[ODE] jointFeedback again... please help

Davide Faconti facontidavide at hotmail.com
Thu Nov 4 09:59:11 MST 2004

Dear all,

I have sent many e-mail asking about jointFeedback behaviour, but no one 
answered me.
I invite Russ to enter in the discussion, since there is something defenetly 
odd in that function.

The force applied to the joints looks fine, instead the torque doesn't:

1) I suppose that t1 should be equal to -t2, according to newton-euler laws, 
but it isn't.
2) I calculated by and the torque that the joint is supposed to generate, 
and ODE gives different values, that I am pretty sure are wrong.

If you are not sure, check try the following code please and read the output 

#include <ode/ode.h>
#include <drawstuff/drawstuff.h>
static dWorldID world;
static dBodyID body;
static dJointID joint;
static dJointFeedback feedback;

static void simLoop (int pause)
   dReal sides[3] = {0.20,0.01,0.01};
   dsDrawBoxD (dBodyGetPosition(body),dBodyGetRotation(body),sides);
   dWorldStep (world,0.01);
   printf("t1 %f %f %f\n", feedback.t1[0],feedback.t1[1],feedback.t1[2]);
   printf("t2 %f %f %f\n", feedback.t2[0],feedback.t2[1],feedback.t2[2]);

static void start()
  static float xyz[3] = {0.1f,0.5f,0.4f};
  static float hpr[3] = {-90.0000f,-10.5000f,0.0000f};
  dsSetViewpoint (xyz,hpr);

int main (int argc, char **argv)
  dsFunctions fn;
  fn.version = DS_VERSION;
  fn.start = &start;
  fn.step = &simLoop;
  fn.stop = 0;
  fn.path_to_textures = "textures";

  world = dWorldCreate();
  dWorldSetGravity (world, 0, 0, -10);
  dMass m;
  dMassSetBox (&m,1,0.20,0.01,0.01);
  dMassAdjust (&m,1);
  body = dBodyCreate (world);
  dBodySetMass (body,&m);
  dBodySetPosition (body, 0 ,0 , 0.5);

  joint = dJointCreateHinge (world,0);
  dJointAttach (joint,body,0);
  dJointSetHingeAnchor (joint,0.1,0,0.5);
  dJointSetHingeAxis (joint,0,1,0);
  dJointSetHingeParam(joint, dParamFMax,0.4);
  dJointSetFeedback(joint, &feedback);

  dsSimulationLoop (argc,argv,500,500,&fn);
  dWorldDestroy (world);
  return 0;

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