BipedPlus

Ep.11 — Simu Bone · Spring Magic Integration

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Overview

Describes how to properly attach secondary simulations like Spring Magic (hair, smartphone chains, chains) to a BipedPlus rig.
The key is to separate "skin bones" from "controllers" and organize them with Space Groups.

Spring Magic and BipedPlus — Why Be Careful

Standard BipedPlus approach Spring Magic-friendly approach
Offset + Controller (empty node in between) Bones only in a simple chain
Maintains position·rotation at 0 after connection Head → Bone → Bone without intermediate nodes
- Spring Magic may not work correctly if there are offsets (intermediate groups).
- Attaching bones directly under Head without offsets works, but conflicts with BipedPlus Layer·Skin separation rules.

If you use a different simulation tool, test yourself whether it allows offsets. If it does, you can keep the standard BipedPlus approach.

Recommended Structure (video — hair example)

Step 1: Skin Bones (what gets sent to game)

  • Create a bone chain like Hair1, Hair2… in the Skin hierarchy (extending from the head).
  • Weights will be assigned here later.
  • Do not place in the Controller Layer.

Step 2: Controllers (what animators and sims operate)

  1. Clone the same structure → Unparent.
  2. Name controllers per team convention (e.g., Ctrl_Hair1, Ctrl_Hair2…).
  3. Use box display etc. in viewport to distinguish from bones.
  4. Edit Utils → Quick Connect:
  5. Controller list ← Ctrl_Hair items
  6. Bone list ← Skin Hair items
  7. Find → Local Matrix Auto Parent → connect
  8. Verify that moving the head causes the entire Hair chain to follow.

Step 3: Space Group — Solving "Where to place it"

What is a Space Group?
An empty group that has the exact same position·rotation·scale as the reference bone (video: head skin bone).
(The video explains the concept using the Pelvis, then uses the head as the reference for the hair example.)

Why it's needed

  • Placing sim controllers in the Skin Layer → they mix with game bones on FBX export.
  • Using Controller Layer only → they may not move with the head.
  • Placing only Ctrl under Space Group → they follow the head without mixing into the export.

Creation steps (video)

  1. Select Skin Head (head skin bone).
  2. Create Space Group (menu in Figure/Edit area — check location per version).
  3. Disable the Space Group's shape (curve) — make it invisible (may already be off at 100% scale).
  4. Verify the Space Group moves exactly like the head.
  5. Make Ctrl_Hair* children of the Space Group → place in System Layer, etc.

Step 4: Layer Organization

Contents Layer
Ctrl_Hair* Controller
Skin Hair* Skin
Space Group System

Running Spring Magic

  • The video covers up to structure — Spring Magic execution can be done separately.
  • With a simple bone chain + Ctrl under Space Group, the goal is to align with a standard Spring Magic workflow.

Rigging Info Integration

  1. Scan → custom Ctrl_Hair* → Rigging Info Add.
  2. Update.
  3. Ani Utils Reset All — verify that Hair also returns to the default pose.

Scale Warning

  • Quick Connect + Scale keys → possible skin distortion (manage together with Ep.7 Stretch/Squash).

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