I experienced my 2nd crash with my APM2.5 last evening. The first crash destroyed a super sky surfer then last night destroyed an X8 Wing. The exact same scenario. Took off in manual mode (never switched out of it), flew one circle, during the second circle the APM took over, banked full right, went to full throttle and dove into the ground at full speed destroying the plane. I was using telemetry at the time and have logs on my laptop but not sure how to read them. I've attached them to this thread.
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For anyone finding this thread later on I wanted to report the final outcome. I have since installed this same unit in another airframe and it works fine. I'm pretty sure I had made a mistake during the radio calibration phase for the other two aircraft, I think I had a surface reversed. However, this still doesn't explain the automatic mode change but I have learned to deal with that by setting all the modes available to manual during initial testing then enabling each mode one at a time until I have tested each one. Thanks for all the responses.
Looks like your logs say the APM is in RTL mode right at the start. I'd say it's trying to circle back to the launch point but doesn't have enough altitude. Google APM Log Visualizer. It's a great program and helps a lot.
In one your logs, it looks like you went Manual, Circle, Manual before GPS even got a lock (guessing as I'm no expert), then very shortly after that it goes to RTL mode. There's also a lot of "Unknown" mode switches. I didn't even know that was possible. I'm guessing that means the radio channel went outside it's configured range? Or the radio signal flatlined to zero? Your last four logs all have RTL mode in them and very curiously, there is no throttle input in any of them.
Don't know what else I can say. Go back to the basics. Go over the radio and connections. Do range tests before you launch. Take the prop off and make sure the APM board is correcting for your external input and so on. I'd seriously get either a 3D Radio setup or a long usb cable so you can see what mode the APM thinks it's in while you are testing it.
Ugg...sorry to hear you have lost two planes because of your problem.
Have you verified that your PWM output for manual mode has not somehow shifted so that it is on the envelope between manual and your next mode?
Just a thought as I am a newb who just now setting up my APM 2.5. Initially I had my PWM values adjusted too close to the threshold of two modes and there was enough wander in the signal to cause it jump to another mode on its own.
But I guess that may not explain the behavior of it rolling hard to one side and gunning it into the ground unless the adjacent mode is "suicide".
Sorry about your loss. I know it doesn't help you but this reminds me of the point why one may consider APM1 be the more appropriate autopilot for planes due to its hardware multiplexer. I'm fairly sure that this crash wouldn't have happened in that case. I think it has been discussed earlier that there are also external RC multiplexer available that could at least help in early stages (every plane setup is different).
On a more productive note: I haven't looked at your logs but two things that would come to my mind are the (relatively new) throttle failsafe and maybe a brownout of your board. Which part of your setup (UBEC or internal ESC voltage regulator) powers your APM?
Additional note - I'm aware of the issue with the 2.5 and have my APM in the official case offered by diydrones.
Can't see much at all on the tlog, doesn't actually look like a flight, can you get the last .log file off the APM with the mission planner?
Haven't looked at the logs yet, but have you had successful flights with APM2.5? ie: you tested stabilization throws on the ground to make sure they move right, and have a proper failsafe set up on your Tx/Rx?
Off hand it sounds like you hit a failsafe, and didn't have it set for RTL or something more manageable.
What Tx/Rx are you using?
JC