Copter crash a few second after takeoff. Need help!

Hello Everyone,

Yesterday I had a strange crash with my quadcopter, 4S battery with Cube Black autopilot, Here2 GPS+Compass.

It took off successfully, but after that a few second, copter leaned on roll axis, uncontrollable and crashed on the ground. I saw some EKF error messages so I think something is wrong with the autopilot IMU or the GPS/Compass, or Cube Black was defected but I’m not sure.

I need your help to find the root cause of this crash, link for the log file here:

Any suggestion or comment is highly appreciated.

Thank you very much!

The copter is constantly commanded to climb during first 5 seconds of the flight, rather than waiting for the autopilot to learn the hover thrust. This makes it difficult to determine your true hover thrust, however, it seems to be around 1750-1800 PW. This suggests that the copter has a very low thrust to weight ratio.

Also, the RCOUT(motor commands) are always near the saturation limit during the climb phase, which leaves very little control authority for attitude control. This makes the copter unable to follow any attitude command.

Please follow the tuning instruction page before using any auto mode like LOITER.


1 Like

Hello @Emre_Saldiran , thank you so much for your help!

  • Yes, you are right that copter have hover thrust at around 1750-1800 PW, this copter is quite heavy, but we have another copter with the same weight and tuning values that is flying normally. We did the PID autotune successfully before. So I think it is not a tuning issue. Thank you for your reference links, I will check it carefully again. Yes, for next flight I will start will Stabilize first to check copter behavior before Loiter.

  • I also noticed that the battery voltage reading drop faster than normal, from around 17V to 10V a few second before that crash, so this is also not normal. Do you think this can be a defect of battery or power cables issue?


Hi, Nghia

I think you are right, your 4S battery show around 17.1 Volt at the start of the flight, which indicates either the BATT_VOLT_MULT parameter is wrong, or your battery is overcharged. Also, the voltage drops from 16.2 Volt at the armed state to 11.2 Volt at the start of the climb phase. This is a significant drop in voltage for what appears to be a fully charged battery.

Your analog voltage monitor and ESC voltage reading are contradicting each other. Reading reported by ESCs do not show the same voltage drop as the battery monitor. I dont think the capacitor in ESCs can compansate for this much voltage drop for 6-7 seconds.