I recently setup a ~400mm quad with a Pixhawk with 3.1.4 firmware, and 3DR external compass/GPS. Using all default values the quad flies pretty well, but I wanted to test out AutoTune to see how well it works. I noticed the AutoTune settings make the quad feel very twitchy, and unstable. When I went to land the quad immediately flipped over and despite throttle at full down-yaw right (habit from other controllers), however the motors continued to spin for several seconds upside down, breaking props. [edit: jogging my memory, I think I landed OK after initial AutoTune and the flip happened on the very next flight…]
I thought possibly the AutoTune procedure didn’t work properly, so I installed new props, restored PID values to default and tried again. After disarming and saving the new tune, and trying a flight with the new tune, again the quad flipped over in the same manner as before on landing, and again despite throttle down, the motors continued to spin.
The frame is very stiff, and the Pixhawk is mounted using the self adhesive damping foam. Using 2212 - 980kV motors, 1045 props, 20A ESCs running simonk, 3S lipo and an AUW around 950g.
I’m not sure what’s causing this behavior, but I’m uploading the logs in hopes someone here has seen this problem before and knows how to resolve it. Please let me know if any additional information would be helpful.
I’m not sure if this belongs in another thread or not, but I’ve noticed my quad flipping over several more times since I posted this message, always upon landing in stable mode.
I’m extremely hesitant manually landing this quad now, it’s just not safe landing in stab mode. Yesterday it flipped on my deck immediately after touching down. Today on the last run of the day I set it down extremely gently in the grass and again, immediately after touchdown it flips. I’m at 5 so far.
The thing I find most disturbing when this happens is the lack of throttle control I have when this occurs. When I’m in stability mode with the throttle fully planted to idle, the motors should NOT spin up above idle, EVER! When the craft is sitting on its lid, motors revving up uncontrollably, shards of props flying through the air and you cannot bring the motors back to idle, that’s a pretty serious problem in my opinion. Waiting those 1-2 seconds for disarm command to be accepted seems like an eternity.
I am very interested in seeing if this gets figured out. I switched my quad from APM 2.5 to Pixhawk and this same thing happened on the second landing. I looked at the log and didn’t see anything unusual. After putting new props on, checking everything over and going to firmware 3.1.3, I have now flown it half a dozen times without further incident. The firmware it flipped on was 3.1.2.
The APM never even hiccupped a single time in over a year of flying. I’ve read about ESC sync issues etc but that can’t explain the ESC/MOTOR’s suddenly accelerating after touch down and the throttle being at idle. The forward motors went what sounded like full throttle and it flipped over so quick it was over before I realized what was happening. I wish I could find that log to post because it seemed to end right when the quad touched down and didn’t show anything being logged after that. The log just ended with the motors at hover throttle in stabilize with no pitch or roll input or output being shown. It didn’t show the throttle input drop to idle after touch down either. It just ended like a freeze or something. Not sure if that’s even possible but the logging just stopped. If it happens again, I’ll just put the APM back on since it was ultra reliable. This is a machine I like to go on FPV runs with and I would like it to be very trustworthy and also to have the new hybrid mode. Hybrid should be great for FPV work.
I’m using Pixhawk with 3.1.5 and it happens to me. When I’m landing manualy my quad just flips while landing then even if my throtle is off the motors spin again for a second. Result is often a broken prop.
This problem never occurs with RTL or Land mode.
