[ODE] joint problem

[tullio.molitierno at libero.it]

In my simulation there are several boxes connected with universal joints and
some spheres.

 These spheres are connected to the boxes with ball joints (the ball's anchor
point is the box's position).

 It happens that  if these spheres collide with a body the center's sphere
traslates respect to box's center. 

I want  box's and sphere's centers are the same.

Someone can help me?

Best Regards

Tullio