Set Driven Key
A Set Driven Key is a powerful tool for a TD. It’s a simple concept, but when I was first learning about it, I got confused by the GUI that maya used to create them. I found later that it was much easier to use MEL to script the creation of a Set Driven Key. People call ti a Set Driven Key because of the name in the menu. But they are actually “Driven Keys” and the command in the Maya menu will “Set” them. Driven keys allow you to create relationships between different object. So, the value of one attribute can “drive” the value of a different attribute. They are used for many things. These relationships can be manipulated in the graph editor.
Making hand/finger controls.
You might have an attribute called “makeFist” on a hand control. When “makeFist” is 0 then the hand is open. When “makeFist” at its highest value, the hand is a fist. This is done by creating a driven key where the value of “makeFist” drives the rotation values of the joints that control the fingers.
Deformers driven by Joints.
You can set a driven key so that a deformers envelope comes on as a joint moves into a certain oientation. This can also be used for corrective blendshapes and influence objects.
A Set Driven Key can be created using a simple mel command.
setDrivenKeyframe [flags] [objects]
setDrivenKeyframe -value 1 -driverValue 120 -currentDriver leftKneeJoint.ry cluster1.envelope;
setDrivenKeyframe -v -dv -cd leftKneeJoint.ry cluster1.envelope;