Set Driven Key (SDK) is very powerful and it allowed you to have a node's attribute drive the attribute of another node. It's very useful for animation.
1.While the pelvis still selected, go to Animate -> Set Driven Key -> Set option to bring up the Set Driven Key window.
Load pelvis joint as Driver, then select Jaw joint and load as Driven. Next, select Jaw from pelvis joint and rotate Z
from Jaw joint. Make sure that pelvis joint's Jaw attribute and Jaw joint's
attribute set to 0, then click on Key.
Jaw's value 0 (Min) has been set. Then I will set Jaw's value 10 (Max).
2. Key 10 for pelvis joint's Jaw attribute value, then 30 for Jaw joint's Rotate Z value. Click on Key.
Close the window and we have done.
Now, Let's test the Jaw attribute. With the Jaw attribute selected in pelvis joint, MMB click on the perspective window and drag it right to left and you will notice the jaw is open gradually.
This is only a simple example of how to connect a node's attribute drive the attribute of another node.
You may want to add other attributes to drive other node according to your setup.