Armature's arm bones not deforming mesh like I expect

Hi, I’m working on a very low poly, N64 style character. I’m trying to get his arms and legs to deform properly when bending, so I added two edge loops around his elbow to start. However, no matter what I try, I can’t seem to get his upper arm mesh to stay with the upper arm bone in the armature. It always trails behind, but only after I added the two edge loops.

Capture6 Capture7 Capture8

That last picture is the model deforming with just the one edge loop it started with. While not exact, it’s closer to the upper arm bone than the second attempt. It’s causing the arm to deform wildly. My goal is to prevent it from looking like this:

I’m unsure of where to proceed. I’ve tried adding more edge loops, putting more distance between the three edge loops, adjusting the weights on the vertices, and which vertex groups the vertices belong to. Nothing seems to resolve it. I even tried recreating the situation in a new file, but in that version it actually deforms as expected, keeping the bones inside the geometry. Although I’m sure I just have it set up differently there and don’t realize it.

Here’s the blend file I’m working with: weasel.blend (766.2 KB)

Any help for advice is much appreciated. I’ve been at this for a few hours today troubleshooting to no avail.

I looks like the chest bone is influencing the arm mesh, that causes that weird bend. Remove any chest bone influence on the arm Mesh.

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That solved it! Very much appreciated miketche. I didn’t even consider trying to check the other vertex groups that weren’t a part of the arm to see if I put weight there too by mistake. Now the arm is deforming along with the bone as expected.

One last thing if you happen to know, but is there a technique or method I would use to make the deformation a bit smoother when the arm is bent 60+ degrees? It starts to form a hard point and I’m not sure if more edge loops is the right way to go. I adjusted the weight ratio so that the lower arm bone gets 1.0 weight and the upper arm gets 0.2 and that seems to help, but wasn’t sure if there’s more I should do.

Ya, you’ll need to play with maybe a few more loop cuts and then weight painting the areas effectively.

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Thanks, it’s all sorted out now. I didn’t have to add more edge loops and just spread out the two new ones I had so they were a bit further away from the middle/elbow edge loop. Then I tinkered with the weights and viola.

Works in pretty much every extreme position, and actually works somewhat better than the original model I’m mimicking. Again thanks so much for your help, it saved me lots of headache.