Open the mechBugRig_v01.ma scene from the chapter5scenes directory on the DVD.

The bug model is a combination of NURBS and polygon geometry. The bug's parts have already been parented in the Outliner to form a basic hierarchy (see Figure 5.2).

Figure 5.2. The mechanical bug is created from NURBS and polygon surfaces. Its various parts are organized in the Outliner.

The model consists of two main groups: the legs and the bugBody. At the moment these two groups are separate. The legs and body are placed on two different display layers so their visibility can be turned off easily while working.

In the Layer Editor, turn off the BODY display layer so only the legs are visible.

Switch to the Animation menu set, and turn on Grid Snapping. Choose Skeleton

In the Outliner, expand the legs group. Select the frontleftLegBase object. Ctrl+click joint1 and choose Constrain

When you create a constraint node, it appears in the Outliner parented to the constrained object. The icon looks like an exclamation point (see Figure 5.5). In this particular situation, you're only using the constraint to quickly position the joint at the same spot as the geometry, so once the joint is repositioned you can remove the constraint. This technique is a fast and easy way to make one object snap to the world space position of another. Using constraints as an animation tool is discussed later in the chapter.

In the Outliner, expand joint1. Select joint1_pointConstraint1, and press the Delete key to remove the constraint.

Figure 5.3. Place three joints on the grid.

Figure 5.4. The options for the point constraint

Figure 5.5. The point constraint appears as an exclamation point parented to the constrained object in the Outliner.

MEL in Action: Quick Object-Reposition Script

You may find yourself frequently using a point constraint to snap one object to another. You can create a shelf button using a short MEL script so that, instead of repeating the same three steps over and over again, you can simply click a shelf button to instantly snap one object to another. This is an example of how learning just a little bit of MEL can make your workflow faster and easier.

Open a text editor such as Notepad (on Windows) or Text Edit (on the Mac). Type the following line.

string $mySelection[] = "ls -sl";

This creates a variable array that holds a list of the currently selected objects. The list is numbered starting with zero, so once the list has been created from one or more selected objects, the first selected object is referred to as $mySelection[0], the second selected object is referred to as $mySelection[1], and so on.

The ls command stands for "list," and the -sl flag modifies the list command so it creates its list from the currently selected objects. The variable actually holds the result of the list command so the list command is contained within the accent marks. The accent mark key is the one below the ESC key on standard keyboards (not the apostrophe key). All commands in MEL must end in a semicolon.

Hit Enter (or Return) to start a new line. In this line type:

delete "pointConstraint $mySelection[0] $mySelection[1]";

This command is actually two commands in a single line. The command within the accent marks creates a point constraint. The second object in the list, $mySelection[1], is constrained to the first, $mySelection[0]. When you create a constraint, you select the constraining object first and then the object that is constrained. The delete command then deletes the constraint immediately after it has been created, so that when you run the script the second object snaps to the first and you don't need to delete the constraint in the Outliner.

It may seem confusing to nest the point constraint command within the delete command and place them on a single line, but there's a good reason for using this convention. Let's say you wrote the script so that the point constraint command on one line creates the constraint—thus snapping one object to another—and then a second delete command deletes the constraint on another line. The delete command needs to know which point constraint it should delete. If you assume that the new point constraint will be named pointConstraint1, you run the risk of deleting a point constraint that already exists in the scene. You need a scripting strategy that creates a constraint, retrieves the correct name of the new constraint, and then deletes this new constraint. This involves many more lines of code. Hence it is much easier, and simpler, to nest the point constraint command within the delete command. Everything is taken care of within a single line of code. Select both lines in the Text Editor and copy them. In Maya, paste the script into the bottom half of the Script Editor (you can open the Script Editor by choosing Window

To the left of the shelf click the down-arrow button and choose Save All Shelves so this shelf button is available in future Maya sessions.

Create two objects in a Maya scene, select the constraining object first, then Shift+click the object to be constrained. Click the objSnp button in the Custom tab of the shelf to test the script. If you get an error, you can edit the command in the Shelf Editor. Click the down-arrow button to the left of the shelf, and choose Shelf Editor. Select the Custom shelf in the Shelf tab, switch to the Shelf Contents tab, and select the objSnp command in the Shelf Contents tab. Click the Edit Commands tab, and you'll see the script in the edit area. Correct any typos, and save the shelf.

To see a version of the script open the objSnp.mel script in a text editor. The script is located in the chapter5mel directory on the DVD.

Repeat steps 4 and 5 (or use the shelf button created in the "MEL In Action" section) to reposition joint2 to the frontLeftFoot object.

Turn on Point Snapping (turn off Grid Snapping), and position joint3 at the very tip of the frontLeftFoot.

Rename joint1 frontLeftLegJoint. Rename joint2 frontLeftFootJoint, and rename joint3 frontLeftEndJoint.

Make sure all point constraints on the joints have been deleted. Parent the frontLeftLegBase object to the frontLeftLegJoint, and parent the frontLeftFoot to the frontLeftFootJoint (see Figure 5.6).

Figure 5.6. Parent the parts of the leg to the leg joints.

Create similar joint systems for the remaining five legs. Remember to rename your joints in a descriptive manner (see step 8) to avoid confusion when animating.

When you have finished creating all of the joints, place them in the legs group. To do this MMB-drag each of the top joints in the chain into the legs group in the Outliner (see Figure 5.7).

Save the scene as mechBugRig_v02.ma. To see a version of the scene to this point, open the mechBugRig_v02.ma scene from the chapter5scenes directory.

Continue with the scene from the previous section or open the mechBugRig_v02.ma scene from the chapter5scenes directory on the DVD.

Turn on the display layer for BODY; turn off the LEGS layer so the legs are hidden and the body is displayed.

Create a locator and name it eyeAimLoc. Set the eyeAimLoc's Translate X, Y, and Z channels to 0, 0, and 2, respectively.

In the Outliner, expand the bugBodyGroup. MMB-drag eyeAimLoc into the bugBody group.

Select the eyeAimLoc and choose Modify

Expand the frontBody group, the head group, and the face group.

Select the eyeAimLoc and Ctrl+click the eyeBase group (see Figure 5.8). From the Animation menu set choose Constrain

In the options choose Edit

Figure 5.8. Select the eyeAimLoc locator and the eyeBase object in the Outliner.

Figure 5.9. The Aim Constraint Options window

Move the locator around in the scene, and you'll see that the eyes follow it (see Figure 5.10). Because the locator is parented to the bug body, when you animate the bug, the locator will move with it.

Figure 5.10. The eyes follow the position of the eyeAimLoc locator.

Create two new locators named leftAntennaAimLoc and rightAntennaAimLoc.

Set leftAntennaAimLoc's Translate X, Y, and Z to 1, 0, and 3, respectively, and rightAntennaAimLoc's Translate X, Y, and Z to −1, 0, and 3.

Freeze transformations for both locators. Shift+click both locators and group them together. Name the group antennaAim. Leave the pivot point for the group at the center of the grid.

