Large drone stability problem

Dear colleagues,
I need help because I don’t know what to do anymore.
I have a drone with the following specifications:
Frame - 105cm
Engines - T-motor U8 Pro
ESC - T-motor Flame 60A
T-motor 26x8.5 propellers
Battery - 8S 16000mAh
First, I brought the drone to a state so that it could perform autotune, and then I did autotune for each axis. The drone on a windless day flies very well, but when it starts blowing at a speed of more than 4 m / s it is very unstable. I tried to improve it, but unfortunately nothing brings positive results. Can any of you advise me on this matter?params.param (18.0 KB)

I think a higher P band for all axis will solve the problen i it is sluggish and if it is overreacting you should lower the P band.

The P parameter is set so high that it is not sluggish and doesn’t overreact when moving quickly with the stick. When it blows it becomes unstable. It looks like he is getting a blast under propellers that he can’t handle. From here my question is whether it can be compensated by parameters, or maybe install smaller propellers?

If anyone wants, maybe he’ll analyze the logs. Maybe here you’ll find the answer to my questions. I can’t analyze logs.

I am assuming that the log you put up is from a windy day where the issue is showing up.
The Actual v Desired is showing the issues quite clearly.

Your VIBES are good but the X axis has some spikes that may be from something rattling against the FC, flexible wires coming off the FC, or similar.

The RCout is showing some variance between motors which I am assuming is from the wind direction.

But looking at your battery with Desired and actual

I am seeing a float.

You did say that it flies OK when calm but gets like this when windy.
If the frame is floating then that will be expected.
Main cause I think will be due to running 100kV motors on 8S.
They are big props and low kV motors and need a lot of force to react quickly enough to counter disturbances.
I am not seeing this with your setup.
Have you tried running 12S?
That is the battery setup I would have expected.
You will also need to redo your autotune, maybe a few times while increasing the aggressiveness gradually.

We run a similar setup with 135kV motors and 24” props but on 12S and it is very responsive.

Thank you for analyzing the logs. To clarify the situation, I will write that I have 135KV motors. At the beginning I used 6S battery. Then I changed to 8S and smaller propellers. There wasn’t much improvement. On 12S I have not tried yet because it involves a change in electrical installation, but I probably will not avoid it if this is the only solution to my problem.

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I second to Mike, this size of props with low KV is definitely 12S territory. With lover voltage it has simply too much inertia to react quickly.

Welcome back. I changed the electrical installation and now I am flying to 12S. I have 22.2x7.2 T-motor propellers. The drone with these propellers and 16000mAh batteries takes about 40 minutes. I no longer have the problems I wrote about above. Quad flies well and remains stable even in stronger winds. Now I have a question: can I put propellers on these engines, e.g. 24.2x7.9? I would like to extend the flight time as much as possible while maintaining stability during the flight.

T-motor does recommend using at least 26x8.5 inch props up to 29x9.5 with the U8 kv 135 motors @ 12S. So if you have the spacing between the motors I don’t see any reason why larger props would cause you any issues.

Initial parameters.pdf (82.2 KB)
Change your parameter to this values

Hello. I’ve tested this drone on 26 inch propellers before and the drone did not perform well. The aircraft was very unstable. I have tried to correct the PID values ​​but it has not been able to achieve the desired result. After changing the propellers to 22.2x7.2 T-motor, the drone started flying correctly. Will the parameters you provide improve the stability of the drone on 26-inch propellers?
Should the tension increase, smaller propellers should be given - as recommended by the manufacturer? Will the motors be overloaded in this way?
best regards

I misread the chart, it was recommending 6S voltage with bigger props not, 12S voltage. If the drone did not fly well in the past with the 26 inch props I wouldn’t try it again. Could be worth giving the 24 inch props a shot as they are in the middle of the two sizes. Don’t be surprised if the handling changes again though

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