Rotator.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Rotator : MonoBehaviour {

	public float rotateMin, rotateMax;

	private float rotateSpeed;

	// Use this for initialization
	void Start () {

		rotateSpeed = Random.Range(rotateMin, rotateMax);

	}
	
	// Update is called once per frame
	void Update () {

		transform.Rotate(new Vector3(0, 0, rotateSpeed) * Time.deltaTime);

	}
}