Adventure with APM 2.6

Log Analysis -- deprecated Copter Logs -- deprecated
1

I was flying a bit high and lost orientation of my quad. The sun was reflecting off something shiny and I couldn’t see.

So I switched on return home mode to let the quad come home. All of a sudden the quad was rocking back and forth on the pitch axis then it started to yawing back and forth and wobble. I knew I was in trouble. Then it went into a flip. So I figured oh no I have to hike in the woods to try and find this thing. I want the camera at least.

I did not panic, I flipped the switch back to “stabilized” mode. The quad is still doing all sorts of gyration and I cannot tell what it is really doing. I can hear the motors making all kinds of noise. Seems like different motors are revving up at different time. I figured what the hell I can’t do anything now so I lowered the throttle and advanced it back slowly without really stopping on low throttle for too long. I hope that reset or reduce the wobble. Then I heard a squeal from one of the motors. The quad is still falling fast but it seems to be coming straight down, right side up and flat. Then there was a smoke trail at least 10 feet long and very visible going straight up while the quad is falling straight down. So I dropped the throttle stick a bit more and advanced again. Lo and behold after a bit of yaw wagging the darn thing actually stopped falling and leveled off.

Luckily the darn thing actually came back to me and I landed it.

I also found the log files for all my flights. I don’t know how to interpret them. Can you help?

After some discussion with a friend it seems like it may all started with some intermittent short from one motor.

2

Hi, so I had a look, the log is a bit confusing at first.

I can say that at the beginning, the quad seems to have really good pitch and roll control, it looks to be tuned well. I can actually see two RTL events. You start off in Stab, then do a long RTL, then back to Stab, then RTL again, then Stab, then I see the motors cut, and then restarted. Does that make sense with your memory?

So, during the first long period of RTL, the pitch/roll control looks very good. The attitude is obeying commands coming down from the navigation controller. The only thing is, the navigation controller is giving very wobbly outputs, and I don’t know why. It could be vibration, or something else, I’m not sure. Has this machine successfully flown in Loiter, RTL or Auto before?

When you switch back to Stabilize, it continues to perform well. You’re holding it nice and flat and it’s responding.

The problem really starts when you flick to RTL the first time. Something went wrong here and it goes out of control. The autopilot gives full throttle, probably to stop a descent, and at the same time, it gives a sharp roll command. Both of these combined might have caused a sync problem in your ESC with the pancake motors. Are you using SimonK in the ESC’s?

It appears it’s rolling right over, then you switch back to Stabilize, and then kill the throttle. When you restart the throttle, it actually doesn’t bring the motors up right away as it’s still upside-down. But eventually it comes level and restarts. After this point it is responding, but the performance is poor.

I’d say you were extremely lucky to land safely.

My guess is that when you flicked to RTL, the autopilot really “poked” the ESC’s hard, and one of them lost sync. This is a known problem with SimonK flashed ESC’s, and in particular in combination with pancake motors. It’s really a miracle that you got it back safely on the ground after that.

3

I can say that at the beginning, the quad seems to have really good pitch and roll control, it looks to be tuned well. I can actually see two RTL events. You start off in Stab, then do a long RTL, then back to Stab, then RTL again, then Stab, then I see the motors cut, and then restarted. Does that make sense with your memory?<<

Thanks Rob, you did great. Yes I flip to RTL mode earlier. I lost orientation of the quad when the sun reflected off something and the shininess blinded me. So I flipped to RTL to bring the quad back closer. It was working fine then.

So, during the first long period of RTL, the pitch/roll control looks very good. The attitude is obeying commands coming down from the navigation controller. The only thing is, the navigation controller is giving very wobbly outputs, and I don’t know why.<<

Interesting. That is also what I observed in an earlier flight. Even in stabilized mode right now I have a wobble. Looks like the machine is fighting my transmitter input to stay level. When I push my transmitter stick forward the quad will tilt forward for a little while and tries to return to level. Then it will tilt forward for a little while more and tries to return back to level. Looks like something is fighting against each other.

It could be vibration, or something else, I’m not sure. Has this machine successfully flown in Loiter, RTL or Auto before?<<

Yes but see the paragraph above.

The problem really starts when you flick to RTL the first time.<<

That should be the second time.

Something went wrong here and it goes out of control. <<

Yup.

The autopilot gives full throttle, probably to stop a descent, and at the same time, it gives a sharp roll command.<<

I heard the full throttle in the air.

Both of these combined might have caused a sync problem in your ESC with the pancake motors. Are you using SimonK in the ESC’s?<<

Yup, pancake Multmate motors from iPower and SimonK ESC.

It appears it’s rolling right over, then you switch back to Stabilize, and then kill the throttle.<<

Correct. That’s when it flipped. I had to kill the throttle to prevent it from falling and tried to flip it back over. Just instinctive reaction.

When you restart the throttle, it actually doesn’t bring the motors up right away as it’s still upside-down. <<
Yes I couldn’t quite see the orientation. I just knew it was upside down for a while but I don’t know when it flipped back over. It was more or less tumbling in the air.

But eventually it comes level and restarts. After this point it is responding, but the performance is poor.<<

Correct. Also during all this I heard a loud squeal from one of the motors. So that’s probably when it lost sync. I don’t know if that was before and after the roll over. Of course I cannot forget the smoke trail.

I’d say you were extremely lucky to land safely. <<

I much rather be lucky than good. :smiley:

My guess is that when you flicked to RTL, the autopilot really “poked” the ESC’s hard, and one of them lost sync. This is a known problem with SimonK flashed ESC’s, and in particular in combination with pancake motors.<<

That could be the issue.

it’s really a miracle that you got it back safely on the ground after that.<<

Well it was luck and I think the APM is not a bad controller either. It managed to level the machine and kept if flying.

Hansen

4

Ok, so I think the root cause is the SimonK ESC’s. Basically what is happening, is the APM is very aggressive in sending stabilizing commands to the ESC’s. It highlights, rather than causes, the weakness that SimonK has with losing sync, particularly with low-kV motors.

My recommendation would be to use non-SimonK ESC’s. You will likely still get a very stable copter, but with reduced risk of this problem. It may sound a bit counter-intuitive, but this is becoming more and more clear to us.

5

[quote=“Rob_Lefebvre”]Ok, so I think the root cause is the SimonK ESC’s. Basically what is happening, is the APM is very aggressive in sending stabilizing commands to the ESC’s. It highlights, rather than causes, the weakness that SimonK has with losing sync, particularly with low-kV motors.

My recommendation would be to use non-SimonK ESC’s. You will likely still get a very stable copter, but with reduced risk of this problem. It may sound a bit counter-intuitive, but this is becoming more and more clear to us.[/quote]

Thanks Rob, I think that’s a good recommendation. I will switch the speed controllers.