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SpringConstraint

Show Show deprecated

SpringConstraint

Show deprecated

A SpringConstraint applies a force to its Attachment|Attachments based on spring and damper behavior. Assuming the constraint has SpringConstraint/Stiffness, it will apply forces based on how far apart the attachments are. If the attachments are further apart than the constraint’s SpringConstraint/FreeLength, the attachments will be forced together. If they are closer than the SpringConstraint/FreeLength, the attachments will be forced apart. In addition, if SpringConstraint/Damping is set, there will be a damping component to the applied force that scales with the velocity of the attachments.

This constraint, along with a CylindricalConstraint, is ideal for building vehicle suspension as demonstrated in /articles/building carkit 1|Building a Basic Car.

Note that if this constraint attaches one part (A) to another part (B) that is anchored or connected to an anchored part (Z), part A will not be locally simulated when interacting with a player.

Calculating SpringConstraint Force

The following helper function exhibits how the force of a SpringConstraint is calculated based on various properties of the constraint and its attachments.

local function getSpringForce(spring)
	if not spring:IsA("SpringConstraint") then
		warn(spring .. " is not a spring constraint!")
		return
	end

	local currentLength = spring.CurrentLength
	local freeLength = spring.FreeLength
	if (spring.LimitsEnabled) then
		currentLength = math.clamp(currentLength, spring.MinLength, spring.MaxLength)
		freeLength = math.clamp(freeLength, spring.MinLength, spring.MaxLength)
	end
	local springLength = currentLength - freeLength

	local axis = spring.Attachment0.WorldPosition - spring.Attachment1.WorldPosition
	if axis.Magnitude > 0 then
		axis = axis.Unit
	end
	local effectiveVelocity = spring.Attachment0.Parent.Velocity - spring.Attachment1.Parent.Velocity

	-- https://en.wikipedia.org/wiki/Harmonic_oscillator
	-- f = -k * x - c * dx/dt + fext
	-- Gravity may not be all of the external forces; friction may affect this, but it's harder to account for
	local forceExternal = Vector3.new(0, -workspace.Gravity, 0)
	local force = -spring.Stiffness * springLength - spring.Damping * axis:Dot(effectiveVelocity) + axis:Dot(forceExternal)

	force = math.clamp(force, -spring.MaxForce, spring.MaxForce)
	return force
end

Properties

float

Coils

The number of coils visualized on the SpringConstraint. This can only be set between 0 and 8.

float

CurrentLength

[ReadOnly] [NotReplicated]

The current distance between the SpringConstant’s Attachment.

float

Damping

Damping constant for the SpringConstraint. Multiplied to the velocity of the constraint’s Attachment to reduce the spring force applied.

float

FreeLength

Natural resting length of the spring.

bool

LimitsEnabled

Sets whether the SpringConstraint enforces a minimum and maximum length.

float

MaxForce

The maximum force the SpringConstraint can apply on its Attachment.

float

MaxLength

The maximum separation the SpringConstraint will allow if SpringConstraint/LimitsEnabled is true.

float

MinLength

The minimum separation the SpringConstraint will allow if SpringConstraint/LimitsEnabled is true.

float

Radius

The visualized radius of the spring’s coils.

float

Stiffness

The strength of the spring. The higher this value the more force will be applied when the attachments are separated a different length than the SpringConstraint/FreeLength.

float

Thickness

The visualized thickness of the spring’s coils.

Inherited from Constraint: Show Hide

bool

Active

[ReadOnly] [NotReplicated]

Indicates if the constraint is currently active in the world

Attachment

Attachment0

The Attachment that is connected to Constraint/Attachment1

Attachment

Attachment1

The Attachment that is connected to Constraint/Attachment0

BrickColor

Color

The color of the constraint.

bool

Enabled

Toggles whether or not this Constraint is enabled.

bool

Visible

Toggles the visibility of this Constraint.

