How to use array to create circular array without spiralling

Question

I am trying to build a Colosseum. I have one arch and want to use an array for the rest. I've added an empty at the center and added the array. Done the object offset, but no matter what I do I keep getting a spiral effect instead of all of the duplicates sitting on the same level.

Answer 1

Create an arch or an object to be repeated.

Create a closed curve (circle) This curve will control the perimeter.

On you object add an Array Modifier with the Fit Curve option and your cicle selected. Then add a Curve Modifier using the circle again to control it.

Then add another array!

If you add an empty in the middle of the circle and use it as an offset object you can create variations in size and rotation by changing the placement, size and rotation of the empty.

Answer 2

You are on the right track using a Object Offset for the array modifier.

First make sure that your arch has a scale of 1, You can make the object's scale 1 by applying the scale with CtrlA > Scale.

Second make sure that the object your are using for the Object Offset in the array (I will call it "Array Empty") is at the same location as the object the array modifier is on, your arch. Meaning your arch's origin and the Array Empty should be at the same spot.
I like the use the Properties panel N to quickly view the location and check the scale. Later on this panel will be useful.

You can move the Array Empty to the same spot as the arch by selecting your arch and pressing ShiftS > Cursor To Selected. Now select the Array Empty and pressing ShiftS > Selected To Cursor. They are now both in the same spot. (Verified by looking at the Location for each in the Properties panel.)

Now rotate the empty to create the circle of arches. Knowing how much to rotate the empty is easy, here is the formula 360/C where C is the count of the array.
No need to try to figure out what the division is, just type it right in the the rotation field on the Properties panel.
Look at my answer here if you want rotate the Array Empty by pressing R then typing in the equation.

Last thing to do is line up the Array Empty, so that your arches make a nice circle.
What I do is add an edge perpendicular to the arch extending to the center. Then just move the Array Empty until all the lines meet up at the center, like in the image below. Note how the Array Empty is rotated, but no longer in the same place as the arch.

Quickly recap:

1. Scale set to 1 for both arch and Array Empty.
2. Z location the same for arch and Array Empty.
3. Rotate Array Empty along the Z 360 / Number of counts in array.
4. Position Array Empty to make a perfect circle.

Answer 3

I had this same problem. What worked for me is I applied scale for both an empty object and the object that I wanted to rotate. This can be done selecting an object and then pressing Ctrl+A and then choosing scale in menu that will appear.