Summary

Sick of breaking props while flying my quad copter indoors due to inclement weather, I designed a prop saver.

Please note, while this does work in the sense that my quad does indeed fly with the prop savers attached, I have yet to actually do a crash test with it.

If someone prints one of these and crashes it before I get a chance / have the misfortune to do so myself, please let me know!

Instructions

Please note, these were designed specifically for this motor: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=12916

Should work with minor modifications on other motors - YMMV!

Parts required per motor:

1x - Printed Prop Saver
2x - M3 or SAE #6 machine screws, around 20mm - 25mm long (3/4" to 1")
2x - Corresponding nuts (M3 or SAE #6, although you will probably need to find smaller than average SAE nuts, as the standard ones are too big)
1x - O-Ring. The ones I used were around 18mm in diameter and 2.3mm thick. Get these at an auto parts store (a real one, not Shucks or Autozone) to avoid a prop to the face!

I printed four of these at once, as my printer doesn't have a fan. I used black 3mm ABS plastic from protoparadigm.

My settings for printing (I used Kisslicer, but I'm sure any decent slicing software would work):

0.28mm layer height.
0.4mm width (I have a 0.35mm nozzle)
2 perimiters
100% infill

Edit: UPDATE, I have now crashed twice since installing my prop savers and can confirm that they do in fact work as intended! Save for a single busted O-Ring, the quad and its props are unscathed.

Update #2: Just uploaded v2. I've made this one a bit beefier after having one of the originals break.

Printable Prop Saver for Quad Copter