Hey Rich,
And there we go to the roots of the problem. ;o)
The typical animation of a character is done normally with a good rig. It has handles which makes the complete figure easily to handle. So the artist can focus on the expression, without being heavily limited. It is not recommended to animate, lets say, from the spine over the arm to the hand to the finger—when you want to have a figure grab a coffee and drinks the coffee. The hand is mostly the only part of the arm that becomes keyframes—the handle becomes key-frame to say it clearly. The arm follows based on the Inverse Kinematic (IK). Sometimes the “spine to hand animation” might be more appropriate but the IK is certainly more common for this part of the animation. In short, complex animation is not based on many key-frames, it is based on an clever rig.
Anyway, forgot about Time-track, it has a horrible management, and after a month you have no idea where you have dragged this into. Sorry about my complain, but this tool feels nice for one or two things to connect, but I personally can’t really suggest that for a complex character. ...and certainly there might be cases where someone used it successfully. ;o)
If you look for something more advanced and easily to manage, use e.g., the Animation Clips. You create animations and edit these like a movie and little extraaniamtion can be added on top of that. Yes, it is not a five minute learning curve. But character animation is always seen as the major animation skill and certainly a qualified job in its own rights.
As a side note: For very detailed animation and body-expressions, I guess the best way is since long a motion capture studio visit instead. Standard captures are sometimes available as set. But I haven’t investigated about this in a while.
Back to your question, some people like to define specific gestures, in the area of a hand or a face with the PoseMorp. Here comes as well the “Driver” tag into play. Check it out!
My best advice is certainly (and sorry if I suggest something that you might judge as a lower skill-level) check out the character set ups in the Content Browser. It is a nice Library of options.
Again, character animation and rigging of such a character are two very different things, you need to know what a character is supposed to do. To finally not overload the rig with functionality, but as well not make it too clumsy and or too rudimentary in the handling. “Map it to sliders”, well that might work for (e.g. facial) expressions, and there again we go to the PoseMorph.
Things like CMotion might help a little if at all. However your question indicates to me, that your really want to know it in depth. (?) Well, thinking about that for a moment, perhaps not at all, just one (or a few) slider request shows more a “how do I get a bath without getting wet” mentality, not really hunting the fine expressions, hehe. So—what is it?
What I want to say, it is an advanced art form, and thinking—how simple it should be AND keeping all expression options open at the same time, will lead from my point of view into frustration. (Because there is something that doesn’t work with each other. Core problem again, there is no one size fits all.)
There are many tutorials about that here on Cineversity, but an in depth training about character animation (expression based) is not present. From my point of view that is more a twofold education: take some actor classes, then perhaps the “animation mentor” option to dive deep into it. How to set up these “puppets” is more discussed here.
All the best
Sassi