The
Cow Tutorial
Introduction to computer animation using Maya
Click
here for Preview PlayBlast of final animation
Part 3. Animation
Preparing the model
for Animation
We need to set up
the cow model to be animated by creating groups. The top of the grouping hierarchy
is a single node which is the entire model. The parts which are animated as
a unit (such as all of the parts which make up a single leg) must be collected
into a single node as well. If you model is not grouped at all yet, it is
a good idea to start with the smallest parts first. For instance select all
of the parts which make up the wind-up key and click >Edit>Group (cntrl
g). Name the new node "Key". Next select the two arms, and group
them in a node named "Arms". Now select the base of the body, and
the leg slot parts and group them into a node called "Bottom". Since
the neck moves as a fixed part of the body group the neck parts now too. The
tail parts should be grouped as well. Since the upper body is a single piece.
Now select the "Neck", "Arms" ,"Bottom", "UpperBody"
,"Tail" and "key" and group them. You now have a single
node which you can name "Body".
In the Hypergraph
(>Window>Hypergraph) you grouping should look like this:
Create a similar group
for the Head (include the geometry of the eyes) and the Legs. The eye control
is a separate group. Now select "Head", "Body" ,"Legs"
and "Eye Control" and group them into a single node called "COW".
As your cow walks we will animate the forward motion of the whole character
using this "Cow" node. In order to move the walking cow to wherever
you might need her in the scene you will need an additional node above
"Cow". Select "Cow" and group it to itself (>Edit>Group).
This creates another node for the same objects which can be animated or manipulated
separately. I called this top node "Wind-up Cow".
Moving Pivot Points
The cow's legs move
by rotating from the top of the hip. Right now, if you select the Left leg
and rotate it - the rotation center will be the center of the grid. Whenever
you create a new group, by default, the center - or pivot point - of the new
group is the center of the grid (i.e. coordinates 0,0,0). In order to rotate
the leg properly we need to move the pivot point to the top of the leg geometry.
slect the "Move" tool (hot key w), you will see the Move manipulator
arrows at the center of the grid. Now click "insert" on your keyboard.
The move manipulator changes to a small round, yellow icon. Moving this icon
changes the pivot point. In the side view your leg models should be centered
along the Y axis. You can Snap the pivot to the Y axis, by holding down the
"x" key while moving the pivot. In the front view center the pivot
point each leg.
When the pivots points
are in the correct locations simply click "insert" again to return
to normal mode.
Preparing to Animate
Before we begin
to animate the cow, we want to make sure all of the tools and menus we will
need to use are visible. Switch to the Animation menu. Make
sure the Range slider, and the Time Slider and Channel Box are checked under
Options. Your window should look like this one.
The range slider shows to whole range
of your animation, you can type in 1 and 300 in the boxes to the outside. The
boxes to the inside indicate what range is viewable the timeline. and this can
be adjusted using the gray slider bar in the center. Since our animation
is so short (300 frames at 30 fps = 10 seconds) we can leave the whole range
viewable on the timeline
The Walk Cycle:
The cow will be walking, his legs,
body and head movement are continuous and there fore can be cycled.
Since this sample project is a total of 300 frames long, we want the range slider
to read from 1-300. First we
will make the legs walk in place. We need only set 5 keyframes for each leg
in order to complete a single step. This step when cycled (repeated continuously)
will be a walk.
The 5 poses will look
like this:
Go to frame 1 on the time slider.
You can do this by typing in the number "1" in the area labeled "current
keyframe" on the diagram above, or by clicking the arrow labeled "go to first
frame" in the diagram, or, by simply clicking at the 1 on the time slider
itself. (The Left leg is highlighted in the above illustrations.) Leave
The Right leg where it is, and click >Animate>Set Key. Now at frame one
of your animation you have set the position of the right leg. The Left leg should
be moved forward along the Z axis until it is just infront of the left leg.
(if your model is scaled like mine use a value of .15 in the Translate Z attribute).
Now set a keyframe for the left leg. (This actually
sets a key frame for all the attributes of the leg, and if you notice all of
the value boxes in the Channel box turn color. That is OK - we will get
rid of the non-esssential keyframes later.) Now move to frame 8 on
your timeline. Move the left leg back to Z=0. Rotate the right leg (Rotate X
value -10) and raise it along the Y axis (Tranlsate Y .161). This lifts one
leg over olatform protrusions of the other leg. Set keyframes on BOTH the left
and right legs. Use the following as a guide to set the 5 keyframes for each
leg: (TY=translate Y, RX =rotate X etc.)
