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Logo 400 › Logo 400 vibration level on vbar5 spectrum analyser
10-18-2010 02:22 AM  8 years agoPost 21
Bugcatcher

rrApprentice

Perth, Australia

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Hi Andy,

Acceptable vibration levels on the heli depend on a few things. What Vbar are you using? Where it is mounted does make a huge difference. Using a mini-vbar mounted over the tail boom like on the Logo 400 is always going to have a lot higher vibration levels than say a normal vbar with the remote sensor mounted next to the tail servo on a Logo 500/600.

For me, I'm getting a single spike at the 200Hz mark that was reaching as high as 4094 with carbon tail blades and about 2000 with the stock plastic. Everything else was pretty flat. For my setup i'm running a Hacker 12S 8pole with a 17t pinion via a Ice 100 ESC. With that i'm getting a headspeed of about 2400 at 90% throttle.

Tonight I will run it up on the bench again without the main blades and see what the vibs are again after the belt change I did. The last resort would be the change the mainframes and maybe even to get a BT module to have a look at the vibs in flight.

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12-22-2010 11:55 AM  7 years agoPost 22
Paul Gleeson

rrApprentice

Bonn, Germany

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I was able to significantly reduce my vibrations to around 200 without main blades. :-)

What did the trick was the alignment of the tail gear to the main gear.
I'd really tried hard to assemble this as carefully as I could.

I discovered this by setting the heli level, and checking the main gear was spot on level with a spirit level.
Then I check the boom. It was slight too low.

This would also affect the center of gravity, as I "assumed" the boom is 90 deg to the main shaft.

No chance of seeing this by eye. It was only the combination of leveling the main gear AND the tail boom.

Just thought I'd share this tip.

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12-22-2010 03:23 PM  7 years agoPost 23
Smacka

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PA

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For me, I'm getting a single spike at the 200Hz mark that was reaching as high as 4094 with carbon tail blades and about 2000 with the stock plastic.
What was your forced frequency input at 200Hz to get an output of 4094? How did you measure the output? Accelerometers?

Depending upon your forced frequency input at 200Hz, this could be extremely bad. Anything over 3-times input should be examined, especially at that low of a frequency because the amplitutde of the signal is so much greater at 200Hz than lets say 2000Hz, and will destroy parts in a hurry.

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12-22-2010 03:46 PM  7 years agoPost 24
Bugcatcher

rrApprentice

Perth, Australia

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Not quite sure your meaning by forced frequency.

The reading of over 4000 was directly from the spectrum analyser on the blue mini v-bar. Nothing more.

Paul, it is interesting to hear about the boom/gear mesh angle against the main gear. I did think the way the tail boom mounts and how the plastic doesn't feel precise enough for me. Wanted to try a couple things like you did but as I was setting the backlash directly using a single layer of paper. I wasn't sure what else to do.

On another note. I did manage to get my vib levels down significantly lower to about 650 by changing to mod .7 gears all round. This may have helped get the meshing on the counter gear better, I don't know I would only be guessing. But thought I would share that info none the less.

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12-22-2010 04:23 PM  7 years agoPost 25
Smacka

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PA

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Got it...you are looking at output signals only using V-Bar...

I was referring to actual vibration testing. Every material has a natural frequency at which it resonates. It may be 200Hz or 2000Hz and anywhere in between. The lower frequencies have the highest (and more destructive) amplitudes...which is basically the stroke of the vibe signal from peak-to-peak.

To check and see if your helicopter has any unwanted resonance at lower frequencies, you vibrate the bird in one of two ways...sinusoid signal or random signals at known input levels. You then measure the outputs at known frequencie levels from 150Hz-2000Hz. You are looking for outputs that are greater than 3-times input. If you do have any at that level, you instrument the helicopter with accelerometers (strain gauges) to isolate where the bad vibe is located. Then you redesign the affected area to stiffen it up and drive the outputs up into the higher, non-destructive, frequency ranges.

Examples of a forced frequency would be the vibration from the motor, or the blades, or the gear train...anything that induces an artificial vibration into the airframe of the helicopter.

What I am hearing you say is that Mikado has setup a rudimentary vibration test within the V-Bar software that completes calculations behind the scenes and gives you an output. You then can switch parts, etc...around to try to drive the output down to acceptable levels per the Mikado software.

