Prop saver
From Dronepedia
'Prop Savers' are designed to provide a soft connection between the prop and the motor shaft it's attached to, in order to protect the edge of the motor mount, the shaft, and the prop when a rotating prop encounters an obstacle (in particular an obstacle hitting perpendicular to the plane of rotation). Usually these take the form of a mounting bracket rigidly attached to the shaft, and the prop being loaded onto this bracket using rubber bands.
