Creation of 3D characters and animating them in a realistic way requires a lot of skill. One of the principles of traditional animation is the use of secondary motion to achieve realism. secondary motion is a technique where the illusion of weight and realistic movement is greatly improved by having the extremities of a moving object continue moving after the object stops. For example : a car antenna continues to wiggle when the car comes to an abrupt stop, wiggling of character's ears etc, a simple effect that would take a lot of effort to keyframe by hand.

The Flex modifier can add soft body dynamic characteristics to an object. Flex works with NURBS, patches, meshes, shapes, FFD space warps, and any plug-in-based object types that can be deformed. You can combine Flex with space warps such as Gravity, Wind, Motor, Push, and PBomb to add realistic physically based animation to an object. In addition, you can apply deflectors to soft-body objects to simulate collision.

In this tutorial we will look at a simple yet powerful modifier in 3ds max that can be used to achieve secondary motion on any animated object or 3d characters. Lets do a simple task that will give us the idea of how Flex Modifier works.

1. Create a Cylinder with following parameters

Radius: 5
Height: 100
Height Segments 20

2. Apply Mesh Select modifier to the Cylinder. (Refer image below)

Mesh Select Modifier applied to Cylinder.

3. Expand Mesh Select modifier rollout and select Vertex sub object. Now select all the vertices at the top of the Cylinder. (Refer image below)

4. Now go to Soft Selection rollout and enable Use Soft Selection. and set the Falloff value to 90.

5. Now from the Modifier list, add Flex Modifier.

Flex Modifier on top of Mesh Select.

6. Now select the Cylinder and turn on Auto key (Press n).

7. Move the Time Slider to Frame number 10.

8. Now Move the Cylinder a few units in X or Y axis.

9. Turn off Auto Key and move the Time Slider back to Frame Number Zero.

10. Now in Flex modifier panel under Parameters rollout, Set the Flex Value to 5.

Now Play the animation. and play with the values Strength and Sway in Flex modifier. This tutorial gives a basic idea of how Flex Works. Flex also can be used to create complex animation like Character Cloth animation with dynamic response to wind. Flex works with Forces and Deflectors provided in 3ds max. Next part of Tutorial will deal with the Flag Animation with Flex.