I printed this on my Prusa Mendel with 0.2 mm layer height (0.4 mm for the first). I always have problems with holes in the first layer but once that layer is printed everything else goes perfectly.

I uploaded the .ipt part as well, for if you want to make adjustments (bigger/smaller size motors?). You may want to check the measurements of your motors before you print since I attached the motor on this with a seperate aluminum mount (see pictures).

The oval hole for the cables is a tight fit for 3.5 mm bullet connectors. I managed to put them through by inserting the cables one by one and moving them to the side.

Bill of materials (per motor):
- 1 of each of the plates
- 6 M3x35 bolts
- 4 M3x10 screws
- 16 M3 washers
- 10 M3 nylock nuts
- 1 ziptie for keeping the motor cables out of the propeller

Nevermind the screws I used in the pictures, they were all I had lying around.

I haven't flown with this setup yet, since I'm still waiting on some parts.
If anyone has any tips, improvements or ideas, please let me know!