Swift Physicsbody固定并加入不按预期工作

Question

我正在尝试用SKSpriteNode创建一辆简单的汽车。物理学和一切都很好，除了一件小事：当我的汽车从更远的地方降落在地面上时，汽车车身被推下然后回到原位。

见图片：

我想得到左图，但我得到右图。

当它降落在地面上时，我不希望车身进入车轮，我希望它相对于车轮处于固定的位置，反之亦然。

所以我就是这样做的：

这是在汽车类：

carWheelJoint1 = SKPhysicsJointPin.jointWithBodyA(self.physicsBody!, bodyB: leftWheel.physicsBody!, anchor: leftWheel.position)
carWheelJoint2 = SKPhysicsJointPin.jointWithBodyA(self.physicsBody!, bodyB: rightWheel.physicsBody!, anchor: rightWheel.position)     

这是在GameScene课程中：

//Add vehicle
vehicle = DevCar(color: UIColor.blueColor(), size: CGSize(width: 250, height: 50), cameraThreshold: cameraThreshold)
vehicle.position = (CGPoint(x: 0, y: cameraThreshold))
addChild(vehicle)

self.physicsWorld.addJoint(vehicle.carWheelJoint1)
self.physicsWorld.addJoint(vehicle.carWheelJoint2)

我尝试使用SKPhysicsJointFixed，但这也不起作用。

有什么想法吗？

编辑：这就是物理体的定义方式：

这是汽车类中的车身 汽车等级是SKSpriteNode，是汽车本身，车轮是它的孩子。

    let baseBody = SKPhysicsBody(rectangleOfSize: size)
    baseBody.mass = CGFloat(1)
    baseBody.dynamic = true
    baseBody.affectedByGravity = true
    baseBody.friction = 0.2
    baseBody.allowsRotation = false
    baseBody.density = CGFloat(10)

    self.physicsBody = baseBody

这是同一类轮子：

    leftWheel = SKShapeNode(circleOfRadius: wheelSize)
    leftWheel.position = CGPoint(x: size.width / -2 + wheelSize, y: size.height / -2 - wheelSize)

    rightWheel = SKShapeNode(circleOfRadius: wheelSize)
    rightWheel.position = CGPoint(x: size.width / 2 - wheelSize, y: size.height / -2 - wheelSize)

    leftWheel.physicsBody = SKPhysicsBody(circleOfRadius: wheelSize)
    leftWheel.physicsBody!.mass = CGFloat(0.2)
    leftWheel.physicsBody!.dynamic = true
    leftWheel.physicsBody!.affectedByGravity = true
    leftWheel.physicsBody!.friction = 0.3

    rightWheel.physicsBody = SKPhysicsBody(circleOfRadius: wheelSize)
    rightWheel.physicsBody!.mass = CGFloat(0.2)
    rightWheel.physicsBody!.dynamic = true
    rightWheel.physicsBody!.affectedByGravity = true
    rightWheel.physicsBody!.friction = 0.3

    addChild(leftWheel)
    addChild(rightWheel)

EDIT2：已添加视频 https://www.youtube.com/watch?v=TTwa-t4u4pI