In the Outliner, MMB-drag antennaAim into the bugBody group.

Expand the antennaAim group. Expand the face group (in the bugBody/frontBody/head group). Aim constrain the leftAntenna to the leftAntennaAimLoc locator and the rightAntenna to the rightAntennaAimLoc locator.

When you move each antennaAimLoc locator, the antennae follow; when you rotate the antennaAim group, the locators move and the antennae follow. This gives you a way to animate the antennae separately and together (see Figure 5.11).

Figure 5.11. You can animate the antennae separately or together based on the grouping of the antennaAimLoc locators.

Save the scene as mechBugRig_v03.ma. To see a version of the scene to this point, open the mechBugRig_v03.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section, or open the mechBugRig_v03.ma scene from the chapter5scenes directory on the DVD. In the Layer menu, turn off Visibility for the BODY layer.

From the Animation menu set choose Skeleton

The other option is the Rotate Plane solver (RPsolver). This solver has extra controls that can be used to solve joint-flipping problems, which can occur with more complex joint arrangements. If you create an IK Handle using the ikSCsolver and your joints behave unpredictably, try switching to the RPsolver (you can do this after creating the handle using the menu options in the IK Handle's Attribute Editor). The various types of IK solvers are discussed in Chapter 7.

In general, when adding Inverse Kinematics to a joint chain using the IK Handle tool, you don't want the joints to be aligned in a straight line. There should be a small bend in the joint chain. This helps the solver figure out how the joints should bend as they attempt to rotate based on the position of the End Effector. It's also a good idea to freeze transformations on the joints so their X, Y, and Z rotation channels are set to zero before adding the IK Handle (in the mechBug_v03.ma scene this has already been done).

Turn on Solver Enable and turn off Snap Enable. Snap Enable causes the IK Handle to snap back to the position of the end joint when you release it. You'll create a custom handle using a curve, so this option should be off.

Turn on Sticky. Sticky keeps the IK Handle's position constant as you pose the rest of the skeleton. This is very useful for keeping feet from moving through the floor when animating the other parts of the skeleton (see Figure 5.14).

Figure 5.14. The options for the IK Handle tool

The other settings can be left at the default. With the IK Handle tool activated, click on the frontLeftLeg joint (the joint at the root of the front left leg); then click on the joint at the end of the frontLeftLeg chain. The IK Handle appears at the end of the joint chain (see Figure 5.15).

Try moving the IK Handle; you'll see the rest of the joint rotate based on the position of the handle.

Click Undo until the IK Handle returns to its original location.

It's usually a good idea to use a curve or another easily selectable object as a control for the IK Handle. This makes it easy to select the handle directly in the scene without having to hunt around in the Outliner.

Create a NURBS circle (Create

Figure 5.15. The IK Handle tool creates an IK solver for the front left leg.

Use the objSnp shelf button created earlier in the chapter (see the "MEL in Action" section) to position the circle at the location of the IK Handle. To do this, select the ikHandle1 object, Ctrl+click the nurbsCircle1, and click the objSnp button in the Custom shelf.

Select the nurbsCircle1 and rename it frontLeftFootCtrl. Choose Modify

Select the frontLeftFootCtrl, and Ctrl+click the ikHandle. Create a point constraint so the handle is constrained to the frontLeftFoot circle (Constrain

You can turn off visibility of the ikHandle1 object. To animate the leg, select the frontleftLegCtrl circle and move it around. To reset its position, set its Translate X, Y, and Z channels to 0.

Repeat steps 2 through 12 to create controls for the other five legs (the options for the IK Handle tool should already be stored, so you can just activate the tool and use it to add IK to the other legs).

When you have finished making the controls for the other legs, select the control circles and group them. Name the group legsControlGroup.

Select the legsControlGroup group, and choose Modify

Make another NURBS circle; name the circle legsCtrl. Use the objSnp button to place the circle at the position of the legControlGroup's pivot. Freeze transformations on the legsCtrl.

Select the legsCtrl circle, and Ctrl+click the legsControlGroup. Choose Constrain

Now you have a selectable control for moving all of the legs as well as each individual leg. This will mean less time hunting around in the Outliner.

Finally, you can straighten up the Outliner by grouping the IK Handles. Name the group feetIkhandles. Group the legs and bugBody together, and name this group bug.

Save the scene as mechBugRig_v04.ma. To see a version of the scene to this point, open the mechBugRig_v04.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBugRig_v04.ma scene from the chapter5scenes directory on the DVD.

Create a new display layer named CONTROLS. Turn off the visibility of the LEGS and BODY display layers, select the NURBS circles, and add them to the CONTROLS layer.

Turn off the Visibility of the CONTROLS layer so the scene is blank.

Turn on the Visibility of the grid. Turn on Grid Snapping. Choose Create

Switch to the top view, and use the curve to draw a shape like the one in Figure 5.16. The shape should be a cross with an arrowhead at each end of the cross. Press Enter to complete the curve.

Figure 5.16. Create a cross with an arrow at each end using a linear CV curve.

Center the pivot of the curve and name it bodyCtrl.

In the Outliner, expand the bug group. Click the objSnp button to snap the bodyCtrl curve to the center of the bugBody object. Scale the bodyCtrl curve in X, Y, and Z to 3.5.

Freeze transformations on the curve.

Next, you want to move the curve above the body so you can easily select it. This curve controls the translation and rotation of the bugBody. However, you want to keep the pivot point of the control at the center of the bug body. Since you snapped the curve to the center of the bugBody, the pivot point of the curve is at the same position as the bugBody. So how do you move the curve without moving the pivot point? Simple—you move all of the CVs of the curve above the bug body. This moves the curve without changing its pivot point.

Select the bodyCtrl curve and switch to CV selection mode (right-click on the curve and choose CVs). Drag a selection marquee over all of the CVs of the curve. Switch to the Move tool, and drag up on the Y axis to position the CVs of the curve above the body. Since the pivot point has not changed, it doesn't matter how high you place the curve above the bug; it just has to be easily selectable (see Figure 5.17).

Select the bodyCtrl curve in the Outliner, and Ctrl+click the bug group. Choose Constrain

Figure 5.17. Move the CVs of the bodyCtrl curve above the bugBody; the pivot point of the curve remains at the center of the bugBody.

The parent constraint constrains both the translation and rotation of one object to another object.

Turn on the LEGS layer. Select the bodyCtrl curve and try moving and rotating it. The legs stay on the ground (within a certain range).

At this point you should have a nice set of simple controls for both the body and the legs of the bug. All this work will make animating the bug a much more pleasant experience.

Finally, select everything in the Outliner except the ground plane, and group them together. Name the group mechanicalBug.

Add the bodyCtrl curve and the three locators for the eyes and antenna controls to the CONTROLS layer.

Save the scene as mechBugRig_v05.ma. To see a version of the scene to this point, open the mechBugRig_v05.ma scene from the chapter5scenes directory of the DVD (see Figure 5.18).

Figure 5.18. The completed bug rig is ready for animation.

