Class FrictionEquation

Constrains the slipping in a contact along a tangent

Hierarchy

Constructors

constructor

Properties

B G a b bodyA bodyB contactEquations contactPointA contactPointB enabled epsilon frictionCoefficient index invC lambda maxBias maxForce maxForceDt minForce minForceDt multiplier needsUpdate offset relativeVelocity relaxation shapeA shapeB stiffness t timeStep DEFAULT_RELAXATION DEFAULT_STIFFNESS

Methods

addToWlambda computeB computeGW computeGWlambda computeGiMGt computeGiMf computeGq computeInvC getSlipForce gmult setSlipForce update

Constructors

constructor

Properties

B

B: number

G

G: Vec2

The Jacobian entry of this equation. 6 numbers, 3 per body (x,y,angle).

a

a: number

b

b: number

bodyA

bodyA: Body

First body participating in the constraint

bodyB

bodyB: Body

Second body participating in the constraint

contactEquations

contactEquations: ContactEquation[]

ContactEquations connected to this friction equation. The contact equations can be used to rescale the max force for the friction. If more than one contact equation is given, then the max force can be set to the average.

contactPointA

contactPointA: Vec2

Relative vector from center of body A to the contact point, world oriented.

contactPointB

contactPointB: Vec2

Relative vector from center of body B to the contact point, world oriented.

enabled

enabled: boolean

Whether this equation is enabled or not. If true, it will be added to the solver.

epsilon

epsilon: number

frictionCoefficient

frictionCoefficient: number

The friction coefficient to use.

index

index: number

invC

invC: number

lambda

lambda: number

maxBias

maxBias: number

Cap the constraint violation (G*q) to this value.

maxForce

maxForce: number

Max force to apply when solving.

maxForceDt

maxForceDt: number

minForce

minForce: number

Minimum force to apply when solving.

minForceDt

minForceDt: number

multiplier

multiplier: number

The resulting constraint multiplier from the last solve. This is mostly equivalent to the force produced by the constraint.

needsUpdate

needsUpdate: boolean

Indicates if stiffness or relaxation was changed.

offset

offset: number

relativeVelocity

relativeVelocity: number

Relative velocity.

relaxation

relaxation: number

The number of time steps needed to stabilize the constraint equation. Typically between 3 and 5 time steps.

shapeA

shapeA: null | Shape

The shape in body i that triggered this friction.

Todo

Needed? The shape can be looked up via contactEquation.shapeA...

shapeB

shapeB: null | Shape

The shape in body j that triggered this friction.

Todo

Needed? The shape can be looked up via contactEquation.shapeB...

stiffness

stiffness: number

The stiffness of this equation. Typically chosen to a large number (~1e7), but can be chosen somewhat freely to get a stable simulation.

t

t: Vec2

Tangent vector that the friction force will act along. World oriented.

timeStep

timeStep: number

Static DEFAULT_RELAXATION

DEFAULT_RELAXATION: number = 4

The default relaxation when creating a new Equation.

Static DEFAULT_STIFFNESS

DEFAULT_STIFFNESS: number = 1e6

The default stiffness when creating a new Equation.

Methods

addToWlambda

  • Add constraint velocity to the bodies.

    Parameters

    • deltalambda: number

    Returns void

computeB

  • Computes the RHS of the SPOOK equation

    Parameters

    • a: number
    • b: number
    • h: number

    Returns number

computeGW

  • Computes G*W, where W are the body velocities

    Returns number

computeGWlambda

  • Computes G*Wlambda, where W are the body velocities

    Returns number

computeGiMGt

  • Computes G*inv(M)*G'

    Returns number

computeGiMf

  • Computes G*inv(M)*f, where M is the mass matrix with diagonal blocks for each body, and f are the forces on the bodies.

    Returns number

computeGq

  • Computes G*q, where q are the generalized body coordinates

    Returns number

computeInvC

  • Compute the denominator part of the SPOOK equation: C = G*inv(M)*G' + eps

    Parameters

    • eps: number

    Returns number

getSlipForce

  • Get the max force for the constraint.

    Returns number

gmult

  • Multiply a jacobian entry with corresponding positions or velocities

    Parameters

    Returns number

setSlipForce

  • Set the slipping condition for the constraint. The friction force cannot be larger than this value.

    Parameters

    • slipForce: number

    Returns void

update

  • Returns void

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