Rotate disk from above on touch to choose ball direction.

Hi,

I am trying to allow the user to set the direction of a ball before then choosing power and hitting GO. To do this i have a disk (which will later be completely transparent and just have an arrow on the edge as a transparent gif) sitting at the same X Y Z position as the ball; the ball is at the center of the disk.

I want the user to be able to rotate the disk to choose the direction the ball will follow, using a finger (IOS game). I would then send the rotation co-ordinates of the disk to the ball and add force in that direction when hitting the ball.

Thing is, I can't nail down how to rotate the disk on touch. I can rotate it in the wrong direction on touch - or I can rotate it correctly but then after the finge goes a certain distance it starts to spin the other way.

What I want is to be able to spin the disk like a DJ on a turntable; you can move your finger in a circular motion and the disk will spin with you.

This is the code I'm using so far:

 public class CR_Rotate : MonoBehaviour {
 
  [SerializeField]
     float     _speed = 1f;
     bool _canRotate = false;
     Transform _cachedTransform;
     public bool CanRotate
     {
         get { return _canRotate; } 
         private set { _canRotate = value; } 
     }
 
     
     void Start () {
 
         //Make reference to transform
         _cachedTransform = transform;
 
     
 
     // Update is called once per frame
     void Update () {
 
         if(Input.touchCount > 0)
         {
             Touch touch = Input.GetTouch(0);
  
             //Switch through touch events
             switch(Input.GetTouch(0).phase)
 
             {
                 case TouchPhase.Began:    
                     if(VerifyTouch(touch))
                         CanRotate = true;
                 break;
 
                 case TouchPhase.Moved:    
                     if(CanRotate)
                         RotateObject(touch);
                 break;
                 case TouchPhase.Ended:    
                     CanRotate = false;
                 break;
 
             }
  
         }
 
     }
     
     /// 
     /// Verifies the touch.
     /// 
     /// 
     /// The touch.
     /// 
     /// 
     /// If set to true touch.
     /// 
     bool VerifyTouch(Touch touch)
     {
         Ray ray = Camera.main.ScreenPointToRay(touch.position);
             RaycastHit hit ;
         
         //Check if there is a collider attached already, otherwise add one on the fly
         if(collider == null)
             gameObject.AddComponent(typeof(BoxCollider));
         
                if (Physics.Raycast (ray, out hit)) 
         {
             if(hit.collider.gameObject == this.gameObject)
                 return true;
         }
         return false;
     }
     
 
     
     /// 
     /// Rotates the object.
     /// 
     /// 
     /// Touch.
     /// 
     void RotateObject(Touch touch)
     {
         _cachedTransform.Rotate(new Vector3(0, -touch.deltaPosition.x,0)*_speed, Space.World);
     }    
 
 }

Any help is greatly appreciated.