Keyframe 1
Left Leg: TY=0 | TZ= -0.15 | RX=0
Right Leg: TY=0 | TZ=.15 | RX=0
Keyframe 8
Left Leg: TY=.161 | TZ=0 | RX= -10
Right Leg: TY=0 | TZ=0 | RX=0
Keyframe 15
Left Leg: TY=0 | TZ= .15 | RX=0
Right Leg: TY=0 | TZ= -.15 | RX=0
Keyframe 22
Left Leg: TY=0 | TZ=0| RX=0
Right Leg: TY=.161 | TZ=0 | RX=-10
Keyframe 29
Left Leg: TY=0 | TZ= -0.15 | RX=0
Right Leg: TY=0 | TZ=.15 | RX=0
Notice that Keyframes 1 and 29
are identical. In order for the cycle to work properly the first and last keyframes
must match.
With
your left mouse drag back and forth over the area of the Time slider which has
these keyframes. You should see the legs moving. This is called
"scrubbing" though the animation.
Now we have
one complete step. We will use the Graph Editor to make the legs cycle continuously
throughout the animation, thus walking in place.
With
the left leg selected, open (window> animation
editor> graph editor). (*Note
the track and dolly view manipulators you use to move around in the view panels
also work in the graph editor. (You can frame a curve or key frame with
hotkey "f").
The attributes
are listed by name on the left, and are represented by a curve in the right.
If you recall, when we set the keyframes we set them on all the attributes (animated
attributes are known as channels). We are only interested in the TY,
TZ and RX so let's get rid of the other curves. On the main menu (not
the graph editor menu), with the left leg still selected press (edit>
delete by type> static channels). Now in the graph
editor all of the channels, except the those with keyframes should go away.
To frame these curves in the graph editor, hold RM over the right side of the
graph editor (where the curves are), and click view>
frame selected. Your graph should look something
like this:
Graph Editor
The Keyframes are represented by
black dots, the numbers across the bottom show the time, and the numbers on
the left are the numerical value of the channel. The curves show the transistion
of the attribute value from one keyframe to the next. To make the leg
action continue throughout the animation, select the curve and press (curves>
post infinity> cycle). In order to see the results
of this action press (view> show results) this may take a few seconds but you
should see the curve repeat itself in a sine wave sort of pattern.
We want to
change one more thing about this curves before we go on.Examine the shape of
the curves As the curve passes through a keyframe it can behave in several ways
depending upon the type of "Tangent" of the curve. WE will discuss tangency
more thouroughly in class but for this animation, since we are dealing with
a mechanical toy, we will use Linear tangencies. Select all of the curves (box
select over the curve avoiding keyframes to select curves). Then in the Graph
Editor menu, click >Tangents>Linear.
Now the curves should look more like a zig-zag lines. Since the motion
now doesn't flow through the keyframe, instead, it changes abruptly at the keyframes,
it will give the legs a snappier motion, more robotiv motion. Repeat the
process forthe right leg. Close
the graph editor, and press the play arrow to see your cow legs in action.
PLAYBLAST
As you are
animating your cowyou will want to preview exactly how the motion will look
when you render it out. Simply hitting "play" and watching you animation
in the view window, is not a very good indicator of how your piece will play.
The more complex your view - the slower the playback. You can simplify
your view to help playback more quickly, by always keeping to wire frame mode
(4), rough display (1). However you will also want a more accurate
preview of you animation with surfaces and textures. You can easily do
this using Playblast. Enlarge your persp1 window to full size (space-bar)
and press (Window> Playblast - option box).
To begin with, for early tests, we will not be saving these playblasts.
Later, when you have a version you are happy with you can save the playblast
as an .mov file. For right now set up you options as follows:
Time Range:
Time Slider (for the whole animation) or, if you want to review just
a portion of you piece, choose Start/End and type in the frame numbers
View: Check this to allow you to watch frame by
frame as the playblast renders
Show Ornaments: leave this OFF, unless you want
to render things like IK handles and joints
Viewer: select MoviePlayer
Compression: since we are not saving - leave this
for now
Display Size: Choose "from Window" which
will create the playblast based on the size of you view display rather than
from the Render Globals
Scale: a half-size playblast will be good enough
and will be much quicker so use .5 here.
Remove Temporary Files: check this so that you
are not storing multiple playblasts in RAM
Save to File: Do not check this - right now we
are just testing the motion.
Now press (Playblast).
