Class VariableCenterOfMass

Dynamic center of mass and inertia calculation system that updates Rigidbody properties based on attached mass affectors like fuel tanks, cargo loads, and passengers.

Inheritance

object

Object

Component

Behaviour

MonoBehaviour

VariableCenterOfMass

Namespace: NWH.Common.CoM

Assembly: NWH.Common.dll

Syntax

[DisallowMultipleComponent]
[DefaultExecutionOrder(-1000)]
[RequireComponent(typeof(Rigidbody))]
public class VariableCenterOfMass : MonoBehaviour

Remarks

VariableCenterOfMass enables realistic vehicle physics behavior by automatically adjusting center of mass and inertia tensor as vehicle loading changes. This affects handling characteristics, stability, and acceleration response without requiring complex rigidbody hierarchies.

The system calculates total mass, weighted center of mass position, and inertia contributions from all IMassAffector components. Changes in fuel level, cargo loading, or passenger weight immediately affect vehicle dynamics, creating realistic weight distribution effects.

Critical for vehicle realism: Front-heavy vehicles understeer more, rear-heavy vehicles may oversteer, and high center of mass increases rollover tendency. The system updates these characteristics dynamically based on actual mass distribution.

Fields

affectors

Objects attached or part of the vehicle affecting its center of mass and inertia.

Declaration

[NonSerialized]
public IMassAffector[] affectors

Field Value

Type	Description
IMassAffector[]

baseMass

Base mass of the object, without IMassAffectors.

Declaration

[Tooltip("Base mass of the object, without IMassAffectors.")]
public float baseMass

Field Value

Type	Description
float

centerOfMass

Center of mass of the object. Auto calculated. To adjust center of mass use centerOfMassOffset.

Declaration

[Tooltip("Center of mass of the rigidbody. Needs to be readjusted when new colliders are added.")]
public Vector3 centerOfMass

Field Value

Type	Description
Vector3

combinedCenterOfMass

Combined center of mass, including the Rigidbody and any IMassAffectors.

Declaration

public Vector3 combinedCenterOfMass

Field Value

Type	Description
Vector3

combinedInertiaTensor

Total inertia tensor. Includes Rigidbody and IMassAffectors.

Declaration

public Vector3 combinedInertiaTensor

Field Value

Type	Description
Vector3

combinedMass

Total mass of the object with masses of IMassAffectors counted in.

Declaration

[Tooltip("Total mass of the object with masses of IMassAffectors counted in.")]
public float combinedMass

Field Value

Type	Description
float

dimensions

Object dimensions in [m]. X - width, Y - height, Z - length. It is important to set the correct dimensions or otherwise inertia might be calculated incorrectly.

Declaration

[Tooltip("Object dimensions in [m]. X - width, Y - height, Z - length.\r\nIt is important to set the correct dimensions or otherwise inertia might be calculated incorrectly.")]
public Vector3 dimensions

Field Value

Type	Description
Vector3

inertiaTensor

Vector by which the inertia tensor of the rigidbody will be scaled on Start(). Due to the uniform density of the rigidbodies, versus the very non-uniform density of a vehicle, inertia can feel off. Use this to adjust inertia tensor values.

Declaration

[Tooltip("    Vector by which the inertia tensor of the rigidbody will be scaled on Start().\r\n    Due to the unform density of the rigidbodies, versus the very non-uniform density of a vehicle, inertia can feel\r\n    off.\r\n    Use this to adjust inertia tensor values.")]
public Vector3 inertiaTensor

Field Value

Type	Description
Vector3

isDirty

When true, properties will be recalculated in the next FixedUpdate. Call MarkDirty() when mass affectors change to trigger update.

Declaration

[Tooltip("When true, properties will be recalculated in the next FixedUpdate. Automatically managed.")]
public bool isDirty

Field Value

Type	Description
bool

useDefaultCenterOfMass

When enabled the Unity-calculated center of mass will be used.

Declaration

[Tooltip("When enabled the Unity-calculated center of mass will be used.")]
public bool useDefaultCenterOfMass

Field Value

Type	Description
bool

useDefaultInertia

When true inertia settings will be ignored and default Rigidbody inertia tensor will be used.

Declaration

[Tooltip("When true inertia settings will be ignored and default Rigidbody inertia tensor will be used.")]
public bool useDefaultInertia

Field Value

Type	Description
bool

useDefaultMass

Should the default Rigidbody mass be used?

Declaration

public bool useDefaultMass

Field Value

Type	Description
bool

useMassAffectors

If true, the script will search for any IMassAffectors attached as a child (recursively) of this script and use them when calculating mass, center of mass and inertia tensor.

Declaration

public bool useMassAffectors

Field Value

Type	Description
bool

Methods

CalculateInertia(Vector3, float)

Calculates inertia tensor for a cuboid with given dimensions and mass. Uses parallel axis theorem for rectangular prism approximation.

Declaration

public static Vector3 CalculateInertia(Vector3 dimensions, float mass)

Parameters

Type	Name	Description
Vector3	dimensions	Object dimensions in meters (width, height, length)
float	mass	Total mass in kilograms

Returns

Type	Description
Vector3	Inertia tensor components (Ix, Iy, Iz) in kg⋅m²

CalculateInertiaTensorOffset(Vector3)

Calculates the inertia tensor of the Rigidbody and attached mass affectors.

Declaration

public Vector3 CalculateInertiaTensorOffset(Vector3 dimensions)

Parameters

Type	Name	Description
Vector3	dimensions

Returns

Type	Description
Vector3

CalculateMass()

Calculates the mass of the Rigidbody and attached mass affectors.

Declaration

public float CalculateMass()

Returns

Type	Description
float

CalculateRelativeCenterOfMassOffset()

Calculates the center of mass of the Rigidbody and attached mass affectors.

Declaration

public Vector3 CalculateRelativeCenterOfMassOffset()

Returns

Type	Description
Vector3

GetMassAffectors()

Updates list of IMassAffectors attached to this object. Call after IMassAffector has been added or removed from the object.

Declaration

public IMassAffector[] GetMassAffectors()

Returns

Type	Description
IMassAffector[]

GetWorldCenterOfMass()

Gets the combined center of mass position in world space coordinates.

Declaration

public Vector3 GetWorldCenterOfMass()

Returns

Type	Description
Vector3	World space position of the center of mass

MarkDirty()

Mark properties as needing recalculation. Call this when mass affectors change (fuel consumption, cargo loading, etc.).

Declaration

public void MarkDirty()

UpdateAllProperties()

Recalculates all Rigidbody properties (mass, center of mass, and inertia) based on current settings and affectors. Called automatically when isDirty flag is set.

Declaration

public void UpdateAllProperties()

UpdateCoM()

Calculates and applies the CoM to the Rigidbody.

Declaration

public void UpdateCoM()

UpdateInertia(bool)

Calculates and applies the inertia tensor to the Rigidbody.

Declaration

public void UpdateInertia(bool applyUnchanged = false)

Parameters

Type	Name	Description
bool	applyUnchanged

UpdateMass()

Calculates and applies the total mass to the Rigidbody. Includes mass from affectors if useMassAffectors is enabled.

Declaration

public void UpdateMass()

See Also

IMassAffector

MassAffector

Vehicle