Open the mechBug_v01.ma scene in the chapter5scenes directory on the DVD.

The mechanical bug in this scene has been rigged using the techniques discussed in the first part of the chapter. The major difference is that a circle has been added between the two antenna controls that you can select and animate to control both antennae at the same time.

The controls are color coded so they are more organized visually. The visibility of the joints is turned off in the Show menu of the perspective view; however, they are still present in the scene.

Frame Rate

When you begin an animation, it's always a good idea to set the frame rate in Maya's preferences. The default frame rate is 24 frames per second, which is standard for film. To change the frame rate, choose Window

In the perspective view, select the blue bodyCtrl curve above the bug (the curve that looks like a cross with an arrow on each end; see Figure 5.19).

Figure 5.19. Select the bodyCtrl curve above the bug.

Move the current frame in the timeline to frame 20 by clicking and dragging the timeline until the marker is at frame 20. Alternatively, type 20 into the box to the far right of the timeline.

With the bodyCtrl selected, highlight the Translate Y channel in the Channel Box by clicking on it; then right-click and choose Key Selected from the pop-up menu (see Figure 5.20).

Set the timeline to frame 48. Use the Move tool to pull the bodyCtrl curve up to about two units, and set another keyframe on the Translate Y channel. The keys are represented on the timeline by a thin red vertical line (see Figure 5.21).

Rewind and play the animation; you'll see the bug start moving upward on frame 20 and stop on frame 48.

On the timeline for the mechBug_v01.ma scene, set the current frame to 20.

An easy way to do this is to use the Step Back One Key or Step Forward One Key buttons to the right of the timeline. The hotkeys for moving back and forth one key are Alt+comma and Alt+period.

Shift+click all six of the small purple leg control circles below the bug's feet (see Figure 5.22).

Figure 5.22. Select the leg control circles.

With the control circles selected, press the W hot key to place a keyframe on the Translate channels for all the selected curves.

Click the Key icon to the far right of the timeline to turn on Auto Keyframe.

Set the timeline to frame 40. Select each of the circles and move them in toward the center (see Figure 5.23).

When you play the animation, you'll see that the legs move inward without your having to set a keyframe in the Channel Box.

Using Auto Keyframe is certainly a matter of personal preference. You can easily set unwanted keys on an object by mistake using this feature, so remember to use it with caution.

Save the scene as mechBug_v02.ma. To see a version of the scene to this point, open the mechBug_v02.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBug_v02.ma scene from the chapter5scenes directory on the DVD.

In the Perspective window, select the blue bodyCtrl curve. Hold the Shift key and drag a selection directly on the timeline. You'll see a red area appear as you drag. Keep dragging this area so it covers both keyframes set on the bodyCtrl curve (see Figure 5.24).

Figure 5.24. Hold the Shift key and drag on the timeline to select a range of keys.

To move the keys forward or backward in time, drag on the two arrows at the center of the selection. Drag on these arrows to move the keys so the first key is on frame 10.

To scale the keys, drag on one of the arrows on either side of the selection. The other end of the selection acts as the pivot for the scaling operation; you may need to reposition the keys on the timeline again after scaling.

Scale the keys down by dragging the arrow on the right side of the selection toward the left. After scaling the keys, drag on the arrows at the center to reposition the keys so the animation starts on frame 10.

Snap Keys

As you scale and move keys, you'll notice that a keyframe can be positioned on the fraction of a key. In other words, a key might end up on frame 26.68. You can fix this by choosing Edit

You can move an individual key by Shift+clicking the key marker on the timeline and then dragging on the arrows to move the key.

Repositioning and scaling keys directly on the timeline is usually good for simple changes. To make more sophisticated edits to the animation, you can use the Graph Editor discussed later in the chapter.

When you play the animation, you'll see that the bug jumps up fairly quickly and much sooner than before. You'll also notice that the animation of the legs has not changed.

Spend a few minutes practicing these techniques on each of the legBase objects. Changes made to the position of the keyframes affect selected objects. You can edit each legCtrl circle separately or all of them at the same time.

Save the scene as mechBug_v03.ma. To see a version of the scene to this point, open the mechBug_v03.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBug_v03.ma scene from the chapter5scenes directory on the DVD.

Select the bodyCtrl curve in the perspective view. On the timeline, Shift-drag a selection over both of the keyframes.

Right-click on the selection and choose Copy (see Figure 5.25).

Deselect the keys by clicking on the timeline, move to frame 70, right-click on the timeline, and choose Paste

Figure 5.25. You can copy keyframes directly onto the timeline.

The keys for the Translate Y channel are pasted on the timeline at frame 70. If you play the animation, you'll see that the bug jumps up, moves back down, and then jumps up again.

Other options include the following:

Select the bodyCtrl curve in the perspective view. In the Channel Box, right-click on the Translate Y channel. Choose Copy Selected (see Figure 5.26).

Highlight the Translate Z channel, right-click, and choose Paste Selected.

This pastes the values (including keyframes) copied from the Translate Y channel to the Translate Z channel. The starting point of the pasted keyframes is based on the current time in the timeline. When you play the animation, the bug moves forward as it moves up. The forward motion will be offset (in time) depending on the current frame in the timeline.

Figure 5.26. You can copy keyframes using the menu options in the Channel Box.

You can also cut and delete keyframes in the Channel Box. The Duplicate keyframe operation allows you to copy keyframes from one object to another.

Create a NURBS sphere and set its Translate X to 5.

Select the sphere and then Shift+click the bodyCtrl curve. Right-click on the Translate Y channel, and choose Duplicate Values. This connects the keyframes on the Translate Y channel of the bodyCtrl curve to the NURBS sphere. If you change the values of these keys, both the bodyCtrl curve and the sphere will reflect the changes made to the keys.

Open the mechBug_v01.ma scene from the chapter5scenes directory on the DVD.

Open the Preferences window by choosing Window

Make sure Auto Keyframe is enabled. Press Save to save the preferences (see Figure 5.29).

Figure 5.29. The animation preferences are established in the Settings/Preferences window.

Set the length of the timeline to 120. Set the current frame to 20.

Select the blue bodyCtrl curve in the perspective view. Press W and E to set keyframes on the Translate and Rotate channels.

When blocking out the animation, the only object that needs to be keyframed at this point is the bodyCtrl curve.

Set the timeline to frame 25, and move the bodyCtrl curve down so the Translate Y channel is about −0.78.

Set the timeline to frame 35. Drag up on the bodyCtrl curve until the Translate Y channel is around 7 units.

Set the timeline to 45. Rotate the bodyCtrl slightly, and move the bug a little forward and to the side. This gives the bug a slight wobble as he hovers. Try these settings:

Many of these values were arrived at by simply moving and rotating the bodyCtrl curve in the scene. You can use these exact values or something that's fairly close. Most of the time when blocking in the animation you'll move the objects in the scene rather than type in precise values, but the keyframe values are included here as a rough guide. Remember, right now the only object being keyframed is the bodyCtrl curve.

