IMD 4003: Character Animation V

For IMD 4003: Computer Animation, taught by Chris Joslin

Contents

1. 1. The Mechanics of Walking
   1. 1.1 Four-Step Walk Cycle
   2. 1.2 Specific Body Movements
2. 2. Controlling Movement
   1. 2.1 Multiple Characters
   2. 2.2 Motion Transitions

1. The Mechanics of Walking

1.1 Four-Step Walk Cycle

There are 4 steps to this walk cycle that are repeated for each leg:

1. Extended Position: Feet are far apart and weight shifts to forward foot.
2. Recoil: Lowest point in the cycle; weight is distributed to the forward foot and the forward knee bends.
3. Passing: Forward knee straightens out and the back leg curls under the body.
4. High-Point: As the forward leg straightens, the body moves into its highest position. The weight is transferred to the ball of the forward foot and the passing foot 'catches' the fall.

The image below uses the term, “Contact” where we use the term, “Extended Position.rdquo; There is no difference.

The above image is from idelworm.com. Visit this site for a thorough explanation of how to create your own walk-cycle.

1.2 Specific Body Movements

The following outlines the different parts of your body that are affected when you're walking. One thing to note is that you should always start animating from the extreme poses (ie. start with the Extended Position and fill in the rest).

Feet and Legs

• The feet propel the body forward by pushing your body out of balance and then catch your weight. Always keep your joints slightly bend to look natural.
• Add Personality to the walk by changing the stride:
  • Stride Width: the stide width affects the perceived weight of the character; wide stances appear heavier, stronger and more masculine, whereas narrow stances appear feminine. Faster walks have longer strides (vice-versa for slower walks).
  • Stride Length: should appear equal otherwise your character will look like they have a limp.

Hips, Spine and Shoulders

• Your balance starts at your hips so therefore all of your motions (within reason) start at your hips (it's your centre of gravity).
• 1. Hips rotate along the spine axis with the legs.
  2. At the Passing Point, the free leg pulls the hips out of centre, rocking the hips side-to-side.
• Both of these motions are transmitted through the spine and shoulders (which mirror the hips motion) to maintain balance.
• The spine absorbs the shock transmitted to the hips.
• The head bobs around slightly to stay balanced.
• Add Personality by adding a swing to the hips - this tends to look more feminine.

Arms

• When walking, the arms act like a pendulum, dragging a few frames behind the hips and shoulders. And like the legs, ensure that the arms are always slightly bent.
• Add Personality by adding purpose to the swing (think of the way your arms move when you're in a rush, sad or happy).

2. Controlling Movement

2.1 Multiple Characters

Walk cycles often appear repetitive and lifeless, especially when multiple characters have the same walk cycle (appears robot-like). And normal walk cycle work well only on level terrain.

Solution: Stagger the walk cycle of different characters and give them all different gaits by varying the frames per step, and stride and leg length.

2.2 Motion Transitions

Walk to Run vs. Run to Walk

• Walk to Run: Your body leans forward and the forward knee bends as the body prepares for a leap. Then the body straightens out in the 1^st step of the run.
• Run to Walk: In the last step of the run, the shoulders move back and the hips pivot forward and the knees absorb the shock of the impact. As the energy dissapates, the body slows to a walk.

Turning

• Turns are created by turning the hips and feet with each successive step. The shoulders will lean slightly towards the turn.

Going Up and Down Slopes

• Uphill: You need to maintain relatively vertical stance so the upper body leans forward. Because you're exerting more energy (blame gravity), your knee bend more and the timing of the walk is affected.
• Downhill: The upper body leans back slightly and the arms stay out to maintain balance (walk down a hill with your arms across your chest to see the difference). The knees bend to absorb the shock and the timing of the walk is affected.