% Hi,
% I was wondering if we could a (more scientific) thread going on how
% the internals of such a game are constructed, if anyone knows.
While it is not detailed about the code, there was an interview with
David Kaemmer by John O'Keefe that "touches" on this. The URL is
http://www.racesimcentral.net/~richardn/Kaemmer.html
Here is the part about what is modeled in GPL:
Could you give people insight into how complex the Grand Prix Legends
simulation is? For example I heard somewhere that you model the airflow
into or through the engine? What are some of the most complex aspects of
GPL?
For the engines, I use a model for engine friction that I got from a
couple of SAE papers--the friction is a function of inlet valve
diameter, stroke length, etc.--and it seems to be pretty close (we have
data for all these parameters for each of the cars). The most complex
aspects of GPL...? How much time do you have? :-) The multi-body
simulation is very accurate--each GPL car is made up of the chassis, the
fuel mass (which changes), four wheels with independent hops and spins,
an engine & flywheel rotor, clutch & transmission input shaft, transfer
shaft, and output shaft. Each of these bodies maintains its own linear
and angular momentum, basically. You can see some of this if you watch
the car land on its top after flying through the air (and who hasn't
seen this?)--just when the car lands, you'll see the wheels each
continue to travel downwards until the springs stop them. If you jump
the car in the air (the 'Ring--woohoo), you can see all the gyroscopic
effects that occur when you turn the steering wheel in mid-flight, or
stay on the throttle, or jump on the brakes (doh). Some might say this
is overkill, but not those of us who know the kink before Schwedenkreuz.
:-) The tire model is also extremely complex and accurate. There has
been a lot of excellent work recently by those who have PhD's in the
physics of tire and *** friction, and we have incorporated a lot of
that into the current model. The differential deserves some
mention--notice that with a near open diff (85/85, with 1 clutch), you
have no trouble getting inside rear wheelspin. Or try starting with one
wheel on the grass and one on the road. The constraints which apply
within the drivetrain are non-trivial. The collision system is pretty
complex--and that's an understatement. Outside of the physics, obviously
the graphics system is pretty complex, the multiplayer system design,
the AI--I can't do anything but scratch the surface here, but suffice it
to say that the GPL model is several orders of magnitude more complex
than anything we've done before.
<snip>
--
**************************** Michael E. Carver *************************
Upside out, or inside down...False alarm the only game in town.
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