I have an Octocopter with the help of Rob Lefebvre and had a surprise with altitude hold today. I was a few minutes into a flight, went to Loiter (no problems), then switched to Alt Hold and some seconds later the throttle cut to what felt like zero. I've enclosed the logs. I upgraded the PPM encoder the other day after the fail safe was kicking in when it shouldn't have been. I was only 6-7 meters off the ground but saved it with a quick switch to stable. I can imagine my reaction if I had be in FPV!
The problem starts after 23%. Before and after this there we no problems and I tried altitude hold a few times after this, without a problem. With this problem and the prior problem requiring the PPM update, I'm a bit nervous taking this 6 kilo beast more than 20 meters from me and have not put the camera or gimbal on it until I can be sure there are no glitches.
Can someone take a look at the log and see if they see something that caused it to drop in Alt Hold. Thanks!
Are the flash logs necessary to see what happened or is the tlog enough?
Replies
Marco, do you know if changing THR_ACCEL_P with ch6 happens in real time if you continue to be in Loiter mode? I put ch6 range .4-.8 and put it in Loiter and then started to change the ch6 slider. I didn't notice much change but then when I clicked out of Loiter and then back into Stable and then back to Loiter it shot up like a rocket.
So it seems it's only checking ch6 tuning value at the time you enter the mode and then only checking again if you enter it again. Do you know if that is correct?
I put THR_ACCEL_P on ch6 from .5 to .75 and found .5 to be the best but it still did the up and down dance in Loiter. Should I go below .5? What is the lowest safe range for THR_ACCEL_P?
Marco, I did another flight today and tried out loiter and alt hold. Alt hold was fine but loiter started doing a strange toilet bowl effect but not on a level plane. More like pluto :) and the orbits got larger and larger until I had to stop it after 5 or 10. I've attached the logs. There are 3 loiters at different altitudes and they all do the same angled orbit.
One thing that I did notice before the flight was that the THR_ACCEL_P was back to .75 and THR_ACCEL_I was 1.5. I had changed them via the ArduCopter Config screen yesterday along with the other params you asked me to change but it didn't stick for some reason so I did it in advanced parameters. Now I'm not sure if yesterday's successful loiters were because it was at .75 and changing it today to .5 caused the orbiting loiter?
2013-04-27 12-06 10.kmz
2013-04-27 12-06 10.log.gpx
2013-04-27 12-06 10.log
Marco here is the flash log of the 1 minute loiter followed by a little alt hold. It was perfect!
2013-04-26 19-05 7.kmz
2013-04-26 19-05 7.log.gpx
2013-04-26 19-05 7.log
@Steve, please enable INAV and RAW in your APM (if you use the beta INAV and IMU), try one minute of loiter and send me the flashlog, i want to see your vibrations.
Try with this parameters:
INAV_TC_XY: 3.000000
INAV_TC_Z: 6.000000
INS_MPU6K_FILTER: 20
THR_ACCEL_P: 0.500000
THR_ACCEL_I: 1.000000
THR_ALT_P: 1.000000
THR_RATE_P: 3.000000
THR_RATE_I: 0.000000
I put my i max up to 35 and now it holds altitude pretty good during high speed no more 2 meter drops. The I value obviously needs to be able to climb enough to keep altitude. And the alt hold imax I took to 10 from default 3.
I moved my rate imax up to 15. Maybe I can take it up to 25 but I'm not sure if it will solve this problem. I'm using 2.9.1b on a very small quad with diydrones purple motors and it holds altitude perfectly.
I think the problem on this octo is it's overpowered, especially that I'm not flying with the camera or gimbal yet. Today I did some more test and noticed the same thing in loiter. It will do ok for a while but then it will drop 1 or 2 meters fairly quick and then recovers. Yesterday I grabbed for stable mode but today I resisted and it doesn't crash. It just comes down a couple of meters really fast.
I brought my throttle accel P up to .9 and accel I up to 1.8 but it still does it.
Marco, what parameter controls the throttle rate in altitude hold? I think mine is too strong so it's constantly overshooting and undershooting because I have too much power. My THR_MID set to 320. Not sure how I can set that a better way but the way I did it was look at the MP to see the throttle number which was 1320 which calculated out to 32% throttle which is about what it is. Is there a more accurate way to get this or is it not so critical? Anyway I had the problem when it was at 500 also so I don't think it's that.
My quad just loves to drop altitude if I fly it with moderate speed in alt hold or if I fly it at almost full speed it wants to drop like a rock. I have video and probably a log of it because I had mission planner inside the house running today.
I think I found it: I checked out the kmz file and it seems it's the same as the tlog.
2013-04-25 20-55 145.kmz
2013-04-25 20-55 145.log.gpx
2013-04-25 20-55 145.log
How can I match up a flash log with a tlog? I know this is the right tlog. I downloaded all the logs but there was about 50 or so. Is there some time stamp I can match up? They all have the dates that I downloaded them from the flash.
2013-04-25 15-42-19.tlog
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