IK Rigging

Following yesterday's Forward Kinematics (FK) rigging, I learned Inverse Kinematics (IK) following Academic Phoenix's second rigging tutorial to rig a humanoid character's leg.

Dividing the process into three big parts, it would be

1. Creating Joints

2. IK Handles

3. Creating Controls

I will be employing a life-size humanoid model named 'Julie' for the upcoming tutorials to animate her. The model was given to me by one of my professors during a class.

1. Creating Joints

- Place the joints where the pelvis would be, then press 'enter'. Create connecting joints where the hip, knee, and ankle. Freeze transformation and Delete history after adjusting.

*make sure to place the joints in an orthographic view, and check each side to place them at the proper location.

- Rename the joints accordingly- root, L_hip, L_knee, L_ankle. I used the 'Prefix Hierarchy Names'.

- While selecting the leg joints, click the option button next to 'Mirror Joint' to see a window pop up. Select the YZ axis to mirror across, and type in 'L_' for Search for, 'R_' for Replace with. This will help the mirrored joints to be automatically renamed.

- Connect the two leg joints onto the root joint by parenting.

- Select both leg joints, and click 'Orient Joints'.

- Change the knee joint angle to a create a hypothetical pose of how you would want it to bend. Click 'Set Preferred Angle' and return the rotation back to 0. Do the same with the other leg.

- Freeze Transformation and Delete History for the leg joints.

2. IK Handles

- Click the option box next to 'Create IK Handle' to see the tool settings window. Make sure the solver is set as 'Rotate-Plane Solver', and 'Sticky' to be checked.

- Click the hip joint, then the ankle joint to create an IK handle. Repeat with the other leg.

- You can check if it is applied properly by grabbing the root joint and moving it around. The knee should automatically bend, and even though it may not bend to the exact angle you want it to, there are opportunities to fix this later.

3. Creating Controls

- Create controls for the hip and feet. It is best to create a shape that likely resembles the target area.

* Make sure to snap the controllers' center pivot onto the joint!

Tip I learned: You can adjust the selection hierarchy in the top menu from left to right, including IK handle, joint, curve objects, surface objects, deformation objects, dynamic objects, rendering objects, and miscellaneous objects.

- To make sure the foot controllers are placed on the ground while the pivot remains on the joint, grab the control vertexes and lower to the desired height.

- Freeze and Delete History for the controls.

- Constraint the controls to each matching joint.

- Create controls for the knee. Make sure it's aligned horizontally with the knee joints.

- Select the control, then the IK handle. Click 'Pole Vector' under 'Constrain'. Now, this controls the direction of the knee.

Done! This is how it looks like when the skin is bind, although I will leave it unbind for the next rigs.