Driven keys

Driven keys work by connecting the output of one attribute (channel) to the input of another. A change in a driver attribute alters the value of the driven attribute.

Graph Editor curve that shows the relationship between the linked attributes. Graph Editor's vertical axis lists driven attribute values, and the horizontal axis lists driver attribute values. For each attribute value of the driver, the curve shows the associated value of the driven attribute. You can edit the curve to alter the relationship.

In the example below you will use a ball's y-scaling as a driver attribute and the ball's x-scaling and z-scaling as driven attributes to animate squash.

To set up driven keys for squashes of a bouncing ball animation:

1. Open ball_demo4.mb. The y-translation and y-scaling of the sphere named "ball" have been already keyed.
2. Select the Animation menu set (F2).
3. Select the ball and move to the "ball_scale" node by using the upward-arrow key. While "ball_scale" is selected, open the option window for "Set Driven Key" by selecting Animate -> Set Driven Key -> Set.
4. Click "Load Driver" if nothing is listed
5. Select "scaleY" in Driver window.
6. Click "Load Driven" if nothing is listed.
7. Scale "ball_scale" by 1.0, 1.0, 1.0.
8. Select "scaleX" in Driven window and click "key".
9. Select "scaleZ" in Driven window and click "key".
10. Scale "ball_scale" by 1.5, 0.4, 1.5.
11. Select "scaleX" in Driven window and click "key".
12. Select "scaleZ" in Driven window and click "key".
13. Move in time. The x- and z-scaling values change as the the y-scaling changes.

Open GraphEditor by Window -> Animation Editor -> Graph Editor... GraphEditor shows the relationships between scaleX and scaleY, and scaleZ and scaleY, both of which are linear by default.

A finished file: ball_demo4_finished.mb

Note: Driven keys can be set between attributes of two different entities as well as attributes of the same entities.