Sure;
Apparently, many riggers who have been on the field for longer amount of years, use the method [Fan Bones] to some extend, or have at least heard about the method. I’m still exploring the possibilities, and I’m astonished at, and fail to understand, how there is so little information and content available online, for a Corrective Armature Deform method that is so effective at, specifically, countering, in a very analytic way, the generated algorithms’ Artifacts. This is the kind of technique I’ve been looking for, for the past 2 years or so, in which I’ve been engaged with learning Organic Rigging in Blender.
I believe the guy that invented the Fan Bones method, is Shaun Freeman; the information I have gathered, suggest he is an Australian rigger, animator and professor, and that in 2005 there was an event publication (which I cannot find reference online), 3D World, page 72-75 on a Q&A section, “How do I make the mesh over my character’s joints deform correctly during movement?”; it was based on a CG software called Animation:Master (in which I guess “Smartskinning” is the analogue for Weight Paint [PS: correction: wait, maybe it was Shape Keys] in Blender).
Basically, it’s analytic, Corrective Armature Deform method in which a DEF Limb Bone, such as a Thigh Bone, which usually suffers big Rotations on all directions, has its Weight Paint, on the Joint Region that suffers the most, shared (Blended Weights), with very specific Helper Bones in very specific ways. I’m not sure, but after further investigation, I think there is a simple, ‘reduced’ Fan Bone thecnique, and there is an advanced, ‘full’ Fan Bones technique.
The simple technique, is limited to a single DEF Fan Bone, that starts out exactly the same on Rest Position (Full Alignment) as the DEF Thigh Bone, and is meant to follow all of its Rotations, except that it must then De-Rotates automatically, slightly (5º-30º). Such DEF Fan Bone would have Blended Weights with the DEF Thigh Bone, but around the Joint Region where the Artifact appears strong (near the Hips); the more the Ratios favor the DEF Fan Bone in relation to the DEF Thigh Bone, the less De-Rotation it requires. There might be some shared Weights with the Pelvis Region, but for simplification of the explanation, the main point is the upper Thigh and the beggining of the Hips-Thigh Joint and perhaps a bit beyond, depends.
The advanced technique, I believe should include the original Fan Bone mentioned previously, but it would become a MCH Bone instead of a DEF Bone, and there will be an entire set of Fan Bones, on a circular pattern near and around the Joint of the Limb, that will: 1) follow exactly the De-Rotation of the MCH Fan Bone; 2) perhaps may have their own, secondary motion in an Automated manner, to solve problems and shapes locally, but at their Transforms are already built up on top of the original MCH Fan Bone; it’s just that now these are De-Rotating PLUS extra bonuses if the rigger wants. I’m not 100% sure this is how it works, but before the last link, I developed more information, and on that link, I’m trying to build my own alternative version, based on such findings.
In the link below, there is a video that is didactic, for the first approach on the Fan Bone method:
Link below is an older thread in here, but there are some interesting examples and discussion:
Link below is a less old thread, but not all links are working… might be interesting discussion, but because I was part in it and barely starting to grasp the concept of Fan Bones, might not be very clarifying:
In this timestamp below, there is a small example of the simplest Fan Bone technique:
In this timestamp below, I was on a Live today, I was approaching the problematic of the more advanced Fan Bones technique. One thing is to have a unique DEF Fan Bone for slight De-Rotation of the Joint Mesh Region of a Limb; in this sense, we can visualize the setup as an oriental fan. Another thing is to have DEF Fan Bones working in synch (maybe with their own secondary subtle motions on top of the main De-Rotation motion) for the same Joint Mesh Region of a Limb; in this sense, we can visualize the setup as a household appliance fan, because it may look like an 8-Bones star made out of Bones pointing outwards, probably with the main Fan Bone in the center for main De-Rotation (on my case, in that Live, I’m attempting to mix two concepts: the Fan Bones method and the ‘Profile Bendy Bone Splines’, which relates the concept of “Profile Curves” and “Curve Net” (related to ‘Cage Rig’) that I’ve seen on a supposed Pixar Youtube video. Note: the Profile stuff don’t need to become a Cage which covers all the Mesh Body, they can be used locally whenever it might be advantageous; but, the problem with Profile stuff ONLY, is that they aren’t meant to solve Artifacts on their own! but, more likely, just to give good anatomical shapes because of the easiness of Smoothing out the Mesh, since it can be easily control with Splines.
