//subdivision

This was an animation week centered on making a non-deforming object hierarchy and rig suitable for forward and inverse kinematic manipulation.

Wednesday:
The key topics here were:
Setting up a suitable hierarchy of body parts for IK/FK animation
Placing those body parts' axes in the correct positions for suitable rotation
a) We began by making a simple 'robotic' character out of primitive cubes.
b) We then put these cubes into a parent/child hierarchy matching a human body.
c) Next, we made the cubes editable and moved axes into relevant positions.

This gives us a body in a hierarchy which can be manipulated by FK (Forward Kinematics):
a) Grab a thigh and rotate, keyframe
b) Grab a shin, rotate, keyframe
c) Grab a foot, rotate, keyframe.....etc.

We can attempt to manipulate this body hierarchy with IK (Inverse Kinematics) but the body parts will twist in an unpredictable way without limits. So next we added some limits in the guise of Anchor and Kinematic tags.
a) To set up IK limits on a leg, we select the object where we want the IK to end (the waist or pelvis) and add an Anchor tag.
b) Then, we select in turn the thigh and shin, and add Kinematic tags
c) The Kinematic tags allow us to set limits in degrees, for each limb.

This gives us a body in a hierarchy which can be manipulated by IK (Inverse Kinematics):
a) Turn on the IK tool
b) Grab a foot
c) Move the foot (not rotation)
d) Select all the leg objects that move and keyframe their rotations.

Thursday
Yesterday's setup was one stage in a good character rig. It didn't take too long to set up, and helped with manipulation but animation involved keyframing the rotation of many objects. E.g. a walk cycle would contain keyframes for each of the six objects in the legs, and six main objects in the arms.

If we work more on the rigging stage, we can make animation easier, animating the position of just one object for each arm and leg.

Yesterday we set up limits for the parts of the limbs (e.g. stopping a leg from bending too far)
Today we added constraints (like magnets limbs will pull towards) and targets (e.g. forcing a foot to always face in a certain direction)

Setting up constraints:
a) we create a null object as the 'magnet'. This is used in different areas of a hierarchy depending upon the required effect. E.g. an arm may have a null inside the body hierarchy so it moves with the body, but can be moved to move the arm. To stop a foot falling through the floor, the constraint may be placed outside the hierarchy so the foot is pulled towards it as the body is moved.
b) we then select a body part at the bottom of a hierarchy (foot or hand), apply an IK tag, and link it to the null

Once this is set up, we can manipulate using IK:
a) if an IK tag is applied, there's no need to turn on the IK tool any more.
b) select one of the constraint nulls and animate it's position
c) or in some cases, move the body away or towards a constraint and animate it's position.

Target tags are also sometimes useful to keep a body part oriented in a direction. E.g. apply a target to a foot so it always faces forward.

Tagged as 3D, Animation, Training & Learning + Categorized as Training & Learning