You can create a new target shape that is driven by one or more other target shapes. This allows you to have more control over subtle shapes, such as when doing facial animation. For example, a target shape for a smile on a character's face might work well on its own, but doesn't work as well combined with other target shapes. In this case, you could add a new target shape that enhances or corrects the target shapes when they're combined.
The combination target shape is driven by other target shapes, so when you edit the shape or weight value of the contributing target shapes (drivers), the combination target shape also changes to reflect that. In fact, it has no weight value of its own that you can change directly.
If you already have a target shape that you want to use, you can set that one as a combination target shape.
To create a combination target shape
You can also select one or more groups of target shapes.
A new target shape is created, with the names of the driver target shapes displayed beside it. Its weight (displayed in yellow) is driven by the contributing target shapes according to the Method used.
To use an existing target shape as a combination target shape
You can also select one or more groups of target shapes.
The last selected target shape becomes the combination target shape with the other selected target shapes being the drivers. Their names are displayed beside the combination target shape. Its weight (displayed in yellow) is driven by the contributing target shapes when their weights are at 1 (100% activation).
To use an existing mesh as a combination target shape
Maya adds a combination target shape to the blend shape deformer with the other selected meshes being the drivers. Their names are displayed beside the combination target shape. Its weight (displayed in yellow) is driven by the contributing target shapes when their weights are at 1 (100% activation).
To select the driver target shapes
To add driver target shapes
To remove driver target shapes