how can i make drag and release (like pinball games) to shoot the ball with charge power in 3d mobile game

Hello, I’m new to use unity 5, and I’m now using c# to build a pinball type mobile game. how can i make drag and release (like pinball games) to shoot the ball with charge power in 3d mobile game?

I find this script and it works with my model, but the y axis is too sensitive. how can i set a max length of the movement?
if (Input.touchCount > 0) {
for (int i = 0; i < Input.touchCount; i++) {
currentTouch = Input.GetTouch (i);
if (Input.GetTouch (i).phase == TouchPhase.Moved) {
ray = Camera.main.ScreenPointToRay (Input.GetTouch (i).position);
if (Physics.Raycast (ray, out rayHitInfo)) {
Vector2 v2 = currentTouch.deltaPosition;
Vector3 v3 = new Vector3 (transform.position.x, v2.y*Time.deltaTime/50 , transform.position.z);
cube.transform.position = v3;
}
}
}
}