Hello. I have assembled an arducopter. The specifications are given below.
jdrones default frame (with foams attached under arms)
Configuration: Quad X
The frame was assembled as per the wiki. The ESCs have been calibrated as per the wiki. Props were attached properly and balanced. The accelorometer calibration were also carried out as per the wiki.
The modification that was carried out was just the attachment of foams under arms. Since i was new to the flying, so i wanted to save the arducopter from crashes which i experienced initially. The 4 foams have a total weight of 126 grams.
The pid parameters were adjusted to counter for the heavy motors and sensitive controls. Rate_p and Stab_p were changed. The parameters file is attached.
The arducopter has a tendency to move away from its position after take off. I only alter the throttle input and after it rises to some height it moves away from the point from where it was taken off. May be wind should be considered but that was not enough to move it from the center of a football size ground to almost its end in stabillize mode.
The arducopter also has a tendency to lose altitude sometimes. After it has been taken to a certain height in stabilize mode, the copter loses altitude without any throttle. Though it should have been put in ALT HOLD mode for this purpose, but even in stabillize mode it should not lose altitude of 6-10 meters. Once i took it to about 10m, it was in stabilize mode and after some time it started losing altitude to an extent that when it was about to land i cut the throttle and made it land.
Another major problem that i am experiencing is that it flips over without any other input other than throttle. It happened once in ALT HOLD mode (crash 1, video and tlog file attached below) and two times in stabilze mode (crash 2 and 3, video for both and tlog file for crash 3 attached below.)
Sorry. Don't have a log file for crash 2
i am thinking about using a separate BEC to power my APM and Receiver, this way the ESC would be responsible only for speed control and would not overheat. BECs are easily available and they are also very light weight and cheap. I plan to buy this one and i hope my crashes would never happen again. If this problem re-occurred i would let you know.
I don't fly Multicopters I fly fixed wing but power management with BEC and Motor power are handled in a similar manner. I think you are confusing two separate functions here. The B.E.C. (Battery Eliminator Circuit) of an ESC (if equipped) is a low amperage circuit designed to supply power to control circuits receivers and servos in a limited capacity usually 2-5 Amps. The motor power is distributed to the Motor by a separate circuit within the ESC. Your conclusion however is still valid. It's possible that either the ESC is overheating for some reason and is therfore shutting down, or that the low voltage cutoff is shutting down the motor. Are the ESC's programmable? Do they all have the same settings for low voltage cutoff? If they are programmable I might suggest disabling the low voltage cutoff if possible and monitor the voltage by some other means. Is the motor that is cutting out the only one providing a BEC circuit to the other electronics? How is power distributed to the ESC's? Are the ESC's fed power through a power distribution board or do you have each one fed from a separate battery? If the log files show the proper signals being sent to the ESC's then I would have to believe (as you do) that the fault lies with the ESC or power distribution. If you aren't already doing so I would try using a separate BEC and removing the red + wire from your ESC's connection to the APM.
You guys flying these Multicopters are brave to say the least. As was pointed out before if one ESC shuts down you fall out of the sky. I can't imagine putting $1K to$2K into one of these amazing machines and have it just fall out of the sky. At least when I have a motor shut down I can glide in a land somewhere. I fly a 450 size Heli and even that is a nightmare by comparison to my fixed wing. One small link comes loose and it does the crazy chicken dance right to the ground! OUCH!!
Best of luck!
UPDATE - SOLVED.
My problem was confirmed to be due to one particular bad ESC. Bench testing showed that consistently goes into a low-power state after about 3 minutes of moderate throttle level. Something triggered by heat I guess. I replaced it with a new 30A Simonk-flashed ESC from my local APM agent, and I have flown continuous 9 minutes without problems.
BTW, I have always used a dedicated switching BEC connected to the OUTPUT pins of APM2. My ESCs do have built in switching BEC, but all of them have the red (middle) wire disconnected. You can do this nondestructively by using a sharp pin or blade to press the tab and back out the female plug out of the servo connector body and fold the wire back and tape.
Haha. After having crashed multicopters, helis and fixed-wing countless times, I guess they have their pros and cons.
Multicopters do avoid fixed-wing difficulties like launch and landing accidents, having to go forward all the time and min turn radiuses.
I have quit collective-pitch helicopters altogether though.