Mover Constraints
Mover Constraints
The physics engine includes several Constraint|constraints that apply force or torque to move one or more assemblies. This article outlines every mover constraint and how to create them using Studio’s Create button drop-down.
For a clearer visualization of all mover constraints in this article, toggle on Constraint Details and Draw On Top from the Model tab.
Creating Constraints
All mover constraints must connect one or two Attachment|Attachments. To create a constraint using the tool workflow:
- From the Model tab, access the Create button’s drop-down menu and select the desired constraint type.
- On a part, click to place the first attachment and then, if the constraint requires a second attachment, click to place it. This will complete the connection with the chosen constraint type.
AngularVelocity
AlignPosition
For increased accuracy, you can create and position one or both attachments in advance and then hover-and-click over each to connect the new constraint. This method will use the selected attachments instead of creating new attachments.
Constraint Details
Linear Velocity
The LinearVelocity constraint applies force on a part/assembly to maintain a constant velocity. It can be set to apply force along a datatype/Vector3, line, or 2D plane.
The
LinearVelocity constraint applies a force that attempts to maintain a constant linear velocity. If you want to control the amount of force applied, use a VectorForce constraint. Alternatively, if you only need initial linear velocity, set the BasePart/AssemblyLinearVelocity|AssemblyLinearVelocity property directly on the part/assembly.
| Property | Description |
|---|---|
LinearVelocity/MaxForce|MaxForce |
Maximum magnitude of the force vector the constraint can apply. |
LinearVelocity/RelativeTo|RelativeTo |
If set to World, force will be applied in world coordinates, independent of the parent or attachment orientations. If set to Attachment0 or Attachment1, force will be applied relative to Constraint/Attachment0|Attachment0 or Constraint/Attachment1|Attachment1 respectively.
World
Attachment0
|
LinearVelocity/VelocityConstraintMode|VelocityConstraintMode |
The default mode is Vector, meaning that force is applied along all three axes as set by LinearVelocity/VectorVelocity|VectorVelocity. The mode can alternatively be set to Line which applies force along just one normalized axis (LinearVelocity/LineDirection|LineDirection). Lastly, the mode can be set to Plane which applies force as a bi-directional datatype/Vector2 (LinearVelocity/PlaneVelocity|PlaneVelocity) across the plane. |
LinearVelocity/VectorVelocity|VectorVelocity |
datatype/Vector3 velocity value when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Vector. |
LinearVelocity/LineDirection|LineDirection |
The normalized datatype/Vector3 direction for constraining the velocity along a line, when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Line. |
LinearVelocity/LineVelocity|LineVelocity |
Float value of the velocity when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Line. |
LinearVelocity/PlaneVelocity|PlaneVelocity |
datatype/Vector2 value of the velocity in each tangent direction of the plane, when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Plane. |
LinearVelocity/PrimaryTangentAxis|PrimaryTangentAxis |
The primary axis in the plane, when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Plane. If LinearVelocity/RelativeTo|RelativeTo is set to Attachment0 or Attachment1, applied force depends on that attachment's Attachment/Axis|Axis. |
LinearVelocity/SecondaryTangentAxis|SecondaryTangentAxis |
The secondary axis in the plane, when LinearVelocity/VelocityConstraintMode|VelocityConstraintMode is set to Plane. If LinearVelocity/RelativeTo|RelativeTo is set to Attachment0 or Attachment1, applied force depends on that attachment's Attachment/SecondaryAxis|SecondaryAxis. |
Angular Velocity
The AngularVelocity constraint applies torque on a part/assembly to maintain an angular velocity.
The
AngularVelocity constraint applies a torque that attempts to maintain a constant angular velocity. If you want to control the amount of torque applied, use a Torque constraint. Alternatively, if you only need initial angular velocity, set the BasePart/AssemblyAngularVelocity|AssemblyAngularVelocity property directly on the part/assembly.
| Property | Description |
|---|---|
AngularVelocity/AngularVelocity|AngularVelocity |
datatype/Vector3|Vector3 force applied to achieve and maintain an angular velocity. |
AngularVelocity/MaxTorque|MaxTorque |
Maximum torque the constraint can apply. |
AngularVelocity/RelativeTo|RelativeTo |
If set to World, the angular velocity vector is used as is. If set to Attachment1 — and the constraint's Constraint/Attachment1|Attachment1 property is set to another attachment — the angular velocity will be affected by that of the other attachment as seen by how the upper-left red part's velocity affects the attached blue part's velocity.1
World
Attachment1
|
1
Setting RelativeTo to Attachment1 also exposes the ReactionTorqueEnabled property; see
AngularVelocity/ReactionTorqueEnabled|ReactionTorqueEnabled for details.Align Position
The AlignPosition constraint — connecting two Attachment|Attachments — applies force to move the two attachments together. As indicated by the name, it only affects the position of the attachments, not their orientation (to align attachments by orientation, see Align Orientation).