Set the frame to 60. The bug is starting to turn as he decides which way to fly. Rotate him to his left a little and add a bit more variation to his position. Try these settings:

Now the bug is starting to fly away. Rotate him so he is facing downward slightly. Try these settings:

Set the time slider to frame 95. The bug is beginning his flight, so he turns more to the left and dips down a little. Try these settings:

In the final keyframe on frame 120 the bug is flying away. Try these settings:

Play back the animation a few times. You'll see the bug pop from one position to another. Make changes if you like, but try not to add any more keys just yet. It's best to use as few keys as possible; you'll let the curves do all the work in a moment.

Select the red legsCtrl circle, and keyframe its Translate channels so it follows the flight of the bug. To keep it interesting, place the keys at different frames than the bodyCtrl curve. Remember to set an initial keyframe before using Auto Keyframe.

You can set keys on the individual foot controls, but at this point let's keep things simple and focus on just the bodyCtrl curve and the translation of the legsCtrl curve.

In the Perspective View menu, choose Panels

Select the bodyCtrl curve, and hold the cursor over the Graph Editor. Press the f hot key so you can see all the animation curves for the bodyCtrl object. Since the tangents are set to Stepped, they look like straight lines in a stepped pattern (Figure 5.30).

Save the scene as mechBug_v04.ma. To see a version of the scene to this point, open the mechBug_v04.ma scene on the chapter5scenes folder of the DVD.

Continue with the scene from the previous section or open the mechBug_v04.ma scene from the chapter5scenes directory on the DVD.

In the Display Layers menu, turn off the visibility of the LEGS layer so you can just focus on the animation of the body.

Select the bodyCtrl curve, and in the Graph Editor drag a selection marquee over all the translation and rotation keys. Test how the animation looks when different tangent types are applied to the keys.

On the menu bar of the Graph Editor, click the first tangent icon or choose Tangents

In the Graph Editor zoom in closely to the selected keys (MMB+Alt-drag).

You'll notice that spline tangents add a bit of overshoot to some of the keys, as shown in Figure 5.31, which results in a smooth, natural motion. However, in some cases this may add extra motion where you don't want it. It depends on how much precise control you want over the animation.

Figure 5.31. Switching to spline tangents adds a slight overshoot to the animation curves. Notice how the curve dips below the lowest value of some of the keyframes.

Try switching to the clamped-type tangent (second tangent icon, or choose Tangents

Clamped tangents are very similar to spline tangents; in fact, you'll notice a difference between spline and clamped tangents only when two values in a curve are very close together. Clamped tangents remove any overshoot that may cause sliding or slipping in an object. In the current animation example, you won't see much a difference at all except for a couple keyframes (see Figure 5.32).

Figure 5.32. Clamped tangents are very similar to spline tangents except for values that are very close. In this figure spline tangents (left image) are converted to clamped tangents (right image).

Aside from spline, clamped, and stepped tangents, you can also try using one of these tangent types. A single curve can use any combination of tangent types as well.

With all of the keys selected in the Graph Editor, click on the last tangent icon, or choose Tangents

A good place to start editing the animation is the initial leap that occurs at frame 20.

Make sure you can see both the Graph Editor and the body of the bug in the perspective view. The bugCtrl object should be selected so you can see its animation curves.

In the left column of the Graph Editor, highlight Translate Y to focus on just this individual curve.

The leap has a slight anticipation where the bug moves down slightly before jumping in the air. At the moment the motion is uniform, making it look a little uninteresting. You can edit the curve so the bug leaps up a little faster and sooner. Start by moving the third keyframe closer to the second.

Select the third keyframe, and click the move key icon (first icon on the far left of the menu bar) or use the w hot key. To move the key, hold the MMB and drag to the left (see Figure 5.33). To constrain the movement horizontally so its value is not changed (only its time), hold the Shift key while dragging with the MMB.

Figure 5.33. Move the third keyframe on the bodyCtrl's Translate Y channel to the left, closer to the second keyframe.

You can enter numeric values into the Stats field for precise control. The first field is the keyframe's time in frames; the second field is the value for the keyframe.

Slide the keyframe to the left so it is close to the second keyframe; the curve in between should become more of a straight line. If you want the keys to snap to whole values, select the key and choose Edit

There are two magnet icons on the menu bar of the Graph Editor (these may be visible only when the Graph Editor is maximized). These icons turn on horizontal and vertical snapping, respectively. The keyframes are then snapped to the grid in the Graph Editor (see Figure 5.34).

You can change the shape of the curves by editing the tangents directly. Drag a selection box around the handle to the right of the third key. Press the w hot key to switch to the Move tool. MMB-drag upward to add overshoot to the out tangent (see Figure 5.35).

Figure 5.34. The magnet icons turn on horizontal and vertical snapping.

Figure 5.35. MMB-drag on the tangent handles to directly edit the curve shape.

You'll notice that as you drag upward on the tangent handle, the handle on the opposite side of the key moves downward, maintaining the shape of the curve through the key. You can break the tangency of the curve handles if you want a different interpolation for the in and out tangents.

Drag a selection around both handles of the second key on the Translate Y channel. Choose Key

Drag a selection handle around the in tangent, and MMB-drag it upward so there is a slight bump and then a sharp dip in the curve (Figure 5.36).

When you play the animation, the bug moves up slightly, down quickly, and then leaps into the air. You can unify the tangents by choosing Keys

Save the scene as mechBug_v05.ma. To see a version of the scene to this point, open the mechBug_v05.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBug_v05.ma scene from the chapter5scenes directory on the DVD.

Select the bodyCtrl curve, and in the Graph Editor select the Translate Y channel to isolate the curve. Press the f hot key so the entire curve fits in the Graph Editor.

Drag a selection around the fourth key, and use the MMB to drag it down a little to create a slight dip in the curve (upper left of Figure 5.37).

With the key selected choose Curves

Select the handles and choose Keys

MMB-drag on the handles left or right to extend the length of the handles; notice the change in the shape of the curve (lower-left of Figure 5.37).

Break the tangents on the selected handles (Keys

Pull the outcoming tangent of the fourth keyframe down and to the right (lower-right image of Figure 5.37).

Play the animation, and see how changing the length of the handles affects the way the bug jumps.

Save the scene as mechBug_v06.ma. To see a version of the scene to this point, open the mechBug_v06.ma scene from the chapter5scenes folder on the DVD.

Continue with the scene from the previous section or open the mechBug_v06.ma scene from the chapter5scenes directory on the DVD.

Select the bodyCtrl curve in the perspective view and open the Graph Editor. Press the f hot key so all the curves are visible on the editor.

Drag a selection marquee over all the keys to the right of the third key.

From the Graph Editor menu bar, choose Edit

When the Scale Keys tool option is set to Gestural, the position of the cursor on the graph is the pivot for the scaling operation.

Hold the cursor over the fourth key. MMB-drag back and forth to scale the keys horizontally. Increasing the scale horizontally slows down the animation; decreasing the horizontal scale speeds up the animation (see Figure 5.38).

