Hello all, 

I need your feedback and help, yesterday I was flying my airplane with APM 2.0 I saw in OSD that it changed to Circle mode, that was probably because a low Tx or Rx low signal.

 Since I noticed the mode change I move the switch and put in RTL mode. OSD show me that it was in RTL but later when the airplane was coming back it changed to circle mode itself. So I had to put in manual mode and flew it back to home as I could.

 I did other test and it happened two or three times more.

Each time that switch to RTL mode meanwhile the airplane was coming back it change to circle mode alone.


This sound real strange for me because I understand that when you change to RTL mode it has not change  the mode until you move the switch.

 Could you please help me understanding why this could be happened, in this condition the RTL mode is not reliable.

Thank guys...

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Replies to This Discussion

Hi, This may not be of much help, but i believe when GPS signal is lost, the APM defaults to circle? someone else could maybe clarify if that is the default behaviour?


Do you have a tlog or log file that you can post? It would be much easier to see what mode changes where happening and the status of the GPS etc..

I had the same issue.
The problem is when you transmit mode "RTL", and short failsafe kicks in it is supposed to keep that mode during radio loss.
But what happend to me is my RX went in to failsafe as well during a signal loss. Most receiver failsafes have that kind of behaviour, and that is how the APM detects a loss of signal. the RX will transmit a very low signal on the throttle channel

But here is the catch:

When most RX's go in to failsafe they put all channels into a predefined mode. Usually thottle 900 and all other channels neutral.
This will cause a mode change when that happens, The mode will be set to whatever you have programmed on that signal. Mine was FBWA.
When connection is restored during the short failsafe event (20 secs of circling), and you have your mode switch on your TX set to RTL, the modeswitch doesn't get reset. This is causing your airplane to circle forever until you physicaly change the mode on your transmitter, which you did when you changed mode to manual and flew home.

My solution for this particular problem was to buy a RX with a programmable failsafe on ALL channels.
I set it to default to a low PWM on the mode switch after signal loss has occured, and I set the corresponding mode on the APM to RTL.

Now when I lose signal, the mode gets set to RTL by the RX, while keeping thottle failsafe active thus bypassing the circle mode alltogether.

I hope this helps.

(this was on V2.68, haven't had the time and weather to test V2.71)

thank all  for the feedback, 

Bill I would like to do what you have asked, I have bought the board recently so I am learning about it. If you don`t mine could you please let me know how I can get the tlog or log files just to post them. I understood that I have to put a micro SD in the board but only this .Could you please send me a link or some info with a procedure to do this ? (buy the way I was diving in the forum just to find this information)

Richard, I thought that this could be the problem, I think that if I could send the info asked by Bill this point could be checked and we are going to have more clear data.

Peter, very smart your solution I will focus in your suggestion  meanwhile we identify the root cause of the problem with Bill suggestion  in order to have a  more reliable RTL mode in this time.

Thank you folks

see http://code.google.com/p/ardupilot-mega/wiki/Datalogging

If you have an APM2.5 the memory chip is on-board. You can connect a micro USB cable to download using Mission Planner to your computer

If you had telemetry connected with MP a .tlog file is saved to c:\program files(x86)\APM Planner\Logs

I have APM2.0

Great Bill I read datalogging info I am going to add a 16Mb dataflash memory and get the info, as soon as I record info I will upload it to the forum.


Bill, I have installed in APM2.0 the 16GB Micro SD and I got the following message:

Any idea of this issue, did I make something wrong?

I haven't used a APM2.0, I started with the first APM2.5 when they came out. The dataflash uses a custom format for speed and was supplied with the board.

I'm not sure if you can format a 16GByte card as that is a SDHC device. You can try by going to setup in the cli and typing erase.

see http://www.diydrones.com/profiles/blogs/apm-2-0-release

Maybe somebody else who know more about what the APM2.0 can support can chime in. The APM2.5 is supplied with a 16Gbit card, which is 2MByte of storage. I assume the APM2.0 was the same. I may have a smaller one kicking around that you could try. PM me.


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