Upcoming Deadlines

Eighth Homework (Reverse Video Reference)Due Thursday, March 22nd (This week)20 points (10 points if late)

Spring Break - March 26th to March 30th

Ninth Homework (Stop-motion Character Animation)Due Tuesday, April 10th (In three weeks)20 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

Homework Assignment #8

Normally animators shoot video and use it as reference for their work.

In this assignment, you'll do the reverse.

Specifically, for four different animation clips you’ll shoot video of yourself in which you recreate those clips as accurately as possible.

Go to Homework Assignment 8 on the course website to find the animation clips you’ll recreate:

https://artphysics123.pbworks.com/Homework-8

Homework Assignment #8Upload your four clips to your blog in an entry entitled

“Reverse Video Reference of Walking."

 

This assignment is due by 8am on Thursday, March 22nd (this week).

20 points (if late, 10 points).

For each of the four animation clips the best video clip will get an extra 20 points of credit.

Survey Comments

Like: Demos; Videos; Interesting & organized lectures; Clickers; Grading system & extra credit

Dislike: Term papers; Tracker; Quizzes

Suggest: Change 8am due-time; more clicker questions; more clicker time; clicker points?; fewer term papers; free beer

Survey Question

The amount of time that you’re given to answer the clicker questions is:

A)too short; would like more time.

B)about the right amount of time.

C)too long; don’t need so much time.

Swinging Arms in a JumpThe natural motion when jumping is to swing the arms. To jump as high as possible you should swing them upward:

A)While your feet are still touching the ground.B)Just after your feet leave the ground.C)Either way, since the forces on the arms and on the feet are not related.

Swinging Arms in a Jump

A) While your feet are still touching the ground.

Swinging the arms raises the center of gravity and also increases the downward action force pushing off the ground.

Spin or Tumble?

Rotation around two of these axes is spinning.In this pose, the axis of rotation that tumbles is:A)Twisting axis (Head-to-toe axis;

Turn left-to-right)B) Somersault axis(Side-to-side axis;

Turn front-to-back)C) Cartwheel axis(Front-to-back axis;

Turn head-to-feet)

A

B

C

Spin or Tumble?

B) Somersault axis(Side-to-side axis;Turn front-to-back)

B

Rotating along this axis typically results in irregular tumbling.

Spinning is possible but requires more control than along the other two axes.

Tennis Racket Theorem

When an object turns about its long or its short axis, it tends to spin uniformly.

When an object turns about its middle axis, it tends to tumble.

SPIN

SPIN

WalksPart I

Characters in Motion - Walks

Walking is a great example for studying character motion because it has all the basic elements of mechanics.

Walks with Personality

From the basic walk it’s possible to create many variations to express personality through acting.

Walking (1968)Ryan Larkin created an Oscar-nominated short of people walking, animated in a variety of styles.

This clip is from Chris Landreth’s Oscar-winning short, Ryan, about the troubled life of Ryan Larkin.

http://www.nfb.ca/film/Walking

http://www.nfb.ca/film/ryan/

Stride & Passing Position

One foot in the air

Feet on the ground

Stride Passing Position

Concentrate on these two key poses, the stride and the passing position.

Squash & Stretch

Passing position

Squash Stretch

These are the transition poses between the stride and the passing position.

StrideStride

Animating a Walk CycleIs animating a walk cycle just a matter of getting the right sequence of poses?

No, it’s more complicated. Let’s see why…

Video Analysis

To help us analyze a walk, let’s look at some video analysis using the Tracker software.

Video Analysis

Video Analysis

Head Position

Stride

Passing

He

igh

t

Richard Williams’ Walk

Williams puts the “up” position just after the passing position, which happens if the heel rises in a quick walk.

Preston Blair’s Walk

Preston Blair makes the passing position the tallest point in his basic walk cycle.

Richard Williams also does this in many cases.

PassingStride Stride

PassingStride Stride

But in walks with attitude, he mixes it up.

