I modified a standard ZMR250 frame by removing the alu spacers and the top plate and replacing them with a 3D printed spacer holding all my electronics. Build log here: http://imgur.com/a/Oegau Reddit thread here: https://www.reddit.com/r/Multicopter/comments/3dy145/slim_zmr250_custom_clean_build/ Upon request, I have uploaded STLs of a few variations of the spacer. I hope somebody can make good use of them, or get an idea for his / her own builds. Original versions Spacer_V1.0_all_cuts_original - The original as I used in my build Spacer_V1.0_buzzer_cut - The original with only the buzzer cut-out. Spacer_V1.0_no_cuts - The original with no cuts at all Alternative versions Spacer_V1.1_all_cuts - This version is slightly thicker, has all the cut-outs my original has and has 5 mm bolt holes in stead of the original 3 mm. This allows for using standard 15mm alu M3 threaded spacers to be inserted into the bolt holes - provider better strength and off-loading the pressure on the plastic. Used electronics Instructions on how to use a satellite receiver with the naze board are here: http://www.netraam.eu/nazewiki/pmwiki.php?n=Howto.HookupASpektrumSatellitePrinter settings If you're going for the original version without the aluminium inserted stand-offs, I suggest you use a fairly high shell thickness and fill rate. The only thing transferring the power from the motors to the body is the pressure from the spacer plate. I used 3mm shell thickness with a 30% fill rate on my build. V1.1 provides room for inserted spacers that can take the grunt of the force - offloading the plastic spacer. You can go for a reduced shell thickness and fill rate in that case. Parts The buzzer is a standard KK board buzzer from hobbyking, you can get it here: http://www.hobbyking.com/hobbyking/store/__47014__Piezo_Buzzer_for_KK2_KK2_1_Naze32_Flight_Control_Boards_1pc_.html The switch I used is a Q15 toggle slide switch, any local electronics shop will have something like this in stock.