Drag the lower-left corner of the Scale Keys tool to the right a little to extend the animation and slow it down after the fourth keyframe.

Figure 5.38. The Scale Keys tool stretches or shrinks the distances between selected keys on the graph.

If you want to scale just the values, you can drag up or down. Small changes made with the Scale Key tool can have a large effect, so use this tool with caution.

Another way to edit the keys is to use the Lattice Deform Keys tool.

With the keys still selected, choose Edit

Figure 5.39. The Lattice Deform Keys tool creates a lattice around selected keys to manipulate groups of selected keys.

To change the number of rows and columns in the lattice, open the Tool Options box while the Lattice Deform Keys tool is active. If the lattice does not update properly when you change the settings in the Tool Options box, try reselecting the keys in the Graph Editor.

The Insert Keys tool inserts a key in one or more animation curves. To use this tool, first select one or more animation curves in the Graph Editor, click the Insert Key icon in the Graph Editor toolbar, and MMB-click on the curve.

The Add Key tool is similar to the Insert Keys tool except that wherever you click in the Graph Editor will be used as the value for the added key. Both tools require that you MMB-click in the Graph Editor (see Figure 5.40).

You can copy and paste keys on the graph; pasted keys are placed at the current location on the timeline. This means that if you select a group of keys that start at frame 40, then move the timeline to frame 60 and paste, the keys will be pasted at frame 60. For more precise copying and pasting, use the Copy and Paste options in the Graph Editor's Edit menu.

Practice editing the keys on the Graph Editor for the bodyCtrl curve (both Translate and Rotate channels). When you're happy with the animation, make the legs visible and edit the keys set on the legCtrl circle.

If you decide to use Auto Keyframe when refining the animation for other parts of the robot, switch the default in and out tangents to spline, clamped, or plateau in the preferences. Otherwise Maya inserts stepped keyframes while Auto Keyframe is on, which can be frustrating to work with at this point.

You can add natural-looking motion to the way the bug hovers by simply shifting the keys placed on the different channels back and forth in time so they don't occur on the same frame (see Figure 5.41).

To see a version of the scene where the keys have been edited, open the mechBug_v07.ma scene in the chapter5scenes directory on the DVD.

Open the mechBug_v07.ma scene from the chapter5scenes directory on the DVD.

Turn off the visibility of the LEGS layer so you can focus on just the bug body.

Select the blue bodyCtrl curve and open the Graph Editor. Select the Translate Y channel so it is isolated on the graph.

Drag a selection around the third key on the graph. Switch to the Move tool (hot key = w). Hold the Shift key and drag back and forth on the graph. The other keys on the graph do not move; this is the normal behavior for keys.

Drag a selection around the second key on the graph. From the menu in the Graph Editor, choose Keys

You won't notice any difference in the key itself or its tangent handles. The color of the key tick mark on the graph changes to green, but other than that it looks and acts the same.

Drag a selection around the third key on the graph, and try moving it back and forth.

Open the mechBug_v07.ma scene from the chapter5scenes directory on the DVD.

Set the timeline to 10.

In the perspective view, zoom in closely to the body of the bug; on its left side, select the small piece of geometry that holds the wing to the body. The object is called leftWingMotor (see Figure 5.43).

Right-click on the Rotate X channel in the Channel Box, and choose Key Selected.

Set the frame in the timeline to frame 12. Set Rotate X to 60, and create another keyframe.

Set the timeline to frame 14, set Rotate X to 0, and create another keyframe.

With the leftWingMotor selected, open the Graph Editor. Select Rotate X in the column on the left, and press the f key so the editor focuses on the animation curve for this channel.

Select all the keys, and choose Tangents

Figure 5.43. Select the leftWingMotor on the side of the bug.

Zoom out a little in the Graph Editor (drag using Alt+RMB on the editor).

With the curve selected choose Curves

Choose View

Play the animation in the perspective view. The wing starts flapping in frame 10; it continues to flap at the same rate for the rest of the animation.

Figure 5.44. You can view how the keyframes will cycle by choosing View

Infinity. The animation curve after the last keyframe is shown as a dotted line.

To make the wing flap faster, simply scale the keyframes.

Repeat steps 7 through 11 for the rightWingMotor.

Save the animation as mechBug_v08.ma. To see a version of the animation to this point, open the mechBug_v08.ma scene from the chapter5scenes directory on the DVD.

Open the mechBug_v08.ma scene from the chapter5scenes directory on the DVD.

Switch to the shotCam camera in the perspective view.

Choose Window

Set Display Size to From Window and Scale to 0.75 (see Figure 5.46).

Figure 5.46. The options for Playblast

Click Playblast to record the image sequence. In the case of the bug animation, this should take only a few seconds. A scene that has a lot of dynamics or a lot of geometry may take longer.

Once the playblast is complete, F Check should open automatically and play the sequence. You can also open a sequence in F Check by choosing (from the main Maya menu bar) File

Open the mechBugWalk_v01.ma scene from the chapter5scenes directory on the DVD.

In the perspective view, use the Show menu to turn off visibility of the joints so it's easier to select the leg controls.

Driven keys are set through a separate interface. You'll set up the walk cycle for one leg and then copy and paste the keys to the others.

From the Animation menu set, choose Animate

The upper part of the Set Driven Key window lists the driving object (there can be only one at a time) and its attributes. The bottom part of the window lists the driven object(s) (there can be more than one at a time) and their attributes. The first step is to load the driving and driven objects. Figure 5.48 shows the Set Driven Key window with objects loaded already; you'll load the objects and attributes in the next few steps.

Figure 5.48. The Set Driven Key interface lists the driver objects at the top and the driven objects on the bottom.

Select the bodyCtrl curve and click the Load Driver button.

Select the frontLeftFootCtrl curve and click Load Driven.

To create the walk cycle for the front left leg, the Z translation of the bodyCtrl curve will drive the Z translation of the front left foot (making it move forward) and the Y translation of the front left foot (making it move up as it moves forward). You need to create the first key to establish the starting position of the front left leg.

Select the frontLeftFootCtrl curve, and set its Translate Z channel to −1.

In the Set Driven Key window, select Translate Z in the upper-right corner (this indicates the Translate Z of the bodyCtrl curve as selected in the upper left of the box). Shift+click the Translate Y and Translate Z channels in the lower right (this indicates the Translate Z and Translate Y of the frontLeftFootCtrl curve (see Figure 5.48).

Click the Key button at the bottom of the Set Driven Key window.

When you click the Key button, the current value for the channel selected in the upper right is the driver for the values of the channels in the lower left. So in step 8, the Translate Z of bodyCtrl is set to 0, the Translate Z of frontLeftFootCtrl is set to −1, and the Translate Y of frontLeftFootCtrl is set to 0. A keyframe relationship is set up between the Translate Z of bodyCtrl and the Translate Z and Translate Y of frontLeftFootCtrl. When frontLeftFootCtrl is selected, its Translate Y and Translate Z channels are colored orange in the Channel Box, indicating a keyframe has been set on these channels.

