CAP 202 - Computer Animation II

Lesson 12 - Character Animation: Biped

Objectives:

This lesson discusses animating biped (two-legged) figures. Objectives important to this lesson:

1. Creating and modifying bipeds
2. Using the Skin (not Physique) modifier
3. Functions of character studio
4. Creating a walk cycle
5. Keyframing body parts

Concepts:

The lesson begins with a statement about the relative difficulty of animating characters. One reason not stated in the text is that you can animate objects and viewers will not complain, but if you animate a humanoid figure, viewers will have strong opinions about whether the animation looked natural, or believable. Animating something that looks familiar is more demanding because viewers will expect it to move in familiar ways. The text recommends knowing the program you are using, and also being a good artist to be a successful animator.

The lesson moves on to describe a 3DS Max tool called Biped. The tool provides a functional skeleton with a built-in hierarchy and inverse kinematics for a two-legged figure. Although the tool starts with human proportions by default, you can modify the bones (objects that represent bones of a figure) to represent other bipedal character types (ape, T. rex, alien, etc.).

Exercise Notes and Questions

Work through the exercises and turn in your answers to all questions below as part of the homework for this assignment.

Exercise 1: This exercise begins with a partially completed biped character. It explains that the body tissue part of the character is represented by a mesh, and the skeleton is represented by a Biped object.

In passing, the text reminds us of something doctors and artists must learn. When you are facing a character, his left is on your right, and vice versa. When step 5 tells you to click the character's left thigh, remember that it is on the animator's right. All instructions will be like this: body parts are named in the character's frame of reference, not yours.

Question 1: How does exercise 1 ask you to to select the character's left leg in step 5?
Question 2: What is the effect of pasting the posture of the left leg on the right leg of the Biped? Does it necessarily match the position of the mesh leg?

The lesson has you add bones for a ponytail. This may seem odd. A real pony has bones in his tail. A human does not have bones in his/her hair, even if wearing it in a ponytail style. The leads us to broaden the definition of bone: a Biped bone may represent a theoretical bone the the character's skeleton, or it may just represent the stiffness and articulation of a part of the character.

Exercise 2: Exercise 2 adds a skin modifier to the figure. (The list of objectives says the "Physique modifier". The skin modifier is the improved version.) It first shows you that the body mesh is not attached to the skeleton (Biped object).
Question 3: In exercise 2, step 2, you move the Biped object's left foot.
What does this tell you about the mesh object?
What does it tell you about inverse kinematics?
Question 4: In exercise 2, step 7, you are told to associate some bones with the skin modifier that you added to the mesh object. You are telling the mesh to act like a skin over the bones. As such, be careful to select all of the bones. What feature are you told to use to make this easier?

The lesson breaks away for more new material. You are told that you will use keyframes and layers in animating characters. (We have seen keyframes in earlier lessons.) These are both rollouts on the Motion panel in 3DS Max. (There are several more Motion panel rollouts we will discuss later.)

Exercise 3: Exercise 3 tells us to use a named selection set for the Biped parts.
Question 5: If the student file had not contained this selection set, you would have had to make it. Which previous lesson has the instructions for doing so? (You need to refer to previous lessons throughout the course.)
Question 6: The exercise asks you to change the way the bones are displayed to make them easier to select, to avoid selecting the body mesh by accident. What option are you told to check?

The text jumps immediately into the next exercise.

Exercise 4: This exercise uses the Pose to Pose approach to animation, also known as keyframing.
Question 7: The exercise tells you to select any part of the biped in step 3. The text has told you to do this before. What is the reason, and why doesn't it matter which part you select?
Question 8: The exercise includes a ready-made pose which you paste at Frame 0. What parts of the biped change when you use the Paste Opposite button? (Hint: not all of them.)
Question 9: Review steps 14 through 20. What is the difference between copy/pasting a posture, versus a pose?

Exercises 5 and 6: These exercises change the position of the feet during the walk cycle and use the ponytail bones you put in the figure earlier. The text does not discuss the theory that people (and animals) walk in a series of repeated movements (cycles). Follow the link above for more information in a lesson by David Atkinson.