Child gameObject won't stick to Parent upon rotation

[CrucibleLab]

Folks, I created a rudimentary cannon object with a simple hierarchy as follows:

Using the arrow keys, I can rotate the Gun Base left and right around the Y-axis and rotate the Gun up and down around the X-axis. All the rotation seem to work correctly, but I noticed that my projectiles shoot from inaccurate FiringPoint when the Gun is tilted at a steep angle.

In its initial state, the FiringPoint empty gameObject is at the correct position (This is in the X-axis perspective; the Gun is at the top and the Gun Base is at the bottom). As you can see, the FiringPoint gradually starts lagging behind as the Gun starts tilting upward.

I fiddled with the axis for quite a bit, but can’t seem to figure out how to correct this behavior. I have been away from Unity for a long time, so please don’t be too harsh with your comments.

EDIT 1:

With further troubleshooting, I found out that the ‘Global’ and ‘Local’ toggle button found just below the Unity main menu results in different behaviors for the FiringPoint.

When Global is selected, its Z-axis stays aligned with the initial direction (as shown in the screen captures), but when Local is selected, the Z-axis points to the same direction to which the Gun is pointing to. While the latter result seems to be more desirable, the center of the ‘FiringPoint’ is still off from the intended location, which is at the tip of the Gun.

EDIT 2:

To further elaborate the object setup, I have two separate scripts that are being used in this scene. First script for rotation around the Y-axis is attached to the Gun Base, and the other script for rotation around the X-axis is attached to the Gun Mount Point. There’s probably a better way to achieve the same result and if there is, I’d like to know!

One other caveat I noticed is that the Gun object itself gets heavily skewed when I test the up & down, left & right rotation. It doesn’t happen all the time, but it usually happens when I tilt up the Gun to almost 90 degrees, and then rotate it either to the right or left. And the object remains skewed until I reset the Play mode. Very odd…

[Glurth]

Unchild the mount point from the base.

I don’t see a “rotate base point” object in the heirarchy, but both the base, and the mount point would be children of this, “empty” object.

The reason for this: each parent transform is applied in order, from the “childmost” child on up. So the way you had it, the scale part of the “BASE” object’s transform was being applied to your “mount-point’s” rotation transform. (Note, it was also effecting the size/shape of your gun-barrel).

Order is particularly important when applying transforms. Applying an uneven scaling transform after a rotation transform is generally avoided, as it leads to odd/non-intuitive results. (well, some people can intuit it, not me) An example of such results can be seen in the comments section, where the gun barrel becomes “skewed”.

There is no way, that I know of, in unity to apply a transform to “only this object”, and not have it apply to it’s children. To keep the system consistent, to do something like this would require a SECOND set of transform data (need one for each: “this object only”, “children affecting”), which is effectively, what the empty object we created provide.