Home built quadcopter - Maiden flight

After receiving last missing parts, namely: propellers, battery and flight controller, I had the minimum required parts to have a working prototype.
Another useful addition was a power distribution board, which is crucial to minimize cable mess and organize power lines and provide a single connector to battery. This is specially relevant when motor power draw can reach 60Amps of peak current.
I also bought a propeller balancer, which helps in having well balanced propellers that will help avoid most vibration from the frame.
Balancing a propeller is a simple procedure that resumes to adding duck tape to the lighter side of a propeller, depending on the quantity of tape and position where you add it, you can balance a propeller by simple trial an error, until you instinctively know where and how much tape to add.

During setup, special care must be taken to correctly wire components to the control board, whatever it may be (motor ESCs or radio receiver lines), to prevent swapped connections. We don't want the controller to "think" that it's controlling the forward right motor ESC, when in fact we connect the backward left motor ESC to it, or that it is receiving yaw input, but instead we connect pitch input to it.
Any mismatch and it can be disastrous, specially if we reverse power lines (+ and -), because that will surely fry some component or your entire board almost immediately.
All motors must also be tested for correct spinning direction. If spinning is incorrect, just swap two of the three cables connecting the ESC to the motor, this will reverse the spinning direction. There is also a setting in most ESCs configuration, but it's better, faster and safer to just swap cables.

After setting it all up, I locked the frame to a table, so that it would not fly, even if it wanted to, so that I could try all the motors and direction controls and assert that everything was working as supposed.
Once everything checked out ok, I went outside for my first test flight, the maiden flight. After a few centimeters of lift, it was obvious that there was something out of balance, because the quad kept on moving side-ways when it was supposed to be still. I checked the radio to see if any trimming was being applied, but that was on center, X and Z.
From further inspection it appeared to be some difference where the ESCs are attached to the arms, but it can also be related with the feedback loop constants that came pre-defined with the board, that I have not checked yet.

Did some more test flights in a more controlled environment, with an even level ground (a tennis court).
However, to my surprise, I managed to flip over the quad while it was trying to lift off. After inspection, I noticed that two motor power connections where disconnected, which was probably the cause of the flip over. I also noticed that although the 60Amps connectors that I bought looked great, they were not holding a good connection, and from further inspection I discovered this was happening because there was too much plastic (length wise) in the female connectors, that was preventing connector metal parts to mate and lock correctly.
For a quick solution, I removed all female connectors plastic covers so that this will not happen again. Later I can cut them to size, and prevent metal exposure by using plastic covers for both connectors.

After checking all motor connections again, the quad refused to power on, like if the controller was completely dead. After a few minutes I was starting to convince myself that I had fried the controller. But then I noticed that every time I connected power to the board, a light column of "magic smoke" emerged from the board. After a couple of tries, I managed to identify the SMD component that was leaking "magic smoke". And it was a simple power diode.

Partially disconnected motors (only one cable, + or -) besides flipping the quad, also have the side effect of running too much current through the ground rail, which eventually toasted the small SMD power diode.
I replaced the SMD diode with a more beefy power diode, and the board came back to life.
Once I got the board working, I re-checked every electric connection, to guarantee nothing else was loose or disconnected. I even added a few rubber bands to prevent ESC power connections to disconnect during flight.

Everything checked and ready to go, so I went for another test flight outside. A few seconds later and about 50cm high from the ground, the quad just dove to the ground, and one of the motors decided to fly solo :)
Could not believe my eyes, what was going on ?
Later I realized that on previous flip over crash and some other ruff landings from previous tests, I had cracked one motor support, without noticing it. In this last flight, the cracked support just gave in to the operational stress and finally snapped out, letting the motor loose and propeller almost cut its own motor power cables when it snapped.

Lessons to be learned ?
Check, double check and triple check everything, not just electric or electronic components and connections, but also all mechanical and moving parts, including wiggling cables that can become trapped on moving parts (propellers are killers).