So, last summer my HK Mini quad PNP came out of the box with a KK2 board on it and all the ESCs soldered up, yada yada. The very first flight I hovered it over the driveway for a bit then tried a little rocket. I mean, just a little rocket, like I wanted it to shoot up a meter or so. The durn thing went three meters into the air and flipped over about six times before coming down hard in my neighbor's front yard. Broke one arm off at the end. Total flight time: about ten seconds.

The damage revealed some outstanding weaknesses in the HK design (which I presume they just bought off of somebody else, but who knows). For one thing, the arms are not structurally sound out at the ends where the motors mount. There is no longitudinal bracing for the arm after the point where the ESC solders on. The fiberglass of the circuit board is neither strong enough nor flexible enough to take the stresses of a less-than-perfect return to Earth.

In order to fix my unit I had to do some surgery to the outboard end of the arm and attach a pile of CF strip and square tube to make the arm both strong and stiff enough to handle the stresses of a quad. I scraped away some solder mask on the bottom side of the board and made sure the top side was ready to accept CA. Then I tacked on some CF strips on the outside of the vertical portion of the arm. Once I had the arm end positioned properly I added some square tubes on the inside. The whole mess got a substantial blast of thick CA to bind everything together and form a solid surface to spread out stresses.

This thing works now, but I'm not really happy with the performance. My MultiWii quads are outperforming it right now. Maybe I just need to do some more tuning. Whatever.