(CAUTION: This tutorial is designed to use with 3ds max r3. Things might have changed since then).

Ok. This is the first of a series of tutorials designed to understand how a stable, switchable IK/FK setup works and can be designed. I will design a bipedal (humanoid) kinematic structure, but it's this tutorial's intention to make you understand how to design any FK/IK structure you need.

ATTENTION: Before jumping into the tutorials, I'd like to make clear one thing. This series of tutorials (as the whole site, for that matter), are designed for the intermediate-advanced user. It is highly recommended you posses at least some experience and knowledge on the following topics:

• Bones

• New IK controller

• Forward kinematics

• Inverse kinematics

• Expressions

• Linking and hierarchies

• Procedural animation controllers

• MAXScript and script controllers (basic)

This is required so that you can make the most out of these tutorials. If there's an area with which you're not familiar, I strongly suggest either you read the manuals and tutorials that ship with 3D Studio MAX, or you read the papers section on this site, where you may find some information on these areas. I hope you gain some additional knowledge and some ideas along the tutorials, and if you have any ideas or comments, please let me know. Luck!!

TUTORIAL REQUIREMENTS: 3D Studio MAX R3

OVERVIEW

Let's take a look at what we will be building along the course of these tutorials, so you can have an idea how each part of the character will be assemble and made to work. Each part of the character's structure will be covered in a different tutorial, and at the end everything will be assembled together. I will write the new tutorials as fast as possible, but bear with me if it takes some days. Enough of this. Let's take as look at what we're trying to achieve.

As you can see, my character has a fairly complex skeletal setup. This is due to some particular reasons. First of all, my character Astro is a cartoon character. After taking a look at the storyboards I had designed (Astro is the starring character of an animated short under production) and designing his basic movements, I knew Astro had to had a very wide range of motion, along with a very expressive nature. This, along with the exaggerated nature of cartoon's motions, urged me to design a skeletal structure very flexible but also strong enough so it wouldn't break. Also, I'd have to simplify as much as I could the controls of the structure, so not to get lost during the animation process. It is important to remember that IK structures also need an interface to get to the animator, and the more complicated the interface, the more problems the animator is likely to run into. So, you need to design an interface as simple as you can, but that can provide deep access and control into your character. Ok. So, let's break it up and analyze each part separately.

ARMS

Let's take a closer look at the arm setup and break it down.

Here's the arm setup. As you can see, there are a number of strange objects. These are scripted helpers I use to help me identify exactly what that object does. The green boxes are translator helpers. I often link position end effectors to them. The red spherical objects are rotation helpers. I often link rotation end effectors to them, or I create them in the middle of a FK chain in order to drive rotations. And the blue diamond-shaped object (found at the center of the torso) is a rot-translator helper. This one does both things, rotation and translation. I often use them as the center of mass of my characters. Ok. Getting back to the arm thing, you can see the arm bones inside some boxes set to see-through mode. The standard bones are the actual arm of the character (the one its skinned to), while the boxes (please see previous picture) are the FK arm (they have been hidden in this picture to allow a better view into the structure). The red rotator at the shoulder is the faked Up Vector control, and the black dummy behind it is its up vector constraint. The FK arm also has an up vector object, but we'll get into that when we start building the structure. There's a translator helper at the wrist, and there are a number of dummies. These dummies, along with the sliders you see near the character, build up the IK/FK switching mechanism. The whole IK/FK switching mechanism is based on Ken Morton's work and expressions, so I must say that he's mostly responsible for this setup being possible. One of the sliders controls the IK/FK switching system. The slider behind the arm controls the inheritance of the wrist. This control has been created to help lock the hands to other objects. Say you want the character to push an object, or lean against the wall. Although you can position the IK end effector of the arm near the wall and rotate the wrist into position, and moving the torso wouldn't move the arm from its end position, the hand would inherit any rotation coming form the arm. This switch disables that, so that the wrist will remain in its current orientation no matter what happens to the rest of the object. Of course, all of these controls are animatable and have smooth transitions. I had been working on this solution with Paul Neale, whose work has also been very important for the development of this setup.

TORSO

Here's a closer look at the torso

As you can see, there are a number of rotators in the spine. The whole spine is one FK structure, where the rotators control its behavior. The bigger one drives most rotations of the other two via expressions, so the animation process is easier and the spine's behavior is automated. The two green transaltors at the shoulders are the controls for the clavicle bones. This area is not complicated.

LEGS

Here's how the legs look like

Again, the legs are built around the same techniques and mechanisms as the arms. The legs feature the same FK/IK switching system which allows animators to use IK to create quick motions and locking them onto the ground, and FK for precise posing or complicated motions. Again, the system's transition from one state to the other is controlled by the sliders aside the character.

This has been a very rough and quick look into the skeleton we'll be building in the next tutorials. This setup is somewhat complicated, and although I'll try to explain everything as clearly as I can, I cannot go into much detail because of the time and space constraints. So please, try to read the info I suggested at the beginning of the article, and stay tuned for the next step in the creation of our skeleton.

©Sergio Muciño. maxTD 2000.

[Continue to part 2]