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  3. Physics Constraint Reference

Physics Constraint Reference

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

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

Constraint

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

Property Description
Disable Collision This disables collision between the constrained components.
Enable Projection If the distance error between bodies exceeds Projection Linear Tolerance value, or rotational error exceeds Projection Angular Tolerance, the Physics Body will be projected to fix this. This fixes cases where the visuals look disconnected, such as individual chain links breaking away from each other.
Projection Linear Tolerance If the distance error exceeds this value, in world units, the body will be projected.
Projection Angular Tolerance If the rotational error exceeds this value, in degrees, the body will be projected.
Parent Dominates When set, the parent body in a constraint will not be affected by the motion of the child.

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 constraint 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 constraint 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 constraint 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

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.
Contact Distance Determines how close to the limit we have to get before turning the joint on.
Linear Breakable Whether it is possible to break the joint with linear force.
Linear Break Threshold Force needed to break the distance constraint.

Angular Limits

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

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.
Contact Distance Determines how close to the limit we have to get before turning the joint on.
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.
Contact Distance Determines how close to the limit we have to get before turning the joint on.
Breakable  
Angular Breakable Whether it is possible to break the joint with angular force.
Angular Break Threshold Torque needed to break the joint.

Linear Motor

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

Property Description
Max Force The force limit of the drive.

Angular Motor

Property Description
Angular Drive Mode

Whether this angular motor uses SLERP (Spherical Linear Interpolation) or decompose 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 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 proemtatopm 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.
Stength The force applied to reach the target velocity.

Advanced

Property Description
Max Force The force limit of the drive.

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