Large Quad shakes

I have a large Agro-quad with 30in props. I had a successful autotune with no payload (lightest and most agile configuration), flies nice and stable with no payload. When i put water in the tank it shakes a lot, the more water (weight) i put in the worse the shakes. I’m not sure an autotune with water sloshing around in the tank would be a good idea. Any help in getting rid of the shakes would be great. Thanks


Bin file located here:

Video here:

I noticed that AccY is much higher than AccX

and this is reflected in the vibration in Y direction.

Thanks, any suggestions on what to change?

Please share a flight log without water tank. It might be due to how tank is fixed or water vibration inside the tank that causes this vibration. I am not sure. But there exist a high vibration in Y axis this is the only fact for now.

Just flew it, added Water Tank Empty flight to same folder. Thanks

The upper graph is vibration with no water. The lower one is the original file “vibration with water”
Water does increase vibration in Y direction.

Above graph shows motors “with out water” while the lower shows motors “with water”
The above graph shows that motors M1 & M2 are higher than M3 & M4… that may suggest motors are not perfectly vertical and M1&M2 tries to compensate the yaw generated by M3 & M4.

I am not expert here. but I recommend that you first should fly with no water and the motor graph should give you similar output for the 4 motors. Either motors are not aligned or there is a weak motor.

You have not done even a basic setup. None of the MOT parameters have been set. Follow these instructions line by line.

Hi, i followed the tuning page directions and it still shakes, lightly with empty tank, a lot with full tank. The vibes are good, not showing any yellow or red spikes, but the landing gear shakes a lot and the arms shake mildly. Here are the logs from the latest flight “27 July”, first with empty tank, then i filled it up.

I also balanced each prop, verified all the motors were facing straight up and landing gear and tank were not loose.


Use this spreadsheet or press ALT A in MissionPlanner to set a few more parameters

What motors and ESCs have you got? If they are T-Motor Flame ESCs then there’s some special considerations (listed in that spreadsheet) and probably keep a fire extinguisher handy :slight_smile:

The Harmonic Notch Filter will help a lot too:

HNOTCH phase 1

  • hover test >1 minute, check FFT

HNOTCH phase 2
INS_HNTCH_ENABLE,1 <- set this then refresh params to see the rest
INS_HNTCH_REF, hover_thrust
INS_HNTCH_FREQ, peak freq from FFT
INS_HNTCH_BW, peak_freq / 2

  • hover & dynamic test >1 minute, check FFT results

HNOTCH phase 3

  • no extra logging, assumes HNOTCH is working great

In the log the PWM outputs are quite high, and motors 3 and 4 are working harder. This indicates a physical yaw bias caused by motor 1 or 2 not being perfectly level. And it is underpowered/overweight.

As for the shaking and oscillations, start by lowering your ATC_RAT_PIT_D and ATC_RAT_RLL_D to about 0.0075 or 0.008 and see how that goes. You might be able to increase P and I a little.

Hi, i did everything you suggested, to included releveling all motors with a level. Vibration is gone! Here is the log from my short flight with a full tank of water can you take a look to see if i missed anything or if you have any further suggestions? The Peak freq was at 11hz.

“New July 27 with new PIDS”


First pic is Pre-Notch filter. Second is post 11hz, 5.5BW Notch filter.

Pre Notch filter

Post Notch filter

You need to enable batch logging to collect data useful for FFT analysis to set the Dynamic Notch filter. A 25Hz input rate is not useful for this purpose. And you would not want a Notch filter centered at 11Hz.

Ok, I’ll turn batch logging back on and fly again with a full tank and post the logs.

The attitude control looks a lot better.

There’s still something going on with the motor output imbalance

and the motor output is quite high. Is the payload fitted or is this minimum take-off weight?

This is max takeoff weight, full water tank.

Ideally you would want more thrust/weight than what you have. You may need more headroom for proper stability under more aggressive demand.

Here is the “28July empty tank” log with Batch logging on. What should i set the hz and BW to? Thanks

Good question, there are a few modes here. Typically you would see a peak and it’s harmonics and it’s fairly straight forward. You have a peak in 2 axis at 25Hz a peak in all axis at 35Hz, a peak ~76Hz, a peak ~115Hz and one at 160Hz.

There are probably a few opinions on how to configure this but I would try INS_HNTCH_FREQ at 36 and BW at 18 and make another flight after setting OPT to 2. An alternative would be to set FREQ to 76 and BW to 38, hope the upper peaks are covered and perhaps deal with the lower peaks with the Static notch next.

Thanks, should i try another flight with batch logging with a full tank, max weight and see if i have the same readings? Would the harmonics change with weight?

Here is the post notch flight. “July 28 Post notch flight” . Empty tank.

NS_HNTCH_FREQ at 36 and BW at 18. OPT 2.

I think that will do.



That craft still has a Yaw bias and is underpowered/overweight. You can see it by graphing RCouts and the MOT_THST_HOVER value is indicative also. You could be looking at a potential crash in windy conditions or other high demand circumstances. If you get Thrust Loss errors it will be time to fix this.