Roblox UtilitiesDevlHub Roblox Documentation

Class

AnimationConstraint

Inherits
Constraint › Instance › Object
Memory category
BaseParts

Aligns two BaseParts with an animate-able kinematic or force-based joint that supports physical simulation (ragdoll, arm strength). The default joint type for R15 avatar rigs.

Replaces Motor6D for Avatar rigs#

As part of the Avatar Joint Upgrade, AnimationConstraint is the replacement for Motor6D in R15 player character rigs. When AvatarJointUpgrade is enabled (the default for new experiences), player characters spawn with AnimationConstraints instead of Motor6Ds. Unlike Motor6D, AnimationConstraint supports both kinematic animation and force-based physical simulation — enabling ragdoll physics, arm strength, and other physically simulated character movement without rebuilding the rig.

Migrating from Motor6D#

If you have existing code that uses Motor6D for character rigs, note these key differences. See also the Phase 2 migration recommendations.

  • Finding joints: Use :FindFirstChildWhichIsA("AnimationConstraint") instead of :FindFirstChildOfClass("Motor6D"). For code that must support both old and new rigs, check for AnimationConstraint first, then fall back to Motor6D.
  • C0, C1, Part0, Part1: These properties exist on AnimationConstraint as read-only aliases for backwards compatibility. They map to Attachment0.CFrame, Attachment1.CFrame, Attachment0.Parent, and Attachment1.Parent respectively. Do not attempt to write to them.
  • Do not modify RigAttachment.CFrame directly — this disrupts animation retargeting and causes performance issues.
  • Transform: Works identically to Motor6D.Transform — the Animator writes to it each frame. Layer procedural animations by multiplying into Transform during RunService.PreSimulation, which stacks with active animation tracks without breaking retargeting.
  • IsKinematic: When true (default), behavior is equivalent to Motor6D. Set to false to enable force-based physical simulation.
  • Type checks: animConstraint:IsA("Motor6D") returns false. Update any IsA("Motor6D") guards to also accept "AnimationConstraint".
  • Server replication: Instead of setting C0 on the server, use client-side animation evaluation and synchronize data through custom Attributes or UnreliableRemoteEvent.
Example: Procedural neck rotation#
Luau
-- Before (Motor6D): writing to C0 directly
local originalC0 = neck.C0
RunService.RenderStepped:Connect(function()
    neck.C0 = originalC0 * computeNeckRotation()
end)

-- After (AnimationConstraint): multiplying into Transform during PreSimulation
RunService.PreSimulation:Connect(function()
    if not animator.EvaluationThrottled then
        neck.Transform = computeNeckRotation() * neck.Transform
    end
end)

Description#

An AnimationConstraint constrains its Attachments so that they're offset by Transform. When IsKinematic is true, the parts follow the transform perfectly (identical to Motor6D behavior). When false, the constraint applies forces and torques limited by MaxForce and MaxTorque, enabling physically simulated character movement.

Properties 8#

AngularDampingfloatDamping ratio for the rotational part of the constraint. Higher values reduce oscillation around the target orientation.ReadSafe
AngularStrengthfloatControls how rigidly the constraint enforces the rotational part of its target Transform. Higher values track the target orientation more stiffly.ReadSafe
IsKinematicbooleanToggles whether the constraint is kinematic or physically simulated.ReadSafe
LinearDampingfloatDamping ratio for the translational part of the constraint. Higher values reduce oscillation around the target position.ReadSafe
LinearStrengthfloatControls how rigidly the constraint enforces the translational part of its target Transform. Higher values track the target position more stiffly.ReadSafe
MaxForcefloatMaximum force magnitude the constraint can apply to achieve its goal.ReadSafe
MaxTorquefloatMaximum torque the constraint can apply to reach its goal.ReadSafe
TransformCFrameDescribes the current animation offset of the constraint joint.ReadSafe

AngularDamping: float#

ReadSafe

The damping ratio (ζ) applied to the rotational part of the constraint. Only used if IsKinematic is false.

A value of 1 corresponds to critical damping, where the constraint reaches its target orientation as fast as possible without overshoot in the absence of other forces or constraints. Values less than 1 are under-damped and oscillate around the target before settling. Values greater than 1 are over-damped and approach the target more slowly without oscillation. A value of 0 applies no angular damping, causing the constraint to oscillate.

Even with this property set to 1, an AnimationConstraint at the root of a multi-body mechanism may still exhibit low-frequency oscillation because it does not "see" the full effective mass of the downstream chain. You can compensate by increasing both AngularStrength and AngularDamping beyond their defaults.

