Thumbs up to SK vibration analysis.

[A VIKING]

Had a two per rev vibration showing up in the SK vib logs.
That is a frequency twice that of the main rotor.
I know that it is caused by both main blades changing pitch at the same time at the same amplitude. Full scale helicopters can have the same issue so like full scale I went looking for something that would allow the blades to change pitch together.
For the Goblin it comes down to all three servos being loose, not to likely. The swashplate being loose, likely but it was tight. Mast being loose, it wasn't. The main rotor head itself being loose.
BINGO! The head was loose on the mast allowing it to move vertically up and down the mast which would change the pitch on both main rotor blades simultaneously and in the same direction. A classic two per rev.
I will remove the head later for proper cleaning and inspection but for now all I did was tighten up the cinch bolts on the head and that took care of it.

Good one Skookum, you caught my first mechanical issue before I saw it myself.

[Xrayted]

Very cool! Yes, 2 X head speed RPM points to the head or blades as the source. Worn dampers can do the same thing.

I find the vibe logging both a blessing and curse. I like knowing what's going on, but at the same time i will obsess about some things that would likely cause me no issues in flight at all. It found a bad bearing situation in a brand new motor for me this week, that I would have never known about. It makes me wonder how long I could have gone before anything got really ugly, or if it would have even failed at all?

[A VIKING]

Originally Posted by Xrayted

Very cool! Yes, 2 X head speed RPM points to the head or blades as the source. Worn dampers can do the same thing.

I find the vibe logging both a blessing and curse. I like knowing what's going on, but at the same time i will obsess about some things that would likely cause me no issues in flight at all. It found a bad bearing situation in a brand new motor for me this week, that I would have never known about. It makes me wonder how long I could have gone before anything got really ugly, or if it would have even failed at all?

Add to the list anything with weight like the battery being loose.
That was a motor bearing creating the vibs you had in the other post?
I'll have to revisit it as my vibs for my Quantum are exactly the same as yours.
I could print out both copies and hold them over each other looking at the sun and they would look like one image.

I have 412 flights on this motor but it still seems tight in the bearings.
Like you I can get tunnel vision but I just want to fly the thing now that it's working so well. I'll just keep an ear pealed for any high freq changes in motor sound during flight.

[Xrayted]

Originally Posted by A VIKING

Add to the list anything with weight like the battery being loose.
That was a motor bearing creating the vibs you had in the other post?
I'll have to revisit it as my vibs for my Quantum are exactly the same as yours.
I could print out both copies and hold them over each other looking at the sun and they would look like one image.

I have 412 flights on this motor but it still seems tight in the bearings.
Like you I can get tunnel vision but I just want to fly the thing now that it's working so well. I'll just keep an ear pealed for any high freq changes in motor sound during flight.

Yes it was. Go back and look at the picture of the main shaft I posted in the thread after tear down. The shaft and inner race of the lower bearing were completely burnished after only five flights, so something was going on in there causing the race to freeze on the shaft. The upper bearing was fine. At the very least, it had to be really heating up that bearing more than normal