By default, the constraint only applies force to
Constraint/Attachment0|Attachment0, although this behavior can be controlled through AlignPosition/ReactionForceEnabled|ReactionForceEnabled.
| Property | Description |
|---|---|
AlignPosition/MaxVelocity|MaxVelocity |
Maximum velocity the constraint can use to reach its goal. |
AlignPosition/MaxForce|MaxForce |
Maximum force the constraint can use to reach its goal. |
AlignPosition/Responsiveness|Responsiveness |
How quickly the constraint will attempt to reach its goal. Higher values equal quicker alignment. |
AlignPosition/ApplyAtCenterOfMass|ApplyAtCenterOfMass |
By default, force is applied to either parent at its attachment location. To apply force at each parent's center of mass regardless of where Constraint/Attachment0|Attachment0 and Constraint/Attachment1|Attachment1 are, toggle on AlignPosition/ApplyAtCenterOfMass|ApplyAtCenterOfMass.
false (default)
true
|
AlignPosition/RigidityEnabled|RigidityEnabled |
When set to true, the solver will react as quickly as possible to move the attachments together, effectively "snapping" them into alignment. If false, the force will be determined by the AlignPosition/MaxVelocity|MaxVelocity, AlignPosition/MaxForce|MaxForce, and AlignPosition/Responsiveness|Responsiveness values.2 |
AlignPosition/ReactionForceEnabled|ReactionForceEnabled |
By default, the constraint only applies force to Constraint/Attachment0|Attachment0, while Constraint/Attachment1|Attachment1 remains unaffected. However, force can be applied to both attachments in equal and opposite directions by enabling AlignPosition/ReactionForceEnabled|ReactionForceEnabled.
false (default)
true
|
2
The
AlignPosition/MaxVelocity|MaxVelocity, AlignPosition/MaxForce|MaxForce, and AlignPosition/Responsiveness|Responsiveness properties only appear in Studio (Compliance section) if AlignPosition/RigidityEnabled|RigidityEnabled is false.Align Orientation
The AlignOrientation constraint — connecting two Attachment|Attachments — applies a torque to make the attachments align. As indicated by the name, it only affects the orientation of the attachments, not their position (to align attachments positionally, see Align Position).
By default, the constraint only applies torque to
Constraint/Attachment0|Attachment0, although this behavior can be controlled through AlignOrientation/ReactionTorqueEnabled|ReactionTorqueEnabled.
| Property | Description |
|---|---|
AlignOrientation/MaxAngularVelocity|MaxAngularVelocity |
Maximum angular velocity the constraint can use to reach its goal. |
AlignOrientation/MaxTorque|MaxTorque |
Maximum torque the constraint can use to reach its goal. |
AlignOrientation/Responsiveness|Responsiveness |
How quickly the constraint will attempt to reach its goal. Higher values equal quicker alignment. |
AlignOrientation/PrimaryAxisOnly|PrimaryAxisOnly |
If false, the constraint will apply torque about all 3 axes to achieve alignment. If true, torque will only occur when the primary axes — visually represented by the upward-pointing arrows — become misaligned.3
false (default)
true
|
AlignOrientation/RigidityEnabled|RigidityEnabled |
When set to true, the solver will react as quickly as possible to move the attachments together, effectively "snapping" them into alignment. If false, the force will be determined by the AlignOrientation/MaxAngularVelocity|MaxAngularVelocity, AlignOrientation/MaxTorque|MaxTorque, and AlignOrientation/Responsiveness|Responsiveness values.4 |
AlignOrientation/ReactionTorqueEnabled|ReactionTorqueEnabled |
By default, the constraint only applies torque to Constraint/Attachment0|Attachment0, while Constraint/Attachment1|Attachment1 remains unaffected. However, torque can be applied to both attachments in equal and opposite directions by enabling AlignOrientation/ReactionTorqueEnabled|ReactionTorqueEnabled.
false (default)
true
|
3
Enabling PrimaryAxisOnly also exposes the AlignType property; see
AlignOrientation|AlignType|AlignType for details.4
The
AlignOrientation/MaxAngularVelocity|MaxAngularVelocity, AlignOrientation/MaxTorque|MaxTorque, and AlignOrientation/Responsiveness|Responsiveness properties only appear in Studio (Compliance section) if AlignOrientation/RigidityEnabled|RigidityEnabled is false.Vector Force
The VectorForce constraint applies constant force to a part/assembly. The direction and strength of the force is determined by a datatype/Vector3 and can be relative to an attachment on the part, another attachment, or the world coordinate system.
