reference materialBasics of IK Booster
by Christopher Pope
 

This tutorial will show you how to:

  1. Convert skelegons into bones and record their pivot rotation
  2. Add the ik_booster plug-in to an object
  3. Isolate IK chains with ik_booster
  4. Fix points on the defined IK chain
  5. Set limits using ik_booster
  6. Lock rotation values using ik_booster
  7. Describe key framing options available in the ik_booster menu



1.  First step is to load the desired object into a scene.  When you create the object in modeler, be sure to have both the geometry and skelegons in the same layer.  To convert your skelegons into bones, click on the Setup tab and look under

Add.  You should see a button labeled Cvt Skelegons. 

   
After clicking on the Cvt Skelegons button, a dialog box will appear informing you of how many bones were created. 
   
It is a good idea to record the pivot rotation of you bones before going any further.  Recording the pivot rotation sets all the rotation parameters to zero, which has obvious benefits when posing a character.  You can find the record pivot rotation button in the Setup tab, under Modify.  Click on the dropdown menu labeled Orientation and select Record Pivot Rotation.  Make sure to set a key frame after recording each bones pivot rotation.  




   
2        You are now ready to apply the ik_booster plug-in to your object.  Select the object you wish to apply the plug-in and hit p to bring up the object’s properties menu.  Under the Geometry tab click the Add Custom Object drop down.  From the list select the ik_booster.  You will see ik_booster added to your custom objects.  Double click on ik_booster to apply the plug in to your object.
   
3.      If you were to try animating the object now, you would soon find the process next to impossible.  This is because inverse kinematics have been applied to all the bones in your object without any limits or fixed points.  The first thing we can do is isolate a specific hierarchy of bones to function as IK chains.  To do this, select a bone you wish to start an IK chain with.  I selected the femur (thigh bone) as the bone to function as the root of the IK chain for the leg.  Right click within the red circle at the root of the bone to open the menu.  From the menu select (ik stop) to isolate the IK chain.



   
4.      We now wont to fix a point at the end of the chain to function as a null would using Lightwave’s base inverse kinematics system.  Fixing a point keeps the point locked in place until moved by the animator.  To fix a point, select the point on the IK chain an right click.  From the drop down menu select (fix). 

   
5.      Now that our IK chain is fully defined, we can set limits on the bones rotation parameters.  Select a bone and right click on any of the three values you wish to set limits on.  You will notice that the values are color coded to correspond with its parameter (i.e. heading=red, pitch=green, and bank=blue).  After right clicking on one of the three values, select <set>/unset limit from the drop down menu.  Greater than and less than will appear around your selected value.  Right click on the value once again and this time select edit limit.  Use this menu to set minimum and maximum rotation angles and joint stiffness.  You can also easily copy and paste limit values from other bones through this window. 




         
 
   
6.      You can lock and unlock input parameters using the same menus as when setting rotation limits.  Locking a value will nullify that parameter.  For example, if you wanted a bone to rotate on the pitch only, you would lock the heading and the bank, nullifying their values. 

 
7.      You may have noticed when you applied ik_booster to your object, the words Parent and IKB Menu appeared in the lower left and right corners of your work space respectively.  This is the ik_booster menu.  In this tutorial we will only concern ourselves with the lower left hand corner of the menu.  If you click on the word, you will notice that you begin scrolling through a list of options.  These options include:  parent, child, parent+child, current item, and all items.  These options tell you what the ik booster is creating key frames for.  For example, if you selected parent+child, ik booster would set key frames for all the parents and children within the affected ik chain.  This also means that if you wanted to, you could edit each key frame’s interpolation individually using the graph editor.  On the other hand, if current item were selected, you would only set a key frame on the current item selected.  All of these options have their advantages and should be explored so that they can be used when the situation would most benefit. 
 
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