Everything must be made in groups or components. I use groups as they can be editted without affecting the rest of the model. Also right click on the groups and check that the state is not static and shape is NOT static mesh. There is no such thing as non-static mesh as of yet but you can make the shape of your blades from multiple groups and set the to box or convex hull and group them together. http://sketchyphysics.wikia.com has alot of tutorials for sketchyphysics 3