RTL Error - Drone Flies Away at High Speed Instead of Returning - Discussions

Hi Droners. I've been having a problem with RTL using ArduCopter 2.6 for a while. It's intermittent, but annoying and a bit worrisome. When I take off I always test RTL if I'm going to fly FPV. That way it can come home if I have trouble. The problem is, for the last few versions of AC2, RTL occasionally flies away, instead of flying home. Not only away, but away at crazy high speed.Take a look at the attached video for an example. Note that when switched into RTL mode (mode is shown lower right), the 'copter starts to move (away from me, mind you) and gradually pitches more and more until I abort the RTL and go back to STABILIZE mode. Also note the distance to home, as indicated in the OSD is 24m, which is about right.Looking at the log file (also attached), when switching to RTL mode, the lat_error/long_error goes from 0/0 to 521/1000 (and grows throughout the RTL event). Is that in metres? Lat/Long decimal places?Has this been observed by anyone else? Is it confirmed fixed in a particular version? Are there any other tests I should perform to try to catch this silly bug?Specs:* APM2 hardware* External MediaTek GPS* Spectrum RCRx* AC2.6 firmware* XAircraft Quad* GoPro and VTx streams recordedKeep dronin',FMp.s. I know what many of you will think: "Just upgrade to 2.7.3 and this will go away". Maybe, but I can't install 2.7+ on my current batch of APM2. I can install it on APM2.5, but not APM2. This will be a subject of a future analysis and bug report forum post.

RTLStrangeness-11Oct2012.Proof01_480.mp4

RTLStrangeness-LogExcerpt.txt

This looks familiar, although in my case my quad was running in autopilot and suddenly decided to take it's own route. Within seconds and before I could react, it was completely off course and out of line of site.

As a last resort I activated the RTL failsafe and surprisingly the quad made it back but was flying backwards, unfortunately it fell out of the sky before I could land it.

Analysis of the logs and on board video seem to indicate that there was a compass/heading error which slowly magnified as the mission progressed. As such, it flew perfectly fine on the first 3-4 waypoints, then started to get it's bearings wrong, after which it snowballed into a crazy race across the sky.

I suspect there is something wrong with the compass, but after retrieving and repairing the quad, all bench tests seem to prove otherwise. I will test it again in the field tomorrow.

Replies

Ervine Lin October 15, 2012 at 8:02am

This looks familiar, although in my case my quad was running in autopilot and suddenly decided to take it's own route. Within seconds and before I could react, it was completely off course and out of line of site.

As a last resort I activated the RTL failsafe and surprisingly the quad made it back but was flying backwards, unfortunately it fell out of the sky before I could land it.

Analysis of the logs and on board video seem to indicate that there was a compass/heading error which slowly magnified as the mission progressed. As such, it flew perfectly fine on the first 3-4 waypoints, then started to get it's bearings wrong, after which it snowballed into a crazy race across the sky.

I suspect there is something wrong with the compass, but after retrieving and repairing the quad, all bench tests seem to prove otherwise. I will test it again in the field tomorrow.
Augusto Sala October 14, 2012 at 6:45am

I actually do have the same problem in 2.7.3.

I have to say I didn't test RTL too much. Just 4/5 times. The first time it was ok. Landing point was shifted by 10 to 20 meters but behavior was fine. The other times it was just flying crazy fast in some random direction. My yaw pids are not perfect but I don't think this is a problem. I will test further.
Aleksey Kharlanov October 12, 2012 at 3:51am

Maybe one of the reason, when you take off, Home position saved with same error (in example 1km far from your location). While you flying, GPS got more accurate position. Now you switch to RTL and copter start to moving to inaccurate Home position. If I'm right, this situation must be in logs...

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