Class MotorJoint

Motor joint — drives the relative angular velocity between two bodies toward a target rate, subject to maxForce.

The motor enforces: body2.angularVel - ratio * body1.angularVel → rate

This is a velocity-level constraint (not positional), so it does not enforce a particular relative angle — it continuously applies torque to reach rate. Use an AngleJoint in addition if you also need an angle limit.

Example

// Spin body2 at 2 rad/s relative to body1, limited to 500 N force
const motor = new MotorJoint(body1, body2, 2.0);
motor.maxForce = 500;
motor.space = space;

Fully modernized — uses ZPP_MotorJoint directly (extracted to TypeScript).

Hierarchy (View Summary)

Constraint
- MotorJoint

Index

Constructors

constructor

new MotorJoint(
    body1: Body | null,
    body2: Body | null,
    rate?: number,
    ratio?: number,
): MotorJoint
Parameters
- body1: Body | null
  First body, or null for a static world reference.
- body2: Body | null
  Second body, or null for a static world reference.
- rate: number = 0.0
  Target relative angular velocity (rad/s). Default 0.0.
- ratio: number = 1.0
  Gear ratio applied to body1's angular velocity. Default 1.0.
Returns MotorJoint
Overrides Constraint.constructor
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:40

Properties

debugDraw

debugDraw: boolean = true

Accessors

active

get active(): boolean
Whether the constraint is currently active (enforced by the solver).

Deactivating a constraint suspends it without removing it from the space.

Returns boolean

Default Value
true
Inherited from Constraint.active
- Defined in packages/nape-js/src/constraint/Constraint.ts:150
set active(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.active
- Defined in packages/nape-js/src/constraint/Constraint.ts:153

body1

get body1(): Body
First body (its angular velocity is scaled by ratio).

Returns Body
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:104
set body1(value: Body | null): void
Parameters
- value: Body | null
Returns void
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:108

body2

get body2(): Body
Second body (driven toward the target angular velocity).

Returns Body
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:139
set body2(value: Body | null): void
Parameters
- value: Body | null
Returns void
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:143

breakUnderError

get breakUnderError(): boolean
When true, the constraint breaks if the positional error exceeds maxError.

Returns boolean

Default Value
false
Inherited from Constraint.breakUnderError
- Defined in packages/nape-js/src/constraint/Constraint.ts:330
set breakUnderError(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.breakUnderError
- Defined in packages/nape-js/src/constraint/Constraint.ts:333

breakUnderForce

get breakUnderForce(): boolean
When true, the constraint breaks (fires a BREAK event) if the applied force exceeds maxForce in a single step.

Returns boolean

Default Value
false
Inherited from Constraint.breakUnderForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:316
set breakUnderForce(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.breakUnderForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:319

cbTypes

get cbTypes(): object
The set of CbTypes assigned to this constraint. Used to filter which listeners respond to this constraint's events.

Returns object
Inherited from Constraint.cbTypes
- Defined in packages/nape-js/src/constraint/Constraint.ts:381

compound

get compound(): Compound | null
The compound this constraint belongs to, or null. When set, the constraint's space is managed by the compound.

Returns Compound | null
Inherited from Constraint.compound
- Defined in packages/nape-js/src/constraint/Constraint.ts:122
set compound(value: Compound | null): void
Parameters
- value: Compound | null
Returns void
Inherited from Constraint.compound
- Defined in packages/nape-js/src/constraint/Constraint.ts:126

damping

get damping(): number
Damping ratio for soft constraints (stiff = false).

0 = undamped (oscillates freely), 1 = critically damped. Values > 1 are overdamped. Must be >= 0. Ignored when stiff is true.

Returns number

Default Value
1
Inherited from Constraint.damping
- Defined in packages/nape-js/src/constraint/Constraint.ts:242
set damping(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.damping
- Defined in packages/nape-js/src/constraint/Constraint.ts:245

frequency

get frequency(): number
Spring frequency in Hz for soft constraints (stiff = false).

Higher values make the spring stiffer; lower values make it bouncier. Must be > 0. Ignored when stiff is true.

Returns number

Default Value
10
Inherited from Constraint.frequency
- Defined in packages/nape-js/src/constraint/Constraint.ts:217
set frequency(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.frequency
- Defined in packages/nape-js/src/constraint/Constraint.ts:220

ignore

get ignore(): boolean
When true the constraint is completely ignored by the engine — bodies are not woken, no impulse is applied, and no callbacks fire.

Returns boolean

Default Value
false
Inherited from Constraint.ignore
- Defined in packages/nape-js/src/constraint/Constraint.ts:184
set ignore(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.ignore
- Defined in packages/nape-js/src/constraint/Constraint.ts:187

isSleeping

get isSleeping(): boolean
Whether the constraint's simulation component is currently sleeping.

Only valid when the constraint is active and in a space — throws otherwise.

Returns boolean
Inherited from Constraint.isSleeping
- Defined in packages/nape-js/src/constraint/Constraint.ts:357

maxError

get maxError(): number
Maximum positional error (in pixels) allowed before breaking.

Only meaningful when breakUnderError is true. Must be >= 0. Infinity disables the limit.

