Creating IK/FK rig for use in game

8-Bit

Hey guys!

This is kind of a two part question.
I'm working on a very short game for my senior project and I've come to the point where I need to start rigging things. So far I've been able to make a pretty decent skeleton for most of the characters and even skin them well enough, however once I get to the constraints I'm a bit lost.
I'm currently working on a creature that will never actually put its weight onto anything (it floats) so I don't think I need to use IK, however every tutorial I've looked for about how to set up FK always talks about marrying IK and FK. My focus is in modeling and texturing so I'm not very familiar with the concepts behind rigging, but it would seem to me that you should be able to create a rig that just uses FK if that's all you need. Am I wrong?
The other wall I keep hitting is the constraints. I'd like to be able to rotate parts of the skeleton using nurbs curves, but whenever I try to constrain the curves to the joints it doesn't actually manipulate them. I'm first selecting the driver (curve), then the driven (joint) before I constrain them, but still I get no control over the bone. I know I'm missing something, but I can't seem to figure out what it is, and every tutorial I've found online only furthers my confusion and understanding of the system.

Mark Dygert

I'm not sure what app you're using, but FK is Forward Kinetics which means the joints are solved in their parent order, IK is Inverse Kinetics which means they are solved in reverse.

IK typically there is a end node that you move around and all the joints figure out where they need to be.

With FK its the default bone behavior, you rotate the parent and the children follow, rotate a child and only its children follow, it has no effect on the parents.

So FK = standard rotation based system nothing needs to be done other than define parent and child links if you create bones it normally does this for you by default. IK is typically created from a FK chain, and often people create systems that allow you to blend between the two.

If you're using 3dsmax, start using biped it makes the whole process painless and handles the IK/FK blending seamlessly. Move the hand the arm figures out where it needs to be, rotate the joints and the hands follow along, nice and smart no need for advanced rigging or crazy amounts of learning. Almost every rig I've seen since biped has tried to do something similar and so far only Naughty Dog has manged to pull it off in Maya and it took two amazingly talented guys to do it.

8-Bit

Well through fiddling about with the rig, I've discovered that I can just parent the joint to the control handle. However I'm still concerned about the fact that I've not been able to find anything online about a simple FK rig. Do you need IK for some reason? or am I fine with just FK?
Like I said, this character is not going to be putting any weight upon anything.

jipe

You will only need IK if your character needs to lock the end of its limbs (or tail, or whatever) in place. If your character floats, it's probably not necessary. But you still might want a combination FK/IK spine, depending on what your character looks like and how it moves.

8-Bit

Thanks Mark!
It would seem I figured out my problem without understanding how or why, but you've definitely helped me clear up exactly what FK is. Also, I forgot to mention that I'm using Maya to do all of this.

Thanks again for the explanation! You've made it a lot more comprehensible. I'll post more questions here if/when I hit the next wall.

8-Bit

Jipe,

What is the benefit of an FK/IK spine? Sorry guys for the silly questions, but I'm pretty lost when it comes to rigging.

also this is the character in question http://1.bp.blogspot.com/-5qkCw08BqfQ/TVwcnX0w3nI/AAAAAAAAAPI/9KreUIqhMNY/s1600/Illuminator_LowPoly.jpg