Select the bodyCtrl curve again and set its Translate Z to 1. Select the frontLeftFootCtrl curve, and set its Translate Z to 1 and its Translate Y to 0.8.

Make sure that in the Set Driven Key window, the Translate Z channel is selected in the upper right and both the Translate Y and Translate Z channels are selected in the lower right. Click the Key button again to set another key.

Set the Translate Z of bodyCtrl to 2. Set the Translate Z of frontLeftFootCtrl to 3 and the Translate Y to 0. Click the Key button again.

Set the Translate Z of bodyCtrl to 4. Don't change either setting for Translate Z or Translate Y of frontLeftFootCtrl. Set another key.

The IK applied to the front left leg keeps it stuck in place, which makes the walk cycle easy to animate.

In the perspective view try moving the bodyCtrl rig back and forth on the Y axis. You'll see the front left foot take a step.

Save the scene as mechBugWalk_v02.ma. To see a version of the scene to this point, open the mechBugWalk_v02.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBugWalk_v02.ma scene from the chapter5scenes directory on the DVD.

Select the frontLeftFootCtrl and open the Graph Editor (Window

You'll see the animation curves appear on the graph. Since these are driven keys, the horizontal axis does not represent time; rather it is the Translate Z channel of the bodyCtrl curve. So as the graph moves from left to right, the value of the bodyCtrl's Translate Z channel increases. Moving from right to left, the value decreases.

In the Graph Editor menu, choose View

Select the green Translate Y curve. Choose Curves

By doing this you create a repeating cycle for Translate Y. The foot moves up and down in the same pattern as the bodyCtrl curve moves back and forth. The Translate Z channel is a little different. Since it is moving along the Z axis in space, you need to offset the value for each step so the foot continues to step forward.

Select the blue Translate Z curve and choose Curves

Move the bodyCtrl curve back and forth on the Z axis, and you'll see that the front left leg now walks with the bug.

Save the scene as mechBugWalk_v03.ma. To see a version of the scene to this point, open the mechBugWalk_v03.ma scene from the chapter5scenes directory on the DVD.

Continue with the scene from the previous section or open the mechBug_v03.ma scene from the chapter5scenes directory on the DVD.

From the Animation menu set, choose Animate

Select the bodyCtrl curve and load it as the driver. Select all of the leg control curves except the frontLeftLegCtrl. Press the Load Driven button.

Make sure the Translate Z channel of the bodyCtrl curve is at 0. Set the Translate Z of the five leg control curves to −1.

Select the Translate Z channel in the upper right of the Set Driven Key window. In the lower left, make sure all the leg control curves are selected.

Select the Translate Y and Translate Z channels in the lower right. Click the Key button to create an initial key for the five legs. You can close the Set Driven Key window (see Figure 5.50).

Make sure the bodyCtrl curve's Translate Z channel is at 0. Select the frontLeftFootCtrl curve. In the Channel Box, highlight the Translate Y and Translate Z channels. Right-click and choose Copy Selected.

Shift+click the five other leg control curves. Highlight the Translate Y and Translate Z channels, right-click, and choose Paste Selected.

Figure 5.50. Set an initial driven key on the Translate Y and Translate Z channels of the five remaining legs.

When you move the bodyCtrl curve back and forth, the other legs take one step. You need to loop the driven keys of the other legs in the Graph Editor.

Select the leg control circles for the five remaining legs, and open the Graph Editor. Ctrl+click the Translate Y channels of all the leg controls in the left column of the editor. Drag a selection over the keys on the graph, and choose Curves

Ctrl+click the Translate Z channel for each of the leg controls in the Graph Editor. Drag a selection around the keys on the graph, and choose Curves

Drag the bodyCtrl curve back and forth on the Graph Editor. All the legs take a step; however, they all do so at the same time, which looks a little silly.

To create a more convincing walk cycle for the bug, select each leg control, and open the Graph Editor. Select the keys on the graph and use the Move tool to slide them a little backward or forward in time so each leg has its own timing. See Figure 5.51.

As you change the position of the Translate Z keys on the Graph Editor, you may need to also slide the curves up or down a little to make sure that they remain within the proper leg length range as they step. You can generally figure out the proper setting through experimentation.

Figure 5.51. Add variation to the movement of the legs by sliding the keys for each leg control on the Graph Editor.

Creating a walk cycle this way is a little tricky and will take some practice. You can set keyframes on the Translate Z channel of the bodyCtrl curve so the bug walks forward and then adjust the position of the legCtrl curves as the animation plays. You can also change the position for the keyframes on the Graph Editor for pairs of legs so the midLeftLegCtrl, frontRightLegCtrl, and rearRightLegCtrl all move together, alternating with the remaining leg controls. Study the mechBugWalk_v04.ma scene in the chapter5scenes directory on the DVD to see how this walk cycle was accomplished.

Save the scene as mechBugWalk_v04.ma. See Figure 5.52. To see a finished version of the walking bug, open the mechBugWalk_v04.ma scene from the chapter5scenes directory on the DVD.

Figure 5.52. The completed walk cycle is completely automated for the bug.

Continue with the scene from the previous section or open the mechBugExpressions_v02.ma scene from the chapter5scenes directory on the DVD.

Select one of the yellow locators in front of the bug, and open the Expression Editor using the Edit menu in the Channel Box.

To create a condition, you'll make a variable that can hold a value. The value will be different depending on the outcome of the test performed by the conditional statement. In this case, the variable can hold a value, which will be a multiplier for time in the noise(time) statement applied to the locator's Translate Y channel. Before you can use the variable, you should declare it at the start of the expression. This lets Maya know what type of data the variable will hold. In this case, the variable can be an integer (a number without a decimal). The variable you will create is called $antSpeed, for antenna speed. All variables must be preceded by a dollar sign.

In the Expression Editor, select the text and press the Backspace or Delete key to clear the Expression field. Type int $antSpeed; in the field.

Press the Return key (the Return key on the keyboard, not the Enter key on the numeric keypad), and enter the following lines:

if (antennaCtrl.translateY<0){
     $antSpeed = 10;
}
else
{
     $antSpeed=2;
}
translateY = noise(time*$antSpeed);

Since the expression is testing to see the height of the antennaCtrl group, you need to specify the path to the antennaCtrl group's Translate Y channel. Expressions for channels are self-contained, so unless you specify the path to another object's channel, Maya won't understand what you're talking about. Figure 5.55 shows the expression in the Expression Editor.

Figure 5.55. Create a conditional statement as an expression to make the antenna move faster when it's closer to the ground.

Add the same expression to the other locator in the group. Use different values for the $antSpeed variable so that the two antennae move in different ways.

Save the scene as mechBugExpressions_v03.ma. To see a finished version of the scene, open the mechBugExpressions_v03.ma scene from the chapter5scenes directory on the DVD.

Open the mechBugPath_v01.ma scene from the chapter5scenes directory on the DVD.

Turn on the grid display and choose Create

Draw a curve on the grid using any number of points; make sure the curve has some nice twisty bends in it.

