[ODE] My rays don't want to stay

[Frugier Kevin]

Hello there,

I'm a programming a robot simulation.
My robot has 8 sensors.
For each sensor I create a ray like this :
    sensors_bodies[i] = dBodyCreate (world); //this is only a body but
i'll use it for the drawing stuff of the sensor's box
    dMassSetBoxTotal (&m, SENSOR_MASS,SENSOR_SIZE,
SENSOR_SIZE,SENSOR_SIZE);
    dBodySetMass (sensors_bodies[i],&m);
    sensors_geom[i] = dCreateRay (space, 2*BOX_SIZE); //here i create it
    sensors_distance[i]=2*BOX_SIZE;
    dGeomSetBody (sensors_geom[i],sensors_bodies[i]); //i attach my ray
to the sensor's body

Then I put my ray in the good position and direction :

For exemple the first :
   dGeomRaySet
(sensors_geom[i],1.5*SENSOR_SIZE,KHEP_RADIUS-1.5*SENSOR_SIZE,WHEEL_RADIUS+KHEP_HEIGHT+SENSOR_SIZE,0,1,0);

And to finish I attach the sensor to my robot's body, because the
sensors move and turn with it...

     sensors_joint[i] = dJointCreateFixed (world,0);
     dJointAttach (sensors_joint[i],khep_bodies[0],sensors_bodies[i]);
      dJointSetFixed (sensors_joint[i]);

In my NearCallback i look at what my sensor's see :

for (unsigned int i=0; i<8; i++)
  {
    if ((o1 == sensors_geom[i])||(o2 == sensors_geom[i]))
    {
       dContact contact;
       n = dCollide (o1,o2,1,&contact.geom,sizeof(dContact));  
       if (n == 1)
       {
         sensors_distance[i]=contact.geom.depth;  
        
       }  
        return;
    }  
  }

For the first Time Step everything is ok !

But At the second, my rays have ALL changed there orientation : they all
look UP. (Z axis)
So the sensors don't see anything anymore....except the beauty of the sky.

I think my mistake is easy to find but this is the first time i use rays
so maybe i don't understand everything.

Thanks a lot for your (coming) answers

Kevin