I have been flying the APM for about a year and have generally had good luck with it. I fly the APM on a custom built frame that has always flown well (image below from the build).
When the crash happened I was hovering in stabilize mode, the quad suddenly flipped and crashed to the ground.
I have attached the log and was hoping someone could have a look and suggest what might have happened.
same with me, but here it was an H-copter, quad copter, hexa copter. all with FW 3.1.3
There's no smoking gun in your log. Your Vcc was a little low, but OK, and you had power to the APM all the way to the ground so that should rule out an APM power failure or brown out.
Your actual roll and pitch matches your inputs well, until the very end when it departed from what you were requesting. The log shows a huge roll to the right and a pitch up, but not as large as the roll. Given the mass distribution for an H quad, its moment of inertia would make rolls easier than pitching motions. This would be consistent with some sort of electrical or mechanical failure of the right rear motor. It could be a bad electrical connection (loose solder joint or bullet connector) or a failing/failed ESC or motor. But I'd focus on the right rear.
Nice woodwork on that quad, BTW.
Thanks for looking into this . I will inspect the electrical connections and see if I can come up with anything. Interesting that you mention the Vcc was a little low, I have always felt it was as well but given I am using the DIY drones power module to supply the power I always assumed it was OK.
Thanks for the kind words about the woodwork but I cheated. I designed it in solidworks and cut it out on my CNC machine. The idea behind the design was to make the arms detachable so it could be packed into a case and carried on my KLR650. The wood is a great vibration dampener but does not stand up all that well to crashes. That being said, replacement parts are as simple as loading a piece of popular in the cnc and pressing run.