Physics Constraint Reference

A reference for all the properties available on Physics Constraints in the Unreal Engine Editor.

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This page contains a reference listing of properties for Physics Constraints separated by major categories.

Constraint

Constraint Properties

Property

Description

Constraint Actor 1

When a Physics Constraint is placed into the level editor you must specify Actors to constrain. This is the first of 2 Actors.

Component Name 1

The first target component that will be constrained. This can be specified when using Actors to constrain only a specific component and not the Actor root.

Constraint Actor 2

When a Physics Constraint is placed into the level editor you must specify Actors to constrain. This is the second of 2 Actors.

Component Name 2

The second target component that will be constrained. This can be specified when using Actors to constrain only a specific component and not the Actor root.

Joint Name

When constraining in the Physics Asset Tool, this is the name of the Bone that is initially constrained.

Constraint Bone 1

When constraining in the Physics Asset Tool, this is the name of the first joint to constrain.

Constraint Bone 2

When constraining in the Physics Asset Tool, this is the name of the second joint to constrain.

Constraint Behavior

Constraint Behavior

Property

Description

Disable Collision

This disables collision between the constrained components.

Enable Lenear Projection

Linear Projection is a post-solve fixup where the child body is translated to resolve remaining errors using a semi-physical correction. Use this to make chains stiffer at lower iteration counts. Projection only works well if the chain is not interacting with other objects.

Enable Angular Projection

Angular Projection is a post-solve fixup where the child body is rotated to resolve remaining errors using a semi-physical correction. Use this to make chains stiffer at lower iteration counts. Projection only works well if the chain is not interacting with other objects.

Enable Shock Propagation

Shock Propagation increases the mass of the parent body for the last iteration of the position and velocity solve phases. It can help stiffen up joint chains, but is prone to introduce energy down the chain. Use this for world constraints and ragdoll physics.

Projection Linear Alpha

The amount of linear projection to apply, with 0 being no projection and 1 being full projection.

Projection Angular Alpha

The amount of angular projection to apply, with 0 being no projection and 1 being full projection.

Shock Propagation Alpha

The amount of shock propagation to apply, with 0 being no propagation and 1 being full propagation.

Parent Dominantes

When set, the parent body in a constraint will not be affected by the motion of the child.

Linear Limits

Linear Limits

Property

Description

XMotion

Indicates the linear constraint applied along the X-axis.

Type

Description

Free

No constraint along this axis

Limited

Limited freedom along this axis. The limit is defined for all axes by the Linear Limit Size property.

Locked

Fully constrained along this axis.

YMotion

Indicates the linear constraint applied along the Y-axis.

Type

Description

Free

No constraint along this axis

Limited

Limited freedom along this axis. The limit is defined for all axes by the Linear Limit Size property.

Locked

Fully constrained along this axis.

ZMotion

Indicates the linear constraint applied along the Z-axis.

Type

Description

Free

No constraint along this axis

Limited

Limited freedom along this axis. The limit is defined for all axes by the Linear Limit Size property.

Locked

Fully constrained along this axis.

Limit

The distance allowed between the two joint reference frames.

Scale Linear Limits

If true, linear limits scale using the absolute min of the 3D scale of the owning component.

Advanced

Advanced Linear Limits Properties

Property

Description

Soft Constraint

Whether we want to use a soft constraint (spring).

Stiffness

Stiffness of the soft constraint. Only used when Soft Constraint is on.

Damping

Damping of the soft constraint.

Restitution

Controls the amount of bounce when the constraint is violated.

Linear Breakable

Whether it is possible to break the joint with linear force.

Linear Break Threshold

Force needed to break the distance constraint.

Linear Plasticity

Whether it is possible to reset spring rest length from the linear deformation.

Linear Plasticity Type

Whether linear placticity has a operation mode.

Linear Plasticity Threshold

Percent threshold from center of mass distance needed to reset the linear drive position target.This value can be greater than 1.

Contact Transfer Scale

Collision transfer on parent from the joints child. The maximum range is 0.0.

Angular Limits

Angular Limits Properties

Property

Description

Swing 1Motion

Indicates whether the Swing1 limit is used.

Type

Description

Free

No constraint around the axis

Limited

Limited freedom around this axis. The limit for each Angular Motion is controlled individually by a correspondingly named Limit property: Swing 1Limit Angle, Swing 2Limit Angle, and Twist Limit Angle

Locked

Fully constraint around this axis

Swing 2Motion

Indicates whether the Swing2 limit is used.

Type

Description

Free

No constraint around the axis

Limited

Limited freedom around this axis. The limit for each Angular Motion is controlled individually by a correspondingly named Limit property: Swing 1Limit Angle, Swing 2Limit Angle, and Twist Limit Angle

Locked

Fully constraint around this axis

Twist Motion

Indicates whether the Twist limit is used.

Type

Description

Free

No constraint around the axis

Limited

Limited freedom around this axis. The limit for each Angular Motion is controlled individually by a correspondingly named Limit property: Swing 1Limit Angle, Swing 2Limit Angle, and Twist Limit Angle

Locked

Fully constraint around this axis

Swing 1Limit Angle

Angle of movement along the XY Plane.

Twist Limit Angle

Angle of movement along the XZ Plane.

Swing 2Limit Angle

Symmetric angle of roll along the X-axis.

Advanced

Advanced Angular Limits Properties

Property

Description

Swing Limits

Soft Constraint

Whether we want to use a soft constraint (spring).

Stiffness

Stiffness of the soft constraint. Only used when Soft Constraint is on.

Damping

Damping of the soft constraint.

Restitution

Controls the amount of bounce when the constraint is violated.

Twist Limits

Soft Constraint

Whether we want to use a soft constraint (spring).

Stiffness

Stiffness of the soft constraint. Only used when Soft Constraint is on.

Damping

Damping of the soft constraint.

Restitution

Controls the amount of bounce when the constraint is violated.

Angular Breakable

Whether it is possible to break the joint with angular force.

Angular Break Threshold

Torque needed to break the joint.

Angular Placticity

Whether it is possible to reset rotations from the angular displacement.

Angular Placticity Threshold

Degree threshold from target angle needed to reset the target angle.

Linear Motor

Linear Motor Properties

Property

Description

Position Target

Enables the position linear motor on one or more axes and sets the local position desired.

Strength

How much force to apply to reach the desired position.

Velocity Target

Enables the velocity linear motor on one or more axes and sets the desired velocity.

Strength

How much force to apply to reach the desired velocity.

Advanced

Advanced Constraint Motor Physics

Property

Description

Max Force

The force limit of the drive.

Angular Motor

Angular Motor Properties

Property

Description

Angular Drive Mode

Whether this angular motor uses SLERP (Spherical Linear Interpolation) or decomposes into a Swing Motor and a Twist Motor (cone and roll constraints). SLERP will not work if any of the angular constraints are locked.

Property

Description

SLERP

Sets the motor to SLERP (Spherical Linear Interpolation) mode. SLERP mode will not work if any of the axis of the angular constraint is locked.

Twist and Swing

Sets the motor to Twist and Swing (cone and roll constraints) mode.

Target Orientation

Target orientation relative to the body reference frame.

Drives

Depending on the Angular Drive Mode setting, you can enable or disable the different motors for that mode.

Strength

The force applied to reach the target orientation.

Target Velocity

Target angular velocity relative to the body reference frame

Drives

Depending on the Angular Drive Mode setting, you can enable or disable the different motors for that mode.

Strength

The force applied to reach the target velocity.

Advanced

Advanced Constraint Motor Physics

Property

Description

Max Force

The force limit of the drive.