Your animation should play very slowly, at half
size in the lower left corner of your window. When it has played through
once, a new window will appear, click in this window to activate the movie
player and study the motion of your animation. It is a good idea to do
fairly frequent playblasts while tweaking the animation.
Body &
Head Motion:
Reminder:
(To set a key frame, you may use hotkey "s", or, in the channel box-
LM "Channel> keyframe all' (or if you have attributes highlighted you may choose
"key selected" ) or from the main menu press (Animate>
Set Key).
The body of the cow
rocks as she walks - it moves both side to side (Rotate Z) and front to back
(Rotate X). Remember when you made the grouped the body parts the pivot point
of the new group was the center of the origin. Select the node called "Body"
(this includes the neck and arms) and center the pivot (>Modify>Center
Pivot). The body tilts in relation to the legs so we will set the keyframes
at the same points as the legs. (1,8,22,29). At frame 1 the feet are both flat
on the floor so the body is not tipped. Therefore set the RZ and RX values to
0 and set a keyframe. At frame 8 the left leg is raised and moved forward -
the body should tilt back and toward the right leg. I used a Rotate X value
of -3 and a Rotate Y value of 3:
At frames
15 and 29 the feet are flat on the floor so the body has no rotation. At frame
22 the right leg is raised so I used RZ of -3 (the opposite of frame 1) and
an RX of -3 (same as frame 1). In the graph editor cycle these motions the same
way we did the legs. The cow should now be walking in place.
The
head tilts back and forth in relation to the legs as well. When the right leg
is lifted - the head tilts left and vice versa. Since in our 5 keyframe cycle
we have one frame where the left leg is raised (frame 8) and one frame where
the right leg is raised (frame 22) Set the head tilts at those two frames.
If you recall for a
cycle you need the first and last keyframes to be the same. Since we only have
two keys set on the head we want it to oscillate (back & forth) rather than
cycle. In the Graph Editor select the curve and click >Curves>Post Infinity>Oscillate.
You can animate the
key turning by setting a key at RX=0 at frame one and RX=-360 at frame 30 (one
full rotation in 30 frames or one second) and cycling it. (In this case a regular
cycle is OK with 2 keyframes since we want it to go back to 0 after -360)
Now all that is left
to get her walking is the forward motion. In order to make the cow walk forward
we need to determine how far she moves forward with each step. As she lifts
one leg the other should remain planted. Right now if you examine the "staionary"
foot you notice that it slides back as the other foot goes forward. We need
to make the position of this foot remain constant until it is raised in turn.
To do this you can create a dummy object which is not animated to determine
the foot placement. Create a Cube and translate & scale it to be directly
below and the same length as the right foot(the forward foot) in frame 1:
select the "Cow"
node (this includes all cow parts including the legs) and set a key frame at
Frame 1 for Translate Z=0. In frame 8 the left leg is raised, and in frame 15
it touches down. We want the right leg to remain exactly where it is during
these frames. Go to Frame 15, you will see that the right foot is now behind
the dummy cube. Select the "Cow" node and move the cow
forward until the right foot is again directly over the cube, which has not
moved.
Set a key frame on the
Translate Z of the body. This establishes the distance of a single step. In
the Graph Editor select the curve for TZ of "Cow" and click >Curves>Post
Infinity>Cycle with offset. The offset will add the value of a single step
distance as it cycles the forward motion. Thus if the TZ value at frame 15 is
.3 then at frame 30 it will be .6. Repeat this process for the left foot. Move
the cube under the left foot at frame 15 and adjust the "Cow" TZ if
necessary at frame 29 and set this keyframe. The cow feet now stay planted step
to step.
Secondary
Motion:
You
can also make her look around by setting key frames on his Eye_Control.
There should always be a blink or two in an animation, most of us don't go too
long without blinking. Select the eyelid spheres and animate RX to make
your cow blink. A blink consists of four keyframes. I used 3 frames to
close - three frames closed - 3 frames to open for the timing in this animation.
First keyframe an open position, 3 frames later, key a closed position, 3 frames
later another closed position keyframe. This keeps the eye closed for
3 frames, then key another open position 3 frames later to open the eyes again.
Animate some eye motion
to make your cow look around by keying translation of the eye control node.
Keyframes can
be deleted by holding the right mouse over the red keyframe line in the Time
Slider and choosing delete from the menu. You can also delete keyframes
from within the Graph Editor, by selecting the keyframe and from the Graph
Editor's own menu pressing Edit>delete.
Run some more
Playblasts and continue to tweak the motion. When you are happy with the
entire sequence we will go on to render it.