boneDynamicsNode

A custom node that applies dynamics to one section of a joint chain. It can be included directly into the rig, or Bake & Purge over the rig.

⚠Warning⚠
Internal Use ID 0x7b001 is used.

Installaion

1. Put boneDynamicsNode.mll in C:\Users\<USERNAME>\Documents\maya\<MAYAVERSION>\plug-ins.
2. Load "boneDynamicsNode.mll" from Plug-in Manager.

Basic Usage

Create any joint chain and connect the boneDynamicsNode per section. The minimum required connections are as follows:

Required Connections

• Time
• Bone Translate
• Bone Joint Orient
• Bone Parent Matrix
• Bone Parent Inverse Matrix
• End Translate
• Output Rotate

To rotate joint1, with joint2 as the tip...

Let's move the current frame to 1 or later and move the root. The joint-chain shakes!

💡Requirements for Joint
Joint chain must meet the requirements here.

💡Sample Script
basic_usage.py is a script to connect bonedynamicsNode to any joint chain. Please select and execute them in order from the root of the joint to the tip of the joint.

Attributes to Check

• Enable : Turning it off disables all calculations.
• Reset Time : Dynamics are disabled when the current frame is equal to or less than this value. In other words, start frame of the simulation.
• Fps : Used to calculate delta time. Enter a value equal to the FPS of the scene. Default is 30.

Dynamics Attributes

• Damping : Attenuates speed. The larger the value, the harder it is to accelerate.
• Elasticity : Force to return to the original posture.
• Stiffness : Suppresses changes between frames (steps). Setting to 1 will result in loss of motion.
• Mass : Affects the force to return to the original posture.
• Gravity : If Y-up and the unit is in centimeters, set [0,-980,0].
• Gravity Multiply : Will be multiplied by Gravity.

Bake to Keyframes

Select the joint and execute "Bake Simulation" from the "Key" menu. Then delete the boneDynamicsNode.

Requirements for Joint

• Rotate should be [0,0,0], with only the Joint Orient having a value.
• Do not edit rotatePivot, rotatePivotTranslate, scalePivot, or scalePivotTranslate.
• Rotate Order is only available for xyz.
• Rotate Axis should remain [0,0,0].
• Leave Inherits Transform checked.
• Leave Offset Parent Matrix at its default value.
• Receive InverseScale from the parent Scale and leave Segment Scale Compensate checked. Shear not supported.

All of the above checkpoints can be satisfied by making joints as usual.

Features

Collisions

4 types of collisions are available: ground, sphere, capsule, and infinite plane. Colliders can be created with maya_expressionCollision.

• Radius : Radius of the end-joint.
• Iterations : Higher values increase the accuracy of collisions. Recommended value is 3 to 5. 0 disables collisionss.
• Enable Ground Col : Enable ground collision.
• Ground Height : Height of the ground.
• Sphere Col Matrix : Connect the sphere collider worldMatrix.
• Sphere Col Radius : Radius of sphere collider.
• Capsule Col Matrix A Capsule Col Matrix B : Connect worldMatrix on one side of the capsule collider.
• Capsule Col Radius A Capsule Col Radius B : Connect the radius of one side of the capsule collider.
• Infinite Plane Col Matrix : Connect worldMatrix of infinite plane collider.

The attributes that connect the collider are in a list, so you can use more than one. Ground Collision do not need connections.

💡Visualize Radius
Place a nurbsSphere or implicitSphere as a child of end-joint and connect Radius.

💡Note
Colliders do not necessarily need to use expcol. It can be anything as long as the required attributes are connected.

Angle Limitation

The Angle Limit attribute allows for limiting the rotation angle of bones. It has a higher priority than collision, so depending on the posture, it may be penetrated in the colliders.

💡Visualize Angle
Place an implicitCone node and a transform nodes in the same space as the joint, and set and connect their attributes as in the following image:
⚠️If joint.ty and tz contain values, cone direction will not match accurately.

Specify Target Pose

The converging pose can be manipulated by duplicating the joint-chain and connecting Rotate to Rotation Offset.

Offset Transform

You can cancel the transform by connecting the worldMatrix of the node you do not want affected (such as the root controller of character) to the Offset Matrix.

Supports Scale per Section

Connecting each scale value to Bone Scale, Bone Inverse Scale, and End Scale enables a scale per section.

⚠Please avoid non-uniform scales.

Branching

Branching is possible, but good results are obtained with joints like the one on the left of the image. The right one does not give good results.

💡Sample Script
advanced_usage.py is a script to connect bonedynamicsNode to any joint chain. Please select and execute them in order from the root of the joint to the tip of the joint.

• Enable per-section scaling.
• If place the collider created by expcol as a child of 'collider_grp', to be connected.
• If duplicate the joint-chain to be simulated and add '_target' to the end of the name, to allow manipulation of the target posture.
• If a node named "offset" exists, will be connected to cancel the transform.

Pre-built plug-ins

Pre-built boneDynamicsNode.mll in the plug-ins folder. Install to the appropriate Maya version and ready to use.

How to Build

For example, Maya 2024 in Windows:

1. Install Visual Studio 2022
2. Install CMake 3.22.1 or higher
3. Donwload SDKs from Maya API | Autodesk Platform Services (APS)
4. Set devkitBase path in the DEVKIT_LOCATION environment variable.
5. Generate a project with the following command:

cd src
cmake . -Bbuild_2024 -G "Visual Studio 17 2022" -A x64

6. Build with Visual Studio or with the following command:

cmake --build build_2024

TODO

• Additional Force
• Stretchable

Links

• Maya用お手軽ボーンダイナミクスノード「boneDynamicsNode」詳細解説 - Qiita
• boneDynamicsNode Demo - Example of integration into FK rig - YouTube