Loiter Problem with low % of compassmot

Dear all,

I have been struggling with loiter issue for some days now and somehow I feel stuck. I have been searching all around and trying everything I could find, but seems like my issue is not yet resolved. I have built quad with APM 2.5 and Ublok 6 H compass. I flashed APM with Arducopter 3.1.2 and did all the standard calibration. I run 5 different flight modes (stabilize, alt hold, loiter, auto, RTL). I always perform althold check first before loiter and auto or RTL. However, my loiter doesn't work as it keeps on toilet bowling or simply drift (not too fast), to make it simple it doesn't lock in one position, that's why I haven't performed yet auto nor RTL. Alt hold works well. I check the compassmot and it is now at 9% rate which I think is acceptable (before I move the compass and GPS it was 84%).

Please if any of you could probably help me with analyzing the log it would be really fantastic. I tried to check the log by graphing DesVelX vs VelX and DesVelY vs VelY (as written in :

http://copter.ardupilot.com/wiki/loiter-mode/#Tuning

I found that the actual velocities (direction x and y) are always trying to catch the desired velocity in the "extreme" way (kind of straight jump into the desired one but not gradual change). I assume it is one of the sources of the problem.

I attach here three logs.

thank you so so much and I really appreciate any help.

Best,

Rai

2014-08-27 16-37-55.log.gpx

2014-08-27 17-48-59.log.gpx

2014-08-27 19-03-54.log.gpx

Easiest way I can think of to check without worrying what hardware you are running would be while it is hooked up to mission planner. Preferably a laptop so you can go outside and pickup better satellite reception. On the flight data screen you should see how many sats it picked up, and it should show where the copter is at within a few feet. Check and see where it is showing the nose is pointing, try rotating the copter on it's z axis and make sure it continues to point in the correct direction. The more I think about it, this may be more related to your compass settings. As that controls it's headings. I would definitely go through everything but you can confirm it is all working in the flight data screen before taking off.

Replies

George Randall August 31, 2014 at 4:08am

Are you sure your gps module is set to the correct orientation in Mission Planner?
- Rai > George Randall August 31, 2014 at 4:16am
  
  Hi George,
  
  Thanks for your response, I think it is. I'll have it checked again now. I have moved the GPS module higher than before and bingo! the compassmot shows 9% only which I think good. However, I still have the toilet bowl effect now. The quad doesn't want to stay when I activate "loiter". It stays for a second or two and then start to toilet bowl... I really don't know what's really going on
- George Randall > Rai August 31, 2014 at 4:19am
  
  The other thing to check would be to log vibrations and see where they are at. When I initially setup my pixhawk I had the gps orientation set to where I thought it was supposed to be. Found out it was wrong.
- Rai > George Randall August 31, 2014 at 4:38am
  
  Hi George,
  
  Thanks lot. Stupid question now (sorry ...) how to know our GPS orientation actually from Mission Planner ? thanks lot
- George Randall > Rai August 31, 2014 at 4:48am
  
  Easiest way I can think of to check without worrying what hardware you are running would be while it is hooked up to mission planner. Preferably a laptop so you can go outside and pickup better satellite reception. On the flight data screen you should see how many sats it picked up, and it should show where the copter is at within a few feet. Check and see where it is showing the nose is pointing, try rotating the copter on it's z axis and make sure it continues to point in the correct direction. The more I think about it, this may be more related to your compass settings. As that controls it's headings. I would definitely go through everything but you can confirm it is all working in the flight data screen before taking off.
- George Randall > George Randall August 31, 2014 at 5:00am
  
  It is the compass I was thinking of the whole time. I hooked mine up just to double check and it is the compass you need to make sure the orientation is correct. As long as you have the GPS which from your original post has the external compass with it is mounted with the front facing front. Then check your orientation setting under initial setup and mandatory hardware. Looking at it's orientation through the flight data screen will confirm it.
- Rai > George Randall August 31, 2014 at 5:07am
  
  Thanks lot George, I'll give it a try again, thanks lot
- Moderator
  
  Graham Dyer > Rai August 31, 2014 at 5:33am
  
  One way to check compass orientation is to place the copter outside pointing any direction (lets say pointing east) and after booting and connecting via telemetry (don't move or rotate it) then look at your compass heading, it should show ~90°.
  
  If it shows 0 then the compass is not working at all (although it will show change if you now rotate it as the inertial nav comes into play) but if anything other than about 90° (+/-10°) then your orientation is wrong or possibly even the magnetic declination is out.
- Rai > Graham Dyer August 31, 2014 at 11:07pm
  
  Hi Graham,
  
  Thanks lot for the advise. I did check to compass orientation and you are totally right!! Mine was not correct , so I did calibrate again (manual with roll 180 degrees) and everything works fine now. Loiter is dead locked!!!!
  
  thanks lot
  
  R
- Rai > Graham Dyer August 31, 2014 at 8:51am
  
  Thanks lot Graham...

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