ribbonTwist.ma (scroll to the bottom to download related material)

A Maya user was trying to create a curling ribbon with a paint effects brush. He wanted to know if it was possible to control the twist rate along the ribbon to make some areas flat while other parts were twisted. Unfortunately the paint effects brush only has a global "Twist Rate" attribute with no control along the stroke. However there is a simple trick for doing this that uses the curl ramp on a hair system, while also disabling the hair's dynamics evaluation.

1. Create a curve. (MENU "Create: Cv Curve Tool", drop 6 or so points on the ground and hit return)

2. MENU "Hair: Make Selected Curves Dynamic"
In the option box turn off "exact shape match"

3. MENU "Hair: Assign Paint Effects Brush To Hair"

4. Delete "hairSystem1OutputCurves" (select in the outliner then hit the delete key)
The output is paint effects so we don't need the output curve.

5. On pfxHairShape1 set:
drawAsMesh = ON

6. On the paint effects brush ("brush2") set
brushType = Mesh
globalScale = 1

"Brush Prorfile" flatness1 = 1.0
"Shading" color1 = white
"Illumination" illuminated = ON

7. On the hair system ("hairSystemShape1") set:
Simulation Method = "Static"
Hair Width = 0.1
Sub Segments = 10

Also delete the far right entry on the hairWidthScale ramp so it no longer tapers at the end.

8. Edit the hair system Clump Curl ramp to set the amount of twist along the length of the ribbon. A value of 0.5 is flat. Type in values greater than 1 or less than 0 into "Selected Value" if you wish to have very tight curls. You can edit and animate the position of the cvs on the original curve if desired. Note that the interpolation performed for the sub segments is "hermite and may not match the interpolation of your original curve well. If you wish to match it better you can make the hairsystem sub segments 1 and increase the sample density on the follicle node instead.

Thats it. If you don't want to render the ribbon with paint effects you can simply do MENU "Modify: Convert: Paint Effects to Polygons".