Hi,
I am fairly new to the ArduCopter and RC flying in general. I have about 50 flights behind me and most have gone really well. Today, I crashed twice as a result of my quad ascending very rapidly even though I was using moderate control inputs--it was definitely not behaving as it has in the past. In both cases, I panicked, cut the throttle completely and was unable to recover before crashing into the ground. The first flight was in loiter mode. I then removed my brand new (now broken) gimbal and recalibrated the compass and accelerometers. The second flight started in stabilize and I then switched to altitude hold mode as was trying to rule out a GPS issue. The same basic thing happened. Logs for both flights are attached. Can someone help me make heads or tails of what is going on?
Frame: DJI F450
Controller: 3DR Pixhawk
Arducopter 3.2.1
Many thanks!
Colin
Replies
Maybe this
Common Problems
Hi Milo,
I got the quad rebuilt (it goes a lot faster the second time when you know what you are doing) and did a bit of testing. Vibration seems OK. See the graph below. The axis for each value is set to the allowable limits (+/-3 for x/y and -15 to -5 for z). I also plotted the barometer's altitude since I was not just hovering the whole time. You will see I was bringing it up and down fairly quickly in the second half. It definitely was getting more throttle than when I saw problems in alt hold, though they are not directly comparable. There are some excursions on the z-axis out of the range, but that does not appear to be vibration--its right at the point I am peaking and cut the throttle back quite a bit, so it was indeed accelerating quite aggressively. Thoughts?
vibration.log
Screen Shot 2015-04-03 at 7.02.06 PM.png
Hi _Milo_,
Thanks. I did this measurement back when I first built the quad, and while I do not recall the exact results, everything was well within the prescribed limits. I have not changed anything with the quad that should have affected that. I am still using the same stock DJI propellers and my controller is still mounted with the 3DR-supplied vibration dampening foam.
I should add that my recollection is not that it climbed right as I engaged alt hold. I believe it was raising the throttle just a little bit from the level I had it at when hovering.
I will make new vibration measurements, but first I need to fix the damage. Did the logs lead you to suspect that was the problem, or was it just the symptom?
Thanks!
Sorry, no I haven't looked at the logs,
I had a similar problem with Vector FC I upgraded motors on, and would get a huge uncommanded throttle, like WOT, it was from a vibration problem stemming from one of the motors. It would do this like in a alt hold mode, when I turned against the wind at speed, turning into the wind, would increase vibration.
Even though you did a vibration test in hover, you may be getting more vibration at different throttle levels, that is enough to trigger this. Also even if you were fine before, if like a motor bearing is wearing out, or props nicked, etc...could be that you now have excessive vibration.
Good points. Thank you. Once I get it rebuilt, I will rerun the vibration test, though I am a little afraid to get airborne again without knowing the cause yet. Is it safe to assume that if I stay in stabilize mode I am reasonably safe against this happening?
Yes I'd say so, I'm still a noob on pixhawk, when it happened on my Vector switching out of alt hold mode would regain control, also the vector would kind of re-set itself. It would look pretty scary, but I kept enough altitude to recover.
I have a video of what that behavior looked like if it might help, different controller but same issue.
Thanks again. If you want to link to the video, I'd definitely have a look. The behavior will long be seared in my memory ;-)
I thought it was some kind of tuning issue, because of the new motor/esc DJI secret sauce mix, but it turned out I had one bad motor (vibrations), tried balancing it, but I think it may just be like a magnet is slightly misplaced something is not equally balanced inside.
https://www.youtube.com/watch?v=ffu5jgNL4Os