Start this thread to have a place for focused discussion of the new vibration logging function of AC3.3. I'll start by copy-pasting my initial discussion from the AC3.3 beta testing thread.
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I use my T-rex500 Helicopter AC3.3rc7 FW tested different frequencies INS_ACCEL_FILTER and INS_GYRO_FILTER, showing the different curves characteristic vibrations.
Respectively 20Hz and 15Hz, the obvious can be seen, at 15Hz parameter value AccY shock is much smaller!
Yes, the filtering definitely helps reduce the vibration noise. However, it can also reduce the stability of the helicopter. For a while I was using 10Hz, but then found that the machine was much less stable so I stick with 20Hz now.
Thank you very much! Now I were tested between 10、15、20Hz, when 10Hz, vibration curve looks a lot smaller, especially AccY, and at 15Hz, I feel like more stable, I do not know whether other parameters related to changes, because I also adjusted the value of FF Roll and Pitch, I will make further elimination to individually test.
Do you want any of us other users to post logs for comparison? Or just if we're noticing something strange?
Hi Rob,
thanks for opening this thread!
Have you tried a FFT on your rc7 data?
Ok, so new content now.
I test flew the gas heli again last night, it was a little closer to myself so I could see it better (I normally keep it quite far away) and I noticed something. The Auxilliary fuel tanks are vibrating very badly. These are 800cc tanks full of gas, weighing something like 1lb each, mounted on cantilevered G10 slabs. It's not a great system and I was aware of that but throught I'd try the "cheap" system first. Anyway, you can see them vibrating badly, amplitude had to be about 5mm, and probably at the main rotor frequency of about 25Hz. Obviously, this is super bad.
I then tried emptying those tanks so they weigh very little. This drive up their natural frequency, such that they don't resonate at the same frequency as the main rotor. They aren't visibly shaking anymore. Here is the comparison between these two flights.
So, a fair improvement.
Also very interesting, is I've changed nothing with the electronics, except updating from RC6 to RC7, and the logging seems to be working much better. The data is much cleaner, and you can now see the sine waves from the main rotor. Very odd. I can't explain that. Same card, same everything.
I still find it troubling that, with two 1lb masses visibly shaking at ~25Hz, the Vibe message shows no problem at all. I do wonder if you had something like a very large Octocopter, with large, low RPM props, if the structure was not sound or the rotors unbalanced, and the motor booms were shaking at the 30-40Hz frequency of the rotors, would it notice this? I think it won't. This vibration frequency might not be enough to cause a problem for the control loops, but I think the Vibe message should be showing this problem to the user, because it's not OK.
Here's a flight where you can see the gas tanks shaking. The video was originally shot at 60p, and it was hard to see. When I downsampled to 30p for Youtube, it became super obvious how much they were shaking.
The tanks seem to be shaking at main rotor speed.
I will point out that they also probably absorb a lot of High frequency vibrations.
Wow! :-)
Seems EKF is doing a perfect job.
Yeah, it is impressive.
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