[ODE] conveyor belts and moving platforms

[Benny Kramek]

> 
>>>Also, if i want to simulate moving platforms (boxes with bodies) that the player can jump on, should friction keep the player on the platform or will I need a special contact joint?
>>>
> 
>>Friction will keep the players on the platform with no problem. Just make sure that there is enough friction.
>>
> 
> I created a box geom with a body and dropped a sphere geom with a body on it.  There sphere comes to rest on the box while the box moves back and forth (on a sine wave with SetVel) underneath it.  But the sphere doesn't move back and forth with the box!!
> 
> Friction doesn't seem to give the sphere any motion.  I tried infinite and 1.0 friction with the same results.
> 

This is a known thing with ode. A ball that is rolling on the ground 
will never slow down, even if there is friction. Try replacing the 
sphere with a box.
Also, you shouldn't change the velocity of the platform with 
dBodySetVel(). This is not the correct way to do things. You should only 
apply forces. If you want to give a body a certain velocity you should 
use a motor.