Windmill

A simple windmill
http://www.youtube.com/1200V2
The only problem I have is the fact that it isn’t possible to animate the object with only one Ipo.
If it would be possible to give the rotation along the axis to a parented object. It would be more fluid and more easy to animate this object.
start rotation left…__ (parented object)
negative rot right…|__ (parented object)
rotation left…|__ ipo end. (parented object) Is this possible?