Using Spline IK

Introduction to Character Rigging

Creating and Editing Character Bones

 

Autodesk 3ds Max Tutorials > Character Animation Tutorials > Character Animation without Biped > Introduction to Character Rigging > 

Mirroring IK

It takes a lot of time to set up the rig for an arm or a leg, and it'd be nice to not have to do all that work twice. If you follow a few simple rules when creating the bones and IK structure for a character, you can set up the IK for one side (an arm or leg) and then mirror it, and have it work.

In this tutorial you will learn:

• How to mirror bones with IK
• The rules for setting up mirrored bones

Set up the lesson:

• Choose File menu > Open, and open tut_mirror_ik_start.max from the \tutorials\character_animation\intro_to_rigging folder.

  This file contains a simple leg bones setup.

  

  Simple leg setup

Check the parent space and hierarchy:

1. On the animation playback controls, click the Play button to play the animation.

   The leg assembly takes a short hop.

2. Move the time slider back to frame 0.

   You will explore this IK setup a little before you mirror the IK.

   There are two simple rules to follow when mirroring a character rig with bones and IK. The first is that the IK chain's Parent Space has to be set to Start Joint, not IK Goal.

3. Select either IK chain control (the blue crosses at the ankle and ball of the foot), and then open the Motion panel.
4. In the IK Solver Properties rollout, find the Parent Space group and confirm that Start Joint is turned on, not IK Goal.

   

   Tip If this is not the case, turn IK Enabled off, change to Start Joint, and turn IK Enabled back on.

   The second requirement is that the root of the IK chain must be linked to something that doesn't have IK on it. You can tell whether this is true by looking at the Motion panel.

5. Select Bone01, the thigh bone in the structure.
6. On the Motion panel > Assign Controller rollout, you can see the Transform controller is IK Control.

   

7. Now select the Hip Dummy at the top of the thigh.

   In the Assign Controller rollout on the Motion panel, you can see the Transform Controller does not say IK.

   Rule number two is satisfied. The root is parented (linked) to something that doesn't have IK.

8. In the Left viewport, move the hip dummy up and down, left and right.

   

   Move the dummy

   You can see that the hip dummy is the parent of the thigh bone.

9. Undo using Ctrl+Z until the leg is back in its original position.

Mirror the leg assembly:

1. Activate the Front viewport and select everything.

   When you mirror, it's important that you select the parent of the root bone.

2. On the main toolbar, click the Mirror Selected Object button.
3. In the dialog that appears, choose Copy so you create a mirrored clone of the leg.
4. Use the Offset field to move the two legs apart. Change the Offset to 111.

   

   Mirrored IK

5. Play the animation.

   The bones are successfully mirrored, and the animation works.

   TipBe sure to select the entire hierarchy when you do the mirror. If you have anything that is constrained to another object, be sure to include the object that things are constrained to. Otherwise your mirrored IK will become confused.
6. Save your file as my_mirror_ik.max.

   You can find a completed version of this scene in the file tut_mirror_ik_finished.max.