The only option that seems to make sense to me would be to
use the contact closest to the "front" of the wheel,
depending on which way the wheel is rotating. Has anyone
else considered this situation? Any ideas?
Jason
379
It seems that could eat up a lot of collision detection cycles though if you
happened to be sitting in the middle of a triangle fan or something.
Actually, you might need to take the average of the two forces and their
direction vectors. With a system like this it seems that your tire could
actually be contacting two or more ground triangles (or whatever surface you
use) at a time. Then, if you had two triangles on a ground plane (ignoring
curbs for now), the force would suddenly double, so maybe you could take the
average of the two.
With a curb compressing the tire .02 meters at an angle of 30 degrees to the
car/suspension's vertical axis, and the ground below compressing it at .1
meters, assuming a tire spring rate of 10000 N/M (I don't have a feel for
metric units well, bear with me), you'd have:
Fx = Force longitudinal
Fy = Force vertical
Curb Ground
Fy = [.02 * Cos(30) + .1] * 10,000
Fy = 1173 N
Fx = [.02 * Sin(30)] * 10,000//Ground has no longitudinal effect here
Fx = 100 N
Something like this maybe? But then the problem is, what if you have two
contact "points", both at ground orientation (because there might be a
collision at two ground triangles/polys, even though the surface is flat and
indistinguishable from one big triangle). Both compressions might be .1, but
you'll have a sum of .2 for compression.
You'd wind up with:
Fy = [.1 * Cos(0) + .1] * 10,000
Fy = (.1 + .1) * 10,000
Fy = 2000 N
When really, you should only have 1000 N.. So maybe the forces from more
than one contact point could be averaged together/combined somehow?
Actually, since the two flat ground triangles are not going to intersect the
wheel at the very bottom, the "compressions" might be lower, giving the same
effect as only having one triangle...
Sorry for the confusing rambling, maybe it will help anyway :0)
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm
If you have two contact on your tire so the total load on the tire
must be distributed on those 2 contacts, so you have two contact with
2 differents load, compute the lateral/longitudinal forces as there
were only 1 contact and just add them.
I don't know how you calculate your tire load, but the sum of the load
of all contact on the tires must be equal of the load if there were
only 1 contact.
But to be honest i din't implement this in our game. but i will
implement it in my personall simulation ;o)
Sebastien TIXIER - Game Developer
Dynamics and Car Physics
http://www.eden-studios.fr
GPLRank Normal:-44.24 Monster:-124.44
There is a problem with that assumption, in that a load say due to a kerb
can is not the same as a normal tyre load, you need to take into account how
the tyre is being driven up the kerb as this will increase the load, and a
tyre contact cuase by a kerb or other non flat surface dosnt follow the same
rules as a normal tyre contact so formulas like Pacejka no longer work
correctly.
To model a situation such as that you need to different approach to tyre
modelling, something like a brush method may be off more help. Its a
complicated area.
I think a good way to handle this is to modify the Pacejak coefficient
according to the number and position of the contacts.
In fact the pacejka coef are already variables according to tire
pressure, tire temperature, etc ...
The problems is to find how to modify this ... i think there's some
information in Giancarlo Genta's book to help but i still didn't read
entirely his book ;o)
Sebastien TIXIER - Game Developer
Dynamics and Car Physics
http://www.eden-studios.fr
GPLRank Normal:-44.24 Monster:-124.44
Carol, check your mail please :-)
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm
>> ok try to come up with theroy engine is not good stuff.
>> Please consider the physics.Apply then the theory engine.
>> mm weight transfer verses spring rate!! mm
>> NO please choose a tire manufacturer
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm
>> ok try to come up with theroy engine is not good stuff.
>> Please consider the physics.Apply then the theory engine.
>> mm weight transfer verses spring rate!! mm
>> NO please choose a tire manufacturer
I am not going mad! All your physics belongs to us! :D
Ash
>>Umm, wha?
> Seems the Martians have *just* landed.
> This is all way beyond our heads.
