Control Rig Dynamics : Add Physics to Any Rig in Minutes

Stephane B
3 days ago
3 min read

Unreal Engine 5.8 • Animation & Physics • Advanced Level

Unreal Engine 5.8 introduces Control Rig Dynamics, a new way to add procedural physics to virtually any character without replacing your existing IK/FK setup. Tails, ears, cheeks, spines everything can now benefit from dynamic motion with just a few nodes.

Complete demonstration of the Control Rig Dynamics system on a full character setup.

https://video.wixstatic.com/video/564e23_3a6b06a389e2406987e94a22f27f2d17/1080p/mp4/file.mp4

What Is Control Rig Dynamics?

Available in preview in Unreal Engine 5.8, Control Rig Dynamics is a physics simulation layer designed to integrate directly into a character's Control Rig. While the older Rig Physics system required a more complex setup, Dynamics takes a chain-based approach: define a root bone, and the system automatically simulates all its descendants.

The key advantage is that the simulation is layered on top of your existing rig logic. FK and IK controls continue to function normally while physics is applied procedurally on top. The simulation can even be enabled or disabled through a simple boolean channel.

The Three Core Nodes

The entire system revolves around three essential nodes found in the Rig Dynamics category.

Spawn Dynamic Solver

Creates the physics solver. Typically placed in the Construction Event, it defines gravity, simulation space, drag forces, and kinematic thresholds.

Spawn Dynamics Chain

Defines the bone chain to simulate from a chosen root bone. This node contains all behavioral settings, including stiffness, damping, collisions, and curves.

Step Dynamics Solver

Placed in the Forward Solve, this node advances the simulation every frame. Without it, nothing will move at runtime.

Particle Properties: Fine-Tuning the Behavior

Most of the physical behavior is controlled through the Particle Properties section of the Spawn Dynamics Chain node.

Parameter	Purpose
Radius	Collider size for each simulated particle
Mass	Influences interactions between physical elements
Simulated / Kinematic	The first bone is kinematic by default; all others are simulated
Gravity Multiplier	Scales local gravity. Negative values create anti-gravity effects
Stiffness	Controls rigidity and responsiveness. 0 = very soft, 25+ = very stiff
Damping Ratio	Determines how quickly motion settles. Lower values create longer oscillations
Drag Force	Air resistance, similar to Niagara drag forces
Angle Limits	Restricts rotation angles to prevent extreme deformations

All these parameters can be modified at runtime through the Forward Solve by targeting chain particles with a Set Dynamic node and a For Each loop.

This means you can animate the physics itself. For example, an animator could keyframe the Gravity Multiplier of an ear to create a highly specific dramatic effect.

Chain Curves: Where the Real Power Lies

Chain Curves allow different values to be applied along a single chain—without custom logic and without additional nodes.

Every major parameter, including stiffness, gravity multiplier, and damping, has its own curve. The X-axis represents the normalized position along the chain:

0 = Root
1 = Tip

The system automatically interpolates values between curve keys.

For example, setting stiffness to 1.0 at the root and 0.1 at the tip creates a chain that remains firm at the base while becoming increasingly flexible toward the end—exactly how a real tail or animal ear behaves.

Switching interpolation from Linear to Auto often produces even more natural results.

To visualize these values in real time, enable Particle Value Display in the Step Dynamics Solver node. The calculated values will appear directly on each particle in the viewport.

Colliders and Confiners

To prevent dynamic chains from intersecting with other parts of the body—for example, a tail clipping through a leg—Colliders can be added directly from the Spawn Dynamics Chain node.

Available collider types include:

Capsule
Box
Plane

Position and size are controlled through the Radius, Length, and Transform settings.

Confiners

Confiners define spatial boundaries for simulated particles.

Instead of moving freely, particles remain constrained within a predefined volume. This is particularly useful for secondary motion elements that should never stray too far from their resting position.

How Far Can You Push It?

By stacking multiple Spawn Dynamics Chain nodes, you can cover an entire character: