Driven key animation is a rigging technique used in 3D animation to link the movement or value of one attribute to the movement or value of another.
This powerful method allows animators and technical directors to automate complex motions or relationships between different parts of a 3D model or scene.
Understanding the Core Concept
Setting driven keys is a technique for driving the animation of one object or attribute, using another attribute. At its heart, this technique establishes a direct, dependent link between two specific attributes.
Here's how it works:
- The Driver Attribute: This is the attribute that initiates the action. Its value changes, often through direct animation or another constraint.
- The Driven Attribute: This is the attribute that responds to the change in the driver attribute. Its value is automatically altered based on the driver's value, following a relationship defined by the driven key.
With driven keys, you create a dependent link between a pair of attributes. A change in the driver attribute then alters the value of the driven attribute. This means animating the "driver" attribute automatically animates the "driven" attribute, simplifying the animation process for interconnected movements.
Key Aspects
- Dependent Link: A fundamental aspect is the creation of a direct relationship where one attribute's state dictates another's.
- Attribute Control: It allows one attribute (like rotation) to control another attribute (like visibility, scale, or position).
- Automation: It automates secondary motions or complex rig setups, reducing the need to animate multiple attributes independently.
How Driven Keys Work
Imagine you have a character's arm and hand. You want the fingers to curl into a fist automatically as the arm rotates upwards, as if picking something up. Driven keys are perfect for this:
- Driver: The rotation attribute of the arm joint.
- Driven: A control attribute on the hand rig that controls the curling of the fingers (e.g., a single "Fist" attribute).
You would set keyframes for the "Fist" attribute at different values of the arm's rotation. For example:
| Driver (Arm Rotation) | Driven (Fist Control) | Result |
|---|---|---|
| 0 Degrees (Down) | 0 (Open Hand) | Hand is open |
| 90 Degrees (Up) | 1 (Closed Fist) | Hand forms a fist |
Now, as you simply rotate the arm from 0 to 90 degrees, the "Fist" attribute automatically goes from 0 to 1, animating the finger curl without needing separate keyframes for the hand.
Practical Applications
Driven keys are incredibly versatile in 3D animation rigging:
- Facial Animation: Blinking eyes tied to a single control, smile intensity linked to cheek deformation.
- Character Rigs: Foot roll automatically lifting toes, elbow bend compressing a muscle bulge.
- Mechanical Rigs: Gear rotation driving piston movement, lever position controlling door opening.
- Prop Animation: Opening a book cover simultaneously spreading the pages.
By using driven keys, animators can control complex systems through intuitive "master" controls, making the animation process faster and more manageable, especially for intricate rigs.
