[ODE] [Where m I ]always simulating spring.

[elekis]

hi,

always trying simulate a spring, this is where I m (see below for trouble)


int main(){
        //Create a dynamics world.
        World = dWorldCreate();
        dWorldSetERP (World, ERP);


        //Create bodies in the dynamics world.
        Box1 = dBodyCreate (World);
        Box2 = dBodyCreate (World);
        Box3 = dBodyCreate (World);

        dBodySetPosition (Box1, 0.0, 0.0, 0.0);
        dBodySetPosition (Box2, 10, 10, 10);
        dBodySetPosition (Box3, 20, 20, 0);



        joint12 = dJointCreateSlider (World ,0);
        dJointAttach (joint12, Box1, Box2);

        joint23 = dJointCreateSlider (World ,0);
        dJointAttach (joint23, Box2, Box3);


        osgProducer::Viewer viewer;
        viewer.setUpViewer (osgProducer::Viewer::STANDARD_SETTINGS);

        CreateOSGWorld();
        viewer.setSceneData (root.get());
        UpdateOSGWorld();

        viewer.realize();

        osg::Timer_t prevTime = osg::Timer::instance()->tick();

   while (!viewer.done())
   {

      viewer.sync();
      viewer.update();
      viewer.frame();

      const double MAX_STEP = 0.01;
      const osg::Timer_t now = osg::Timer::instance()->tick();
      double deltaSecs = osg::Timer::instance()->delta_s (prevTime, now);
      prevTime = now;




      while (deltaSecs > 0.0)
      {
         const double step = std::min (MAX_STEP, deltaSecs);
         deltaSecs -= MAX_STEP;
        static dReal kp12 = 10; // spring constant
        static dReal kp23 = 20; // spring constant

        dReal tmp12 =  dJointGetSliderPosition(joint12);
        dReal tmp23 =  dJointGetSliderPosition(joint23);

        dReal f12 = - kp12 * tmp12;
        dJointAddSliderForce(joint12, f12);

        dReal f23 = - kp23 * tmp23;
        dJointAddSliderForce(joint23, f23);


        dWorldStep (World, step);

      }

      UpdateOSGWorld();
   }
dWorldDestroy (World);

  // viewer.sync();
}

to be simple there are two box 1 and 3 who doesnt' move, and box 2 who has
to move attached  by springs.

I have two trouble, the first is,  That doesnt' move like I want, the box 2
move in the 1-3 axis and not in up-down axis (like a real spring)


the second thing is box 1 and 3 have to be immuable.

in faq you say
"   he answer is to create a geom only, without the corresponding rigid body
object ... Then in the contact callback"

but I don't need collision world so how to do that.


thanks a lot for all

a++
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