AngularStrength: float#

ReadSafe

Controls how rigidly the constraint enforces the rotational part of its target Transform. Only used if IsKinematic is false. The resulting torque is capped by MaxTorque.

AngularStrength is defined as a normalized natural frequency, AngularStrength = f / 60, where f is the target natural frequency in Hz. The default value of 1 corresponds to a target frequency of 60 Hz and produces strong tracking of the target orientation. A value of 0 applies no torque. Values less than 1 produce a softer, more compliant rotational response, and values greater than 1 produce a stiffer response.

Use values significantly greater than 1 with caution, as they may cause the simulation to become unstable.

IsKinematic: boolean#

ReadSafe

When true, the connected parts follow the Transform perfectly without participating in physics simulation. When false, the connected parts follow the trajectory using forces and torques limited by MaxForce and MaxTorque.

LinearDamping: float#

ReadSafe

The damping ratio (ζ) applied to the translational part of the constraint. Only used if IsKinematic is false.

A value of 1 corresponds to critical damping, where the constraint reaches its target position as fast as possible without overshoot in the absence of other forces or constraints. Values less than 1 are under-damped and oscillate around the target before settling. Values greater than 1 are over-damped and approach the target more slowly without oscillation. A value of 0 applies no linear damping, causing the constraint to oscillate.

LinearDamping has no effect when LinearStrength is 0.

LinearStrength: float#

ReadSafe

Controls how rigidly the constraint enforces the translational part of its target Transform. Only used if IsKinematic is false. The resulting force is capped by MaxForce.

LinearStrength uses the same normalized natural frequency definition as AngularStrength, LinearStrength = f / 60, where f is the target natural frequency in Hz. The default value of 1 corresponds to a target frequency of 60 Hz and produces strong tracking of the target position. A value of 0 applies no force. Values less than 1 produce a softer, more compliant positional response, and values greater than 1 produce a stiffer response.

Splitting angular and linear parameters lets you make orientation tracking stiff while keeping positional tracking soft, or vice-versa. As with AngularStrength, use values significantly greater than 1 with caution, as they may cause the simulation to become unstable.

MaxForce: float#

ReadSafe

Maximum force magnitude the constraint can apply to achieve its goal. Only used if IsKinematic is false.

MaxTorque: float#

ReadSafe

Maximum torque the constraint can use to reach its goal. Only used if IsKinematic is false.

Transform: CFrame#

ReadSafe

The internal CFrame that is manipulated when the constraint is being animated.

Note that AnimationConstraint transforms are not applied immediately, but rather as a batch in a parallel job after RunService.PreSimulation, immediately before physics steps. The deferred batch update is much more efficient than many immediate updates. If the AnimationConstraint is part of an animated model with an Animator, then Transform is usually overwritten every frame by the Animator after RunService.PreAnimation and before RunService.PreSimulation.

Inherited members#

Inherited from Constraint 8
Properties (6)

Active, Attachment0, Attachment1, Color, Enabled, Visible

Methods (2)

GetDebugAppliedForce, GetDebugAppliedTorque

Inherited from Instance 58
Properties (10)

Archivable, archivable, Capabilities, IsInSandbox, Name, Parent, PredictionMode, RobloxLocked, Sandboxed, UniqueId

Methods (39)

AddTag, children, ClearAllChildren, Clone, clone, Destroy, destroy, FindFirstAncestor, FindFirstAncestorOfClass, FindFirstAncestorWhichIsA, FindFirstChild, findFirstChild, FindFirstChildOfClass, FindFirstChildWhichIsA, FindFirstDescendant, GetActor, GetAttribute, GetAttributeChangedSignal, GetAttributes, GetChildren, getChildren, GetDebugId, GetDescendants, GetFullName, GetStyled, GetStyledPropertyChangedSignal, GetTags, HasTag, IsAncestorOf, IsDescendantOf, isDescendantOf, IsPropertyModified, QueryDescendants, Remove, remove, RemoveTag, ResetPropertyToDefault, SetAttribute, WaitForChild

Events (9)

AncestryChanged, AttributeChanged, ChildAdded, childAdded, ChildRemoved, DescendantAdded, DescendantRemoving, Destroying, StyledPropertiesChanged

Inherited from Object 6
Properties (2)

ClassName, className

Methods (3)

GetPropertyChangedSignal, IsA, isA

Events (1)

Changed