My ball can jump more than once. How to fix it withing this code?

Unity Engine
1 
using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class PlayerController : MonoBehaviour {

    public float speed;
    public Text countText;
    public Text winText;
    public Transform prefab;

    private Rigidbody rb;
    private int count;

    void Start ()
    {
        rb = GetComponent<Rigidbody>();
        count = 0;
        SetCountText ();
        winText.text = "";
    }
  
    void FixedUpdate ()
    {
        float moveHorizontal = Input.GetAxis ("Horizontal");
        float moveVertical = Input.GetAxis ("Vertical");

        float jumpers = 0;
        if (Input.GetKeyDown (KeyCode.Space))
        {
            jumpers = 15.0f;
        }

        Vector3 movement = new Vector3 (moveHorizontal, jumpers, moveVertical);

        rb.AddForce(movement * speed);

    }

    void OnTriggerEnter(Collider other)
    {
        if(other.gameObject.CompareTag("Pickup"))
        {
            other.gameObject.SetActive (false);
            Instantiate (, transform.position, transform.rotation);
            count = count + 1;
            SetCountText ();
        }
    }

    void SetCountText ()
    {
        countText.text = "Count: " + count.ToString ();
        if (count >= 49)
        {
            winText.text = "You win!";
        }
    }
}

I tried with a private variable isGrounded and used an if statement, yet it still did not work. Can someone give me a hand here, please?
Thanks in advance.

2

you’ll be best of wrapping your code in the code tags (there is a icon on the toolbar for “insert” which allows you to do it or use the [plain]``[/plain] tags

3

Show your script with the isGrounded logic in there. That was the right approach to take, you probably just left something out. You need to be setting your isGrounded flag to true or false depending on whether or not you are touching the ground (a couple different ways to detect this), setting it false otherwise, and only allowing jumps is you are grounded.

4 
using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class PlayerController : MonoBehaviour {

    public float speed;
    public Text countText;
    public Text winText;

    private Rigidbody rb;
    private int count;
    private bool isGrounded = true;

    void Start ()
    {
        rb = GetComponent<Rigidbody>();
        count = 0;
        SetCountText ();
        winText.text = "";
    }
   
    void FixedUpdate ()
    {
        float moveHorizontal = Input.GetAxis ("Horizontal");
        float moveVertical = Input.GetAxis ("Vertical");

        float jumpers = 0;
        if (isGrounded)
        {
            if (Input.GetKeyDown (KeyCode.Space))
            {
                jumpers = 15.0f;
            }
        }

        Vector3 movement = new Vector3 (moveHorizontal, jumpers, moveVertical);

        rb.AddForce(movement * speed);

    }

    void OnTriggerEnter(Collider other)
    {
        if(other.gameObject.CompareTag("Pickup"))
        {
            other.gameObject.SetActive (false);
            count = count + 1;
            SetCountText ();
        }
    }

    void SetCountText ()
    {
        countText.text = "Count: " + count.ToString ();
        if (count >= 49)
        {
            winText.text = "You win!";
        }
    }
}