如何简单地移动SKNode？

Question

所以我是Swift的初学者，并且一直试图制作一个涉及两个角色的游戏。两个角色的主体由头部和身体SKSpriteNode组成，与常规SKNode绑定在一起。当我触摸屏幕的左侧时，我希望播放器向左移动，依此类推。我不确定我是否只是遗漏了一些东西，但我似乎无法使用applyImpulse方法让角色移动到任何地方。

var playerNode = SKNode()
var playerBody = SKSpriteNode()
var playerHead = SKSpriteNode()

var opponentNode = SKNode()
var opponentBody = SKSpriteNode()
var opponentHead = SKSpriteNode()

var ground = SKSpriteNode()

override public func didMove(to view: SKView)
{
    playerNode = self.childNode(withName: "playerNode")!
    playerBody = playerNode.childNode(withName: "playerBody") as! SKSpriteNode
    playerHead = playerNode.childNode(withName: "playerHead") as! SKSpriteNode

    opponentNode = self.childNode(withName: "opponentNode")!
    opponentBody = opponentNode.childNode(withName: "opponentBody") as! SKSpriteNode
    opponentHead = opponentNode.childNode(withName: "opponentHead") as! SKSpriteNode
}

override public func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?)
{
    for touch in touches
    {
        let location = touch.location(in: self)

        if (location.x < 0)
        {
            playerNode.physicsBody?.applyImpulse(CGVector(dx: -10, dy: 0))
        }
        else if (location.x > 0)
        {
            playerNode.physicsBody?.applyImpulse(CGVector(dx: 10, dy: 0))
        }
    }
}

override public func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?)
{
    playerNode.physicsBody?.velocity = CGVector(dx: 0, dy: 0)
}

任何帮助都将不胜感激。