a script that can cause an object to spin in place?

i have created a “ceiling fan” and it have a capsule as the “motor” of the fan and 5 “blades”. the 5 blades are children of the “motor” and i would appreciate if somebody could create a scrip that could make these pieces spin all to the same direction either left or right. please and thank you.

using UnityEngine;
using System.Collections;

public class ObjectRotater : MonoBehaviour
    public float rotationSpeed;

    void Update()
        transform.RotateAroundLocal(Vector3.up, Time.deltaTime * rotationSpeed);

use Vector3.right or Vector3.forward instead of Vector3.up if you need other axis to rotate around

negative speed will make it rotating to another direction

Works but the object does not rotate around it’s center,how can I change the center?