Rotating a child gameobject relative to immediate parent - unity3d

Question

Hi everybody, I'm trying to rotate a child game object relative to another child game object. For example, as shown in this heirarchy below, I'm trying to rotate PA_DroneBladeLeft (and PA_DroneBladeRight) with respect to their immediate parents PA_DroneWingLeft (and PA_DroneWingRight) respectively. I want these blades to spin in place. Instead I'm getting them to spin globally in the y-direction relative to the main parent (Air Drone). I would think that the line in Update method that I commented out should have worked, and it did but it still rotated relative to Air Drone and not in place. The second line, RotateAround method I've tried to create an empty game object called Left Pivot and put it approximately in the center of the left wing and have the left blade rotate around that, but it was no use.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class LeftBladeRotation : MonoBehaviour
{
GameObject leftBlade;
private float speed;
private float angle;
GameObject leftPivot;
// Start is called before the first frame update
void Start()
{
speed = 10f;
leftBlade = transform.Find("PA_DroneBladeLeft").gameObject;
angle = 0f;
leftPivot = GameObject.FindGameObjectWithTag("Air Drone").transform.Find("PA_Drone").transform.Find("PA_DroneWingLeft").transform.Find("Left Pivot").gameObject;
}
// Update is called once per frame
void Update()
{
angle += speed * Time.deltaTime;
Quaternion rotation = Quaternion.Euler(new Vector3(0f, angle, 0f));
//leftBlade.transform.localRotation = rotation;
leftBlade.transform.RotateAround(leftPivot.transform.localPosition, Vector3.up, angle);
}
}

Answer 1

This is your script with some little changes. It actually works when I attached it on the blade gameObject.
using UnityEngine;
public class BladeRotate : MonoBehaviour
{
private float _speed;
private float _angle;
private void Start()
{
_speed = 400f;
_angle = 0f;
}
private void Update()
{
_angle += _speed * Time.deltaTime;
var rotation = Quaternion.Euler(new Vector3(0f, _angle, 0f));
transform.localRotation = rotation;
}
}
The second line does not work because you rotate the blade around global y-axis by Vector3.up
Here is an alternative. Attach the following script on your blades.
using UnityEngine;
public class BladeRotate : MonoBehaviour
{
[SerializeField] private int speed = 400;
private Transform _transform;
private void Start()
{
_transform = transform;
}
private void Update()
{
transform.RotateAround(_transform.position, _transform.up, speed * Time.deltaTime);
}
}