Parenting a model into a skeleton hierarchy

Learning Resources > Tutorials > Getting Started with Maya > Animation > Lesson 5: Inverse kinematics >

Parenting is the term used when placing a node beneath another in a hierarchy so it becomes the child of the node above it (its parent) in the hierarchy.

In the following steps, you add the surfaces of the mechanical arm model into the skeleton hierarchy. This process links the models’ surfaces to the skeleton hierarchy making it possible to pose and animate the model like a real mechanical arm. Using the Hypergraph to select the nodes allows you to better visualize the process and the hierarchical relationships that result.

NoteThe following parenting procedure works well for the mechanical arm (no organic bending or deformation occurs) and provides one technique for adding modeled objects to a skeletal hierarchy.

A more common technique for combining a character model into a skeleton hierarchy is referred to as skinning or binding. The Bind Skin tool combines the surface components and joints together into a hierarchy and also takes into account any deformations that may occur when a character bends or flexes (knees, waist, neck, elbows etc.). Maya provides a few methods for skinning. For more information see Skeletons and skinning in the Maya Help. For a tutorial on skinning see the Smooth Skinning lesson in the Character Setup chapter in this guide.

To parent the mechanical arm into the skeleton

In the Hypergraph menu, select View > Frame All.
The Hypergraph displays all the nodes for the scene.
In the Hypergraph, select the node named ArmEnd and then shift-select the node named joint4.
The order of selection is important. You want to select the child node first, and then shift-select the item that will become the parent node second.
In the main menu, select Edit > Parent (Hotkey p).
In the Hypergraph, joint4 is now the parent node for the Arm_end node in the skeleton hierarchy.
Repeat the parenting process for the following items:
- pin3 is parented under joint3
- pin2 is parented under joint2
- pin1 is parented under joint1
Your new hierarchy should appear as shown in the diagram below.

In the next steps, SwivelBase becomes the parent node for the new hierarchy so that the entire arm assembly swivels about the center of the base component.
In the Hypergraph, select the node named joint1 and then shift-select the node named SwivelBase.
In the main menu, select Edit > Parent (Hotkey p).
Change the panel display to a layout that allows you to view the hierarchy in the Hypergraph.
In the side view menu, select Panels > Layouts > Two panes side by side.
The panels display in a side by side configuration.
Dolly the Hypergraph view as required to view the new hierarchy.
In the Hypergraph, select the node named Swivel_base.
In the side view, observe that both the mechanical arm model and the skeleton are selected. Swivel_base is the parent or root node for the hierarchy. If you rotate SwivelBase, everything else below that node (the entire arm with skeleton) rotates.
Select the node named joint3.
Observe that the last two components of the mechanical arm are selected. If you rotate joint3, only the components below that node in the hierarchy will be affected.
Select the node named pin2.
Observe that only one isolated segment of the model is selected. No other components or joints are selected when pin2 node is selected. If you rotate the model at pin2, only the component at pin2 will rotate in isolation from the rest of the hierarchy because it is located lower in the hierarchy.

It is now possible to select and rotate the skeleton joints to pose the mechanical arm as a unit, and then set keyframes to animate it. Posing a character using joint rotations is referred to as Forward Kinematics (FK). FK allows for precise control when setting up a pose, but it can be a time consuming process to select and rotate each joint into the desired position.

When an animation is more focused on the goal of placing the end joint in a hierarchy in a particular position, (for example, a hand or a foot), it is more efficient to use Inverse Kinematics to pose the skeleton. For more information on forward and inverse kinematics, see Posing skeletons in the Maya Help.

NoteIt’s not a simple matter to state that one technique or another is the only approach to achieving a desired result when animating in Maya. You must decide whether a particular technique works for a particular scenario based on the options it provides. A combination of animation techniques can be creatively used in a variety of ways.