Why arent the wheels connected to Havok

Question

Ok I am totally lost with this havok thing. I am trying to
understand what gets attached to the havok physics engine when
designing a car racing game. However, after downloading both the
jeep car and the remote control car games from director-online
havok archive site, I noticed something very stange. While trying
to decipher the code on both files it seems to me that the wheels
are not attached to the Havok physic's engine. Now I could be
wrong, but I wanted to ask you guys if this is correct, and if so,
then how do the wheels follow the car as well as stay on the ground
and without going through the ground? I am asking this becuase I
could not pick it out through its lingo. There are so many
behaviours attached to the 3d world that it is impossible to know
where Director starts to read each behaviour.
I understand a little bit about havok, such as if you want
something movable then you attach a movable rigid body to it and if
the object is fixed then you would attach the fixed rigid body to
it. In addition, I also know a little bit about mass which sets the
weight of the object. However, it seems to me that both of these
games are way too advamced for me especially when just for now all
I am trying to unserstand is how the wheels of a car can follow the
body of the car and also for the wheels to stay on the ground and
without them going through the ground.

Answer 1

Roofy wrote:
>
quote:
IIRC, the example you?re talking about has a "chassis" whose
model
> consists in 4 wheels and the car itself it?s only
attached to the
> chassis by a spring or dashpot to give the amortiguation
effect.
>
> ok, I might be wrong on this, but after pressing play
and typing the following
> syntax in the message window...
> form the jeep demo ....
> put member("blankHavok").lineardashpot
> put member("blankHavok").spring.count
>
> and from the RemoteControl Car demo
> put member("carHKE").lineardashpot
> put member("carHKE").spring.count
>
>
>
> ... doing this in both files and after pressing play, I
get an emplty list
> returned back for the dashpot and 0 for the count of the
spring. So I don't
> think there are any dashpots nor springs on either demo.
Sorry, I thought you were talking about this demo:
http://director-online.com/havok/demos/demo-dashcar.html
> However, what I am
> concluding is that I think they are using 2 custom
handlers called
> initializeHover and updateHover which is somehow
detecting the chassis and its
> wheels if they collide or not. I did a test by disabling
both of these custom
> handlers and by doing so, the chassis would fall through
the wheels and land on
> the ground instead. On the other hand, if these 2 custom
handlers are causing
> this effect, then I srill don't understand how the the
wheels are following the
> chassis. Therefore, I am wondering if it would be easier
to use modelsUnderRay
> considering that all I am trying to do is do collision
detection? What do you
> think?
Actually, this RayCastCar demo uses modelsUnderRay() for
collision
detection of the wheels with the ground:
-- For each wheel do
repeat with i = 1 to pWheelPointList.count
pIsHoveringList
= false
worldWheelPoint = pChassisMDL.transform *
pWheelPointList
intersectDetails = pMember.ModelsUnderRay(worldWheelPoint,
worldDownDir, 2, #detailed)
So the physics and control are applied to the chassis and the
wheels are
just "floating". At which distance should they float is what
modelsUnderRay() is used for.
This doesn�t mean that you don�t need Havok at
all and you can use
modelsUnderRay() instead since havok handles all the driving
physics and
MUR just the distance of the wheels to the chassis.
Regards,
Agust�n Mar�a Rodr�guez
www.onwine.com.ar > Macromedia Director demos & code