Creating an Inverse Kinematic Skeleton Maya 2012

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Ada Daniel
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1 Michael O'Rourke Creating an Inverse Kinematic Skeleton Maya 2012 Concepts In standard hierarchical animation, transformations are calculated down the hierarchy from parent to child This is called forward kinematics See the Hierarchical Animation (Forward Kinematics) tutorial in this set This is not very convenient for complex limbed creatures -- for example, a human, an animal Requires individually rotating each joint It is easier to think of just translating the hand, as in real life Based on the hand s translation, the software will calculate the rotations of the arm backwards up the hierarchy That is, in the inverse direction This is called Inverse Kinematics (also, just IK) To control your model, you first build an IK skeleton Consisting of joints and bones

2 Skeletons can get quite complex for some models See the tutorials in the Character Animation set for more details) Our example here is deliberately simplified Legs >Animation module >Skeleton >Joint Tool [] >Reset Tool, to get the defaults >Close Your cursor changes In the Front window, click to locate the following joints: (You can use grid snapping to help you keep the joints aligned) pelvis hip knee ankle In the Side window, Click to locate the Toe Use the UP-arrow key on your keyboard to go back up to the knee joint Hit the Insert key, to go into pivot point mode In the Side view window, move the knee forward a bit to give the leg a slight bend Hit Insert again to leave pivot point mode Use UP-arrow key again to go all the way up to the pelvis joint

3 As before, click in the Front and Side windows to define joints for the other leg -- hip, knee, ankle, toe Adjust the knee position with the Insert key Hit Enter key to leave joint tool >Window >Hypergraph Notice that the joints form a parent/child hierarchy Rename some of the joints For example, pelvis, hipl, hipr Joint Display Size >Display >Animation >Joint Size Drag the slider to adjust the thickness of your joints Note: This has nothing to do with how they function It is a display issue only Spine, Arms, Neck, Head To make the spine, we will start a little bit above the pelvis joint, and move up toward the neck >Skeleton >Joint Tool [] In the Side view, click just above the pelvis joint, to place the first joint It is not yet connected to the leg joints Continue clicking as you move upward, making about four joints, and giving the joints a natural spine curvature

4 If necessary, use the Insert key to go into pivot point mode, and adjust the locations of the spine joints Still injoint Tool mode, make sure you are at the top joint of the spine In the Front view, click to locate Shoulder In the Side view, click to locate elbow wrist Give these two joints a slight bend backward at the elbow UP-arrow key to go back to the neck joint Click to define the opposite arm joints in the same way UP arrow to go back to the neck joint Click to define one joint for the base of the skull Click to define a joint at the top of theskull Hit Enter key to leave joint tool In the Channel Box, rename some of the new joints For example, navel = the first spine joint you drew also, shoulderl, shoulderr, skullbottom Connect the Upper and Lower skeletons >Window >Hypergraph Notice that the spine and its joints are not connected to the legs navel should be a child of pelvis so the entire skeleton can move together Middle-mouse drag navel onto pelvis It becomes a child of pelvis The entire skeleton is now a single hierarchy pelvis is the root joint that is, the topmost node Notice in the modeling windows,

5 that there is now a joint connecting pelvis and navel Fine-tune the proportions Select a joint Either in the modeling windows, Or in the Hypergraph or Outliner windows Hit the w key to go into Translate mode Move the joint That joint and all its children move Hit the Insert key to go into pivot point mode Move the joint Only the selected joint moves >File >Save Scene to save your file (You will re-use this skeleton model in other tutorials) IK Handles There are several ways to control the movements of an IK skeleton Most common is to define an effector at the end of the joint structure Maya does this with an IK Handle Ankle IK Handles Make the Persp window full screen It is usually easier to make your selections in the Persp window >Skeleton >IK Handle Tool [] >Reset Tool Make sure Solver = ikrpsolver = Rotation Plane solver This makes it easier to control rotation planes of limbs (See the many tutorials in the Character Animation set for more details) Check on Sticky This will cause the feet to stay in place, if you move the character

6 >Close This is usually what you want Your cursor changes Click on hipl Click on anklel An IK Handle is defined connecting hipl to anklel Look at the Hypergraph window Maya has added an effector1 node inside the left leg hierarchy A dotted line connects hipl to effector1 Maya has also added an ikhandle1 node outside of the hierarchy Next to the effector1 node is a small dot icon Click on the dot icon The ikhandle1 node is selected You can also click directly on ikhandle1 to select it Select the IK handle for anklel either in Hypergraph or in modeling window Translate the IK handle The joints of the left leg bend/rotate Repeat the same process for the other leg >Skeleton >IK Handle Tool [] Connect hipr to ankler Check the connection in the Hypergraph Test by translating the new IK handle IK Handle Display Size >Display >Animation >IK Handle Size Drag the slider to choose the size Wrist Handles Repeat the process for each of the two arms >Skeleton >IK Handle Tool [] connect shoulder to wrist Check the Hypergraph

7 Test the movement of the Handles The arm joints should bend/rotate Save your Scene File You will re-use this model in other tutorials

Rigging (Part 1): Creating Your First Skeleton by Gary Wu. Here s a quick tutorial to help you get started on creating your first biped-skeleton.

Rigging (Part 1): Creating Your First Skeleton by Gary Wu Here s a quick tutorial to help you get started on creating your first biped-skeleton. 1. Make sure you are in animation mode by selecting the