Skinning the model - Part 2



      Having finished skinning the bottom part of the model, I have moved up towards the top side, starting with the lower spine bone (or the lower back). Looking back on it, the lowest back area must’ve been the hardest to deal with out of all three back sections, as that’s where the pelvis vertices need to be blended in with the spine vertices. That means that the character’s back needs to bend in a natural way, slowly crossing from the pelvis section to the back section. If the vertices are not carefully blended and the jump is too abrupt between the two cross sections, then the character’s back will ‘break’ instead of bending as one would normally expect. This I found out by myself within minutes, having initially set the absolute effect value of the lower back section to 1.0 (or 100%), making the model look as if he’d snapped his spine each time I would try to bend him into a position. After multiple attempts I managed to get the hang of it and made a decently smooth transition between the two parts. The mesh would now deform in a rather natural looking way when bent, albeit not perfect:



       Moving on to the other two back sections, skinning went considerably faster as the transition between the different back (spine) sections was easier to set up. That is due to the fact that the highest bending angle is between the pelvis and the first section, with the middle and top sections of the back barely ever bending. I have thus continued up towards the neck and the head of the character, where I encountered no problems.

      The shoulders and the clavicles of the model on the other hand, proved to be the absolute most difficult parts I had to skin, having spent well over 10 hours alone on the two shoulders and the two clavicles. Initially, this is how the left shoulder and clavicle were reacting upon bending or moving the arm around:



       It can clearly be discerned from the picture above that the mesh deformation was far from anything anatomically correct and even further away from looking both real and natural. After a few unsuccessful attempts at weighting the clavicle and shoulder vertices, I have decided to watch several videos of athletes performing various tasks, getting a closer look at their arms movement. I have also consulted various forums, trying to get some insight on how I should proceed. Now, there are two things I have found out that proved extremely helpful:


  • First and foremost, the shoulder joint itself can not rotate. It is the upper arm bone that rotates, and not the shoulder. That explains why most of the times I was getting weird, noodle-like deformations. Because I was rotating the shoulder joint, when instead I should have made use of the shoulder roll bones I had set up in place. This I found out from a forum post where the following GIF had been posted:
(Posted by Jaroslav Jerryno Novotny - model by Angela Guenette, rig by Nathan Vegdahl; 2015)


  • Secondly, the arm can only go as high horizontally, with the clavicle raising the shoulder and implicitly the arm from that point on. That meant that by raising the arm the shoulder should deform correctly only up to a certain point, then the clavicle takes over, as seen in the next GIF:
(Posted by Jaroslav Jerryno Novotny - model by Angela Guenette, rig by Nathan Vegdahl; 2015)

       The research helped me greatly in setting up both the clavicles and the shoulders skin deformation. The result was the following:



        I have then moved on to the lower arms and the elbows, and finished off with the hands. Both tasks were significantly easier to complete than the shoulders and the clavicles, with the elbows only bending straight into one possible direction. However, I have not yet skinned the fingers. The hands and the wrists were a matter of correctly selecting the affected vertices, applying an absolute effect and blending them so that the transition between the lower arms and the wrists was smooth:






References:

Novotny, J. (2015). Shoulder deformations. [online] Blender Stack Exchange. Available at: https://blender.stackexchange.com/questions/41539/shoulder-deformations/41550#41550 [Accessed 22 Jan. 2019].
Autodesk 3ds Max Learning Channel. (2012). Skinning a Character in 3ds Max - Part 7 - Shoulders. [online] Available at: https://www.youtube.com/watch?v=gd5Waw-PB9I&list=PLnKw1txyYzRlxh1-BT4CifPXC5TBg2vUd&index=18 [Accessed 21 Jan. 2019].
Autodesk 3ds Max Learning Channel. (2012). Skinning a Character in 3ds Max - Part 9 - Hands. [online] Available at: https://www.youtube.com/watch?v=jMJwGpHtBlQ&index=20&list=PLnKw1txyYzRlxh1-BT4CifPXC5TBg2vUd [Accessed 24 Jan. 2019].
     

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