I created a pants model, and bones for it in a blender. Bones work in blender, but when I import it to Unity, they are not doing anything.
I used automatic weights when I was rigging.
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This is a very common problem that happens when you export from blender and import to unity. The solution is simple. Open the .blend file and clear the scale by pressing Alt+S. This does most of the stuff but you could face some minor issues. So I recommend also clearing the location and rotation by pressing Alt+G (clear location) and Alt+R (clear rotation), after doing this, export as .fbx and import it in unity. I hope it helps.
P.S If you want a step-by-step video tutorial, Below is the link: https://www.youtube.com/watch?v=ysl0qYq5p9w
P.S.S This link is for versions 2.8 and above but should mostly work for versions 2.7 and above too. I am also providing the link to a QnA similar to your question if you prefer stuff in written format: Exporting a rigged object to Unity (as FBX) produces massively distorted mesh, affecting normals