Right-click on the curve and choose Control Vertex. Use the Move tool to move the CVs of the curve up and down so the curve is three-dimensional (see Figure 5.56).

In the Outliner, select the mechanicalBug group and Ctrl+click the curve. From the Animation menu set, choose Animate

Figure 5.56. Draw and shape a curve in the scene.

In the options, choose Edit

Figure 5.57. The options for Attach To Motion Path

The default Time Range is set to Time Slider so the bug will travel the length of the curve based on the current length of the time slider (200 frames in this scene). You can change this after the motion path is created.

The Follow option orients the animated object so the front axis follows the bends in the curve. The Bank option adds a rotation on the Z axis around bends in the curve to simulate banking.

Play the animation. The bug follows the path (see Figure 5.58).

At this point the animation looks a little silly; the other parts of the bug need to be animated, which you can do using the techniques described in the chapter. By attaching the mechanicalBug group as opposed to the bodyCtrl group, you now have the option of adding additional animation to the bodyCtrl curve to add variation in the movement of the bug as it flies along the curve.

Figure 5.58. The bug is attached to the motion path curve. As the animation plays the bug travels along the length of the curve.

You can change the rate at which the bug flies along the curve by editing the motionPath1 node's U Value attribute on the Graph Editor.

In the Outliner, select the mechanicalBug group. In the Channel Box under Inputs, select motionPath1.

Choose Window

In the left-hand column, select the motionPath1 U Value attribute, and press the f hot key to focus the graph on its animation curve.

Use the graph-editing tools to edit the curve.

Save the scene as mechBugPath_v02.ma. To see a version of the scene to this point, open the mechBug_v02.ma scene in the chapter5scenes directory on the DVD.

Open the mechBugConstrain_v01.ma scene from the chapter5scenes directory on the DVD.

This scene has the bug rigged and sitting at the origin of the grid. A cattail is bobbing up and down in the breeze. Above the cattail, a curve defines a motion path (see Figure 5.59).

Figure 5.59. The scene contains an animated cattail and a motion path.

A locator named bugLanded is constrained to one of the joints of the cattail using a parent constraint. On the motion path is another locator named bugFly. To make the bug sit on the moving cattail, you'll create a parent constraint between the bug and the bugLanded locator.

In the Outliner, select the bugLanded locator and Ctrl+click the mechanicalBug group. From the Animation menu set, choose Constrain

Figure 5.60. The options for the parent constraint

The mechanical bug now appears on the end of the cattail. You can reposition the bug on the cattail using the bodyCtrl and legCtrl curves.

In the Display Layers window, turn on the CONTROLS layer. Select the blue bodyCtrl curve, and pull it upward to move the bug up above the end of the cattail.

Turn on Wireframe view. Select the red legCtrl circle, and move it upward with the Move tool so the legs are positioned on the end of the cattail. (Use the Show menu in the viewport to turn off the visibility of Joints so that you can easily see the geometry.)

Position each of the small purple leg control circles so the bug's legs are posed on the end of the cattail geometry (see Figure 5.61).

Play the animation. You'll see the bug sticking to the cattail as it moves up and down.

Set the timeline to frame 320. In the Outliner, select the bugFly locator, and Ctrl+click the mechanicalBug. Create another parent constraint; the same options should be applied automatically when you create the constraint.

When you play the animation you'll see that the bug is floating between the two locators, thus inheriting a blend of their animation. This is because the strength of both constraints is at 1 (or full strength).

Figure 5.61. Pose the legs using the legCtrl curves so the bug is standing on the cattail.

Set the timeline to frame 353. This is a point where the two locators are very close and a good time for the bug to start to fly off.

In the Outliner, expand the mechanicalBug group. Select the mechanicalBug_parentConstraint1 node.

In the Channel Box, set Bug Fly W1 to 1 and Bug Landed W0 to 0. The bug reorients itself to match the orientation of the bugFly locator.

Shift+click both the Bug Landed W0 channel and the Bug Fly W1 channel in the Channel Box (see Figure 5.62). Right-click and choose Key Selected.

Figure 5.62. Set the weights of the parent constraint and key it at frame 353.

Set the timeline to 347. Reverse the values of the two weights so Bug Landed W0 is at 1 and Bug Fly W1 is at 0. Set another keyframe.

Rewind and play the animation. You'll see the bug sitting on the cattail as it bobs up and down. At frame 347 the bug switches to the motion path and flies off.

With the mechanicalBug parentConstraint1 node selected, open the Graph Editor. Select the Bug Landed W0 and Bug Fly W1 channels on the left column of the Graph Editor, and press the f hot key to focus on their animation curves.

Use the curve-editing tools to fine-tune the animation so the transition between the cattail and the motion path is smoother. This usually takes a fair amount of experimentation (Figure 5.63).

In some cases you can create a smoother transition by extending the length of time between the keyframed weight values. It depends on what type of motion you are trying to achieve and your own personal taste.

Save the scene as mechBugConstrain_v02.ma. To see a version of the scene to this point, open the mechBugConstrain_v02.ma scene from the chapter5scenes directory on the DVD.

Open the mechBugLayers_v01.ma scene from the chapter5scenes directory on the DVD.

Set the current frame on the timeline to 1. Select the blue bodyCtrl curve above the bug, and set its Translate Y channel to −0.5. Create a keyframe for this channel.

Set the current frame to 20, set Translate Y to 0.5, and create another keyframe.

Create three more keyframes for the bodyCtrl curve:

In the Layer panel in the lower-right corner of the screen below the Channel Box, set the Mode to Anim. This switches the Layer Editor to Animation layers as opposed to Display or Render layers.

Choose Layers

In the perspective view nothing has changed regardless of which layer is selected.

Double-click on AnimLayer1 and rename it bounce (see Figure 5.64).

Figure 5.64. Create a new animation layer in the scene and rename it bounce.

Select the bodyCtrl curve. In the Animation Layer panel, select the bounce layer, RMB+click on it (or select it from the Layer menu), and choose Add Selected Objects. This adds just the bodyCtrl curve. Notice that all the channels in the Channel Box are now yellow. You'll also notice that in the INPUT section under the Channel Box for the bodyCtrl curve, bounce has been added to the list of inputs.

When creating an animation layer you have the option of creating the layer from selected objects in the scene or copying an existing layer (using the options in the Layers menu). When you copy a layer, the keyframes are also copied to the new layer. The Layers menu has a lot of options you'll explore as you go through the next few exercises.

Select the bounce layer, and a green circle appears on the right. This indicates that the layer is active.

Play the animation. It looks the same as before. Notice that there are no keyframe tick marks on the timeline. Select the BaseAnimation layer; the tick marks reappear. So what does this mean?

In the Layer Editor, select the bounce layer. Choose (from the menu in the Layer Editor) Layers

If you switch to the BaseAnimation layer, you can see the keyframes on the timeline, but the bug still doesn't move. This is because even though the bounce layer is not selected, it is overriding the BaseAnimation layer.

