With the file you provided, I can actually see the bend in the arm when the animation is set downwards.
The issue stems form a combination of weight paint, bad edge-loop and triangulation.
This is the same loop that you see doing this In UE4
Blender:
UE4:
It’s definitely accentuated in UE4. this may be in part because it is triangulated vs the current version which is not triangulated.
https://docs.unrealengine.com/en-US/…hes/index.html
Triangulating in blender and applying the triangulate modifier does lessen the spike:
and
Note that I also messed with the weight paint, but you shouldn’t have to do too much with that. it’s basically coming down to bad geometry.
I would suggest going back to the T pose, taking the edge loops in section and using the LoopTools addon to get the spacing between the edgeloops to be identical before triangulating.
You can see that adjusting the spacing with the Space function on just one edge loop throws things off
Ideally it should get to where things no longer move around - or you can bypass that, triangulate, and adjust the triangle edge…
You also have other issues with your geometry though
Also, just noticed that using the Flatten option from the loop tools seems to do exactly what you need to fix that loop section
It does create other issues (the underarm though is not the issue, it’s because I messed with the weight paint).