This Crazyflie protector was built as a prototyping tool to allow myself to add components safely as payload to the quadcopter. Additionally, the case protects the propellers and the circle allows it to continue navigating after running into walls.
The design attaches to the corners of the board and holds on tightly when a rubber band is applied to the bottom of the legs. Additionally, a small tray can be held in the legs to create some cargo room in the event of wanting to attach a camera or something of the sort :)

Printed on a Makerbot Replicator 2. Rubber band around legs to hold quadcopter firmly in place.