how to make a gameObject rotate around another gameObject in Unity in the rotating plane

Question

I've two gameObjects, sphereOne and sphereTwo as the children of an empty gameObject both.

I've this C# code attached to a sphereTwo

private void Update() =>
    transform.RotateAround(sphereOne.transform.position, 
        new Vector3(0, 1, 0), 100 * Time.deltaTime);

This lets sphereTwo rotate around sphereOne.

When I rotate the parent gameObject both, it rotates only on that specific plane.

How do I dynamically update the transform position of the rotating sphere so that it lies on the same plane as the parent Object's rotation?

Answer 1

The second parameter in Transform.RotateAround() is the axis which determines the orientation of the plane on which sphereTwo rotates around sphereOne. Right now, you have this set to a static value of new Vector3(0, 1, 0), basically the world's up vector.

To have the axis instead be based on the orientation of sphereOne, use its Transform.up vector instead - this will change based on the world-space rotation of sphereOne's transform:

private void Update() 
{
    transform.RotateAround(sphereOne.transform.position, sphereOne.transform.up, 100*Time.deltaTime);
}

(You could probably alternatively use both.transform.up, depending on the situation.)

Hope this helps! Let me know if you have any questions.