UPDATE 28.6.2016:

• I've been busy last few months, hope to find time for this hobby and to finalize this project page
• Motor mount holes are rotated 90° in ARM_ALT.STL

X550 is a Work-In-Progress - here's my To-Do list:

• upload some video
• more details on wiring (requires adjusting some cable lengths i.e. soldering and crimping new connectors)
• APM:Copter-3.3 parameters I use with this setup

This is a remix from Brendan22's T4 Quadcopter

Soon after building my Prusa i3, I started printing T4 parts but found problems especially with arms because of heavy ABS warping and deforming. I started designing arms with more bonding surface and that meant the body needed changes too. While waiting for all the electronics I decided to redesign the whole frame. First frame was asymmetrical like T4 but I found problems when tuning it to stable hover. So I moved to X-style frame. Later I learned that center of thrust (CoT) needs to be coincident (or close enough) with center of gravity (CoG). Still wanted to stay with X-style frame as it felt better.

After a lot of tweaking and testing I found frame design that seems to work great.

• 550mm motor-to-motor distance allows to use 10-12" propellers (I use Gemfan 11x5" CF+Nylon props) and gives a bit more stable flight and better wind resistance.
• The body has minimal unused space and has few dividing walls to make it more rigid.
• FPV video Tx is located front left corner and receiver's antennas are positioned opposite to minimize possible RF-interference.
• Battery compartment's end cap is held in place with screws as it makes frame more rigid and handles possible crashes better (the flight battery weights about 400g). The end cap has also place for velcro straps that are holding an auxiliary battery.
• ø5mm carbon fiber tubes are used as GPS mast and long feet (required with gimball) for overall better performance. Feet are fixed to body with the same screws as arms.
• For additional cover to Pixhawk and it's vulnerable cables and connectors I designed canopy mold that can be used with a vacuum forming machine.

CoG tends to be few mm's behind CoT when flying without G-3D gimball and GoPro - yet copter performs great. In fact I just got the G-3D gimball and made few adjustments to get it mounted properly.

As I found the frame performing excellent, I wanted to share it. Anyhow, most of the geometrical and mechanical design choices are copied from Brendan22's T4 Quadcopter. I give my respects.

This frame is designed to work with following gear:

• Motors: NTM Prop Drive Series 28-30S 900kv or equivalent.

  12x6E - 11.1v - 195W - 17.8A - 1.01kg thrust              11x7E - 11.1v - 188W - 17.0A - 0.89kg thrust10x5E - 11.1v - 133W - 12.0A - 0.75kg thrust

• Propellers: 10x4.5" - 11x5" (haven't tested 12" props yet)
• Electronic Speed Controller (ESC) / BEC: Q Brain / Hobbywing Skywalker 4x25A
• Flight Battery: Turnigy 3S 5000mAh (146x50x27mm compartment size)
• Flight Computer: 3DR Pixhawk
• GPS / compass: 3DR uBlox
• Receiver: FrSky D4R-II

Optional gear:

• 3S auxiliary battery for LEDs, gimball and FPV gear (I use this)
• 4 x Super Bright 3W LED with Aluminium Heatsink (+ constant current driver)
• Walkera G-3D 3-Axis Brushless Gimball + GoPro3 / iLook
• Fatshark 600/700TVL CMOS FPV camera
• MaxBotix MB1242 I2CXL-MaxSonar®-EZ4™ Ultrasonic sensor
• ImmersionRC 25mW 5.8GHz A/V Tx
• MinimOSD
• Bluetooth Data Link for Pixhawk at least when using canopy

Required hardware:

8 x M3 40mm machine screw (arms)8 x M3 nut + washer (arms)20 (+2*) x ø3mm 12mm self-tapping screw for plastic (body, deck, bottom, gimball*)1 x ø5mm 120mm carbon fiber tube (GPS stand)4 x ø5mm 140mm carbon fiber tube (feet)2 x ø3mm 135mm antenna tube (Rx)2 x small rubber bands (A/V Tx and Rx)few cm's double-sided tape, eq. Scotch® VHB™ (fixing electronics)

The self-tapping screws I used have been salvaged from broken stuff.
http://de.screwerk.com/en/products/stp/stp32.html

Additional information:

                  WEIGHT           PRINT TIME *         FILAMENT USAGE (3mm)Body              128g             11h 50min            20.45 mDeck               37g             2h 30min              5.45 mBottom             46g             3h 20min              7.20 mArm (1)            44g             3h 15min              6.75 mFeet (4)           25g             2h 20min              3.60 mCanopy mold                        4h 31min             12.15 m                    TOTAL WEIGHT: (with gear listed above):- without batteries (dry weight)       1170g- with batteries                       1675g- with G-3D gimball and GoPro3         1975gSTABLE HOVER THROTTLE:- with G-3D and GoPro3, 11x5" props    about 52%FLIGHT TIME: (using 4000mAh = 80% capacity):- without G-3D gimball and GoPro3      ≤20min- with G-3D gimball and GoPro3         ≤12minMEASURED POWER CONSUMPTION:FPV-gear + LEDs          450mA = 1h 45min of safe usage time with 1000mAh battery FPV-gear + LEDs + G-3D   1.0A = 50min

(*) printed with E3D v6 Belt Driven Extruder.