Lesson 09 Skeleton

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Drawing a Skeleton Chain

  • Draw a skeleton chain, but there are several things to watch out for.
  1. Joint Tool
    • – Open A New Scene
    • ANIMATION || Skeleton > Joint Tool
      • Joint Tool Options:
      • Orientation: None;
      • – Click on [CLOSE]
    • – Switch to the side view
    • LMB + CLICK two times to create a joint chain
    • – Press [ENTER]
  2. Joint  Hierarchy
    • – Open the HyperGraph
    • Note: the joint hierarchy is composed of two nodes
  3. Adding Joints
    • – Click on the Joint Tool icon or press Y
      • Access the Last Tool Used: Y;
    • – LMB on the end of your joint chain;
      Note: Tool will highlight the end joint . Follow the direction of the arrows.
    • – LMB + CLICK two times to create a Z-like joint chain.
    • Note: the added joints are the children of the previous joint that was selected.
    • – MMB + DRAG to move the position of the last joint created.
    • – Press [ENTER].
  4. Automatic Joint Orientation
    • Using Automatic Orientation, causes all three joint axes to align to the right-hand rule. Ex: Selecting XYZ, the positive X-axis points into the joint’s bone and toward the joint’s first child joint. The Y-axis points at right angles to the X-axis and Z-axis. And the Z-axis poinssideways from the joint and its bone.
    • Note: If you look in perspective view, you can see these axes and where they point.
    • – DBL + CLICK on the Joint Tool for the options window.
      • Joint Tool Options
    • – [CLOSE]
    • – Create a second joint similar to the first one
    • – Note: As you draw the joints they are automatically oriented toward their child.
  5. Joint Rotation Axis
    • To understand the effect of joint orientation you need to roate in local mode and compare the two
    • – DBL + CLICK on the rotate-tool to bring up the options box;
    • – Select Local as the rotation Mode;
      • (specifies that you want to rotate nodes based on their local orientation rather than using the global world axis)
    • – Close the tool window.
    • – Select the second joint of both chains and see the difference in rotations as you rotate them.

Complex Joint Chain

Using a complex joint chain can simplify your work. i.e. ( navigate in a hierarchy of joints as you create them or reorient all the joints automatically with a command.

  1. Navigate in Joint Hierarchy
    • – Delete  all the joints in your scene;
    • – Switch to top view.
    • – Press the y hotkey to access Joint Tool. (make sure Orientation is XYZ)
    • – Draw three joints as follows:
    • – Draw the Thumb made of two joints
    • – Press the arrow up twice to put the selection on the wrist. (arrows help you navigate joints)
    • – Draw the index joints and press the up arrow to navigate back to the wrist when you create the other fingers
  2. Snap To Grid
    • – Press the up arrow until the selection is on the shoulder joint
    • – HOLD X, to snap to grid. Add a spine bone.
    • Notice that the shoulder joint is the parent of the spine bone( by the direction of the joint). The spine joint should be the parent of the shoulder.
  3. Reroot A Skeleton to change the direction of the joint. Change who is parent or child of who.
    • The shoulder and spine joint are not in the proper hierarchy. Fix this by a simple command.
    • – Select the spine joint which was the last joint created.
    • – Select ANIMATION || Skeleton > Reroot Skeleton
  4. Mirror Joints
    • Mirror a joint chain is useful and will help save time.
    • – Select the shoulder bone
    • – Select ANIMATION || Skeleton > Mirror Joint >
      • Mirror Joint Options Box
      • Mirror Across: YZ plane;
      • – CLICK [MIRROR];


Penguin Skeleton

Create a skeleton for the penguin.

