How to stop rotating sub child in u nity 3d

Question

I have three game objects A, B and C. A is the parent of B and B is the parent of C. A is rigidbody and main moving object. B is non rigid transform object which rotates from 0,0,0 to 0,0,45 constantly. I want that when When B rotates the B's child C also rotate but its local y axis must be 0 (locked). For example each wiper of old school buses have also a sub wiper when main wiper moves, the sub wiper also moves bus its axis remains vertical. Thats what i want. Plz any body help...

Answer 1

The simplest solution is to simply have the C object update its rotation so that transform.up is always the same value.

Vector3 upDir;

void Awake() 
{
    upDir = transform.up;
}

void Update()
{
    transform.up = upDir;
}

If you're interested in keeping its rotation the same as the grandparent, just set its rotation to be equal to that of the grandparent:

transform aTransform;

void Awake()
{
    aTransform = transform.parent.parent;
}

void Update()
{
    transform.rotation = aTransform.rotation;
}