rec.autos.simulators

For example, if you have an SLA setup with the upper and lower arms
actually the same length and the vertical distance between the inner
and outer ball-joints the same. This will give a KPI of 0 degrees and
assuming that the inner ball-joints are fixed at the same X offset
from the CG (assuming that +Z points to the front of the car) this
will give you 0 degrees camber.

If we then wanted to add some camber we would either have to change
the length of one of the arms or change the vertical distance between
either the inner or outer ball-joints. Right?

Take another example, if you had a more traditional SLA setup, long
lower arm, short upper arm, upper arm has a larger X offset from CG,
and about 5 degrees of KPI. Surely the camber for this system could
possibly be different for when the tires are touching the ground as
when the car is up on jacks? Also, wouldn't changing the spring rates
or dampers change the camber?

And now for the question, is camber merely a variable used to
represent the angle between the wheel and the contact surface for a
stationary vehicle? Stating that the front wheels on a vehicle have
say 5 degrees of camber is only a valid statement when the vehicle is
not in motion?

I really need to get this straight in my head before I code it all up.

TIA, Colin Reed

-----------------------------------------------------
My homepage : http://www.racesimcentral.net/
-----------------------------------------------------

...

Camber is quite dependent on I think most everything you change in the
suspension links.
Just like I read about bump steer for example, which is the change in
toe-in as a function of suspension deflection. It's how you attach
your wheel to the chassis. (too many parameters for me at times)

Right. There is something like 'camber change per cm deflection', so
if you're in bump, the camber will/can change, depending on how the
links are done.
What I intend to do is define things like 'camber change per m
deflection' instead of really going through all the links and
constraint force stuff (which Gregor for example is doing). Although
ODE (www.q12.org for those interested) might make things more
possible, I don't think it will do much good for performance, and I
still doubt that the links will do more than the resulting parameters
(camber change/m) can simulate.
It depends on your input data; do you know the rod lengths, the angles
and such? Then just entering the links directly might be more
suitable. But I generally have no knowledge about these things, so
I'll use the other, resulting parameters.

Dampers only change timing, so they only change the camber change per
time (which is implicitly calculated anyway in most sims).
But a spring rate that would cause a different range of deflection,
that would case a different range of camber (notice I leave out
steering effects here, which are also there ofcourse, just like camber
changes, as if camber & steering weren't related, lol).

Right. So it changes according to the track, the wheel and suspension
deflection.

Right (or at least I'd think that's the only workable definition when
you're standing in a pits). And that's also on a flat surface.

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

TIA,

SB

That's the way I've seen it done.  The handling model I played with
for my FYP had 'static camber' and 'camber gradient', as well as
'static toe' and 'toe gradient' - units as you're suggesting.

You can probably assume linearity for road/race cars; if you're
going off-road, you might want to consider at least a quadratic
approximation or even something more accurate.  Depends how camber-
-sensitive your tyres are, I suppose ;-)

Jonny

And then do some angle stuff (haven't investigated this in detail yet,
so no formulae).

As a body in a 10 degree angle roll has 10 degree 'camber' with
respect to the track, it certainly does make a difference. If you're
with 2 wheels of the ground, the wheels touching the ground will have
an added 10 degrees of camber, which is a lot ofcourse.
At that point though, you also start to wonder, 'hmm, shouldn't I have
3 points at which I look at the tire-track collisions?', since one end
of the tire is probably in the air, the middle is so-so, and the outer
part firmly touches the ground.
Nice for those temperature calculations.

</rambling>

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

Good to know, thanks for that piece of info.

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

DUH!  ;-)  Guess that makes sense, even to ME; hard to get roll without deflection, assuming all your wheels are on the track.

Interesting (read: baffling to me).  Is anyone modeling tire casing/contact patch deformation currently, or will that not get you
anything useful?

Thks,

SB

Someone like a Milliken would be a useful source of confirmation,
for instance!

