Mockup of a DJI Phantom 2 prop guard.

This is an approximate representation of a DJI Phantom 2 prop guard.  It can be imported into your FreeCAD drawings to check that it fits with your plan.

Outline shape of an SG90 9 gram servo.

This can be imported into your FreeCAD drawing (Part -> Import CAD).

For example, you could import this file into a drawing of a servo mount to check that the servo will fit correctly. Alternatively you could even cut this "part" to from a block to create a servo shaped recess.