bovineracing.com/EOA/pt1/Pt1.htm

by **Stephen Smit** » Wed, 25 Jul 2001 02:56:00

I'm just now getting around to mastering FF. Unlike every other FF-equipped
racing sim, GPL models caster return. Thus, it's a remarkably effective
teaching tool. If you're driving correctly (at least, if your steering
input is correct), you'll never feel the caster return. If you're doing it
wrong, you'll feel it: the c.r. practically rips the wheel out of your
hands.

[GPL's caster return also provides some otherwise-hidden input on how your
shocks are set up. If you don't have the suspension properly damped, the
caster return will oscillate, which you can definitely feel thru the wheel.]

Remarkable. We're still discovering new stuff in GPL 3 years on.

--Steve

by **Ruud van Ga** » Wed, 25 Jul 2001 06:24:07

On Mon, 23 Jul 2001 13:08:15 -0400, "Art McEwen"

>> I'm trying to get a feel for suspension and steering systems, but I
>> don't have a good starting point yet (mathematically).

>If it's not answered in this series, I'm sure the author knows....

>http://bovineracing.com/EOA/pt1/Pt1.htm

Ah, that one shows up in every place again and again! ;-)

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Ruud van Ga** » Wed, 25 Jul 2001 06:25:58

Ah, and what about Pollux?

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Ruud van Ga** » Wed, 25 Jul 2001 06:28:18

On Mon, 23 Jul 2001 17:56:00 GMT, "Stephen Smith"

>I'm just now getting around to mastering FF. Unlike every other FF-equipped
>racing sim, GPL models caster return. Thus, it's a remarkably effective
>teaching tool. If you're driving correctly (at least, if your steering
>input is correct), you'll never feel the caster return. If you're doing it
>wrong, you'll feel it: the c.r. practically rips the wheel out of your
>hands.

>[GPL's caster return also provides some otherwise-hidden input on how your
>shocks are set up. If you don't have the suspension properly damped, the
>caster return will oscillate, which you can definitely feel thru the wheel.]

Ah, I always thought the oscillations were caused by the delay set too
high or low in the FF section. Now that I reread the previous
paragraph, no I never felt anything remotely like it! ;-) Uh...

It's amazing at the complexity that complex systems give; you can
never really understand the results your own product somehow, but it's
there. :)

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **J. Todd Wass** » Wed, 25 Jul 2001 06:51:23

I thought lateral force caused the aligning torque to begin with. ?

Are you calculating forces independently at all five links? I've currently
got a 2-D approximation (front view only) of the upper and lower control arms
and the shock/spring axis so bump camber occurs and dynamic motion travel and
shock/spring angle effect wheel rate. My plan was to rotate the tire
orientation vector and contact patch force centroid around the steering axis to
get wheel rise and fall with steering, as well as camber change from caster and
kingpin angles, run the lateral force (in body coords) along the ground plane,
then apply the jacking force from roll center location as well. If this was
done in the side view (instant center) and front view (roll center), would it
have the same effect as calculating and applying the forces through all the
links individually? It seems this is what RCVD describes.

Thanks,
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

by **Ruud van Ga** » Wed, 25 Jul 2001 10:02:59

Hi Gregor,

And here R is the radius of the normal contact patch center to the
point where the new axis (with caster) hits the ground?

Sounds like it only gives more feedback than usual, but doesn't really
make that much of a difference, or does it?

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Stephen Smit** » Wed, 25 Jul 2001 10:43:32

<<Ah, I always thought the oscillations were caused by the delay set too
high or low in the FF section. Now that I reread the previous paragraph, no
I never felt anything remotely like it!>>

Check it out: run the FF values (particularly damping) up & down; say 0 to
80; with yer stock setup. Next, leave the damping where you usually leave
it (I have it at 30 in both the LWFF Profiler & core.ini; I'm not sure if
they're additive, mutually exclusive, or what), and run the springs & shocks
up & down (1/1 & 50 lb. springs & bars, to 5/5 & 200 lbs. springs & bars,
with GRE). See? Dead soft, what yer feeling is the chassis rocking from
side to side, and, as it does so, the see-sawing tries to steer the car, and
you get a "tank-slapper." Damp the rocking and you damp the caster
kickback.

