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HomeRC & Power✈️Aircraft🚁HelicopterFlybarless Rotor Head SystemsOther › Can a FBL unit mask/correct vibration?
12-15-2013 09:55 PM  5 years ago
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don s

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Chesapeake, VA

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Can a FBL unit mask/correct vibration?
I set up a TT E620 with a used CGY750. Flew great for 15 or so flights, including the trim flight. Then the CGY died and it crashed. I'm attempting to fly it NOBAR, and it has a pretty bad shake. Tail up/down, skids shaking, etc.

I've replaced almost everything that I can in an attempt to fix the problem, but it's still there. Some of the parts I pulled, don't seem to be bad. I replaced the main shaft, grips, spindle, tail rotor hub and shaft.

Balanced blades, tail rotor assembly, etc. Running without mains is super smooth. I've tried 3 sets of blades, same difference. Pitch is 0.2 degrees different between blades. Checked and rechecked all pitch measurements.

So, was my CGY masking something? Am I stuck in resonance?
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12-16-2013 12:15 AM  5 years ago
Ronald Thomas

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Gainesville, Fl, USA

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A FBL unit cannot mask a vibe. It may fly great instead of one but most likely that happened in the crash. Now, trying to figure it out will be the PITA.Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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12-16-2013 12:24 AM  5 years ago
don s

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Fortunately I am running out of parts to replace (lol), so the solution should present itself soon (again lol).
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12-16-2013 12:53 AM  5 years ago
G-Limo

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Europe

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Check the static tracking. Set the blades straight with each other then at zero pitch measure between the blade tip and boom for each blade. They should be equal. If they are out you still have a problem. Have you checked the blade holder bearings and thrust races for notchy movement since the crash.. This could also mask a blade tracking issue when the head is up to speed.

BTW.. Where is the CofG set?

/DG
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12-16-2013 12:58 AM  5 years ago
don s

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CG is under shaft. Static tracking is 0.2 degrees different between blades over the entire pitch window. Pitch on the grips is damn near perfect, with identical link lengths.
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12-16-2013 01:04 AM  5 years ago
G-Limo

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Static tracking/alignment is a measure of where each blade will track with no pitch. Best done at hovering head speed with zero pitch and different coloured blade tips, but can be roughly checked by measuring the blade to boom distance when stationary. So not an angle but a distance. .
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12-16-2013 01:07 AM  5 years ago
don s

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During what little hovering I did, the tip paths did not appear to separate.
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12-16-2013 01:16 AM  5 years ago
G-Limo

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And that is how every one does it. But if at rest (or zero pitch at hovering speed) both are not in the same plane, then tracking them equal will forcing in head shake. Measure both the tips from the boom, the should be identical. If not you still have some work go do. If they are the same its not a tracking issue.
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12-28-2013 05:48 PM  5 years ago
don s

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After replacing almost everything, it turned out to be the head block.
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12-28-2013 05:59 PM  5 years ago
Ronald Thomas

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Well at least you found it. I remember the Kasamas had that issue as well. Lots of people replaced a bunch of parts before it was discovered to be a mix machined head block...Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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12-28-2013 06:04 PM  5 years ago
don s

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It had crashed. No way to tell by looking at it, even when comparing with a new head block.
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12-28-2013 10:29 PM  5 years ago
BobOD

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New York- USA

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I think it's safe to figure it got damaged in the crash rather than having been machined incorrectly. Unless the FBL controller was masking the vibrations. Actually, that is possible but not so in your case.Team POP Secret
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12-28-2013 10:54 PM  5 years ago
Ronald Thomas

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Please explain how a FBL unit can mask vibes.Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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12-29-2013 01:37 AM  5 years ago
BobOD

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Sure.
I've seen some people have a vibration that caused the fbl controller to freak out and dump the heli so fast that they had no way to see the vibration. Masked it pretty good.

On the flip side, a guy I know just recently had his heli freak out and dive into the ground out of the blue. He went through the heli looking to see if something came loose, or maybe a static issue??? Then when he sent his logs to Mikado, they asked him to return his unit back for repair. I call this reverse masked. LOL
Team POP Secret
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12-29-2013 02:02 AM  5 years ago
Ronald Thomas

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Oh, ok. Not masked then, just freaked out by vibes. Yeah I have seen people fly FBL units after previous crashes and the FBL units fail as well. At least Mikado will repair it and it not take 3 months of emails Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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12-29-2013 02:05 AM  5 years ago
BobOD

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No, masked indeed. Never saw the vibration. LOL

And in this case, no crashes...at least not until the sensor failed.
But, yes, I have seem them fail some time after a crash as well.
Team POP Secret
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12-29-2013 02:25 AM  5 years ago
Ronald Thomas

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If it was so bad that it freaked out a FBL unit, he would have seen it evidenced some where. No FBL unit can hide that one.Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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12-29-2013 02:42 AM  5 years ago
don s

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I don't think the sensor was hiding anything. I was just trying to rule it out by asking the question. I just think it was a "well-used" 750. Last time I buy used electronics.
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12-29-2013 05:31 AM  5 years ago
BobOD

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Yeah, that's clear in your case.
So, have you tried NOBAR yet? How it going?
Team POP Secret
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12-29-2013 01:35 PM  5 years ago
don s

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NOBAR flew fine. Not as stable, but controllable.
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