Sudden crash with full throttle

Hi all,

We are using the cube in an octoquad config with a tethered power system. Until recently, this drone has flown fairly well, and we’ve been able to iron out most issues that come up.

However, during our last 3-4 flights, we received “Potential Thrust Loss” errors, and even with adequate power the drone falls from the sky with full throttle input. I’ve attached a log from our last flight before the airframe broke, hopefully one of you can see something we don’t. Thanks in advance!

A link to the log (too big to upload as an attachment):


How much is your power source? how many watts?
The FW version you have?
MAybe a video of how the drone felt?

I only see this motor behavior, almost on all the pairs (8-7,6-3,5-4,1-2), some motors on the bottom and some on the max, that make sense with the power lost.

I see on the telemetry your max amp was 55Amp and average voltage 22V, so you powersource must have at least 1200Watts

Do you have a power converter on your drone? what kind of cable are you using to connect the power from the ground?


Thanks for the quick response. We are running ArduCopter 4.0.3, but I’m unsure of our power source MAX limits (I am one of a few working on this vehicle). Unfortunately we didn’t get this flight on video, so logs and broken props are all we have to remember it by. We’re sending roughly 400 V DC through the tether (an amazon special for this prototype :D), with another converter in the drone to keep a consistent power source of around 24 V.

We’re determining through your feedback, and others, that between the weight of our drone and the inconsistency between motors’ power, we may just need to lighten the vehicle a little. Thoughts?

what is the specs of the converter on the drone to go down de 400V?

in telemetry is dificut to see 24V, so maybe your voltage measure need calibration or your power converter is not giving 24V.

What motors an props are you using? totale weight?

The converter in the drone is 24V w/ no load, with a limit of ~62 A continuous current. We are using 380KV motors, with 13" props. The drone weighs in at just over 9lbs.

You can see on your outputs that the copter is struggling.
M6 is pegged at max causing your SybSys25 errors

  • 1 = Thrust Loss Detected (altitude may be prioritised over yaw control)

Have a look at your RCout

You can see how low it was dropping M3 to compensate.

My opinion is that it was working as hard as it could and the controller had to drop the power to maintain control.

Thank you for the info. We’re also looking into reducing weight in any way we can, but if M6 is maxed out would that indicate a bad motor as well?

9lb will be ok for 6 of those motors, what is the brand? did you check the motor specs? How much weight can lift each motor with that prop and that voltage? what about your ESC?