CODEWITHSUNDEEP
bulletphysics
Irbis
Irbis

Reputation: 13369

bullet physics - object stabilization after picking

Many of the bullet examples inherit from CommonRigidBodyBase. Objects are picked based on btPoint2PointConstraint. I have analyzed a SimpleBox example.

When a falling object is picked it starts rotate around a pick point but rotation decreases with time. After some time a picked object should become stable.

In SimpleBox example I have changed a collision shape form (1,1,1) to (2,2,2):

btBoxShape* colShape = createBoxShape(btVector3(2,2,2));

When I pick falling object (which is bigger than before) more or less at the same high above the ground it rotates much longer around pick point. Why ?

I wonder how can I control the time which is needed to stabilize object after picking. Let's assume that a gravity is fixed (9.8). I have only one idea: assign a bigger mass to the object. Are there any other parameters ?

Upvotes: 1

Views: 593

Answers (1)

LastBlow
LastBlow

Reputation: 707

Instead of btPoint2PointConstraint, I use btGeneric6DofConstraint with all angular motion suppressed.

m_pickedRigidBody->setActivationState(DISABLE_DEACTIVATION);

btTransform pivot;
pivot.setIdentity();
btVector3 localPivot = m_pickedRigidBody->getCenterOfMassTransform().inverse() * rayCast.point;
pivot.setOrigin(localPivot);

btGeneric6DofConstraint* DOF6 = new btGeneric6DofConstraint(*m_pickedRigidBody, pivot, true);

bool bLimitAngularMotion = true;
if (bLimitAngularMotion) {
    DOF6->setAngularLowerLimit(btVector3(0, 0, 0));
    DOF6->setAngularUpperLimit(btVector3(0, 0, 0));
}

m_dynamicWorld->addConstraint(DOF6, true);

m_pickedConstraint = DOF6;

float cfm = 0.5f;
float erp = 0.5f;

for (int i = 0; i < 6; i++) {
    DOF6->setParam(BT_CONSTRAINT_STOP_CFM, cfm, i);
    DOF6->setParam(BT_CONSTRAINT_STOP_ERP, erp, i);
}

Upvotes: 1

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