Concept art house Framestore worked on designing the Sentinels in X-Men: Days of Future Past — both the 1970s and future versions. And now they've released a bunch of concept art that shows just how weird these mutant-killing robots could have looked.

None of these designs quite looks like the comic-book versions, but some are closer. And you can see them trying to integrate Mystique's "shape-shifting" effect, which is interesting.

Check out some of our favorites below, and more over at the Framestore blog.

[via Screen Crush]