Inherited from Instance: Show Hide

bool

Archivable

Determines if an Instance can be cloned using /Instance/Clone or saved to file.

string

ClassName

[ReadOnly] [NotReplicated]

A read-only string representing the class this Instance belongs to

int

DataCost

[ReadOnly] [NotReplicated] [Deprecated]

The cost of saving the instance using data persistence.

string

Name

A non-unique identifier of the Instance

Instance

Parent

Determines the hierarchical parent of the Instance

bool

RobloxLocked

If true, the Instance and its descendants cannot be indexed or edited by a Script or LocalScript and will throw an error if it is attempted

bool

archivable

[Hidden] [NotReplicated] [Deprecated]
string

className

[ReadOnly] [NotReplicated] [Deprecated]

Functions

Inherited from Instance: Show Hide

void

ClearAllChildren ( )

This function destroys all of an Instance's children.

Instance

Clone ( )

Create a deep copy of a Roblox instance and descendants where Archivable = true.

void

Destroy ( )

Sets the Instance/Parent property to nil, locks the Instance/Parent property, disconnects all connections and calls Destroy on all children.

Instance

FindFirstAncestor ( string name )

Returns the first ancestor of the Instance whose Instance/Name is equal to the given name.

Instance

FindFirstAncestorOfClass ( string className )

Returns the first ancestor of the Instance whose Instance/ClassName is equal to the given className.

Instance

FindFirstAncestorWhichIsA ( string className )

Returns the first ancestor of the Instance for whom Instance/IsA returns true for the given className.

Instance

FindFirstChild ( string name , bool recursive )

Returns the first child of the Instance found with the given name.

Instance

FindFirstChildOfClass ( string className )

Returns the first child of the Instance whose Instance/ClassName|ClassName is equal to the given className.

Instance

FindFirstChildWhichIsA ( string className , bool recursive )

Returns the first child of the Instance for whom Instance/IsA returns true for the given className.

Objects

GetChildren ( )

Returns an array containing all of the Instance's children.

string

GetDebugId ( int scopeLength )

[NotBrowsable]

Returns a coded string of the Instances DebugId used internally by Roblox.

Array

GetDescendants ( )

[CustomLuaState]

Returns an array containing all of the descendants of the instance

string

GetFullName ( )

Returns a string describing the Instance's ancestry.

RBXScriptSignal

GetPropertyChangedSignal ( string property )

Get an event that fires when a given property of an object changes.

bool

IsA ( string className )

[CustomLuaState]

Returns true if an Instance's class matches or inherits from a given class

bool

IsAncestorOf ( Instance descendant )

Returns true if an Instance is an ancestor of the given descendant.

bool

IsDescendantOf ( Instance ancestor )

Returns true if an Instance is a descendant of the given ancestor.

void

Remove ( )

[Deprecated]

Sets the object’s Parent to nil, and does the same for all its descendants.

Instance

WaitForChild ( string childName , double timeOut )

[CustomLuaState] [CanYield]

Returns the child of the Instance with the given name. If the child does not exist, it will yield the current thread until it does.

Objects

children ( )

[Deprecated]

Returns an array of the object’s children.

Instance

clone ( )

[Deprecated]
void

destroy ( )

[Deprecated]
Instance

findFirstChild ( string name , bool recursive )

[Deprecated]
Objects

getChildren ( )

[Deprecated]
bool

isA ( string className )

[Deprecated] [CustomLuaState]
bool

isDescendantOf ( Instance ancestor )

[Deprecated]
void

remove ( )

[Deprecated]

Events

Inherited from Instance: Show Hide

RBXScriptSignal

AncestryChanged ( Instance child , Instance parent )

Fires when the Instance/Parent property of the object or one of its ancestors is changed.

RBXScriptSignal

Changed ( string property )

Fired immediately after a property of an object changes.

RBXScriptSignal

ChildAdded ( Instance child )

Fires when an object is parented to this Instance.

RBXScriptSignal

ChildRemoved ( Instance child )

Fires when a child is removed from this Instance.

RBXScriptSignal

DescendantAdded ( Instance descendant )

Fires when a descendant is added to the Instance

RBXScriptSignal

DescendantRemoving ( Instance descendant )

Fires immediately before a descendant of the Instance is removed.

RBXScriptSignal

childAdded ( Instance child )

[Deprecated]