(Log included)Fail TakeOff with 900mm frame quadcopter

hello everyone i’m Sebastian, i’m working on this project for weeks but i cannot find the cause of crash of my quadcopter, i mounted a pixhawk 6x with four t motor 490rpm/v - t.motor 80A ESC calibrated by qgroundcontrol, two 4s 5000mah battery with 40-70c of discharge and 15X6 wooden blade. the problem is that: when i arm the drone it’s all ok, i selected takeoff and after one second of takeoff it pitched drastically. here the log file of the last crash.


It is obvious that your battery capacity went Zero and finally crashed !! You cannot use 4s Lipoly for a 900 mm quadcopter. Must use minimum 6s config for a stable throttle. What is the C rating of your battery .

Ok thank you, I used this kind of battery because I have a lot of this, they are 40-70C as I wrote in the post

in this case connect them in series and check what is the voltage and whether your escs can accept these voltages

I cannot do easily because I’ll have 8s and that it’s not supported by power module for the pixhawk, that it take max 6s if I remember

I think the 4S batteries shouldn’t be the main problem here. When I search for the information you gave about the motor, google comes up with this one. It mostly uses 6S, however the test data for your used KV490 motors also has a 4S setup, they just use much larger props up to 17x5.8 or so. So that setup should be rather safe to use.

I’m still not sure about what caused your crash in the end, because your description doesn’t really match what’s shown in the plots. According to the log you only use takeoff mode for roughly a second and then it switches to position mode where it’s stable for a few more seconds before it crashes.

So, or I buy a 6s battery pack or I need to buy larger props for a safer use of the quadcopter, thanks for the suggestion! For the log vs what I see: I clearly see the drone trying to takeoff and from a very tiny altitude the drone pitched drastically, I saw on the logs that switched to Pos mode but I don’t know why, this weekend I’ll try another flight and I’ll post the logs

The motor are exactly that you linked, now I made a propeller guards for trying another flight without braking the props