Introduction

IK Bone Baker is an Unreal Engine 5 editor plugin that adds one Animation Modifier: Bake IK Bones (Auto Pairs). It copies a skeleton's IK bones onto the FK bones they are meant to follow, for the whole animation, and works out which bone belongs to which by itself.

The problem it solves

The UE5 Mannequin carries an IK bone chain that hangs off the root rather than off the limbs:

root -> ik_foot_root -> ik_foot_l, ik_foot_r
     -> ik_hand_root -> ik_hand_gun -> ik_hand_l, ik_hand_r

Foot IK Control Rigs use ik_foot_l and ik_foot_r as their goals. Most source skeletons have no equivalent bones, so the retargeter leaves those chains unmapped and they stay at the reference pose on every frame.

The Control Rig then solves the legs towards a goal that never moves, and the character animates from the waist up while the legs stay put.

Disconnecting the Control Rig makes the legs work again, because the FK pose shows through. That is the giveaway that you are looking at this and not at a bad animation.

To be sure, open a retargeted animation, select ik_foot_l in the skeleton tree, and scrub. If it sits still while foot_l moves, this plugin is what you want.

What it does

• Works the pairs out from the skeleton itself, so there is nothing to fill in.
• Resolves against each animation's own skeleton, so one modifier covers a whole folder of retargets.
• Handles IK bones that hang off other IK bones, like ik_hand_l under ik_hand_gun.
• Bakes the same whether or not the animation has root motion.
• Prints every pair it resolved.

Where to go next

• Installation to get it into your project.
• Quickstart to bake your first folder.