Understanding constraints

Our toy train has 12 wheels that we want to spin as the train moves along the tracks. Because they’re all part of one train on one set of tracks, these wheels may all rotate in sync. Each wheel on one side of the train is joined with the wheel on the opposite side for a total of six wheel objects. That’s better than 12, but it’s still a lot for us to animate. Using constraints will make our task much easier.

Constraints are a kind of object relationship, like parenting, but more advanced. An object can have multiple constraints, even if it already has a parent. There’s a variety of constraint types to choose from:

Figure 4.14: The Add Object Constraint menu

By using Copy Rotation constraints in this section, we can make five wheel objects copy the rotation of one – much easier than keying (or driving) the rotation of all six.

Adding a constraint

We’ll start by adding a Copy Rotation...