  1. Open a scene with a clean version of the Penguin you modeled.
    • – Switch to smooth shade mode.
    • – Select STAGE || Shading > X-Ray
  2. Create A Character Spine
    • Determine a good placement or the pelvis joint which will be the root of the hierarchy.
    • – Select  ANIMATION || Skeleton > Joint Tool
    • – Switch to side view
    • – LMB CLICK to create the pelvis joint
    • (It is recommended that the pelvis is aligned with the hips)
    • – LMB CLICK to create three equally spaced joints that represent: spine, spine1, and neck
    • – LMB CLICK to create two equally spaced joints that represent: neck1 and head joints.
    • – LMB CLICK to create the nose joint.
    • – Press ENTER to complete the chain
    • – Each each joint accordingly.
    • Note: A spine can have more joints. The nose joint is just a visual representation of the head when the geometry is hidden, but you can deform the beak to create a cartoony animation.
  3. Create a Leg
    • Create the legs of the character. This joint chain will be in a separate joint chain but will be connected later on.
    • – Select ANIMATION || Skeleton > Joint Tool
    • – CLICK + DRAG the hip joint to it’s proper location
    • (the hip joint should be in the center of the body, hip GEOMETRY is approx. located. Very close to the pelvis joint)
    • – Draw the remaining knee, ankle, and toe joints, and create an extra joint at the tip of the foot, which is called toesEnd.
    • – Press [ENTER]
    • – Switch to front view.
    • – Translate the hip joint on the X-axis to fit the geometry as follows:
  4. Connect and Mirror the Leg
    • – Select the hip joint then SHFT+ SELECT the pelvis joint. Make sure you select the joints in this order to allow correct parenting.
    • ANIMATION || Skeleton > Connect Joint >□|
      • Connect Joint Options:
      • Mode: Parent Joint
      • – Click [CONNECT]
      • (leg is parented to the pelvis) or (pelvis is the parent of the leg)
    • – Note: you can use p to parent two joints, but it won’t have a special connection that is created when using the Connect Joint command.
    • – Select the hip joint
    • – Select ANIMATION || Skeleton > Mirror Joint > □
      • Mirror Joint Options:
      • Mirror Across: YZ
      • Mirror Function: Orientation
      • (This option will cause the legs to have the same behavior)
      • – Click [MIRROR]
      • (If your model was modeled symmetrically, it should now have two legs properly placed)
    • – Rename all the joints accordingly
    • Note: prefix the joints with “l” for left and “r” for right. ex: lAnkle
  5. Arm and Hand Joints
    • ANIMATION || Display > Animation > Joint Size
    • – Set Joint Size to .25
    • (This will make it easier to place joints closer together for the fingers.)
    • – Switch to front view.
    • – Draw a joint to represent the clavicle between the spine1 and neck joints
    • – Press [ENTER]
    • – Switch to top view
    • – Move the lClavicle on the  Z-axis to better fit the geometry.
    • – Draw the model’s elbow, wrist, and wristEnd joints.
    • – Change to front view
    • – Translate the joints on the Y-axis to better fit the geometry.
    • – Make sure the joints are properly positioned in perspective view
    • Note: It is best to rotate your joints into position rather then translating them.
  6. Joint Pivot
    • Move a joint without moving the entire children. Press the [INSERT] key [HOME] key MAC to move a joint on its own Or HOLD + D. EX: if the angle defined by  the shoulder, elbow and wrsit is not appropriate you can correct it by moving a joint on its own.
    • – Select the elbow joint
    • – Select the move tool.
    • – Press [INSERT] PC or [HOME] MAC or HOLD “D”
    • – Move the pivot of the elbow
    • – Press [INSERT/HOME] again to exit the tool.
  7. Connect and Mirror the Arm
    • – Select the lClavicle then SHFT + CLICK the spine1
    • ANIMATION || Skeleton > Connect Joint
    • (Arm is now parented to the spine)
    • – Select the lClavicle joint
    • – Click ANIMATION || Skeleton > Mirror Joint >
      • Mirror Joint Options:
      • Mirror Function: Behavior;
      • (this option cause arms to have mirrored behavior)
      • – Click [MIRROR]
  8. Details (Add joints for the eyes, mouth, and tail)
    • – Select the Joint Tool;
    • – Switch to the side view. Click on the head joint.
    • (By clicking on the joint tells the tool you want to start drawing from that joint)
    • – Draw one joint to the eye and two joints that lead to the tip of the jaw all originating from the head joint. See image below.
    • – Draw two joints for the tail starting from the pelvis joint.
    • – Rename your joints that you just created.


Joint Orientation

You are done with the skeleton. You need to double check all the joint orientations using the rotate tool.

  1. Hide the Geometry
    • – Uncheck STAGE || Show > Polygons to hide them
    • – Uncheck STAGE || Show > NURBS Surfaces to hide them
  2. Default the rotation Values
    • It is standard that all rotations are zeroed out. Meaning all rotation values at default are a value of zero.
    • – Select the pelvis joint.
    • MAIN || Modify > Freeze Transformations
  3. Reorient All Joints
    • Reorient all the joints in a hierarchy automatically to your preferred orientation, such as XYZ.
    • – Select the pelvis joint.
    • – Select ANIMATION || Skeleton > Orient Joint >
      • Orient Joint Options
      • – Orientation: XYZ;
      • – Click [ORIENT];
      • All the joints are now reoriented to have the X-axis pointing toward their children
      • before
      • after
  4. Local Rotation Axes
    • The Orientation of the joints are not always perfect. Depending on how your skeleton was built,  it can flip certain local rotation axes and you’ll need to fix them manually.
    • – Select the pelvis joint
    • – Switch to component mode: F8 and enable “?”
  5. Manually Set The Local Rotation Axes
    • X-axis points towards the first child joint. See http://jasonschleifer.com/ for tips on rigging. In some cases, you would not want automatic orientation setting. Problems usually arise when you select multiple bones and rotate them. For instance if you switched to object mode and selected the spine up to head joint, and rotate along the Z-axis then you might notice joints rotating in the wrong direction.
    • ex
    • – Fix for Local Rotation Axis: Switch to component mode:
    • – Select “?”
    • – Select the troubled Joints that are facing the wrong direction.
    • – Bring up the rotation tooloptions
      • Discrete Rotate: checked (means snap) to every step size.
      • Step Size: 45 degrees
  6. Test your Skeleton
    • Test your skeleton and rotate it every which way and fix whatever problems you find by the previous steps outlined above.
    • – Below I lined up the Y-axis green and the Z-axis blue with the wing flap.
    • If rotated along the Z-axis, the wing would bend under the arm. If rotated along the Y-axis, the wing would bend forward as if making a muscle.
    • Note: The end joints are usually not important since it might not be used for animation.
    • – Save your file 022112_09-bigz_04.ma