Troubleshooting X-axis vibration

I’m troubleshooting x-axis vibration on a re-engineered Hexsoon TD-650.

The first version of this copter didn’t have this problem. The Cube/carrier board mounting has not changed. What has changed is:

  1. 4-in-1 ESC instead of 4 standard PWM ESC.
  2. Replaced Crossfire Diversity receiver and RFD900x with HereLink.
  3. Relocated the battery from a plate on standoffs above the top plate to a mount below the bottom plate.

I’ve tried to identify possible causes of frame issues such as how things are mounted - and added some rigidity in several places that seemed suspect… I even tried re-installing the top battery plate, and using a thicker plate for the battery mount.

What has worked the best was I installed 8 additional standoffs between the top and bottom plates - that cut the X-axis vibration substantially - but it’s still higher than I’d prefer.

Attached is a vibe graph, photos of the copter, and an upload of the test flight used for the vibe graph.

I’d appreciate suggestions on where to further investigate.

Many Thanks!

When it’s just one axis the problem is usually something like wires pulled tight in one direction, or something rubbing against the FC.
If it was motor or prop balance you’d expect to see vibes in X and Y of nearly equal amounts.



I had considered the wiring to the carrier board. I thought it was OK, but I’ve re-routed them a bit - and made them as “loose” as I could manage. I also re-balanced the props - one was just slightly out of balance.

The result was about the same - if there is an improvement - it’s just marginal.

Interesting that the 3rd IMU (hard mounted in the Cube as I recall) has significantly less vibration than the 1st and 2nd.

I use the 3M mounting tape pads that came with the Cube - I’m wondering if I need to remove them and just use some VHB tape to mount the carrier board directly to the frame. The 3M mounting tape pads have worked OK for me before.

I’m also wondering if maybe there’s something a little loose in the carrier board itself. And there is the ADSB antenna. I’m wondering if I ought to tape it down to the side of the carrier board - as I’m not using ADSB.

The “mean” vibes are all below 30 - which I’ve read is acceptable. The 3rd IMU’s vibes are all below 25.

It’s the peaks of the x-axis vibes that catch my attention - they aren’t uniform - there are in peaks every 2 to 5 seconds - not uniform. It’s like something is loose that bangs around occasionally.

My next step is to do an auto-tune - so I think I’ll go ahead and do that tomorrow. It will be interesting to see if goes OK.

Thanks for taking a look - I really appreciate your help. If anything else comes to mind, I’d appreciate any thoughts you might have.

I taped down the ADSB antenna - and it helped quite a bit.

I still have those odd spikes though.

I finally resolved my X-Axis vibration problem by setting my antenna to the 25 degree position so that they are pointed under the center of the copter.

I don’t know if this helps because of geometry - or maybe because it keeps the antenna out of the prop wash. But I now have no more spikes above 30.

The frame is still making high vibration, As a frame builder i would add one more connection to the CF arms in the center hub, shorten the arms sliding them into the hub. Then reducing the landing post 40% Your right buy mounting the FC with tape. My 2 cents. When I was a carpenter the rule was to have 70% connection with 30% overhang.