Jonny

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

My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm

Here ya go - SB
-------------------------
Camber, it is such an interesting term, thrown about in conversation
willy nilly but what EXACTLY is it a product of?

For example, if you have an SLA setup with the upper and lower arms
actually the same length and the vertical distance between the inner
and outer ball-joints the same. This will give a KPI of 0 degrees and
assuming that the inner ball-joints are fixed at the same X offset
from the CG (assuming that +Z points to the front of the car) this
will give you 0 degrees camber.

If we then wanted to add some camber we would either have to change
the length of one of the arms or change the vertical distance between
either the inner or outer ball-joints. Right?

Take another example, if you had a more traditional SLA setup, long
lower arm, short upper arm, upper arm has a larger X offset from CG,
and about 5 degrees of KPI. Surely the camber for this system could
possibly be different for when the tires are touching the ground as
when the car is up on jacks? Also, wouldn't changing the spring rates
or dampers change the camber?

And now for the question, is camber merely a variable used to
represent the angle between the wheel and the contact surface for a
stationary vehicle? Stating that the front wheels on a vehicle have
say 5 degrees of camber is only a valid statement when the vehicle is
not in motion?

I really need to get this straight in my head before I code it all up.

TIA, Colin Reed

-----------------------------------------------------
My homepage : http://www.cersoft.com
-----------------------------------------------------

  Thanks for reposting this, Steve :0)

Everything!  lol  Especially the phase of the moon...

  Right.  I've got two other adjustments in my suspension system in addition
though that are important IMO.  We're doing a little radio controlled car sim.
The VectorNT chassis, for example, has two little screws in each front wheel
that can be turned in and out to adjust camber and track width.  So I've also
got two additional "arms" that stay perpendicular to the mounts at the hub
carrier/wheel assembly that can have their lengths adjusted as well.  This is
good to do because you can easily allow a user to add camber plates or other
devices to their sim car if they want, which will change the track width
slightly in addition to changing camber.

  Yes, the camber will most likely be different in those two situations.  In
our sim, we're allowing the users to setup the cars much like they do with the
real cars.  They can set "elevated" camber, which is the camber when the car is
on jacks, as well as setting "driving" or "resting" camber, which is the camber
when it's not up on jacks (which is what all the current driving sims probably
are approximating).  "Elevated" camber can be set by changing all the arm
lengths and positions and what-not.  "Driving" camber can be set the same way
as well, but changing spring rates, spring preload, and spring rest length
alter the driving camber even further..  Actually, changing tire width or
diameter alters the camber a little too.  Changing dampers won't change the
"driving/resting" camber though...

  In short, in our little sim, the user doesn't just adjust camber by clicking
a button, they've got about 10 different ways to adjust it (2 for the tires, so
really 8 suspension adjustments effect camber), and they'll all have different
effects on the "dynamic" camber, or camber while driving around...   And we all
think GPL is hard to set up!!  lol

  "Yes" to both of these..  

 Sounds like you've got the idea just fine.

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

My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm

[Can you tell I started racing karts this year? :) ]

I'm not totally familiar with the actual form of a suspended car's front
end, but camber adjustment is surely possible without changing out a
swingarm.

--
Pat Dotson

  I've done this, but it's not incorporated into my sim.  It's really slow
'cause there are so many calcs..  If you've got good Pacejka constants for the
tires you want, that's better anyway probably.

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

My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm

Ben

Camber doesn't mean much if the wheel isn't attached to a car, so tire test
machines use their own axis system (SAE and ISO are different, both are
commonly used).  Afaik, definitions aren't standard (yet) but we use the
following to help keep this straight:

  Camber angle is measured between wheel and chassis
  (positive = top of wheels tilted away from car)

  Inclination is measured between wheel and ground - the tire axis system
  (SAE positive = lean to the right, looking in the direction of travel)

Confused yet?  See Race Car Vehicle Dynamics pp61-63 and Chapter 4.

-- Doug Milliken
   http://www.millikenresearch.com  (hint--under Books is purchase info)