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I'd like to take a ring and animate a increase in diameter without changing the thickness. The issue I'm running into is this: in order to get the thickness to stay the same I have to attach a mesh to a curve, then scale that curve. However, doing so requires me to add more to the mesh's array modifier. I intend to use this object in unreal so I'm looking to rig and animate this ring. Is there a way to get the ring to actually stay a ring whenever I scale it?

The starting size and the size i'd like to scale to:

What happens when I scale the ring:

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    $\begingroup$ Can Unreal deal with curves? That would be unusual in a game engine-- usually, your options are either shapekeys or armatures. Armatures would require spline IK, probably baked to transforms. A single shapekey wouldn't work, but two used in conjunction might. $\endgroup$ – Nathan Mar 30 '20 at 20:12
  • $\begingroup$ @Nathan One shape key would be enough? Only relative translations involved? $\endgroup$ – Robin Betts Mar 30 '20 at 20:57
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    $\begingroup$ @Robin Betts I guess i was overthinking it. I was worried about the thickness during interpolation. One shapekey ought to work. Untested though. $\endgroup$ – Nathan Mar 31 '20 at 5:10
  • $\begingroup$ @Nathan .. that's OK, I tested it before commenting ;) $\endgroup$ – Robin Betts Mar 31 '20 at 7:56
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The Array modifier can automatically adjust to the size.
Just choose Fit Curve and select your Bezier circle.

enter image description here

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If you create a single edge, and give it a Screw modifier through 360, with no height, and an Axis-Orientation object (the Empty, here):

enter image description here

.. then moving the edge along itself towards or away from the axis will have the effect you're looking for. It can be done in Edit or Object mode.

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An easy solution is to make a ring of vertices with no thickness, then add a solidify modifier.

This way, you do not need to increase an array modifier because the vertices remain the same no matter the size. This will allow you to animate without the actual number of vertices changing, which would mess things up. This should work much better in the game engine because it is easy to apply the modifier, and the topology is not changing as the object is animated.

enter image description here

I noticed that this method does not add faces for some reason, but after animating and applying the modifier, it is easy to add them.

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