HTML5 prototype: player movement like in TwinSpin game with Phaser

TwinSpin was a fun Flash game I am not even able to find anymore. If you know a working link, please tell me. All I was able to find at the moment is an iOS version.

Basically you have two spinning orbs. Each orb spins around the other orb, one clockwise and one counter-clockwise. Tapping or clicking the screen, the spinning orb stops and the other orb starts spinning. Have a look:

Click or tap to stop one orb and move another. It would have been very easy to handle everything with a single sprite with an anchor point in the centre of the fixed orb making it rotate clockwise or counter clockwise but there’s a detail: orbs move along a circular path but do not rotate themselves. We can solve it with three sprites: one for each orb and one for the arm. We’ll move orbs using trigonometry, and here is the very basic source code:

var game;

var ballDistance = 160;
var rotationSpeed = 4;

window.onload = function() {	
	game = new Phaser.Game(640, 960, Phaser.AUTO, "");
     game.state.add("PlayGame", playGame);
     game.state.start("PlayGame");
}

var playGame = function(game){};

playGame.prototype = {
     preload: function(){
          game.load.image("firstball", "firstball.png");
          game.load.image("secondball", "secondball.png");
          game.load.image("arm", "arm.png");
          game.scale.pageAlignHorizontally = true;
          game.scale.pageAlignVertically = true;
          game.scale.scaleMode = Phaser.ScaleManager.SHOW_ALL;
     },
     create: function(){
          this.arm = game.add.sprite(game.width / 2, game.height / 2, "arm");
          this.arm.anchor.set(0, 0.5);
          this.balls = [
               game.add.sprite(game.width / 2, game.height / 2, "firstball"),
               game.add.sprite(game.width / 2, game.height / 2, "secondball")                   
          ]
          this.balls[0].anchor.set(0.5);
          this.balls[1].anchor.set(0.5);
          this.rotationAngle = 0;
          this.rotatingBall = 1;
          game.input.onDown.add(this.changeBall, this);
     },
     update: function(){
          this.rotationAngle = (this.rotationAngle + rotationSpeed * (this.rotatingBall * 2 - 1)) % 360;
          this.arm.angle = this.rotationAngle + 90;
          this.balls[this.rotatingBall].x = this.balls[1 - this.rotatingBall].x - ballDistance * Math.sin(Phaser.Math.degToRad(this.rotationAngle));
          this.balls[this.rotatingBall].y = this.balls[1 - this.rotatingBall].y + ballDistance * Math.cos(Phaser.Math.degToRad(this.rotationAngle));                    
     },
     changeBall:function(){
          this.arm.position = this.balls[this.rotatingBall].position
          this.rotatingBall = 1 - this.rotatingBall;
          this.rotationAngle = this.balls[1 - this.rotatingBall].position.angle(this.balls[this.rotatingBall].position, true) - 90;
     }
}

I don’t think it needs comments but anyway you are free to ask questions. Download the source code.