not trying to be pesimist, but the circle is the best because it represent the shape of your octo-rotor. there are many shape that can be better, such as hexagon, triangle etc. the logo will be better in visual but weaker concept.
actually that is the same reason why I make circle in the middle rather than hexagon like on your sketch.
but if you have any idea you can tell me, I will try to visualize it even I don't agree with it :)