My RotorX Atom quad is a bit too peppy to be used indoors without being overly careful, so I designed a prop guard so that I could bump into things without stopping the blades or damaging anything.

Update 1: I've added some new versions. One without the arches (which were weak points) and one without the arches with an extra 2mm added all around for reinforcement. These will need to be positioned above or below the props, as without the arches they will interfere with them, but it should print easier and be much stronger.

Update 2: I've added a cut version of the reinforced archless version. This was slightly reinforced as well around the weak points and the cut. You should be able to print two and just flip one after printing. If you're a stickler for appearance you can flip one in the slicer so that the top and bottom print surfaces look the same when mounted.

SeeMeCNC

Rostock MAX

Doesn't Matter

Yes

0.25mm

100%

I printed in ABS, but I imagine anything would probably work. I've tried PLA 30% but it shattered in a small outdoor crash. Indoors it should be fine.