Marco Gugel wrote:
> My idea is to develop a truck simulation inside FlightGear and I
> have thought to start from Yasim because it uses the rigidbody
> dynamics;

Right.  That's the RigidBody/Integrator/BodyEnvironment
implementation.  You set masses on the body, calculate forces inside
the environment, and let the integrator figure out the result.

> But there is a "little" problem: the collision detection, which is
> not implemented.  Moreover the airplanes on the gorund don't follow
> the slope of the terrain in a realistic manner: [...] is this
> behavior due to the fact that the only point of reference is the cg
> of the aircraft and not the position of the wheels?

This is a different problem, and not the only one you are going to
discover.  Indeed, the collision detection is a hack right now, which
presumes a horizontal ground plane under the aircraft.  This works
just fine for airfields, but not so well for hills (or ships/carriers,
for that matter).

It's not related to c.g. or positioning issues at all; in fact the
application of force at the position of the wheels *is* modelled
correctly in YASim, and the c.g. is computed dynamically from the mass
distribution; it isn't a "user visible" parameter...  All (heh) that
is required to fix this bug is for the gear model to calculate a
proper intersection with the terrain polygons instead of using a
ground plane defined for the whole aircraft.

A more serious problem, though, is that the current YASim gear force
model works rather poorly for ground vehicles.  It "slips" against
side forces instead of holding position.  See recent posts about the
gear model for more notes.  A few ideas have been kicked around, but
all of them are kinda scary to implement.


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