Is this a great game or what?

--Steve

by **Ben Colema** » Wed, 25 Jul 2001 17:28:59

Interesting....I had trouble with tank slappers when I was running very soft
and high Brabham setups.

Ben

by **Gregor Vebl** » Wed, 25 Jul 2001 17:38:54

Hi Ruud,

> And here R is the radius of the normal contact patch center to the
> point where the new axis (with caster) hits the ground?

> Sounds like it only gives more feedback than usual, but doesn't really
> make that much of a difference, or does it?

Well, if you need to define R this precisely, then the R is actually the
length of projection of the vector from the center of the wheel to the
contact patch onto the new steering axis. But since we are in a linear
approximation here anyway, setting it to the radius of the tyre is what
is sufficient.

Indeed, it's mostly about the feedback, and the camber behaviour in
steering inputs. Definitely a secondary thing to consider in a car sim.
If you want to see the effects in a sim, Nascar 4 does this extremely
well. It makes a huge difference in FF and control of the vehicle, but I
couldn't notice any performance differences due to additional camber, at
least not with my untidy driving style ;).

-Gregor

by **Gregor Vebl** » Wed, 25 Jul 2001 17:47:53

Hi Todd,

> >For steering feedback, what caster does is that it throws the alignment
> >of the rotation of the wheel around its steering axis with the contact
> >patch off. At this point not only the aligning torque contribuites to
> >steering feedback, but the lateral force as well.

> I thought lateral force caused the aligning torque to begin with. ?

Indeed, that is correct. In my sim, for example, I vary the position at
which the lateral force applies, I do not have an actual aligning torque
variable. It's only a matter of description, though. You can always
consider a force acting at a distance from the axis, or put that force
onto the axis and introduce an additional torque, the effect on a rigid
body is always the same.

Yes, I am calculating individual forces at all five (six, if you
consider the spring as an additional link) links. It's a matter of
solving a nonlinear system of equations iteratively (3-5 steps each
iteration). Also, bear in mind that at this point I still neglect the
mass of the tyres and with that the high frequency wheel hopping mode.
Since I am optimizing it for an aero formula kind of a sim, this wheel
hopping mode is sent to such high frequencies and is usually well
damped, so I hope it's not too bad of an approximation.

If what you describe was done, you'd indeed end up with a very similar
system, as the wheel motion and caster/kingpin descriptions can be
largely separated, at least at not too large wheel travels. You only
need to keep in mind that all of the descriptions of these axes, along
with roll centers etc. are linear approximations for small wheel travel,
which, however should usually be more than sufficient and is a complete
description for such travels.

-Gregor

by **Ruud van Ga** » Wed, 25 Jul 2001 18:58:16

On Tue, 24 Jul 2001 10:38:54 +0200, Gregor Veble

>Hi Ruud,

>> And here R is the radius of the normal contact patch center to the
>> point where the new axis (with caster) hits the ground?

>> Sounds like it only gives more feedback than usual, but doesn't really
>> make that much of a difference, or does it?

>Well, if you need to define R this precisely, then the R is actually the
>length of projection of the vector from the center of the wheel to the
>contact patch onto the new steering axis. But since we are in a linear
>approximation here anyway, setting it to the radius of the tyre is what
>is sufficient.

Ah, so that would be cos(casterAngle)*tireRadius. No approximation
needed probably, since this can be precalculated. Unless ofcourse you
build in steering compliance. Skip that, I'll just precompute it and
keep it static. ;-)

Sounds good, I don't want too many primary driving behavior anymore!
Still, it seems nice to build in, since I noticed that the force
feedback is very important to feel your limits, especially now that my
skid volume code is in bad need of repairs! ;-)

BTW I think that:
additionalCamber=caster*wheelRotation should be
additionalCamber*sin(wheelRotation), not sin(caster). But I may be
wrong here. :) And besides, perhaps it's so close to linear for normal
steering that the sin() isn't worth the calculation. Getting some
optimization vibes up my spines.

Thanks,

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

rec.autos.simulators

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle

Car physics; steering caster angle