Physics [split from network thread]

[joevenzon]

The tire model is pretty good -- we're using pacejka's equation and some fancy(er) long/lat force combination -- but the tire constants are not.

Also, about the hinges, here are some excerpts from old e-mails from Sam Varner (the Vamos author) answering some questions I had:

The suspension hinge allows an approximation of suspension
geometries that reduce squat (under acceleration) and dive (under
braking). The usual configuration puts the rear hinge in front of and
higher than the rear axle. The driving force then tends to push the
rear of the car up. Imagine the wheels trying to drive under the
chassis. Braking pulls the rear down. Also, braking torque pulls the
rear down in this configuration.

I avoided trying to simulate multilink suspensions directly. I figured
that the hinge (and roll height) approximated most of the useful
multilink geometries. One effect that's missing is the change in camber
with suspension travel.

In response to my question of how to use measured information about a car's suspension (such as suspension type) to generate a hinge point:

The problem is that just knowing it's a strut or a wishbone doesn't tell
you enough about the geometry. What matters is how the wheel is
constrained to move as it's displaced. You'd need to know the positions
of the joints and how those joints constrain the motion of the wheel in
order to determine how the car will behave. Unfortunately, as it
stands, the code could not use that information even if you had it. I
know that's bad news if you're trying to simulate a particular car.

The hinged suspension in the code doesn't directly correspond to a real
suspension type, but it does (as far as I know) reproduce the important
performance characteristics of real suspensions--anti-squat and
anti-dive. Depending on their precise geometries, two different
multi-link (for instance) suspensions may have different
characteristics, and some multi-link suspension may have the same
characteristics as some double wishbone. There's not a direct
correspondence between suspension type and hinge position.