Problem with stretching and squashing parts of the human body

I am trying to create a mannequin model where the abdomen box bends and twists when I move the thorax or pelvis. The stretched side (left from viewer) looks good but the squashed side looks weird.

I want it to be curved like the stretched side but its sharp. What can I do to fix this?

For this it is not only needed to have more subdivision in the geometry, but also in the bones structure. Like so :

1 Like

How do I weight paint this?

I used With Automatic Weights while parenting the object to the armature.

When I do that with my mannequin its all over the place. Everything gets distorted if I move it.

Don’t move the already associated bones just select in edit mode and RMB → supdivide.

If its not too much to ask for, could you do it in my blender file?
mannequinBendingAbdomen.blend (1.8 MB)

You have a weird setup. You have a hip bone connceted to a pelvis bone which goes up to the ripcage ( to big ) and is moving the lower body (usuall upper)… so any subdivision is not going to work as expected… also there are some remnants of a former rig ? The complete ripcage has a spine3 bone but also vertex groups spine2, spine3, spine.001, spine.002, spine.003, spine.004, spine.006 and pelvis.L, pelvis.R.

I guess you should re-search some skinning , armature, rigging tutorials to make youself a bit more familiar with this, because this setup is… just weird.

And this doesnt’t match to your images too…

I followed this guide for the hip: https://www.reddit.com/r/blender/comments/1b4nypo/how_do_you_bend_the_hips_without_moving_the_whole/ so I could move the hip and legs without moving the whole body.

I just discovered the remnants of a former rig but I can’t delete them. Why?

I already watched a bunch of tutorials and followed along…

I messed around a bit more in the file so it looks a bit different. It seems that I sent you the wrong file, sorry.

mannequinBendingabdomen.blend (1.8 MB)

Ahh… now i see… well there are many different kinds of posible rigs and i was your pelvis bone expection to be something like root bone or something because pevis is more the bones and hip more the body part but both are associated to the same area… (at least for me :wink: ) . Also for forward or/and reverse kinematics. So the difficulty is to “see” for what it is meant for and the remnants i spoke of are the different (unsused) vertex groups… which should be (and are) deletable.

Another very very big difficulty is the workflow in rigging… not only someone has to know a lot about it to build the rig in this way so that does any “special” feature someoen wants but also any alterations is causing an avalanche of finetuning… for example re-weight-painting… so some automatic weighting is nice to have when doing the inital skining… but some alteration need someone to know what to do and be very very concentrated about it.

So my suggestion about subdividing the bones may work nicely without explicite weight painting when doing so from the the start but you have already some weight an this and indeed i also struggle wehnit comes to changes in the armature :sweat_smile:

Another thing i discovered: you have some weight for the pelvis bone butn ot for the hip bone… i’m not sure if this is meant this way…

So you may have to fiddle a bit more with this.