Because the
VectorForce constraint applies constant force and acceleration, very high speeds may result if no other forces are involved. If you only need initial velocity, set the BasePart/AssemblyLinearVelocity|AssemblyLinearVelocity property directly on the part/assembly.
| Property | Description |
|---|---|
VectorForce/Force|Force |
datatype/Vector3|Vector3 specifying the strength and direction of force. |
VectorForce/ApplyAtCenterOfMass|ApplyAtCenterOfMass |
By default, force is applied to the part/assembly at the location of Constraint/Attachment0|Attachment0. Thus, if its center of mass is not aligned with the direction/point of force, torque will be applied as well.
To apply force at the center of mass regardless of where
Constraint/Attachment0|Attachment0 is, toggle on VectorForce/ApplyAtCenterOfMass|ApplyAtCenterOfMass.
false (default)
true
|
VectorForce/RelativeTo|RelativeTo |
By default, force is applied relative to Constraint/Attachment0|Attachment0. If the parent part/assembly rotates, the force will change direction to match the adjusted orientation of the attachment; visualize this behavior in how the thruster of a rocket pushes it forward, regardless of the rocket's rotation.
If set to World, force will be applied in world coordinates, independent of the parent or attachment orientations; visualize this behavior as a directional force like the wind blowing against an object.
If set to Attachment1, force will be applied relative to
Constraint/Attachment1|Attachment1 and, if the attachment rotates, change to match its orientation.
Attachment0 (default)
World
|
Torque
A Torque constraint applies constant torque to a part/assembly from its center of mass.
Because the
Torque constraint applies constant torque and angular acceleration, very high speeds may result if no other forces are involved. If you want to maintain a constant velocity over time, use an Angular Velocity constraint. Alternatively, if you only need initial velocity, set the BasePart/AssemblyAngularVelocity|AssemblyAngularVelocity property directly on the part/assembly.
| Property | Description |
|---|---|
Torque/Torque|Torque |
datatype/Vector3|Vector3 specifying the strength and direction of torque. |
Torque/RelativeTo|RelativeTo |
By default, torque is applied relative to Constraint/Attachment0|Attachment0. If the parent part/assembly rotates, the torque will change direction to match the adjusted orientation of the attachment.
If set to World, torque will be applied in world coordinates, independent of the parent or attachment orientations.
If set to Attachment1, torque will be applied relative to
Constraint/Attachment1|Attachment1 and, if the attachment rotates, change to match its orientation.
Attachment0 (default)
World
|
Line Force
The LineForce constraint applies a force along the theoretical line connecting its two Attachment|Attachments. As the end points (attachments) move, the direction of force will change accordingly.
| Property | Description |
|---|---|
LineForce/Magnitude|Magnitude |
Magnitude of the force. |
LineForce/ApplyAtCenterOfMass|ApplyAtCenterOfMass |
By default, force is applied to either parent at its attachment location. To focus the line force end points (and thus the direction of force) at each parent's center of mass, toggle on LineForce/ApplyAtCenterOfMass|ApplyAtCenterOfMass.
false (default)
true
|
LineForce/InverseSquareLaw|InverseSquareLaw |
When true, the force magnitude is multiplied by the inverse square of the distance, meaning the force will increase exponentially as the two attachments get closer together, like magnets. When using this setting, it's recommended that you set a LineForce/MaxForce|MaxForce threshold to prevent infinite force if the attachments align precisely.
false (default)
true
|
LineForce/ReactionForceEnabled|ReactionForceEnabled |
By default, the constraint only applies force to Constraint/Attachment0|Attachment0, while Constraint/Attachment1|Attachment1 remains unaffected. However, force can be applied to both attachments in equal and opposite directions by enabling LineForce/ReactionForceEnabled|ReactionForceEnabled.
false (default)
true
|