First of my Pixhawk has been working for over a year now without problems.
I have upgraded from an F450 frame to a Tarot 680 with DJI 800 propulsion system. This has worked for over 1 month but now after adding some extra's to the frame (retracts, power module 120A, gimbal...) it seems there is a big problem with the altitude hold function.
When I fly in stabilise mode and check the telemetry the altitude reading seems normal, but when I switch to altitude hold or another function that should keep the same altitude the reading stays the same but the UAV starts descending at a fast rate (+-1m/s). It is a tarot 680 with cover so light and wind should not have an influence on the barometer reading.
I don't think it is a vibration problem, the Pixhawk is mounted on a rubber ball anti-vibration damper. I tried a full reset and installed the beta 3.3 rc8 firmware with no result, lastly I tried to change midpoint throttle.
Attached you can find a log but I don't get any clue what could be wrong, really could use your help!
Replies
So a new day of testing with no solution but some results that could give a better idea of the problem.
Tests
Test1: I removed all the new components to see if induced vibrations could be the problem.
Test2: The 120A power module(hobbyking) was replaced by the bec 5V that was used before.
(could this change have had an influence on the barometer? how could I test this?)
Test3: Taped foam all over my pixhawk to see if the wind/light has an influence on the board.
Test4: Removed the GPS/compass module to see if there was no influence because of the GPS
All of the above test didn't make the problem better or worse, not even a slight change was observed.
Findings
- The problem starts when mode is switched to the alt hold mode, the copter becomes completely unresponsive. All throttle/stick inputs have no influence/impact on the drone.
- Once the mode is changed the altitude reading is completely of, before this the altitude reading is correct.
-The change in altitude on mode change is not constant, sometimes it take 2sec before the copter starts loosing altitude, sometimes it is instant.
Thanks for the previous suggestions, I really hope you could help me solve this. Maybe I should contact 3DR directly?
I solved the problem by doing a full erase of the board by flashing arduplane.
The problem was some of the altitude hold parameters where 0 and thus the mode didn't react to stick inputs. This happened because data was written to early when the board was just connected to mission planner and when not all data was downloaded from the controller. The data with some adapated parameters was written to early to the controller and 0's were written for different parameters. After 2 days of troubleshooting my 680 flies perfectly again.
Maybe your RC3_Trim is not set to what it should be?
Usually it should be in the middle between the RC3 MIN / MAX value, but it depends on transmitter configuration.
Redoing RC calibration would fix this, if it actually is the problem.
Lukas I tried to change the RC3_Trim but it didn't make any difference, I don't think this parameter does change anything. At the end of the calibration the software asks to put the throttle in the lowest position so I suppose it does set the thr_trim at this position. Thanks for the suggestion.
Thomas you are right, RCx_Trim is only relevant for the other channels, not throttle. I should have verified my thoughts before writing them down here, sorry for the confusion.
Can you provide a log (.bin) from one of your test flights? Maybe this can help to find the cause.
The only idea I have now is that your barometric sensor is defective, that would explain why stabilize mode works but none of the assisted modes. I still can't explain though why the altitude reading seems to be correct before switching modes.
In the post below you can read my findings from yesterday, I really think it is a software issue. Tonight I will try to install Arduplane and reflash the Arducopter firmware to have a completely clean build.
Attached you can find a long log file around minute 47 I left the alt-hold hold mode during a longer period.
259.BIN
it looks like you might need to adjust your mid_thr setting perhaps? it does show a lower desired altitude at least for the first couple of autohold events, is your throttle mid-point when you enter auto modes?
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