Pixhawk PX4 Sudden loss of lift 2 minutes after take-off

Hi Everyone.

Finally my first post. I have been carefully trying to absorb all the information i could from this forum for the past three weeks, since i completed my first quad-copter build.

My set up is as follows :slight_smile:

3s Lipo 25c 3600 maH battery - (http://ip-battery.weebly.com/hobby-plane-batteries.html )
Racestar 930KV motors
Gemfan 10x4.5 props
Pixhawk flight controller - (PX4 2.4.8 Flight Controller NEO-M8N GPS Radio Telemetry OSD 3DR 433Mhz)
Diatone Q450 Quad 450 V3 PCB - frame
3 X 30A SimonK ESC Multirotor X525
1 X XXD HW30A 30A Brushless Motor ESC - this is on the rear right motor n0.4
My AUW is 1.32 KG

Earlier on today I went for a little spin that ended up in disaster and my quad copter in the neighbors yard. After taking off on stabilize and engaging ALTH mode, i cimed up about 10 meters or so and started doing a small tour LOS around the neighborhood.
2 min later, it just seems as though the quad dropped out of the sky, but not all at once. Like a slow controlled drop - at which point i applied maximum throttle to regain lift. It just seems like the quad copter was not able to stay in the air or lift itself up.

Its done this on several occasions in the past but i was low flying. Especially when i am in altitude hold mode, sometimes the quad loses altitude as if the battery is low and it would come all the way and touch down before climbing up again with my throttle on maximum. I suspected the batteried at first, but i have 3 batteries that i am running, 2 X 3600mah and 1x6000mah. same effect. I thought maybe the voltage was dipping but i cannot see it on the ogs. if i take off immediately again, the quad-copter easily lifts off and will fly another 3 minutes before the 25% capacity alarm goes off.

I am lost for Ideas. I checked my batteries after the flight, My battery was still above 11v and the capacity at 90% - from a full charge with two minutes of flying mostly climbing. Not bad I think?

Am i wrong all together ? Have I messed up on the build? should I be running a 4s setup?

My logs seem to be too big to upload, so i have uploaded them to dropbox and here is a link.

I have scoured through the logs and cannot figure out what went wrong. Can someone please help. I am completely new to arducopter.

:cry: Help!

Have a look at your RCout figures, especially for channel 3.
It is pegged at max for most of the flight and towards the end just tops out.
If one channel is not producing the lift required then the others will reduce power to maintain stability.

I noticed you had one odd ESC???
Is this the one?

Hi Mike.

That’s a very good observation on RC 3. I am using a Flysky fsi6 transmitter, modded to output 10 ppm channels. So there is nothing directly connected to channel 3. When i hook up my transmitter, the channel is perfectly centered ad responds as expected during the calibration.

I have the odd Esc because one of the original ones popped and that’s all I had lying about. the replacement is on the way. What could be causing the maxed out channel 3? Its my throttle. could it be because i was climbing? or do the motors not have enough lift so that I am having to ride my throttle hard?

The RCout is what the flight controller is sending to your motors so it indicates an electrical/mechanical issue.

Could the motor be going bad?
Is the ESC calibrated with the rest?
So motor 3 is causing the problems by the look of it.

Hi Mike,

Thank you for the clarification on RC out. You know now that you mention it, its a brand new motor on number 3 with the old ESC, but i have noted that after any flight, the motor always seems much hotter than the rest. Perhaps it was a bad motor from the start.

I have a spare motor but not a spare ESC, so ill swap out the motor and do a copuple of minutes hover and see if the motor is still hot in which case i waill have to wait another couple of weeks for my ESC’s to arrive.

I am quite dissapointed with the cheap motors and ESC’s. I will recommend any noob out there, i know motors and ESC’s get expensive fast, but with the waiting periods every time on of the cheap ones burn out, it turns out to be such a pain in the bottom!!

I will get back to you with the results! Thank you once again!!!

I would suspect the odd ESC before the motor.

Hi Mike,

The odd ESC is on motor number 4. would this affect Motor number 3 if it was misbehaving?

The major difference is that its not simonk flashed ;(.

You cannot fly properly with esc that have different firmwares .
Same if they do not have the same calibration.
On a copter all esc should be the same and with the same parameters and calibration.

Thanks Luca, My esc’s are about two weeks out. in the meantime i will see if i am able to flash simonK onto this ESC, otherwise, i will have to be patient and wait. I will give feedback.