I’m facing some challenges with excessive Z-axis vibrations (above 30 m/s/s) on my hexacopter, and I’m hoping someone can point me in the right direction. My goal is to get everything dialed in well enough to safely run Autotune and get the best tune.
Here’s what I’ve done so far:
Enabled FFT
I set up the FFT-based approach for identifying primary vibration frequencies.
Took a short test flight to gather data.
Configured the Harmonic Notch Filter
Using the data from the FFT, I adjusted my Harmonic Notch settings.
Flew again, but still seeing very high Z-axis vibration (above 30 m/s/s).
Despite these steps, the vibrations remain high, and I’m not sure what else to tweak. I’m attaching a log that shows the issue in detail. If anyone could give me tips on:
How to refine the FFT-based approach and harmonic notch settings
Possible frame- or hardware-related causes I should check
Param settings that might help reduce the Z-axis vibrations further
…I would really appreciate it!
Ultimately, I’d like to lower these vibrations enough so that I can run Autotune reliably. Any advice, steps to diagnose, or parameter suggestions would be greatly appreciated. Thanks in advance for your help.
Log attached. Please let me know if you need more info or screenshots from my setup.
Vibration levels above 20 can not be solved in software. You need to reduce them by fixing and improving the hardware. After that, once they are back at acceptable levels, the software is able to do it`s job. But not before.
After your reply, I completely disassembled the drone frame and assembled again making sure that each arm is secured and not moving. I added 3D Printed TPU gaskets at some places to damp vibration. I then lowered the battery plate a bit to get the CG downward.
I changed the FC to more powerful CUAV X7 Plus Pro with latest arducopter version 4.5.7 and GNSS to Neo 3 Pro. At the time of configuration, I used Ardupilot Methodic Configurator. I have also configured CAN based ESC Telemetry of Hobbywing.
I took off in AltHold Mode and flight was smooth. But when I checked the Logs, the Z vibration was getting above 60. I am attaching both video and log of the flight. Please suggest me the further steps.
Do you think that adding payload at the CG will reduce the Z vibration?
As of now, I can’t see any vibration or oscillation visually and audibly. Also, TPU is only used as gasket at only 4 places where payload plate is connected.
What should I do in this condition, please guide me.
Flexibility is not necessarily a good thing - there used to be motor mount dampeners around and they almost always made vibrations worse. Z axis vibration is usually caused by the props passage over the arms and even the base plates if the props are too big.
I suspect the X7 Plus will measure higher vibrations because the IMUs are more sensitive.
The harmonic notch filter wont reduce your vibrations, it’s job is to prevent those vibrations from affecting the control loops as much. So you wont see any difference in vibrations by changing filter settings.
You need to set INS_LOG_BAT_MASK,1 to log the pre-filter and post-filter noise (it seems you had already done all that measurement) - that’s what matters after you’ve done everything you can to reduce physical vibrations. You appear to have the other notch filter settings OK and it should be working with the ESC RPM.
If you are happy with it you can set INS_LOG_BAT_OPT,0 along with INS_LOG_BAT_MASK,0.
Okay,
Let me change INS_LOG_BAT_MASK to 1 and then do a test flight. What do you think, by adding weight at CG will reduce the Z Vibration?
I want to reduce the Z vibration as soon as possible as I want to move forward in tunning procedure.
I have tested the drone with INS_LOG_BAT_MASK = 1. Also, I have tweaked the PID a bit. I am suspecting that the vibrations are maybe because of poor PID and Notch filter as DesPitch and Pitch graph is not following each other, it seems there are certain oscillations, same with Roll. can you please review these settings in the log.
Reduce yaw PIDs just so it’s not affecting pitch and roll. This probably wont affect any behaviour much at all and yaw can easily be improved later if there is a need. Yaw is last on the list.
I have tried everything physically to reduce Z - Vibration. Tighten every screw, balanced the propellers, fixed the motors with rivets, fixed all cables with zip-tie so it won’t vibrate in the air.
After all these efforts, I am not getting any success. Still the vibration I am getting is very high. I don’t know what to do in this situation.
Does low weight of drone cause vibration? as the drone is 13 kg.
Does the 2480 Propeller cause vibration? as 2388 Propeller is also available in the market.
Does CG is not too down cause vibration?
After some trouble, I changed the Flight Controller to CUAV X7 Plus Pro. I don’t know why I am getting this high vibration.
Even after fixing all cables with zip tie, I am getting more and more peak.
I don’t understand why this is happening. Because of this I can’t tune my drone. It is getting frustrating for me to get same result even after doing all this.
Photos would help a lot.
Cable-tying all the cables together can sometimes be part of the problem. They need flexibility where they go from being fixed to the frame to connecting to the flight controller, so they are not transferring vibrations or pulling on the FC.
EDIT:
Good news is the harmonic notch filter is working as planned:
Are you taking off and landing on a slight slope?
If not then you need to calibrate the copters level state as follows:
Get a spirit level of some sort, preferably not too heavy
Connect to Mission Planner, go to Setup / Mandatory / Accel
Pack under the landing gear to get the copter level across the tops of the motors in all different directions
Press Calibrate Level
At the moment attitude control is not great, but it’s not oscillating and going out of control - you did some serious inputs and the copter was Ok with that.
I would be tempted to run autotune - do Roll first then if it works out well do Pitch.
This will suit your spring-centered throttle, and also the copter will try to get to 2m altitude when you take off. You get used to this and you’ll soon see how good this is for large copters, to avoid moving sideways and catching the landing gear on the ground. Same with the NAVALT_MIN param - dont move sideways to waypoints until at least 2m altitude.
I have uploaded some pictures of the drone from various angles in the link below. I fly this drone in this condition without canopy attached exactly as shown in pictures. Drone Pictures
Four small TPU gaskets are placed where Carbon Fiber Battery Plate is connected to the Landing Gear. Please check pictures.
Those label good to have but I think it may create some vibrations, try use masking tape to secure it down with the cables to see it improve. Next build, you may want to have more holes or groove on carbon fiber plate for tying down cables and running cables to different level. Yes, you have cable tie the extra cables length but they appear “floating” to me and not secure to plate to prevent movement. Do you think those cables below the flight controller are knocking the top plate?
How do you secure the Flight controller to the plate? Screw from bottom? Double-sided tape?
Do you think the drone arm joint can flex up or down if you use some force trying to bend it?
You can try cover up the flight controller for a few benefits. Reduce propeller wash vibration, barometer drastic changes especially pitch and roll, etc.
I have used 3M tape to secure the flight controller to the Top Plate. Also, I have tied all the cables and connectors below the FC to prevent it from vibrating. I have inspected all the cables, and they feel firm when pressing.
Also, the part which seems to be moving is rubber seal of canopy. From next flight I will cover the top using canopy, so it won’t move at all.
I have attempted the Autotune for Roll Axis. I first tried the Quiktune Lua script and after that I did Autotune for Roll. Please review the log 00000033.BIN
Also, can you please explain me why we chose 2nd and 4th harmonics in Harmonic Notch Filter Setting.
Another thing is when reading documents of CUAV X7 Plus Pro, I got to know that the FC is equipped with 3 IMUs from these one is industrial grade IMU with damping and other two are hard mounted. Will changing primary IMU to that sensor solve my problem?
