THe Build

I began the build by laying out all the components for the quadcopter.  In the pictures below you can see the frame, motors, propellors, ESC's, batteries and miscellaneous hardware for assembling the frame.
Each of the arms were 36" long and I wanted to notch them so that they could be attached together in a "plus" configuration.  For creating the notch, I lined up the two arms and drew parallel lines across both of them indicating where the notch would be cut out.
I sawed through the arms and cut out the notches going about 0.5" deep into the 1" thick arms.  I then sanded out the notches to get a clean and tight fit between the arms.
I inserted each of the arms into eachother and then added a small bit of wood glue in the middle to form a secure bond.
Next, I had to begin drilling the holes out for the motors to mount to the arm.  I did this by using the motor mount tabs that I had lasercut as templates for the drill.  I placed one tab on the top side, one on the bottom side and then I used them to guide the drill bit through the arm as straight as possible.  
I then went ahead and secured the motor to the arms by passing through a 35 mm long M3 bolt through the motor mount tabs and the arms.  I also attached a propellors at this time to give me an idea of how large the overall build would be. 
Next, I repeated the same alignment/drilling process for the center plate.  These holes were slightly larger because the center plates needed to accomodate M5 bolts for added rigidity.  Once the holes were drilled out I passed through the M5 bolts from above. 
On the underside of the center plates I secured the bolts with M5 lock nuts.  The picture below on the right shows what the top of the quadcopter looked like once all the center plate bolts were secured in place.
Below are a couple pictures showing what the quadcopter looked like at this stage in the build process. 
After the main frame assembly was completed, I went ahead and started working on the electronics.  I started by first soldering the bullets to each of the motor wires.  
I heat shrunl each of the bullets and used zip ties to secure all the wires on the underside of the quadcopter.  I wanted to do this mainly to keep all of the wires and vital components as far away from the rocket blast as possible.  
Below are a couple more shots of what the motors looked like once their wires had been secured on the underside of the quadcoter.
Next, I moved on to preparing the ESC's for the build.  I began by first removing all of the stock heat shrink.
I then moved on to desoldering all of the motor signal wires and I also took this opportunity to flash each of the ESC's with SimonK's latest firmware. 
Due to the quadcopter's large size, I needed fairly long wires leading between the ESC's and the motors.  So I went ahead and cut 12 x 9" sections of wire and then I added bullets and heat shrink to them. 
I took these 12 sections of wire and soldered them to the ESC's.  Then I re-heatshrunk the ESC's with black heatshrink. 
I connected each of the ESC's to the motors using the bullets I had soldered on and then I secured the excess wire to the underside of the arms using a staple gun.  
Once all the wires were secured to the arms, I placed the ESC's on the underside of the bottom center plate and secured them with zip ties.  From the top side of the quadcopter, all you could see were the zip ties. 
Below are some pictures of what the quadcopter looked like in this stage of the build process. 
The next major step was figuring out a clean and practical power distribution method.  I would normally solder all of the wires together in a bundle, but I needed to keep the center of the frame as empty as possible so that I could accomodate the controller board.
I came up with the idea of using power rails.  These rails would essentially distribute the power and ground connections from the battery along the entire length of the rail and it would very low profile along the center of the quadcopter.  I initially envisioned using copper bus bars (like you see below) and attached them to the center plates using small M2 screws.  Unfortunately, the bus bars proved too dificult to solder to without extreme heat, so I switched to using copper-clad PCB.
With the copper-clad PCB, I cut two strips with idential dimensions to the bus bars and then I added black and read heat shrink to them to protect against shorts.  I secured these power rails to the quadcopter center plate using M2 screws.
Once the power rails were in place I began soldering the ESC's wires to them.  It was a fairly simple process; it mainly involved cutting away a small section of heat shrink, tinning the power rail and then soldering on the ESC power and ground wires.
It ended up working very well and kept the center of the quadcopter very clean to leave as much room as possible for the flight controller.
Next, I started working on the flight controller.  I was using a CC3D for this project, so I went ahead and attaches some 35 mm long M3 bolts with nylon spacers to the board.
The board mounted very securely to the quadcopter and thanks to the low profile power rails, there was plenty of room between the board and the quadcopter to allow for wires to pass through.  
After the board was mounted, I started working on the battery leads.  I created some short pigtails using some XT60's and I also cut some slots from my power rails so that I could solder to them.
I tinned the power rails and then soldered the battery leads to them in a parallel configuration.
One of the last things I did was clean up the wires from the ESC's.  I took the signal wires from each of the ESC's and wrapped them around the power and ground cables.  I then routed the signal wires under the CC3D and attached them to their respective pins.
This is what the underside of the quadcopter looked like once everything was complete.  I had achieved the goal of keeping all of the electronics on the underside of the quadcopter and away from the rocket blast. 
A couple minor things to note: I did add landing gear to this build but unfortunately didn't take many pictures of them.  They were simple designs that were made on a 3D printer and just screwed into the side of the arms (you can see them in the pictures below). Also, I had installed a realy system for triggering the launch of the quadcopter.  Unfortunately, I wasn't able to get some pcitures of that setup, but you can find the link to the relay I used on the Parts List page.