Hello All. First off, thank you to all who have worked so hard for this community!!

I am posting this here(as opposed to the main thread) on the advice of other members.

I just had an event happen with a new quad I assembled.

I know the setup was incomplete on this quad. I had intended to fly only in stabilize to test my camera gimble.

I had an RTL trigger with a resulting significant crash and would like to know why.

If someone could please help analyze my Flash log(no telemetry during this flight) for clues, I would greatly appreciate it.

My setup is as follows:

APM 2.5 with ublox and seperate external compass.

Dji 450 motors and arms and 10x4.5 props with a custom spider style frame.

30amp simon K flashed f30 speed controls from RCmanchild

Tarot Gopro gimbal with separate 1000mah 3s pack

Single 2800mah 3s main pack(incorrectly setup as a 5600mah dual pack in apm)

FRsky tfr4-b receiver with ppm single input to apm

Futaba T8FG transmitter

900mhz 3dr telemetry( Not connected during this flight)

The flight went like this. powered up quad, turned on Gopro(in wifi mode) and took off to get an aerial shot of a bus leaving an event. It was windy, but quad was quite stable. I got up to about 100 feet alt and about 100 feet away and quad did a piroette(spelling?) then stabilized momentarily, then pitch hard forward and away it went from 100' to the ground at about a 25degree angle. I know the logs show RTL triggered. Can someone tell me specifically why?

What I assume was a Radio failsafe. But it appears to me the roll in and pitch in are still registering my stick inputs.

******Attached Tlog is for reference only. It is from my only previous test flight. Exact same config as main event. There is outdoors hovering with GPS lock at about 70% in this Tlog*****

Here is a link to the onboard video from this event.

Onboard view of unexpected RTL


Thank you for any help on this,


Views: 1316


Reply to This

Replies to This Discussion

Any chance the GoPro WiFi signal interfered with your transmitter?

That is my #1 suspect. I did have the wifi on.

Although I know the setup was incomplete, any input on the cause of the incorrect action during RTL is also appreciated. It is all a learning experience after all  ;-)

I see from your notes that Telemetry was not connected. You leave a lot to the imagination with the statement, "I know the setup was incomplete on this quad.".

Could you elaborate on what setup or additional setup steps were yet to do?

Doing so may yield more answers for you regarding the failure.


Hello John.
Simply put, I had no intentions of using any mode other than STABILIZE.
Steps that where complete are limited to:
Performed IMU calibration by placing copter in each of the 6 positions requested.
Performed ESC calibrations
Performed Radio Calibration

Items not done:
Did not perform Compassmot
Did not perform compass auto declination
I am not positive the external compass was mounted correctly. Althought it did match my cell phone compass reading reasonably well at rest.

Stabilize was, well, Stable. It handled the wind with no issues.
My biggest mistake other than flying it this way was the fact that I had Radio failsafe enabled for an RTL.
Thanks for your input,

So I hooked up the RSSI output to the apm via input A1. I used an rc lowpass filter per the FRsky documentation.

The voltage from the FRsky is only a max of 3 volts with a full/strong signal(as expected).

Mission planner "rxrssi" shows approx 60% at full signal(also as expected due to 0v to 5v scaling)

I performed a range test to check the signal strength. Outdoors minimum obstructions.

At about 50 feet away, my "rxrssi" drops to about 35% indicated (=approx 60%of full signal value) with the antenna pointed directly at the receiver. Somewhat higher with antenna point vertically.

I then performed the same tests with the Gopro wifi on. No significant difference was noticed. I tried putting the gopro right next to the receiver with no noticable drop in RSSI.

Still working on finding the cause of the failsafe.



Also, can someone please look at my logs and tell me the exact "Home" Lat, Long, and Alt.

When I first powered mission planner back on, it showed my home location as the crash site.

I don't understand how it could have been saved as home.



I've just had a crash that looks very similar to this: RTL went "crazy" resulting in full pitch and throttle being given resulting in the quad flying at top speed into the ground.

I've posted about it here with my log. Here's the bit from your log that looks really similar to what happened to me. 

You say you hadn't finished setup. I've spent a lot of time setting mine up. The previous time I flew two days ago it was working brilliantly with good loiter even in strong wind. I didn't change anything from then until this final flight. I don't have any wifi things on board. So I'm not sure that any of those things are your problem either. 

I don't know what is up though. It's depressing.


So, after a lot more reading, I finally understand one important item I was missing.

To recover from a failsafe RTL event, THE APM MUST SEE YOU SWITCH TO ANOTHER MODE. 

Although I remember this now that I re-read it, I completely forgot about it until now.

I believed I had a complete loss of control, but the fact is the copter ignored my inputs because it was doing what it was programmed to do. It was my lack of completing the setup that caused RTL to fail.

So all that is a mystery now is why the radio failsafe to begin with. 

I have rebuilt the quad and completed setup now. I also added the Rssi monitoring circuit for the rx.

I flew today and had excellent loiter, auto, RTL, and stabilize modes. I tested radio failsafe by switching off transmitter and that worked well.

I flew over 4 times farther away and my rxrssi signal never dropped below about 35% actual. I was able to get it down to about 25% by placing the transmitter behind my metal truck utility bed box. At what point does the FRsky receiver go in to failsafe?

Any input is appreciated,


Yes - that's certainly true and explains why you couldn't seem to regain control and get out of RTL. But, I don't think this explains why the RTL itself failed. RTL should not result in the copter going at full pitch and throttle anywhere!

Having not completed setup properly, the most likely problem would be the compass offsets / interference and this would result in spiral "toilet bowl" patterns. Looking at the graph above, you can see that the pitch / roll (and throttle) inputs in the final section of the flight are fairly constant and maxed out, not oscillating like you'd get in a situation caused by bad compass setup. So I don't think the failure of the RTL was due to bad setup in your case, although the fact that it went into RTL might have been.

RTL by my understanding should never do this! The max speed it tries to achieve should be quite small depending on the nav speed parameter- I think 5 m/s by default. Your copter got to nearly 17 m/s and the APM was STILL trying to accelerate - whilst getting further away from where it wanted to be. Exactly the same thing happened to me. I hope we can get some feedback from some log expert as to why this was happening. 

Harry, I believe it is possible I had the compass installed upside down and or rotated 90 degrees.

If the copter relies on the compass to identify where to apply power, it appears it simply appied power to the motors it thought would correct the "wrong" attitude. Therefore, it did what it was supposed to do.

Can someone please confirm that this would result in a failed RTL like I experienced.



I'm sure that would have an unhappy result, but I don't see how that would result in the huge pitch demand, though, when the APM knew it was going at a speed much greater than the nav speed, or the lack of any change in the demanded pitch when the distance from waypoint (RTL home) was increasing rather than decreasing. On mine I was using the internal compass (with the APM mounted quite high for interference reduction) so that wasn't the issue. 

Reply to Discussion


© 2020   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service