Rules vs. Tools

There is enormous variety in walks and each has unique timing and spacing.

As Glenn Vilppu says,“No rules, just tools!”

Physics is a tool that helps animators create believable walks.

Step, Stride, Gait

stride length step length

left foot

swing phase,left foot

right foot

stance phase,left foot

single-support double-support

one gait cycle

time

Stride =2 Steps

Gait is the timing of movement in walking, running, etc.

Time

Distance

Cadence of a Walking Gait

Strobe photo (5 flashes per second)

A normal walking gait ranges from a third to two-thirds of a second (8 to 16 frames) per step, with a half second (12 frames) per step being about average.

A full stride (both rightand left steps) is, on average, one second (24 frames) per cycle.

Parade march time is 120 beats per minute (one beat per step).

One stride (two steps)

Contact with the GroundEach foot is on the ground about 60% of the time.About a 20% of the time both feet touch the ground.

On the ground

Right Foot

Left FootIn the air

60%

60%

40%

40%

10%

10%

10%

10%

Time of dual contact decreases as walking speed increases.

Walking Slower or FasterGoing from a slow walk to a fast walk you increase both your stride length and your stride rate to increase your speed.

Walk Stride length Stride rate Speed

Slow walk 3 feet 2/3 stride per second

2 feet per sec.(1 1/3 m.p.h.)

Fast walk 4 feet 1 stride per second

4 feet per sec.(2 2/3 m.p.h.)

At around 6-7 feet per second (4-5 m.p.h.) the gait pattern transitions into a run.

Period of a Simple Pendulum

Period of this pendulum is about one second per oscillation

Time required for a full oscillation (one round trip) is called the period of oscillation.

Period of a simple pendulum depends only on its length (distance from the pivot to the mass).

Greater the length, the slower the oscillation.

Period of a Cylinder Pendulum

Period of a cylinder pendulum depends mostly* on its length (distance from the pivot to center of gravity).

X X

* Also depends on the radius; larger the radius, the slower the oscillation.

Greater the length, the longer the period for the swing (that is, the slower stride rate).

Leg swing is like this

Period of Walking Gait

Short legged characters have quicker gait than long legged ones.

During the stride, the passing leg swings at its natural period of oscillation.

Running GaitIn running, you bend your leg and raise your calf and foot to quicken gait by shortening the distance from the pivot (hip) to the center of gravity of the leg.

XCG

XCG

Drag of Articulated Limbs

Fast Swing

Slow Swing

Slow

Fast

Drag (inertia) is seen with

articulated limbs

Drag in Character Effects

Fast Swing

Slow Swing

Slow

Fast

Drag (inertia) is also seen in character effects, such as hair and clothes

Timing of the Walk

Timing is almost even but there is some slowing in and slowing out as the center of gravity rises and falls.

Slowing In Slowing Out

XCGXCG XCG

Inverted PendulumIn the passing position the whole body swings up and down, as an inverted pendulum.

Rolling Egg Timing

The timing of the motion due rising and falling center of gravity (CG) is like that of a rolling egg.

Slowing In Slowing Out

XCGXCG XCG

Home Demo: Carrying WaterTo appreciate the “rolling egg” timing of a walk, carry a shallow tray of water and notice the rhythm of the sloshing.

Slowing In Slowing Out

XCGXCG XCG

Walking stiff legged, like Frankenstein, exaggerates the slowing in and out.

Weight Shift in Walks

Up and down motion in a walk causes weight changes for the character.

Rising & Slowing Down: Lose Weight

Rising & Speeding Up: Gain Weight

Falling & Speeding Up:Lose Weight

Falling & Slowing Down:Gain Weight

With gravity

Against gravity

Weight on the Ground

At which position do you exert the least weight on the ground?

A) StrideB) SquashC) Passing PositionD) StretchE) Same weight at

all times

Stride Stride StrideP.P.P.P.Squash

Squash

Stretch Stretch

Force Plate Experiments

C) Passing Position

Can measure weight shift during walk cycle using force plates.

