Use Twist Curve

– Using twist curves you can have a better control on the way the children twist.
– When you enable the twist curve a graph appears with one starting and one ending point.

– To add a point: click on the curve
– To delete a point: select it and click on the X at the top right corner (but you cannot delete the ending points)
– To move a point: drag it

– After some experiments it seems to me that:

– X axis: position of the twists along the strand (0: root ; 1: tip)
– Area under the curve: multiplicative factor for the number of twists (twist parameter).
– If you find a better explanation please send me an email!

– Example on the left: all 8 twists are rendered along all the strand (area: 100%)
– Example in the middle: children twist only in the 1st quarter and in the 3rd quarter of the strand. Total of twists: 4 (area: 25%+25% = 50%).
– Example on the right: twists are rendered along all the strand but this time not all 8 twists are rendered as total area=50%, so only 4 twists are rendered.

– In this video you can see two animations, one with the twists on the tip ant the other with the twists on the root:

– Another example:

Blender Hair Children Use Twist Curve