A few days ago, my high school team was testing our octocopter when one of the motors stoped spinning. The UAV was at about 230 feet when we lost the motor. When the motor stopped, the UAV spun about 45 degrees. Everything appeared to be fine and we started to bring it back towards us to land it. When we started to bring it back, it started to lose altitude. Our pilot gave it full throttle but it continued to accelerate downwards until it hit the ground.
If someone could help us analyze the logs and figure out what went wrong and why we crashed even though we only lost one motor that would be great.
I have linked to the logs from the flight below. We conducted two flights that day so the log is probably about 45 minutes long.
PS. currently we think that an ESC failed and that we are slightly underpowered.
System:
Motors: KDE4213XF-360
ESCs: KDEXF-UAS55
Props: KDE-CF185-DP
FC: Pixhawk 2.1
Weight: 28.11 pounds
Tested thrust to weight ratio: 2.7 to 1
Power: 2x MaxAmps 23Ah 6S 25C LiPo batteries in parallell
Replies
- Normal operation at 28% throttle
-your CW motors are working harder than CCW motors
-you have a bit much difference between motors when in hover, are all equally perfectly mounted, or may it be some are rotated ?
-Tuning is not optimal, too much/too often changes in throttle per motor.
During descend, at expected sink rate, your motor#2 (CW) failed to provide thrust (then recovered a bit, and failed again)
With that fault, the throttle demand were up to 60% , and it continued to sink at expected rate.
Then the RPAS entered VRS , and increased it's descent rate, until the pilot for a brief moment built up some horizontal speed, which almost got it out of VRS, but then, the pilot actively braked, and got into VRS Again.
Only better pilot training and recognition of reduced power, and vortex ring state could save the day.
Hammering throttle could never save it, as an experienced pilot would know it's in Loiter (/and altitude-controlled mode) , so if it looses altitude, there is simply nothing more than can gained by rising throttle in Loiter mode.
Gaining speed and getting out of VRS would reduce sink rate, and/or even allow the RPAS to land normally.
I used the wrong link. It is fixed now.
Andre K. said:
you need to share your logs with "anyone with the link" rights, - then I can download it. :)