anchor.diff:      b2Def.lowerAngle = lowerAngle;
       b2Def.upperAngle = upperAngle;
   
  +    b2Def.enableMotor = _enableMotor;
  +    b2Def.motorSpeed = _motorSpeed;
  +    b2Def.maxMotorTorque = _maxMotorTorque;
  +
       // Create joint
       return physicsNode.b2World.createJoint(b2Def);
     }
  
positive.code:   final double lowerAngle;
    final double upperAngle;
    final bool enableLimit;
  
    box2d.Joint _createB2Joint(PhysicsWorld physicsNode) {
      // Create Joint Definition
  
negative.code:       this.upperAngle: 0.0,
        this.enableLimit: false,
        PhysicsJointBreakCallback breakCallback,
        double breakingForce,
        bool enableMotor: false,
        double motorSpeed: 0.0,
        double maxMotorTorque: 0.0
      }) : super(bodyA, bodyB, breakingForce, breakCallback) {
      _enableMotor = enableMotor;
      _motorSpeed = motorSpeed;
      _maxMotorTorque = maxMotorTorque;
      _completeCreation();
    }
  
  