Dear Friends,
Today I try to Autotune my big Copter. (Octo, 18inch Props, 4.0.0_dev)
Everything went well until suddenly I got the Message ERROR, THRUST LOST and he was descending, He didnt fall out of the Sky.
First I thought it was a Battery Issue cause its pretty cold at the Moment. Then I took a new preheated pair bút same Problem.
First all was good and suddenly the same Situation appears again.
https://drive.google.com/drive/folders/19AHovZQmioqOy7N2IB5Lq4vF2C33c12h?usp=sharing
Before a lot of people are starting to think. I think i know what It is about.
Tomorrow i take my other Copter . IT is build nearly the same except ECSs / Engines
For me it looks like an ESC / Motor Problem
Indeed, motor 3 seems to be the culprit.
How do you see that, please?
i see, the RCouts. Thanks alot
You seem to have a motor mis-alignment that pushes the CCW motors into running harder. And they can’t actually cope up with FC demands.
They are either over-propped or under-ESCd. I’ve experienced both. But looking at your 18-inchers, without knowing your setup, I’d go for the former.
I don’t see a mis-alignment, motors run together fine till the power loss, when the CCW/CW difference comes from the stopped/throttled motor3.
today I flow my other Octo. As i told before, everything same except Engine / ESC.
Absolutly perfekt. No Problems at all.
So its def. an Engine / Esc Problem. The funny thing is, that he flys absolutly perfekt and then suddenly, after more or less the same Time time he is descending with that Error Message like a thermal heat Problem
The ESC ist the OctoBLC from MK, which is normally a wonderful ESC and the Engines are from KDE Direct 340KV. Both are normally very good and reliable Products but together they are unfortunately not working.
Sad…
This is why when I autotune, I am doing it at 100meters AGL. 
