When modeling and rigging for the T-pose, what orientation should the thumb joints be?
"CAT rig" as in the animal cat? So you are going from a quadruped to a biped?The differences between a biped and a quadruped are quite complex. You will most likely have to build some sort of special setup to accomodate your animation. One thing I would do is check how the animation moves it, and then reproduce that on your thumb so that it works better. You might have to do some trial and error.In a real biped T-pose, the thumb is flat. That is to simplify the job of the character rigger so he/she can create the thumb joint flat. You can however model a T-pose with the thumb down and that will be no problem at all, as long as you are always doing the same thing! :-)A modeler should be modeling in A-pose or semi relaxed pose simply because all articulations should be half-way bent. Doing so minimizes the extreme deformations of a certain body area. For instant, if the arm is half bent, then you have 50% rotation to fold it and 50% rotation to extend it. That is best so you don't have 100% rotation in just one direction. However, in a production studio, you are usually not allowed to model in half bent pose because that is so much harder to rig! So sad...(You could model the half-bent pose and use it as a deformation blendshape.)
How do I get started with Blender 3D?
If you are experienced with 3D modelling in other programs:Start with recreating a project you did in your previous program… Figure out how the modelling workflow works (usually not much difference). You may find the UV unwrapping or texture painting tools a lot simpler and faster in Blender. I did, when I switched over from 3ds Max.If you are new to 3D modelling:Start with very basic stuff. I can not stress this enough. Beginners have the tendency to see a Pixar movie and then decide they’re going to create something that epic right away.Don't try to create anything ambitious right away; you'll fail…And then be demotivated to continue.For example, don't start with modelling a character. Start with making something more geometric, like a vehicle or object.This will build confidence and help you get accustomed to handling the complex UI that 3D programs have.Once you've created a bunch of simple shapes, use these assets to create interesting compositions/scenes. Use these compositions to learn how to do lighting and rendering.Now that you've accomplished something that looks good, go to the next step/milestone. Learn to texture your models…Now learn advanced modelling… And so on.Visit Blender Cookie and Blender Guru for some really detailed and helpful tutorials.
When modeling a character for a game, is it common practice to model no more than the teeth or to also have a basic interior as well?
This is a classic problem, and as Glyn Williams answer notes it's not one the games do very well because it showcases several things that conventional skinning and rigging don't capture: the the sliding of skin over teeth, the combination of muscle bulging and skin stretching involved in making mouth shapes, and the different thicknesses and densities of different parts of the face. In high end productions (mostly films, but also 'money-is-no-object' games like Ryse: Son of Rome the developers use a much more elaborate combination of muscle systems, hand-sculpted morph targets, and special skin solvers that handle all of these thing more correctly. Even in high end productions it's pretty rare to get a detailed interior of the mouth (if you notice even in that Ryse cinematics reel there are few opportunities to really see into the character's mouth) but it's done sometimes for unusual images like big marketing screenshots or box covers.If you're curious how it's done Jason Osipa's book Stop Staring is an excellent introduction to facial rigging and animation.For the modeling side proper you could check out The Face: Modeling and Texturing from Ballistic Publishing, who do a lot of great titles on high-end 3d modelling technique.
When I rig my 3D characters, as I turn the head controls, the chest pulls out also. How do I fix this?
That is usually a bone influence problem.IN Lightwave when that happens there are two ways to correct it, and it probably follows in other programs as well.You can apply a weight shade - or map to define the influence of the bone.or You can add a second bone to hold the area thats being influenced by the head bone. The second bone provides local influence to the chest area. You can bump up it's influence as well until the chest doesn't move anymore, conversly you can decrease the head bone influence as well.at least in lightwave you can.That is a common bone influence problem.
Are there quick and effective techniques for rigging in Maya, 3DS Max, etc.?
Rigging = Creating the skeleton structure. Yes there are ready made structures. CAT is most popular at least in 3Ds, don’t know about Maya.Weighting = Attaching model to the skeleton structure. Run autoweight tool and then create few extereme poses on the animation timeline. Fix the errors left over from autoweight manually.
Is it feasible to have a somewhat complex rig in 3ds Max and have this rig adjusted to other model with somewhat different proportions? How to do that?
It's actually quite common for larger-ish studios to have a single universal rig that is built to make the most out of their pipeline. It's also extremely common for game studios or any other studio that uses motion tracking.However, this is mostly common when dealing with humanoid rigs (though there are a few creature rigs as well).It essentially works by having 2 rigs:one rig for repositioning and adjusting the proportions of the model, some even shape the model itselfa 2nd rig for animation that is actually linked to the first rigI can't think of any free to use examples for Max, but check out Anim School's Malcom or the Animation Mentor's BishopBut just like any other pipe-lining process, you need to define what you are trying to achieve before actually building it. Thinking of various scenarios that your solution will have to work in, then RnD-ing for those scenarios first, otherwise you can end up spending quite a few months on this rig.
Why is weight painting so difficult?
Weight painting is not difficult—not at all. But the concepts surrounding weight painting can be very tricky to wrap your head around. Be patient, once you get it it will come naturally.Skin weights are a way of telling a mesh how you want it to deform when an underlying skeleton (or any series of influence objects) moves. Weights are very simply a zero to one value that tells the skin to follow a given influence by a certain percentage. For each weighted influence, that vertex will match the influence’s movement, only weighted by it’s percentage. So for a vertex with two influences, influnceA weighted at 0.8 (80%) and influenceB weighted at 0.2 (20%), the final movement of the vertex will be 80% of influenceA’s movement from the default, and 20% of influenceB.Where things get tricky is in characters, where you can easily have 100+ influences driving your mesh. The best advice here is to start small. Start by weighting a cylinder with two bones. Practice blending the weights between those bones. Then work your way up from there. For games, it’s not uncommon to have a maximum count of influences at four per vertex, which is fairly easy to blend between. For feature animation or visual effects, it could be many more, but the basic principles are the same.I think where most beginners get caught up is in using automatic weighting systems in the software they choose. These will try (and usually fail) to find a pleasing weight for all of the influences. Once this is in place, it can be very tricky to adjust weights well.An easier approach (if more work-intensive up front) is to weight each bone with a weight of 1.0. This produces what is known as ‘rigid’ skinning, but from this, you can begin adding weights for other influences selectively. After 15+ years of painting skin weights, this is still my preferred workflow, because it’s simple and direct, without trying to figure out where a given influence is coming from.