Adding Constraints
Constraints make your rig work. You could say that they make bones react to other bones; for example, if you move a bone, you will cause a certain reaction in another part of the skeleton. Throughout this chapter, you’ll use a lot of constraints, but for now let’s see how they work and how you can add them to bones.
First, you need to know that most of the constraints have a “target,” which means that when a constraint is applied to a bone, it also targets another bone and the constraint is then created between them. For example, if you use the Track To constraint for an eye, you’d apply the constraint to the eye and you’d select as a target the bone that you want the eye to look at.
Caution
You can apply constraints to any object in your scene but there’s a difference between Object Constraints and Bone Constraints. If you’re in Object Mode and add a constraint, it will affect the whole armature. If you’re in Pose Mode when you add a constraint, a new tab will appear in the Properties Editor: Bone Constraints. The Object Constraints tab has a chain as its icon, while the Bone Constraints tab shows an icon with a smaller chain near a bone.
With this in mind, there are two main ways to add constraints; just remember you have to be in Pose Mode:
Select the bone to which you want to add the constraint. Go to the Bone Constraints tab in the Properties Editor, click the Add Bone Constraint button, and select the constraint type you want to add. You’ll see that the constraint is then added to the stack similar to the way in which modifiers are added to it. Inside the Constraints panel, you’ll see a field for the Target. Enter the name of the armature and a new field for the bone’s name will appear where you should insert the name of the bone you want to have as the target for the constraint.
Another, usually faster way to add a constraint is to first select the target bone and then select the bone to which you want to add the constraint while pressing Shift. Then press Shift + Ctrl + C to open the Constraints menu to add the constraint (or go to the Armature menu on the 3D view header and find the Constraints category). This way, when you add a constraint, it will automatically pick the first selected bone as a target and you won’t have to add it manually in the Constraints panel.
Tip
Whenever you need to insert the name of an object in a text field, start typing the name and a list will appear with the names of objects that start with the letters you’ve typed. This is another reason why keeping your objects named correctly can help a lot! Also, you can select an object or bone, place the cursor over its name field, and press Ctrl + C to copy the name; then, select the object with the constraint, go to the desired field, place the cursor on top of it, and press Ctrl + V to paste the name you copied before.