Throttle when changing motors

copilot · July 21, 2021, 1:09pm

Hi all,

Today I changed my 300kV motors for 360kV motors on a fairly large X8 copter (which has done more than a hundred good flights already). I kept the same props (18x5.5) and only changed the motors. On the first take-off in (AltHold mode) the drone climbed about a meter and for a second or two seemed okay, but then started swaying from side to side. I could land it without damage but would like to know what went wrong.

My first thought was that it could be that the hover throttle is way off, as it was last flown with the 300kv motors and carrying an additional payload of about 1kg. Anyway, I looked at the logs and it looks like the throttle maxed out for some reason. I checked afterwards and all motors are still working. Below are the throttle and altitude plots:

Looking at the desired altitude there should have been no reason to suddenly increase the throttle to 100%

The motor outputs also looks okay (there was a strong breeze blowing):

Could it be that the tuning is so different with these motors that the drone tried to correct for the breeze but due to the untuned response became unstable?

Does anybody have some insights as to what could be a possible cause?

dkemxr · July 21, 2021, 1:32pm

Post a link to the .bin flight log.

copilot · July 21, 2021, 2:22pm

Here is the .bin file for the flight:
https://drive.google.com/file/d/1KwD-NR5RgHZ6Gymcsoj_cDogKsiOWWjD/view?usp=sharing

dkemxr · July 21, 2021, 3:58pm

Not much to conclude form such a short flight attempt. Why haven’t you updated to latest Stable?

copilot · July 21, 2021, 4:14pm

Thanks for taking a look, I have some custom ground control software which does not fully work with the newer releases due to the way waypoints and fences are handled.

In your experience, would you say it is unlikely for a too high/low hover throttle to have such an effect?

copilot · August 5, 2021, 9:14am

Just an update for anybody else experiencing a similar issue:
I set all gains back to the default values and performed an auto tune. Now the drones flies stable with my new 360kV motors. So I guess the lesson here is that a jump of 60kV on a tuned drone could have a bigger influence then I thought.