Check out the whole "T" copter family: I've been experimenting to find a strong "tubular" profile that could be printed reliably. The angled sections in these designs are 35 degrees to vertical - so well within the typical 45 degree capability of most printers. They arms only present about 11mm of flat surface to minimize obstruction to airflow. The rest of the design are a collection of ideas that have accumulated over the past year building various quadcopters and Y6 configurations (3D printed, aluminium and bought frames). 3 August 2014 Version 1.05 Just a small change to add slots to the arm motor mount holes so that 4 bolts can be used (in a 16-19mm pattern) regardless of which "corner" of the motor the wires exit. 1 April 2014 Added a T4 univeral camera plate accessory as a separate thing. 22 March 2014 Version 1.04.1 8 March 2014 I flew a few different batteries today to compare. This is with my 880kv 3DR motors which is a bit over-weight as it is version 1.00 and has most of the power components from my T6 inside. I'm guessing a 1.02+ version with something like the 3DR 850kv motors would weigh at least 100 grams less with longer flight time. The results: 7 March 2014 CRASHED HARD!! But this frame handled it well (see photo above). I printed off another arm after work, reassembled and had time for a quick test flight - all back to normal. Replacing the arm was about a 10 minute job. 5 March 2014 I just noticed a hole missing at the front of the top plate. It's not required (or any real issue if missing) so I've just updated T4TopPlate.stl and the Sketchup file without changing version numbers. 4 March 2014 Version 1.02: I've spent another full day drawing on this thing. The biggest parts are now 199mm long and 140mm wide. Hopefully that will squeeze onto a few more print beds out there. The arm will also fit onto that sized bed if you rotate it a bit. I've started to version the Sketchup files and left older ones in the files if anyone prefers an earlier design. 3 March 2014 Version 1.01: As requested I've put this thing on a diet. It now only requires a 140mm wide (and 220mm long) build platform so it should fit easily on a Replicator 2. Also I've updated T4Arm.stl adding a small hole to allow a cable tie to be used for strain relief where the wires exit the motor. I printed all parts in PLA, 0.25mm layers with 40% infill, 2 shells and 3 top/bottom layers. Feel free to experiment. I didn't play around too much with the settings as these gave me a good strong result. Calibration test TubeSocketArm.stl contains a cut-down socket you can use for testing the fit of your arms before committing to the full Body print. I found a 0.1mm clearance between the arm and socket provides a firm press fit. Some light sanding may help if you find the fit too tight but I recommend keeping the tolerance as small as possible. A quick word about scaling According to Wikipedia apparently "there is no scale information [in STL files], and the units are arbitrary". There is often confusion with STL files and metric versus imperial (inches) units. I designed these parts in Sketchup using metric units and they import correctly into my slicer (which is also set to metric). If you have issues, check your application to see if has a way to select metric or alternatively scale down by a factor of 25.4. Also, the Sketchup file contents are scaled up by 1000 (attempt to solve some Sketchup quirks). I scale each component down by 0.001 before exporting the STL so they are in real millimetre sizes. If your new to RC copters then the ArduCopter wiki is a great place to find out everything you need know. The default APM parameters for the 3DR Iris should be very close for this quadcopter. Some tips from maverik0106: