Tuning the Harmonic Notch

Maybe it has something to do with FFT_FREQ_HOVER = 80

Edit- I tried changing it to 40 and it didn’t seem to make any difference in the logs.

Hi Giorgio, pretty sure the weird output you see is because the log is corrupted. There are many data entries without a corresponding header (I have seen this when logging using FRAM) and I suspect this with a combination of too few samples is giving the analysis artifacts you are seeing.Blockquote

What’s the fastest Sd card you are using for Arducopter logs? I’m pretty sure the above issue was because I’m using an old 8 GB SD card and with the lowest speed class. Is it safe to buy a fast class 3 32Gb like a Samsung one?

About log, main loop and scheduling, yesterday I was watching this https://www.youtube.com/watch?v=2yMO9CPhNdU&t=628s
could we have already some small issue under 1k mainloop?

Fast 32Gb should be fine. I have seen issues with 64Gb on Durandal

If you are using ESC telemetry then INS_HNTCH_FREQ is the only thing that matters - that determines the lower bound of the notch center frequency.

Ok interesting - looking at your log your RPM is 5000 which is roughly the 90Hz you are seeing. Does that seem right physically? If it does the the large spike at 45Hz is some kind of half harmonic. If 5000 seems too high then I guess you have the number of poles set wrong for your motors.

5000rpm seems right physically. I double checked my poles setting, which is correct at 14. What would be the best way to take care of the spike at 45hz? Should I try the static notch?

Yes static notch - it will be frame resonance, but I’ve never seen something as pronounced as this. It will be interesting to see if you set the static notch how things look when you fly more aggressively.

Same considerations as above apply - this is likely into your control bandwidth, set the bandwidth narrow and be careful

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I tried to use a static notch to deal with a 32Hz peak and it greatly affected stability control. I think you have mentioned this before Andy.

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What size aircraft was that 32hz peak on?

It’s a ~500 with 13" props. The arms are very rigid but the frame not so much. It’s really just a beater to test with and fly around for fun, there is nothing of high value on it so it’s a good test bed for new features.

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I set the static notch at 45hz and it flies without issue. The graphs look great as well.

I don’t know if it can get any better than that, but if it can I’m open to suggestions.

Wow, that looks like my bench rig w/o props :grinning:

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I think that’s pretty good. What BW do you have on the static notch?

@dkemxr 32Hz is really into your control bandwidth. Maybe a really narrow notch might work?

Yes, I might try that. Thinking about it now I didn’t consider what a 30Hz BW filter would do with a 32Hz center frequency. That wasn’t very smart and seems obvious now!

Yes you will have been filtering out the pilot input :smiley:

BW for the static is currently 20. ATT at 15.

You can safely go higher on ATT, I wouldn’t make the notch any wider

I bumped it to 20. I’m going to try another auto tune. It feels good in the air, but the graphs say the PIDs could be better.

Yes, I realize that now.


It’s worth re-tuning once you have the notches where you want them as you can push stuff higher. You can also generally push higher than the values autotune gives you, although I’m sure @Leonardthall would slap me for saying that. But beware - a really crisp tune with a good notch is probably not going to fly without the notch.

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Those graphs look pretty amazing :+1:

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