I recently built a 7-inch FPV drone using a custom frame that is structurally similar to the iFlight Chimera7.
The post by andyp1per titled [ArduCopter 7” Long-Range Standard Build] was very helpful throughout the build process.
Today I did the maiden flight, and although the drone seemed to fly well,
I checked the flight logs and found that it was experiencing high levels of vibration.
It doesn’t seem to be just a filtering issue — I believe it’s likely a hardware-related problem.
My flight controller is soft-mounted using dampers, similar to how most FPV drones are built.
The arms of the drone are indirectly connected to the flight controller.
It seems like vibrations from the motors are traveling through the arms and being transmitted to the FC, which is mounted above the arm plate.
Most FPV frames are designed this way — with a single arm plate securing all four arms — and I believe this could be one of the causes of the vibration.
Even so, the vibration levels on my drone seem excessively high.
What can I do to reduce them?
You may want to share a photo of the actual build. Sometimes even a small thing, such as a tight wire soldered to the controller and touching the frame, may counteract all your dampening attempts. On the other hand, some dampers need to be properly tightened or otherwise they give too much slack…
Thank you for taking the time to look into my issue.
The wires connected to the ESCs have some slack and are not under tension.
The flight controller is mounted loosely — if I press it with my finger, it moves slightly, so it’s not rigidly fixed.
Racing quad propellers aren’t very well balanced usually so I would try some other propellers you have to see if any others are better, you might only have a single bent propeller.
To see if it is due to some prop, you can select the vibe tool in MP, and then run high speed motor test in MP, i.e. you set maybe 50 - 70 % throttle for 10 seconds for each motor and observe the vibes. Must be very careful with props, i.e. maybe you can tie down the copter by the central part of the frame.
I suspect though that the long, slender arms could be the cause of the problem or the top bottom plates. It depends a lot on the thickness of the carbon. I am not sure why people use flat plates, if you do something like DIY, a round tubing is way better. The reason why commercially produced cheap drones use flat arms is because it is much easier to manufacture, not because it is better.
Can you twist by hand the arms? If so, where does it bend more, the arm itself or the base where the arms are bolted between the top and bottom plate?
Thank you for your response. I’ll try testing with a new set of propellers as well.
That said, the propellers I’m currently using appear to be fine on visual inspection.
In fact, when I used a previous frame with carbon tube arms of the same size/specs,
I experienced almost no vibration.
So this might be related to the frame design itself.
However, assembling carbon tube arms is significantly more complicated than flat arms —
especially when it comes to aligning the motor level properly.
That’s the main reason I switched to flat arms.
The flat arms I’m using now are 7mm thick and 14mm wide, and they are mounted very rigidly.
I’m now considering a way to further isolate the FC from the arm plate as a potential solution.
Or I have to go back to tube arm.
While you can improve slilghtly the vibration levels using better mounts (maybe reducing them by 30 .. 50 %) very high vibrations indicate a structural problem which should be solved. If you know how to work with epoxy, round tubing is quite easy to work with, and there are tecniques for leveling the mounts.
But it all depends on how much force you need to apply to twist these arms compared to round arms. I also suspect that 7 mm in vertical direction could be not enough, but I am not sure.
As a general rule, stick with propellers from known brands like DYS, Gemfan, DAL, HQprop avoid anything unbranded. I found that very cheap propellers are almost always warped. Propellers are one part of my quad that i never cheap out on, as you can ruin your video footage with a bad propeller.
I took a look at the Chimera, and it states that the arms are 6 mm thick, and top and bottom plates are 2 and 3 mm thick. That means that this copter here has thicker plates, and vibrtions should be less… strange.
One thing which is not clear from the photos, is whether the arms are correctly cut and bolted. One can see two or three bolts in a row, but it is not clear if the arm base widens and whether the FC long bolts penetrate the top, bottom, and arm. If there are those two or three bolts in a line, and FC long bolts do not go through the arms, then it is possible that the arms would lack tosional rigidity at the joint. Otherwise, it is an enigma.
There might be an issue with my frame design.
The M3 bolts securing the flight controller go through the arms,
which might be causing vibrations from the arms to transfer directly to the FC.
Anyway, since the FC is positioned on top of the arms, the vibration levels seem higher compared to drones that use tube arms.
bottom plate is 3T,
top plate is 2T,
middle plate (which fixes the arms) is 2T,
arms are 7T.
It doesn’t seem like the thickness is insufficient in terms of vibration resistance.
The arms are firmly secured.
The long bolts for the FC go through the bottom plate, the arms, and the middle plate.
The arms are fixed not only by two or three bolts but also by the long bolts used for mounting the FC.
Each arm has about a 1mm gap between them rather than being tightly pressed together.
I found that when the arms are touching each other, it actually leads to more vibration.
Perhaps the holes in the arms that the FC’s long bolts go through should have been slightly larger than 3mm.
I haven’t performed an FFT analysis yet, and I’m currently using filter settings that I previously used on a similar drone as a temporary measure.
However, considering the excessively high vibration levels, I suspect the issue is more likely related to hardware rather than the filters.
I’m using M3 silicone rubber dampers, and although they are quite soft, the vibration levels are still very high.
Right, no performance difference in terms of thrust but I wonder if the airflow difference could be a factor. I have nothing to base that on but your frame looks plenty rigid to me.
