SetTorque questions

[misho]

Can someone (Julio?) please shed some light at this behaviour:

I have 2 objects set up "suspended" in space (no gravity). 2nd object has Angular and Linear damping values set to zero. (I have also tried very small values, as advised in WIKI).

I have it set up so that at each key "F" press (or, while the key is down, each cycle), both objects are given an x torque some small value.

Object 1 starts to rotate while the "F" is down, but slows down to a stop when the key is released - this is as expected, since the damping value is non-zero.

Object 2 also starts to rotate, and given sufficient torque, it keeps rotating. That is as expected, also.

BUT, if I apply just a small amount of torque, the object 2 starts to rotate slightly, but then it stops. That is unexpected behaviour. Why would it stop on small torques, and not on large? When it rotates, I checked the Omega, and it doesn't change (i.e. it doesn't slow down gradually)

I understand that damping can't be completely eliminated, but why does it seem to work for large torque (no slowdown), but not for small ones?

Thanks in advance,
Misho

[ledahut]

Maybe autoSleep is set to true.
Try again with autosleep to off.
See NewtonBodySetAutoSleep

[Julio Jerez]

yiss that was a problem, when an omega was very small auto sleep keek in a stop teh body.

but it was fixed in some vertion of teh SDK, are yuo using 2.24?

Try setting auto sleep off like ledahut

[misho]

Thanks guys, that helped! However, it still happens for very small torques and resulting omegas... Anything less than 0.03 rad/s will stop. Omegas larger than 0.03 will "keep going".

Actually, applying very small torques is not moving the object at all. Perhaps it is not enough to overcome angular inertia?

Misho

[Julio Jerez]

Are you the same person that was making a demo with a submaring whe the body was not moving when a small force was applied?
I remember I fixed that.

[misho]

No, that's not me I'm the guy waiting for the VS2010 SDK Example compatibility

Misho

[Julio Jerez]

if autosleep is off I believe it should spin

How do I test that?

[misho]

Hi Julio,

Testing that is easy - set up your body like this (I'm using entity class from tutorials, just to easily visualize the bodies)

Code: Select all

   eStage2 = sceneManager->CreateEntity();
   eStage2->LoadMesh ("dumb.dat");
   eStage2->m_curPosition.m_x = 0.0f;
   eStage2->m_curPosition.m_y = 0.0f;
   eStage2->m_curPosition.m_z = -2.0f;
   eStage2->m_prevPosition = eStage2->m_curPosition;

   // add a body with a Convex hull shape
   shape = CreateNewtonBox (world, eStage2, 2);
   Stage2Body = CreateRigidBody (world, eStage2, shape, 20.0f);

   NewtonBodySetLinearDamping( Stage2Body, 0.00000000000f);

   dFloat angularDamp[3];
   angularDamp[0] = -0.0000000000000000000000000f;
   angularDamp[1] = -0.0000000000000000000000000f;
   angularDamp[2] = -0.0000000000000000000000000f;
   NewtonBodySetAngularDamping(Stage2Body, angularDamp);

   NewtonBodySetAutoSleep(Stage2Body,0);
   NewtonReleaseCollision (world, shape);

Then, in ApplyForceAndTorqueCallback,

Code: Select all

      dFloat Torques[3];

   Torques[0] = 0.0f;
   Torques[1] = 0.0f;
   Torques[2] = 0.0f;

   if(FKey)
      Torques[0] = 0.5f;
   if(GKey)
      Torques[0] = -0.5f;

   NewtonBodySetTorque(body, Torques);
   NewtonBodyGetOmega(body, mOmega);

FKey and GKey are booleans that are true when F and G keys are down. You can use them to apply torque to the object in + and - direction on x axis, effectively speeding up or slowing down rotation.
With this setup, you'll see that small omegas of less than 0.03 rps will "stop". Also, you'll notice that, if you just tap the F/G key and add very small torque, there will be a small Omega value displayed momentarily, and it will instantly go back to 0. I have the omega values displayed on screen:

Code: Select all

   Print (dVector (1.0f, 1.0f, 1.0f, 1.0f), 10, 124, "Omega: x = %5.8f", mOmega[0]);
   Print (dVector (1.0f, 1.0f, 1.0f, 1.0f), 10, 144, "Omega: y = %5.8f", mOmega[1]);
   Print (dVector (1.0f, 1.0f, 1.0f, 1.0f), 10, 164, "Omega: z = %5.8f", mOmega[2]);

Cheers,
Misho

[Julio Jerez]

I will try tonight

can you post this in the Bug Track forum?

[misho]

No problem - done!