My hexacopter has some pretty intense, high frequency vibrations after auto tune and I am having a hard time determining the root cause. Interestingly enough, the copter actually flies great and holds position really well. Its just vibrating like the energizer bunny and I want to clear it up.
As you can see - my vibes are borderline. I also notice that the actual pitch and roll tend to oscillate around the desired pitch and roll with some decent frequency - which look to me to be a tuning issue. Maybe too much D? This particular tune is straight from the auto tune. I dont recall it having the same vibration prior to auto tune - I had originally just dropped in some internet engineer’s PID values who had the same frame (s550), motors, and 4s that I am running and it flew OK.
I have re-balanced all of my props and confirmed no loose motors, props, etc.
Should I reduce my D term by 10%? 20%? Am I even correct to assume its a tuning issue let alone which parameter? Or should I be looking at my propulsion system?
The pitch/roll vs desired looks pretty bad… I’d assume it’s a tuning issue.
Try lowering the auto tune aggr and do another auto tune. Or just jump in and start manual tuning… It’s not difficult if it’s flying. I start with large jumps, then fine tune from there. So if D is .004, go to .002 and see how it does. If it’s better, see if you can go to .003, etc.
I always have trouble telling if I should go higher or lower… Both cause similar results… Too low a D will let the P term oscillate, so too high or too low, you get similar oscillations when tuning D.
How did auto tune change it compared to the tune you were originally using?
My understanding was that excessive P would cause larger, slower, almost drift-like oscillations and excessive D would cause higher frequency, lower amplitude and more intense oscillations. I was interpreting both the feel of the copter in flight and the log as high speed oscillations.
Finally got a replacement Cube flying. Auto tune yesterday resulted in the same results: flies smooth but a bit sluggish pre-autotune, then tight, responsive post-tune but vibrates like the feedback on a PS4 or X360 controller 100% of the time.
I can see this in the Des_Pitch vs Pitch and likewise for _Roll:
I did an FFT with batch logging today:
Significant spike at 100Hz - I assume a harmonic at 200Hz? Something in the autotune resulted in PIDs that are causing a 100Hz vibration.
That looks like motor noise. The question is whether it is hardware or software. Try putting a notch at 100Hz and see if that improves things, but also check motors and props for balance/alignment/bell movement.
I did put Roll_kD on a knob on my transmitter to see if decreasing kD would help, but maybe I didnt give it enough range. I setup the knob for ±15% of the autotune value - didnt change much at the min.
I also tried the same with kI thinking maybe the controller was trying to straddle the target value too hard. kI does result in the equivalent value to kP in both Roll and pitch…
So I think it would be reasonable to raise the filter settings to about 50Hz for gyro, pitch and roll. That may make things worse by letting more noise through, but also may give the controller more headroom. So worthwhile as an experiment, but be careful!
Seems a bit aggressive in the range, but idk if that is just the FC making adjustments. It does seem like any random motor adjustment is counter-acted with a sharp reversal of PWM; like overshoot. However, I dont know what to think of the range of 1500 to 1652 over this window. Is 150 a significant motor signal adjustment? How smooth (or not) should the motor output be?
I think I am going to give tuning the PIDs a shot before filtering and take larger steps. Maybe I just wasnt making a large enough change.
try once to fly in stabilize mode and see whether vibrations get better. You avoid therefor the impact of the altitude control.
you can try to reduce the following values:
ATC_ACCEL_R_MAX and ATC_ACCEL_P_MAX To 60.000 - 65.000 to reduce overshooting
Most important, try once to improve the damping of the fc. VibeZ of 25 for hovering is not good in my opinion. I have max. 5-7 on several copters with hovering and max. 20 with full throttle/speed
What frame do you have, please picture.
I was out flying/tuning/logging this afternoon, too. I just compared my logs from what I perceive as a good tune, with yours… My copter has no noticeable vibrations in the video… That’s about all I can go by.
Our logs look very similar. Yours might be slightly more jagged, but at the same zoom level, they look about the same. Your oscillations around desired roll look to be a higher frequency, but about the same amplitude as mine, and it’s not something I can perceive in flight. I’m not sure what this is worth, as we have very different copters… Mine is a little 120mm frame w/ 1402 motors, 2s battery.
In my previous replies to you, I didn’t notice the zoom level…
So, maybe tuning isn’t the issue… Sorry, i know I’m just confusing the matter at this point, so I’ll stop replying unless I get a more solid answer for you… But maybe your tuning isn’t that bad, after all.
It might help if anyone else can look at their ATT logs and maybe post a pic, so we know what’s normal…
Thanks Harald, I usually try both Stabilize and AltHold because I havent noticed a difference from the beginning. Ill look into the ACCEL parameters, thanks for the tip.
Im using a Cube, which ProfiCNC claims should be hard mounted due to its internal damping for the IMU. Frankly, I think its too heavy to mount the whole thing on vibration isolation. Based on the wiggle that my GPS generates while flying, I think additional vibration isolation for the FC would actually make matter worse.
I wish my vibes were lower, too, but I think theyre acceptable. X and Y average 5-7. Z is significantly higher and is likely exactly what we are trying to resolve here. I would prefer to eliminate the vibration rather than add vibration isolation.