How to create an bone springs??

How to create an bone springs??

For example I has bone_parent and bone_child,
and the actor are actor_parent and actor_child.
the joint between them is a SphericalJoint: the_joint.

so there is:

Ogre::Bone* bone_parent,bone_child;
NxOgre::Actor* actor_parent,actor_child;
NxSphericalJoint* the_s_joint;


I am planning to use swingSpring and twistSpring moving the actors ,so that it look like an animation.
I planing to change the swingAxis and the targetValue of twistSpring to do this.

But how to calculate the correct number of swingAxis and targetValue??

I hope some one can help me.