How to add touch drag controls on Space Shooter?

So i've completed Space Shooter tutorial, also i finished tutorial on how to port it on mobile device, everything works fine except touch controls showed in tutorial doesn't fit me well, it's like it emulates joystick and ship sometimes goes out of control. Can someone please hint me some answers on how can i change player controller script to add drag feature please?

 using UnityEngine;
 using System.Collections;
 
 [System.Serializable]
 public class Done_Boundary 
 {
     public float xMin, xMax, zMin, zMax;
 }
 
 public class Done_PlayerController : MonoBehaviour
 {
     public float speed;
     public float tilt;
     public Done_Boundary boundary;
 
     public GameObject shot;
     public Transform shotSpawn;
     public float fireRate;
     public SimpleTouchPad touchPad;
     public SimpleTouchAreaButton areaButton;
     
      
     private float nextFire;
     private Quaternion calibrationQuaternion;
 
     void Start()
     {
         CalibrateAccelerometer();
     }
 
     void Update ()
     {
         if (areaButton.CanFire () && Time.time > nextFire) 
         {
             nextFire = Time.time + fireRate;
             Instantiate(shot, shotSpawn.position, shotSpawn.rotation);
             GetComponent<AudioSource>().Play ();
         }
     }
 
     //Used to calibrate the Iput.acceleration input
     void CalibrateAccelerometer()
     {
         Vector3 accelerationSnapshot = Input.acceleration;
         Quaternion rotateQuaternion = Quaternion.FromToRotation(new Vector3(0.0f, 0.0f, -1.0f), accelerationSnapshot);
         calibrationQuaternion = Quaternion.Inverse(rotateQuaternion);
     }
 
     //Get the 'calibrated' value from the Input
     Vector3 FixAcceleration(Vector3 acceleration)
     {
         Vector3 fixedAcceleration = calibrationQuaternion * acceleration;
         return fixedAcceleration;
     }
 
     void FixedUpdate ()
     {
         //        float moveHorizontal = Input.GetAxis ("Horizontal");
         //        float moveVertical = Input.GetAxis ("Vertical");
 
         //        Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
         //      Vector3 accelerationRaw = Input.acceleration;
         //      Vector3 acceleration = FixAcceleration (accelerationRaw);
         //      Vector3 movement = new Vector3 (acceleration.x, 0.0f, acceleration.y);
         Vector2 direction = touchPad.GetDirection();
         Vector3 movement = new Vector3(direction.x, 0.0f, direction.y);
         GetComponent<Rigidbody>().velocity = movement * speed;
         
         GetComponent<Rigidbody>().position = new Vector3
         (
             Mathf.Clamp (GetComponent<Rigidbody>().position.x, boundary.xMin, boundary.xMax), 
             0.0f, 
             Mathf.Clamp (GetComponent<Rigidbody>().position.z, boundary.zMin, boundary.zMax)
         );
         
         GetComponent<Rigidbody>().rotation = Quaternion.Euler (0.0f, 0.0f, GetComponent<Rigidbody>().velocity.x * -tilt);
     }
 }