Hi,
today I experienced a strange behavior testing RTL. A few days ago I tried RTL for the first time and as I've read quite a lot about possible fly-aways, I only flew my quad about 60 meters away and a few meters high before activating RTL (channel 7 option). That worked very well, the copter raised to 15 meters, turned around, came back in a gentle curve to where it was armed and descended slowly (my settings are rtl_alt=15 meters, rtl_alt_final= 2 meters and rtl_loiter_time=5 seconds).
Yesterday I was wondering, how RTL behaves if the current height of the copter is higher than rtl_alt (e.g. copter flies at 50 meters height when RTL is activated and rtl_alt=15 meters). I was hoping that the copter would stay at the current height while returning, but could not find an answer in the wiki.
So I tried that today. First I did another test with the quad being about 5 meters high which worked flawlessly. Then I did the same thing with the quad being about 25 meters high and it flew off in a completely wrong direction. I waited whether it would come back but when it was about 200 meters away I decided to switch back to alt_hold and bring the copter back.
I did the same test again, with exactly the same behavior. RTL worked great when the copter was flying low and seemed not to work at a greater height.
Attached you can see what happened in the file "rtl_issue01.jpg" (1st try, there's also the matching log) and in "rtl_issue02.jpg" for the 2nd try).
The red arrow indicates the arming position. The yellow path shows the low-height flight until I hit RTL, the blue path marks the successfull return on RTL, the orange path is the higher-height flight until I hit RTL again and black shows the supposed fly-away.
I did not have a chance to do further tests, so it could still be coincidence that the fly-aways happended when RTL was activated above rtl_alt. Has anybody experienced a similar behavior or would volunteer to do the same test? I will not be able to fly for the next ten days, but at the moment I have no confidence in RTL. However, it could well be something in my settings (compass?) or pilot error (not waiting long enough), so I would really appreciate if somebody would find the time to check my log-file.
Best regards,
Robert
Replies
Which GPS model? MediaTek or uBlox?
Happenned to me too with 2.9.1b and MediaTek GPS. RTL sometime works, sometime not. Same with Loiter and Auto. Someone said is because of MediaTek. I did downgrade to 2.8.1 and same MediaTek works fine. I personally believe it is an issue with s/w (firmware) rather than h/w. Hope next release 3.x will solve this. I can not afford now to go with uBlox.
Try to have compass learn option disabled in 2.9.1b, this could help. But I always had it enabled in 2.8.1 without any issue.
I tested my APM 4.5 in the similar conditions (RTL from above rtl_alt) and it worked pretty well. Could it be that you GPS lost fix?
BTW, how did you do these nice plots on Google Earth? Did you just import a telemetry logs there or you used some add-on?