One of the principles of traditional animation is the use of secondary motion. The illusion of weight and realistic movement
is greatly improved by having the extremities of an object continue moving after the central moving object stops. For example,
a car slams on the brakes, comes to an abrupt stop, and the car antenna continues to wiggle.
In this topic, using the Flex modifier, you will animate secondary motion with the antennae on a beetle's head.
To add secondary motion with the Flex modifier:
Reset 3ds Max.
First, you’ll animate the beetle's head so he looks in one direction and then another.
Turn on Auto Key.
Move the Time Slider to frame 23.
Rotate the beetle’s head to the left.
If you want to be precise, press F12 to open the Transform Type-In, and offset it by −70.0 degrees around Z.
Move the time slider to frame 29.
Rotate the head in the opposite direction, about 30 degrees around Z.
Turn off Auto Key.
Next, you'll adjust the interpolation on the last rotation key for a more abrupt motion.
To set up the beetle head for secondary animation:
Right-click the key at frame 29 in the track bar, and choose the Head: Rotation key at the top of the menu.
In the dialog, set Tension and Continuity to 0.0, and Bias to 50.0. Close the dialog.
Play the animation. The head should whip around to the right.
Go to the Modify panel.
In the stack display, directly beneath the MeshSmooth modifier, choose Mesh Select.
The Mesh Select modifier lets you use a soft selection for the Flex modifier, so the effect of the modifier on the mesh will
taper off gradually.
Choose Vertex selection mode.
Select only the vertices at the end of the antennae.
Choose the end vertices only.
Scroll down and open the Soft Selection rollout.
In the Soft Selection rollout, turn on Use Soft Selection.
Increase Falloff while watching the viewport.
The vertices change color showing the area of influence to be used by the Flex modifier.
Adjust Falloff to include the eyebrows (about 30.0).
Soft Selection adds the eyebrows
On the Modifiers menu, choose Animation modifiers > Flex.
This adds a Flex modifier only to the selection of vertices, rather than to the whole head.
In the stack display, expand Flex and choose the Center sub-object level.
If you don’t see the Transform gizmo, open the Views menu and turn on Show Transform Gizmo.
Move the center of the of the Flex modifier up to the beetle’s forehead, using the Transform gizmo to restrict the movement
to the Z axis.
Move the Center of the Flex up to the forehead
Play the animation.
The antennae have their own movement now. Watch the free secondary animation you’ve got in the last 70 frames of the animation.
Imagine how much work that would be to keyframe by hand.
Experimenting with the Flex modifier:
While the animation is playing, change the values for the different parameters of the Flex modifier.
Change the parameters one at a time to see what they do.
Different combinations of the three parameters can create different wiggles and wobbles. Also try lowering the Flex modifier's