I would like to share with community bug that has caused crash of my quad X. I hope someone might help or explain what happened. Unfortunately I don’t have sd card to provide some logs
Frame: Quad X – Mark4 5 inch;
FC: Mateksys F405-STD STM32F405 F405, BMP280;
ESC: XRotor Micro 60A 4w1 BLHeli-32 6S v. 32.7;
Engines: Emax RS2306 2750 kV with 5050 propellers;
Arducopter v. 4.0.7
I have calibrated my quad for 3s 2200 mah battery and it was stable in stabilize and altitude hold modes. I set failover to RTL. At this stage quad was flying fine.
My 3s battery was old, so I have bought new one – 4s 1550 mah.
Now what I have done (I will describe accurately, I don’t know what is important and what is not):
I have connected USB to FC (battery was disconnected) and clicked “calibrate level (NOT accel!)” – MP hanged so I disconnected usb. I tried this again and it hanged again. I thought it might require battery, so I have plugged battery and USB, I pressed “Calibrate level” (NOT accel!) and this time it was success. I have verified that artificial horizon is level better.
Know I took quad to backyard and connected battery. I have armed it and pushed throttle in stabilize mode to move quad slightly up. As I pushed throttle stick 1 mm up my quad fired up at full speed. After 2 seconds It was at my roof level (about 7 meters high). So I moved throttle stick full down, so my quad turned engines to idle and started falling like a rock. Then I pushed throttle again as little as possible UP, and quad again jumped even higher at maximum throttle.
At this point my control allowed either 100% throttle with throttle stick slightly above minimum and throttle 0% and engines in idle (like after arming) when throttle stick completely down at minimum. Obviously when engines there idling quad was loosing height but it was uncontrollable, so wind has drifted it far far away. I was trying to turn on throttle a little and directing it in my direction, but quad was not reacting much for control and then I was putting engines to idle to lower the flight.
I even switched it to RTL mode hoping it will stabilize altitude, but as I did it quad jumped up and the turn engines to idle again, so RTL was also unable to control engine speed fluently.
To summarize I was able to give 100% throttle or 0%, nothing between that, so I was unable to get back safely. Finally thanks to God’s blessing I managed to crash quad in the grass, but It was very close to hurting someone or damaging parked cars. I almost had an heart attack.
Actually I was planning to do some hovers at 2 meters in my backyard just to test new battery flight time.
What is most strange I have recovered quad. I have noticed arducopter didn’t knew it has crashed, so it was spinning engines lying back, so 2 engines burned out. Later I cleaned it and turned on without propellers to check which engines are working and if I can repeat throttle control loss, but this time it was reacting to my throttle stick properly. I didn’t change ANY settings while doing this test after crash. This is weird and creepy and now I am scared to fly arducopter again, as I was unable to determine what has happened. Is it ESC or arducopter flaw? I could have ended in the jail (injuring someone) or hospital (getting heart attack) for me Please help, what could have happened and more important howto avoid it in the future?
I have emergency engine stop programmed and working, but everything happened so fast and my mind was working to slow that day to cut off engines on time.