Body Weight

Stretch

PassingPosition

PassingPosition

Squash Stretch

Stride

Squash

Weight Shift – Normal Walks

Weight Shift – Normal Walks

The weight on the back foot is peaks just as the heel of the front foot touches the ground.

Moments later, the weight on the front foot is peaked right as the back foot leaves the ground.

Andrew Harkins, Dreamworks animator

Weight Shift – Normal Walks

In the middle of the passing position the weight on the planted leg dips to a minimum.

This weight is actually 20%-40% less than the person's weight when standing stationary on one foot.

Inverted PendulumIn the passing position the whole body swings up and down, as an inverted pendulum.

Rising & Slowing Down: Lose Weight

Falling & Speeding Up:Lose Weight

Weight Shift – Normal Walks

The reason that the weight decreases is that the body rises upward then downward during the passing position, swinging like an inverted pendulum. Due to the centripetal force required to move your body in a small arc during the passing position causes your weight to be lower. This effect is seen in overlapping actions, especially if a character has long hair or loose fitting clothes.

I’m going to kill Garcia for this!

“Counteraction”

Richard Williams calls this effect of varying weight the counteraction.

Williams writes, “When the character goes up – the drapery or hair or soft bits go down.”

Lose Weight Lose WeightGain Weight

Normal, Slow, and Fast GaitsNotice the differences in the three walks yet the similarities among different persons.

Slow walk has less variation in the weight shift

Fast walk has more variation in the weight shift

Normal walk

Force Plate – Slow Walks

Force Plate – Fast Walks

Walking with a Limp

On the ground

In the air

With a limp, the painful leg is still on the ground 60% of the time but walking slowly reduces the force spikes in the squash and stretch.

Stride P.P

P.PStride

Forward & Backward Forces

From passing position to stride the leg on the ground is pushing the body forward.

From stride to passing position it is pushing the body backward.

Walking at constant speed these forces average to zero.

Center of Force during a Step

The center of weight travels from heel to toe as the torso travels over the planted foot, almost half the time located near the ball of the foot.

Heel Strike

Squash

Passing Position

Stretch

Squash

Passing Position

Stretch

“Butterfly diagram” of force vectors.

Walking this way

Pressure on the Foot

http://www.soe.uoguelph.ca/webfiles/mleuniss/index.htm

Combined frames Center of Pressure

Center of pressure travels from heel to toes.

Quadruped Animal Walking

Walking for animals is very different than for humans, not so much because they walk on 4 legs but due to bone structure.

101 Dalmations (1961)The walking gaits of the dogs in this scene is modified to match that of their masters.

Walk cycles animated by Frank Thomas and Blaine Gibson

Click

http://www.youtube.com/watch?v=wpj9E3H4_Ag

Shoulder, Elbow, WristFront legs of mammals have the same joints and bones as our arms but with varying lengths.

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Shoulder

Elbow

Wrist

Horse Human Dog Cat ???

Dog Legs

Notice the joints circled in this skeleton of a dog; on a human these would be:

A) Elbows and KneesB) Elbows and AnklesC) Wrists and KneesD) Wrists and AnklesE) None of the above

B) Elbows and Ankles

Dog Legs

AT-AT WalkersIndustrial Light & Magic (ILM) filmed the AT-ATs using stop-motion animation with models from 2 inches to 2 feet in height.

Walking mimics elephants

Star Wars Episode V: The Empire Strikes Back

Tennis Shoes & Stripped Socks

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Chuck Jones presents a good way to remember animal anatomy: Tennis shoes & Stripped socks.

Knee

Ankle

Sole

Sole, Ankle, Knee

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Knee

Ankle

Sole

Knee

Knee

Ankle

Ankle

Sole

Sol

e

HorseHuman Dog

What you think is the “knee” on the animal’s hind leg is actually the ankle.

Next LectureWalks, Part II

Next Assignment:Reverse Video Reference

Due this Thursday

Please turn off and return the clickers!