Creating joints

A skeleton is made of bones and joints. When you create a skeleton in Maya, you create a series of joints in the skeletal locations where you want the character to bend or twist.

A common technique for creating a skeleton is to create several independent joint chains—one for each arm, one for each leg, one for the spine/head—then group the chains together to create a single skeletal hierarchy. In the steps that follow, you create the joints for the legs.

To create joints for the legs

1. Select Window > Settings/Preferences > Preferences. In the Preferences window, click the Kinematics Category. Enter 0.4 for the Joint size, then click the Save button.

   This displays the joints smaller when you create them in the next steps. At the default size, 1.0, the size of the joints makes them hard to position accurately for this character.

   Note

   The default joint size of 1.0 has been used to create the joints pictured in the following illustrations. The joints you create may appear smaller than those pictured in this lesson.

2. Select Skeleton > Joint Tool. This is the tool for creating the joint chains that make up a skeleton.
3. In a side view, click at the hip, knee, ankle, ball of foot, and toe to create joints at these positions (see the following figure). Make sure the knee joint is in a position that creates a slight forward bend. The forward bend ensures that you will be able to animate the leg easily in a direction natural for a leg.
   
   Tip

   Press +b (Windows) or +b (Mac OS X) to toggle between default background colors in the scene view.

4. Press Enter (Windows and Linux) or Return (Mac OS X) after creating the toe joint. This completes the joint chain.
5. Select Window > Hypergraph: Hierarchy.

   The Hypergraph is a convenient place to select, rename, and parent objects. It is similar to the Outliner, but it has features tailored for character setup. For example, it depicts all parent-child relationships in an easy-to-read indented format.

   The Hypergraph shows the default names given to the joints just created: joint1, joint2, and so on. The joints have a hierarchical relationship. Joint1 is the parent of joint2, which is the parent of joint3, and so on. Joint1 is the root of the hierarchy. If you reposition joint1, you reposition the whole joint chain.

   In the scene view, joints are represented by spherical icons. Bones separate the joints, and are represented by elongated pyramid icons. The narrow part of a bone points in the downward direction of the hierarchy.

   The reason you create the hip joint first and the toe joint last is to have the hip at the top of the hierarchy and the toe at the bottom. You’ll usually want the toe (and other joints) to move whenever you move the hip, but not necessarily vice versa. In general, joint chains emanate from the interior of the character outward.

6. Rename the joints as left_hip, left_knee, left_ankle, left_ball, and left_toe. To rename a joint, right-click the joint name in the Hypergraph and select Rename from the drop-down menu. Type the new name and press Enter.
7. In the front view, click the left_hip joint to select it. Move it along the X-axis to the center of the top of the left leg. (In this lesson, left and right refer to directions from Jackie’s point of view, not from your view of the scene.)

   As mentioned before, when you move a joint, all joints lower in the hierarchy move with it. If you press Insert (Windows and Linux) or Home (Mac OS X) while a joint is selected, you can move the joint without moving joints below it in the hierarchy. (To exit this mode, press Insert or Home again.)

8. Rotate left_hip so that the skeleton fits inside the leg. It’s unnecessary to fit the skeleton perfectly inside the character, as it won’t be displayed when you render an image from the scene.
   
9. To create the joints for the other leg, you can save time and ensure symmetry by duplicating the existing leg joint chain with mirroring. With left_hip selected, select Skeleton > Mirror Joint > . In the options window, turn on YZ for Mirror Across.

   Jackie’s legs straddle the YZ plane, so mirroring the joint chain across the YZ plane positions the duplicate joint chain in the desired location. This operation illustrates that Jackie’s original position affects the ease with which you can create the skeleton. Had Jackie been positioned away from the origin, you would not have been able to use Mirror Joint to duplicate the leg’s joint chain.

10. Enter left in the Search for field and enter right in the Replace with field.

    The Replacement names for duplicated joints feature automatically replaces the names of all duplicate joints with the specified joint prefix.

11. Click Mirror.

    The right leg bones and joints appear in a mirrored position.

    

In the next steps, you create a joint chain for the spinal column. You also extend a joint from the upper neck region of the joint chain so that you can animate the jaw.

To create joints for the spine and jaw

1. In the side view, use the Joint Tool (Skeleton > Joint Tool) as follows to create a series of joints at the locations shown in the following figure:
   
   • Start at the base of the spine near the existing hip joints (left_hip and right_hip) and end at the top of the head.
   • Make sure you create the first joint a little bit away from the existing hip joint displayed in the front view, otherwise the first joint will be connected to the hip joint.
   • Press Enter (Windows and Linux) or Return (Mac OS X) when you are finished creating the joint chain.

   With the exception of the joints at each end of the joint chain, the joints are located where the character is likely to bend or twist at the spine and neck.

   The S-shaped curvature of the joint chain resembles Jackie’s spinal curvature. This makes it easier to animate the character’s torso and neck naturally.

2. Open the Hypergraph and, starting at the base of the spine, name the joints back_root, pelvis, lower_back, mid_back, upper_back, lower_neck, upper_neck, and crown.
3. To set up the skeleton for jaw movement, extend a joint from the upper_neck joint as follows:
   • Select the Joint Tool, and click the upper_neck joint in the Hypergraph to select it.
   • In the scene view, click to create a new joint near the lips, and press Enter or Return.
   • Name the new joint as jaw.
   

Creating joints for the arms is similar to creating joints for the legs.

To create joints for the arms

1. In the front view, create a series of joints at the locations shown in the following figure. Start at the pectoral region (near the upper_back joint) and end at the wrist.
   
2. Name the joints left_arm_root, left_shoulder, left_elbow, and left_wrist.
3. In the top view, select the left_elbow joint, select the Move tool, press Insert (Windows and Linux) or Home (Mac OS X), then move the joint to the back of the arm. Press Insert or Home again.
   

   Moving the joint to the back of the arm creates a bend at the elbow. This will make it easier to animate the character’s arm in the direction an arm naturally bends.

   
4. In the perspective view, select left_arm_root. Select Skeleton > Mirror Joint. This creates a copy of the left arm’s joint chain for the right arm and renames them in the process.

   The right arm bones and joints appear in a mirrored position.

   

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