Serially connected hinges, base hinge tend to drift...

[jimali]

Hi,

i use a series of hingeConstraints to represent a robot. My problem is that the base hinge, that is the hinge that fastens to a static body, tends to drift quite far...(see illustration). Do i have to do something specific when attaching to a static body?

This is how i create the constraints.

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Transform3D<> wTchild = Kinematics::WorldTframe(joint,state);
Transform3D<> wTparent = Kinematics::WorldTframe(parentFrame,state);

btTransform frameInA, frameInB;
frameInA.setIdentity(); // the joint allready use z-axis for rotation
frameInB = makeBtTransform( inverse(wTparent) * wTchild ); // calculate transform from parent to joint

btChild->setActivationState(DISABLE_DEACTIVATION);
btParent->setActivationState(DISABLE_DEACTIVATION);

btHingeConstraint *hinge = new btHingeConstraint(*btChild, *btParent, frameInA, frameInB);
hinge->setLimit( joint->getBounds().first, joint->getBounds().second );
hinge->enableAngularMotor(true, 0.0, 10);
m_dynamicsWorld->addConstraint(hinge, true);
_jointToConstraintMap[joint] = hinge;
constraints.push_back(hinge);

thx

[jimali]

ok, i actually figured it out in the end. It seems that if you connect a rigid body to some fixed body using:

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new btHingeConstraint(*btChild, *btParent, frameInA, frameInB)

instead of just:

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new btHingeConstraint(*btChild,  frameInA)

makes the rigid body btChild drift relative to btParent. Not sure if this is an actual bug but could be nice if the apidoc for the first method mentioned this

cheers jim

[bindumol]

Hi,
Please read my doubt if you have time...

This is the first stage of equipment loading is in the picture robotgif2.....
Here i am using bullet and irrlicht for developing my applications....
After rotating 90 degree the top body with respect to the point of the attached pin….then I got it like in picture robotgif1
In this i am using btTranform rotation without using any constraints....
But it is not working properly as i want...
So can you say which are the constraints i can give in between the mainshat,MiddleHinge, Pin and Arm Hinge...



Waiting for your reply
thanks& regards
Bindumol