Parenting a child to move on only one Axis !

Hello hello

I am parenting a child to move on only one of it’s axis while the parent moves on all three…

I have an unwieldy paddle in my game, when I touch the child object and pull a trigger, I only want the child to move only up and down on it’s own Y axis. While my parent paddle is moving loosely in all directions, it only effects the child’s Y

   void OnTriggerStay (Collider col)

// Both the child and Parent have colliders 
// When I contact  but the object together and press button :

        if (device.GetTouch(SteamVR_Controller.ButtonMask.Trigger))
            col.attachedRigidbody.isKinematic = true;
//  I need something like col.gameObject.transform.position.y = parent.gameObject.transform.position.y;
// or
//  col.gameObject.transform.SetParent(gameObject.transform.y );

        if (device.GetTouchUp(SteamVR_Controller.ButtonMask.Trigger))
            col.attachedRigidbody.isKinematic = false;

Any ideas?

Where you have your comments in Line 10, replace it with this kind of idea:

Vector3 limitedPaddle = col.gameObject.transform.position; //get the current position of your object you want to move up and down, im assuming thats the "col" object.

//limitedPaddle.y = //howeverYouWantToManipulateTheYAxis;
//Only y will be affected this way.

col.gameObject.transform.position = limitedPaddle; //Now you are applying the full Vector3/Position to this object, but since you never changed X and Z, they stay the same, and only Y was changed, therefore, only Y updates on the object when you apply/set the objects position to 'LimitedPaddle'.

Do the objects need to be parented? If not:

public class ObjectTracker : MonoBehaviour 
    GameObject target = null;

    bool triggerDown, triggerStay, triggerUp;
	// Update is called once per frame
	void Update () 
        //Checks if the trigger is down and the target is currently within range
        //Replace with your own controller code
	    if(triggerStay && target != null) 
            //Changes only the y position of the transform to match the target
            //Possibly replace this with a Mathf.Lerp for a better effect
            transform.position.y = target.transform.position.y;
    //On Collision Enter assigns the target once it is in range
    //Add any other platform initialization code here
    void OnCollisionEnter(collision col) {
        target = col.gameobject;

    //On Collision Exit removes the target when out of range
    //Add any other platform deactivation code here
    void OnCollisionExit(collision col) {
        if (target == col.gameobject)
            target = null;

If you need to move the object with physics replace transform.position.y = target.transform.position.y; with rigidbody.MovePosition() instead.