In the Layer Editor, click the red Mute Layer button (see Figure 5.65). The Mute Layer button temporarily disables the layer; when you click Play, you'll see the bug move up and down again.

Figure 5.65. The Mute Layer button temporarily disables a layer.

Turn the Mute Layer button off, and then play the animation. The bug should stop moving. Select the bounce layer, and drag the Weight slider slowly to the left as the animation plays (see Figure 5.66).

Figure 5.66. The Weight slider determines the amount of influence the layer has over the animation.

As you drag the Weight slider down, the influence of the overriding layer decreases, and you can see the bug start to move up and down again. When the weight is at zero the overriding layer has no more influence. The K button to the right of the Weight slider sets a keyframe on the Weight value so you can animate the strength of the weight over time.

Select the bounce layer. Set the Weight for the bounce Layer to 1, and make sure the layer is not muted. When you play the animation you should see no motion. Select the bodyCtrl curve, and set the following keyframes on the Translate Y channel.

With the bodyCtrl curve selected, open the Graph Editor and select the Translate Y channel. Drag a selection around the keys, and choose Curves

When you play the animation, the bug bounces a little faster. As you lower the Weight for the layer, you'll see the slower bouncing motion of the BaseAnimation layer.

If you turn off the Passthrough option in the Layers

Set Layer Mode to Additive, as shown in Figure 5.67. Set the Weight of the bounce layer to 1, and play the animation. You can see that the resulting animation is now a combination of the keyframe values on the bounce and BaseAnimation layers (the Passthrough option has no effect on additive layers).

In the Options menu of the Layer Editor, turn off Auto Ghost Selected Objects. Click on the red G in the Base Animation layer. This creates a ghost of the animated objects on this layer so you can compare it with the animation on other layers. In this case, you'll see a red copy of the bodyCtrl curve moving according to the keyframes set on the BaseAnimation layer.

Rewind the animation and select the bodyCtrl curve. In the Layer Editor, choose Create Layer From Selected. Name the new layer rock and set its mode to Override.

Figure 5.67. When Layer Mode is set to Additive, the animation of the two layers is combined.

Select the rock layer. In the Channel Box, highlight the Rotate X, Y, and Z channels, and set a keyframe on these channels.

Turn on the Auto Keyframe feature by clicking the key icon to the right of the timeline.

Set the timeline to various points in the animation, and use the Rotate tool to rotate the bug, making him do a happy little dance.

Rewind and play the animation. You'll see him move around. Experiment with the weight of the rock layer; try setting its mode to Additive and observe the result.

By varying the weight, you get a pretty good dancing action (for a mechanical bug) fairly easily.

Save the scene as mechBugLayers_v02.ma. To see a version of the scene to this point, open the mechBugLayers_v02.ma scene from the chapter5scenes folder on the DVD.

Continue with the scene from the previous section or open the mechBugLayer_v02.ma scene from the chapter5scenes folder on the DVD.

In the Animation Layer Editor, mute the rock and bounce layers. You'll notice that the bug still bounces. This is because of the keyframes set on the BaseAnimation layer.

Before creating a hierarchy for the layers, you can quickly move the animation on the BaseAnimation layer to its own new layer. To do this, select the bodyCtrl curve and the BaseAnimation layer. Right-click on the BaseAnimation layer and choose Extract Selected Objects.

Extracting the bodyCtrl object from the BaseAnimation layer creates a new animation layer that contains the bodyCtrl curve and its animation. At the same time, the keyframes from the bodyCtrl curve are removed from the BaseAnimation layer. If you mute all the layers except BaseAnimation, the bug no longer moves when you play the animation.

Name the new layer bounce1, and rename bounce as bounce2.

Make sure bounce1 is below bounce2. Mute all the layers (see Figure 5.68).

Figure 5.68. Copy the BaseAnimation layer, renamed it bounce1, and move it below the other layers. Mute all layers.

In the Layer Editor choose Layers

Select the circle under the front left leg. In the Layer Editor, choose Layers

MMB drag FLeftLegAnim on top of the legAnim layer to make it a child of this layer. A small black triangle appears, and the FLeftLegAnim layer is indented above the legAnim layer (see Figure 5.69).

Figure 5.69. The FLeftLegAnim layer is parented to the legAnim layer.

Repeat steps 7 and 8 for the front right leg circle. Name the new layer FRightLegAnim.

Select the FLeftLegAnim layer and, in the perspective view, select the circle under the front left leg. In the Channel Box, Shift+click all the channels except the Translate channels. Right-click and choose Remove From Selected Layers (see Figure 5.70).

Figure 5.70. Remove the Rotate and Scale channels from the animation layer.

With the FLeftLegAnim layer selected, set a keyframe on the left leg control circle's Translate channels. Then use the Auto Keyframe feature to create an animation of the leg moving up and down as if it's tapping out a little beat.

Switch to the FRightLegAnim layer, and create a similar animation for the front right leg.

When you have a nice animation going for both layers, unmute the other layers and play the animation.

Click the black triangle on the legAnim layer to collapse the layer. Experiment with the Weight setting of the legAnim layer. The Weight value of the parent layer applies to both child layers as well. This is also true for the Layer Mode, Mute, and Solo settings.

You can create further nested layers within the hierarchy. Each child layer can have its own Mode setting. To keep things simple, you can use empty layers as parent layers. The empty parent layers can be used to set the Weight and Mode operation of the child layers. If the parent layer is empty, you don't have to worry about how the animation in a parent layer is blended with the child layers.

Save the scene as mechBugLayers_v03.ma. To see a version of the scene to this point, open the mechBugLayers_v03.ma scene from the chapter5scenes folder on the DVD.

Continue with the scene from the previous section or open the mechBugLayers_v03.ma scene from the chapter5scenes folder on the DVD.

In the Animation Layers Editor, select the bounce2 and bounce1 layers.

Choose Layers

Turn on the Smart Bake option.

When you merge two or more layers, the animation of the objects on the layers is baked. You can choose to sample the baked keyframes based on the Sample By value. For instance, if you set Sample By to 1, then the object on the resulting baked layer will have a keyframe placed on the animated channels for every frame of the animation. A setting of 2 creates a key on every other frame. The Smart Bake option creates a curve from the combined animation layers with fewer keyframes. The Increase Fidelity setting increases the accuracy of the resulting animation curve to better represent the combined animation of the two layers. The Sample By option is more accurate but creates a lot of keyframes, which can be hard to edit. The Smart Bake option works very well when there are fewer layers or the animation is simple.

You can bake a parent layer and all its child layers into a single layer. You can also choose to delete the original layers or keep them. Figure 5.71 shows the options for merging layers.

Click Apply to merge the layers. A new layer named Merged Layer is created. Rename the new layer bounce. Select the bounce layer. In the perspective view, select the bodyCtrl and open the Graph Editor. You'll see the merged animation curve in the Graph Editor (see Figure 5.72).

Save the scene as mechBugLayers_v04.ma. To see a version of the scene, open the mechBugLayers_v04.ma scene in the chapter5scenes folder on the DVD.