Servers by jDrones

Vibrations - Hardware? or PID Tune?

(Andyp1per) #12

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!

(...) #13

So in your opinion, this doesnt look like a tuning issue?

Ill give 50Hz a try this weekend.

(Andyp1per) #14

Autotune works pretty well for the the things it tunes. So either there is something needing tuning that it doesn’t touch (e.g. filter settings) or it’s hardware.

What happens if you graph the motor outputs? That might tell you where it’s coming from.

(S) #15

The FFT certainly seems like motor noise, but the pitch/des pitch really looks like oscillations to me… It’s almost a perfect sine wave on top of the desired pitch.

If the filters don’t fix it, maybe decrease D as another experiment and see what the graph looks like. I’ll admit, this is just a random guess. But I’d try it.

(...) #16

Showing all of them at once doesnt show well. here is one (RCOU.C11), but they all look about the same:

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.

(...) #17

I tried without success to get rid of these vibrations today.

Here is what I tried:

  1. swept Roll_kP over the range 0.100 to 0.200 (Autotune value was 0.149). I was able to experience the change in parameter, but it had little to no effect on the vibrations. ATT_Roll look bad as ever.
  2. swept Roll_kD over the range 0.004 to 0.012 (Autotune value was 0.008). Again, I was able to experience the effect of kD. Again, this had little effect on the vibrations.
  3. tried increasing ATC_RAT_RLL_FILT and ATC_RAT_PIT_FILT to 50Hz. little to no effect in either the feel nor the log trace.

Is it possible that Dshot1200 is causing problems?

These vibes are pretty bad. My GPS swings around on some constructive vibration interference ~2"!

Here is a log file from today:

I didnt realize log while disarmed was turned on, so its all in one log file. Here is what I attempted at each takeoff:

EDIT: I just tried a little flight with Dshot300 instead of Dshot1200 - little to no difference.

(Harald Schmid) #18
  1. try once to fly in stabilize mode and see whether vibrations get better. You avoid therefor the impact of the altitude control.

  2. 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

  3. 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.

(S) #19

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…

(...) #20

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.

Here is my copter:

(...) #21

The thing is that it actually flies very well! position is held well on GPS aided modes. It just vibrates in place. I am able to put it into PosHold or Loiter and feel the vibes through the landing gear.

I can see the vibrations when holding a hover. not only in the frame itself, but the GPS mast is basically getting is perfect harmonic frequency and vibrating all over.

I just feel uneasy about letting a copter go fly missions on its own with vibrations like this. Something about the harshness of these vibes bothers me.

…It also bothers me that my OLD APM2.6 flies with fewer vibrations than this top-of-the-class Cube…lol

(Harald Schmid) #22

S550, born for vibes. Had also many vibes with that copter because of the soft arms. There are to different types of arms available. One with and one without carbon rod in the arm. The one with carbon rod inside have small slots on the bottom side and improves vibration. Carbon propellers (well balanced) and aeronout Propeller also Improved in my case.
And your z-value is to high. The higher the weight of the fc the better is the damping effect (physics) if you use anti-vibe mount. Measured vibrations will also cause additional vibrations. You really should try to damp better perhaps with tape. I have excellent success with this: https://de.aliexpress.com/i/32839652501.html
Try to use anti-vibe. If it does not help you can remove, but you will see imporovements as I have seen.

You should also think about a different frame (i.e. Tarot 680/690), which is much more stable. You are using a quite expensive FC on a very cheap frame

(...) #23

Yes, I did my research prior to purchasing. I made sure to get the version with carbon rods in the arms. Purchased from Hobbyking. I am aware of its reviews, but this is the size range I was looking to build. The Tarot 680/690 is a totally different size class and power system required. I made the choice to spend my money on a high end FC rather than a frame. I realize that it is possible I am struggling with that decision at this point.

Do you know of any other, higher quality, ~550mm hex frames? I was unable to find any. I did consider cutting down the arms on a 680/690, though.

(Harald Schmid) #24
  1. I cutted the arms of Tarot 680 down to 570 and used this motor mounts: http://s.aliexpress.com/yIBZFvqE. As ESCs I used DYS 40A and put them in the tube. FC is an CUAV Pixhack v3 and Air Gear 450 motors
  2. another Copter I have is: http://s.aliexpress.com/7nEJvyEV, which is even better than the tarot. More stable arm mounts. Same ESC in tube and same FC and same motors

S500 went into the bin

(Andyp1per) #25

Here’s a suggestion - find the resonant frequency of your arms and props (just pluck both like a tuning fork) using iAnalyzer lite on your iphone. If either matches your peak then applying a notch may well help - the vibration will be a feedback effect, so reducing the noise should help.

(...) #26

Good idea! ill try it.

I am also going to try:

  • a different battery plate I have that has the rubber damper rings - might allow de-coupling of battery mass from the frame
  • stiffening/shortening my GPS mast - IDK. Maybe the GPS vibrating/wiggling around is sending some erroneous data.
  • I ordered a set of Xoar PJP-N matched pair propellors, 10x4.5. Hopefully theyre more balanced and stiffer than my current props.

all are grasping at straws, but I like experimenting anyways, so im having fun.

I am reconsidering purchasing a Tarot 680pro and cutting the arms down as well, but I am not done experimenting yet. I havent thrown in the towel quite yet.

(...) #27

The resonant frequency of both my arms and props are somewhere between 20-30Hz…so… Does that rule out the frame & props as a major contributor to my vibes?

(Andyp1per) #28

There will be harmonics. So let’s say its 25Hz then there will be harmonics at 50Hz and 100Hz - if your motor peak is at 100Hz then that would explain it.

(...) #29

Wouldnt we expect to see the harmonics in the FFT?

(S) #30

Have you mentioned what settings you’re using for the notch filter?

(Andyp1per) #31

You are testing my physics here, but not neccessarily I don’t think - the motor peak is at 100Hz which will then vibrate the arms at the 3rd harmonic. But this is all theoretical - I think you need to experiment a little to get more data. One other thing you could do is add some weight - this will increase the hover throttle and might stop the resonance (if that is what it is).