Question about vibration "magnitude" vs ""index"

[P@reez]

Here are few logs I collected with descriptions.

BEFORE_LOG129_no_blades_on_towel: I just removed the main and tail blades and spooled up on a towel. No adjustments were made to meshes etc.

LOG130_pinionSupportRemoved: I removed the pinion support

LOG133_pnionGearRemoved: The pinion gear was removed. This is only the motor running now.

LOG138_no_blades_on_towel_pnionSpprtReAdj: I put the pinion gear back on, adjusted the gear mesh, put the pinion support back on, played around with the how tight the screws are for the pinion support. This is the lowest I could get the motor vibe peak down to. 1.8 in the up-down direction. Fore/Aft and lateral seem to be below 0.5

Georgi, do you still see bearing issues in my log?

It might be a few days till I get a chance to get a hover log.

Oh and I also noticed that my foam strips are not running down the length of the sk720 but rather they run down the width. I may play around with that at a later date. Right now I'm itching to fly this baby.

[georgi UK]

=] hi, it just shows with a bit of fine fitting how the vibes can be reduced, motor only looks ok considering the rev's it's pulling. it's annoying me because I know something is wrong with the way the motor is spinning?

like a subtle mis-alignment or tight bearing because of a poor fit, something like that? it's not bad by any means so lets move on.



the end result says you need to fly it, I really would like to see a proper load on the motor, so over to you!

[P@reez]

Ok Georgi, I finally got a chance to get a hover log. Here is what I did for reference:

Hover in IU1 for some time then switch to IU2
Land and adjust turnbuckle for main blade tracking
Hover in IU2 then switch to IU1

I seem to have some resonant freq thing going on at IU1 with my tail. It calms down in IU2. Let me know what you think of the IU2 vibes.

[georgi UK]

=] looking at the tail vibe, I feel pretty certain there is a drive issue at the front TT gearbox? this needs to be checked out. the motor looks fine so that's a plus!

[P@reez]

Thanks for the input Georgi. Other owners of this heli have also reported that at certain throttle RPMs it has resonant vibes which go away if you change the throttle % a bit. So I think the large tail vibe I'm seeing might be at a rpm that the heli doesn't play nice at.

To determine which throttle % plays nice, I did a test this morning where I cycled through 8 throttle values. 50% to 67.5% in 2.5% increments. I haven't yet taken a look at the vibe log. I'll do that later in the day.

Once I have the "good" throttle %ages, I'll stick to those and start flying instead of debugging vibes.

[georgi UK]

=] yes that's what I'm seeing in the log, lets see how it goes?

[P@reez]

Here's the log with 8 throttle values. Looks like when my throttle was between 50% and 60%, the vibes were under 4.7. Above 60% (I went till 67.5%) the vibes started increasing in the motor region, they also become dirtier (spanned more frequencies)

[georgi UK]

=] can't open until tomorrow, not on windows now! your previous log was showing tail, motor, and TT vibes dependant on RPMs, which decreased as RPMs increased, this is counter intuitive, any resonance takes place at start up, so I don't follow that bit? might help if we know this heli type?

[P@reez]

The heli is a Kasama Faifa.

[georgi UK]

=] narrow frames??

[P@reez]

Yes, very narrow. Just a tad wider than the thickness of a jive 120 esc.

[georgi UK]

=] the Trex 550 is also a vibe framey heli, by design (unintentionally) it reaches a point where no further adjustments can help and we need to resort to gel type mountings for the unit, and sanities sake! the vibes are going as I predicted, more rpm's more vibes.

[P@reez]

I'm going to stick with what I have now. I'll keep my max throttle at 60%. Jive recommends 60%-65% as max throttle anyway, so I'm in the ball park.

I'll proceed to fine tune my bell/hiller gains and what have you and start flying this baby. This morning I was surprised to find that I mustered the courage to do inverted circuits with this heli. Just 2 days ago, I tried inverted circuits with my 450 and was finding that I would loose my nerve and bailout to upright. I think the visibility of the larger heli goes a long way in keeping the confidence up.