Hey. I have a quadrotor with Pixhawk, APM:Copter V3.3.3 (acf2e10c). I have tested it in Stabilize & AltHold modes, works fine. Also tried switching to Land mode from Stabilize & AltHold, and the drone lands perfectly.
I wanted to try AUTO mode, as a first test I defined this mission based on the tutorials here:
1. Takeoff to 10 meters
2. Loiter there for 5 seconds
3. Land
I went out for a test, as soon as I raised the throttle in AUTO mode, the copter started climbing VERY quickly, and it kept climbing up until it was about 60 meters above the ground. I waited for like 10 seconds and it kept climbing, so I panicked & switched to AltHold mode. I'm a newbie pilot so I could not control it properly at that altitude and...crash!
I thought maybe it was a bug in my planned mission or a gps glitch or something, so I fixed the copter and tried agian. This time with this mission:
1. Takeoff to 3 meters
2. Land
Again, same thing happened. This time, I switched to Land mode, but it kept climbing like crazy. Switched to stabilize and eventually...another crash.
I reviewed the logs, DAlt (desired altitude) does not match my planned mission altitude (figure below). I have attached the log, can someone please help me with this?
DAlt Plot:
Replies
Thanks for taking the time to respond, Andre. I have done plenty of searching about this indeed, and I have seen on many pages or forum discussions that vibrations could cause climbing up in AltHold mode. Sorry, I didn't mean to repeat a question with an obvious answer. What I want to verify exactly is that if vibrations can cause the DAlt (desired altitude) parameter to go up or not.
I think the vibrations should be causing the copter to climb through the distorted Z acceleration numbers, which can make the flight controller detect falling and try to counteract it by increasing throttle. But I can't figure out how a constantly increasing "desired altitude" could be caused by distorted acceleration data.
I just wanted to make sure that high vibration is the only cause here, before I go out and crash for the 3rd time just to find out there were also other problems causing this rapid climbing thing.
Again, sorry if my question is stupid, or already answered. I could not find anything about this specific question.
What you're describing does sound like Z-accel problems. It can as you say detect falling and try and counteract it, and because it tends to do this at full throttle will then exacerbate the problem - so DAlt can look to be chasing itself. Have you re-calibrated your accelerometers? And try different anti-vibration/dampening for the pixhawk, this is a common problem and either over or under dampening can cause what you're describing. I've had precisely the behaviour you've described when I moved my pixhawk to a different foam mounting that invoked high z-accel. It's a simple thing to diagnose, just change the pixhawk mounting, even try without mounting - it looks like your props are reasonably balanced from xy-accel.
I updated my Copter firmware just the day before the (2nd) crash, so I had re-calibrated everything before the test.
I am going to try this, but I'm a little afraid because if the vibration damping does not fix this (or if the new mounting is not effective enough), the crazy climbing is going to happen again and I might crash again. But all I can do is to hope that this time it won't happen again!
Thanks Fnoop!
I looked at the log and it shows that you have high vibrations at full throttle. Also the desired altitude is lower than the altitude but it keeps climbing. There is a similar post with the opposite problem where the copter will not climb but will fall to the waypoint.
I would like to see the logs from a flight in Alt-Hold to see what it looks like.
Thanks for your response Michael. Unfortunately, after the second crash my copter has been damaged and I need to do some repairs before I can fly it again. I will post a log as soon as I can get it back in the air.
As a comment: a strange behavior that I observed in AltHold mode was that when I raised the throttle above the middle zone to increase the altitude, the motors immediately started spinning faster & it went up, but when I decreased the throttle it took a few seconds to decrease the motor speeds & stop climbing up.
Do you think the vibrations could be causing the increase in the desired altitude?
BTW This is the result from Log Analyzer:
Autotune = NA -
Test: Balance/Twist = NA -
Test: Brownout = FAIL - Truncated Log? Ends while armed at altitude 5.69m
Test: Compass = GOOD - mag_field interference within limits (7.13%)
Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = FAIL - Check vibration or accelerometer calibration. (Mismatch: 2.10, WARN: 0.75, FAIL: 1.50)
Test: Parameters = GOOD -
Test: PM = NA -
Test: Pitch/Roll = NA -
Test: Thrust = NA -
Test: VCC = GOOD -
I searched about the problem a little more, some people have suggested that vibrations distorting the Accel data could be causing this issue. But I am not sure if this is the case here, because Pixhawk is increasing the "desired altitude", that does not look like a problem with IMU data being noisy.
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