Returns number

Default Value
Infinity
Inherited from Constraint.maxError
- Defined in packages/nape-js/src/constraint/Constraint.ts:295
set maxError(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.maxError
- Defined in packages/nape-js/src/constraint/Constraint.ts:298

maxForce

get maxForce(): number
Maximum force (in Newtons) the constraint may apply per step.

When the required force exceeds this value the constraint becomes slack. If breakUnderForce is true the constraint breaks instead.

The clamp only applies to soft constraints (stiff = false): a stiff constraint ignores maxForce unless breakUnderForce is set. MotorJoint and SpringJoint are the exception and always clamp. Must be >= 0. Infinity disables the limit.

Returns number

Default Value
Infinity
Inherited from Constraint.maxForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:272
set maxForce(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.maxForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:275

rate

get rate(): number
Target relative angular velocity in rad/s.

Positive values rotate body2 counter-clockwise relative to body1.

Returns number

Default Value
0.0
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:183
set rate(value: number): void
Parameters
- value: number
Returns void
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:186

ratio

get ratio(): number
Gear ratio applied to body1's angular velocity.

The motor drives: body2.angularVel - ratio * body1.angularVel → rate

Returns number

Default Value
1.0
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:203
set ratio(value: number): void
Parameters
- value: number
Returns void
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:206

removeOnBreak

get removeOnBreak(): boolean
When true (default), the constraint is automatically removed from its space when it breaks. Set to false to keep it in the space after breaking.

Returns boolean

Default Value
true
Inherited from Constraint.removeOnBreak
- Defined in packages/nape-js/src/constraint/Constraint.ts:345
set removeOnBreak(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.removeOnBreak
- Defined in packages/nape-js/src/constraint/Constraint.ts:348

space

get space(): Space | null
The space this constraint belongs to, or null if not in a space.

Assign to add/remove the constraint from a space:
```
joint.space = mySpace;  // adds to space
joint.space = null;     // removes from space
```
Cannot be set if the constraint belongs to a Compound.
Returns Space | null
Inherited from Constraint.space
- Defined in packages/nape-js/src/constraint/Constraint.ts:85
set space(value: Space | null): void
Parameters
- value: Space | null
Returns void
Inherited from Constraint.space
- Defined in packages/nape-js/src/constraint/Constraint.ts:89

stiff

get stiff(): boolean
When true (default) the constraint is stiff/rigid. When false the constraint uses a soft spring model driven by frequency and damping.

Returns boolean

Default Value
true
Inherited from Constraint.stiff
- Defined in packages/nape-js/src/constraint/Constraint.ts:200
set stiff(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.stiff
- Defined in packages/nape-js/src/constraint/Constraint.ts:203

userData

get userData(): Record<string, unknown>
Arbitrary user data attached to this constraint. Lazily initialized to {} on first access.

Returns Record<string, unknown>
Inherited from Constraint.userData
- Defined in packages/nape-js/src/constraint/Constraint.ts:370

Methods

bodyImpulse

bodyImpulse(body: Body): Vec3
The impulse applied to body by this constraint in the last simulation step, expressed as a Vec3 (fx, fy, torque).
Parameters
- body: Body
Returns Vec3
Overrides Constraint.bodyImpulse
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:231

copy

copy(): Constraint
Creates and returns a copy of this constraint with the same parameters. The copy is not automatically added to a space.

Returns Constraint
Inherited from Constraint.copy
- Defined in packages/nape-js/src/constraint/Constraint.ts:424

impulse

impulse(): MatMN
The impulse applied by this constraint in the last simulation step.

The shape of the returned MatMN depends on the constraint's degrees of freedom (e.g., 1×1 for AngleJoint/MotorJoint, 2×1 for PivotJoint/LineJoint, 3×1 for WeldJoint).

Returns MatMN
Overrides Constraint.impulse
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:221

toString

toString(): string
Returns string
Inherited from Constraint.toString
- Defined in packages/nape-js/src/constraint/Constraint.ts:428

visitBodies

visitBodies(lambda: (body: Body) => void): void
Invokes fn once for each distinct body linked to this constraint.
Parameters
- lambda: (body: Body) => void
Returns void
Overrides Constraint.visitBodies
- Defined in packages/nape-js/src/constraint/MotorJoint.ts:248

Class MotorJoint

Example

Hierarchy (View Summary)

Index

Constructors

Properties

Accessors

Methods

Constructors

constructor

Parameters

Returns MotorJoint

Properties

debugDraw

Accessors

active

Returns boolean

Default Value

Parameters

Returns void

body1

Returns Body

Parameters

Returns void

body2

Returns Body

Parameters

Returns void

breakUnderError

Returns boolean

Default Value

Parameters

Returns void

breakUnderForce

Returns boolean

Default Value

Parameters

Returns void

cbTypes

Returns object

compound

Returns Compound | null

Parameters

Returns void

damping

Returns number

Default Value

Parameters

Returns void

frequency

Returns number

Default Value

Parameters

Returns void

ignore

Returns boolean

Default Value

Parameters

Returns void

isSleeping

Returns boolean

maxError

Returns number

Default Value

Parameters

Returns void

maxForce

Returns number

Default Value

Parameters

Returns void

rate

Returns number

Default Value

Parameters

Returns void

ratio

Returns number

Default Value

Parameters