Use Auxiliary Effectors in Motionbuilder2017 to fix unwanted motion

So lets say that you have some unwanted motion e.g. a foot slip OR in my case a mocap of a performer on a swivel chair. Because of the mocap system used (in this case Xsens) there is unwanted motion, where the centre of rotation (i.e the chair swivel) isn’t fixed on the spot but circles around with a planetary motion –as if the chair were moving instead of just the performer spinning. So instead of doing a lot with keyframes I’m going to use an Auxiliary Effector.

  1. So the motion is driving a characterised character and I’ve plotted it to a Control Rig. 
  2. I make one keyframe on the Hips on a new Animation layer set to Full Body with T set to X=0, Z=0
  3. RClick on the Hips node in the Character Controls and add an Aux Effector.  This is basically a static object that doesn’t move.
  4. Set the IK Blend of the Aux Effector to 100 T and 0 R — so that it only can effect Translation- we want the chair to still rotate
  5. Set the IK blend of the Hips Effector T to 0 – so hips are getting all translation inputs from Aux Effector
  6. Set the IK Blend of both feet to 0 for both T & R — so all motion comes from Hips.

Now the character rotates but remains on the spot, 0,0. If I want to I can blend in some of the original Hips movement by increasing the IK blend of the Hips -to 10 or 20 – – this gives it a little movement.

 

I hope to be able to use this method to fix foot slipping too. We will see