I guess it is one way to get a very fundamental result from an extremely complex field of work

If it were my company, I would want to complete R&D testing using a vibration table in order to induce random and sinusoidal signals into the helicopter and measure the outputs using many strain gauges applied to the exterior of the bird. I would look for any resonance 3-times input and then set the table to dwell on that frequency for 8-hours per axis (X, Y and Z). Should the helicopter survive, it is a robust design. Should it break, I would redesign the weak component and repeat the testing until there are zero resonances 3-times the input at any frequency lower than 1000Hz...that way the birds would last a lifetime

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12-29-2010 05:01 PM  7 years agoPost 26
CompyMike

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sacramento, ca

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This has been a very informative thread. I've been plauged with vibration issues with my Logo 400 off and on lately.
I've actually had the stock plastic tail case explode on spool up which was kind of scary.
Now I'm using a Swift tail case and a Trex 600 hub and tail grip unit.
I'm definitly not a fan of the tail drive off the main gear design like the Swift 16 is. And since I have had it apart so many times
I'm wondering if the frames are going to need to be replaced because the 8 bolts holding the front boom mount have made indents into the
frame.

I can tell right away if I have a vibration issue because as soon as the skids get light the heli is unstable in a hover and wants to
tip over on me. And this happens at 2200+ HS. But it will hover perfectly at 2000HS.

Been going between MOD 0.5 and MOD 0.7 gearing because my castle esc gov has a tendency to break teeth off of the main gear.
I don't like the MOD 0.7 gears because they are loud. But they hold up alot better.

When I installed the MOD 0.7 gearing the other night, I noticed I had alot of backlash between the main gear and the front tail drive
gear. I found it very hard to get the mesh right on the MOD 0.7. Does anyone find that they have to file the frame slots to get more
adjustment to get the mesh right on the MOD 0.7 gearing?
I found I had to hold the heli so that the front of the heli was against a wall and push the boom to get no backlash when fitting the boom
with the MOD 0.7 gearing. Makes sense because the MOD 0.7 gears are smaller.

If you have too much backlash on that front tail gear will that cause vibration?

I might try and use the MOD 0.7 gearing again. I will use the level trick on the main gear and boom to make sure the alignment is good.
I will also use a piece of paper to try and get the mesh right. Or would it be best to try and get zero backlash with the main gear
and tail drive gear?
I'm using VBAR 4.0. I might upgrade to 5.0 next month.

Thanks
Mike

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01-05-2011 07:24 AM  7 years agoPost 27
CompyMike

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sacramento, ca

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Turns out both my MOD 0.7 main gear and MOD 0.5 main gear had some flat spots on them from a tip over and a incident on the bench.

Once I put a spare MOD 0.5 gear on the logo 400 that had a chipped tooth my vibrations on the analyzer was alot lower. I did a test hover and got only one raised vibration error. The flat spots on the main gear were causing vibrations.

LOGO 500 VBAR / LOGO 600SE vbar

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01-21-2011 08:49 PM  7 years agoPost 28
Paul Gleeson

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Bonn, Germany

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Hi just converted my Logo 400 to a logo 400SE spinning 470mm blades.
After a really careful rebuild and checking all my angles with a digital gauge (Particularly the boom to main shaft angle) here is the result with edge tail blades fitted.

To say I am pleased is an understatement.

I also checked all the angles for the vbar mounting. All within 0.2 degrees. It flies like a dream now.

:-)

Paul

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01-21-2011 09:17 PM  7 years agoPost 29
CompyMike

rrVeteran

sacramento, ca

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I did something very similar. I used my iphone and took measurements on the boom and on the actual main gear.
Your level instrument looks like it will fit on the edge of the main gear maybe? I also added bits of tape to the tail blades until my vibration spike at 11,000rpm was reduced. My vibration high is 450 and sits around 300 when running on the bench with tail blades on and the mains off and 2200HS. You get a weird spike above 18,000 rpm. I bet that is a bearing in the tail maybe? Do you know what RPM the heli was running at when you took that screen shot?
But other than that it looks really good. I'm still new to all this fbl stuff so take it or leave it.

LOGO 500 VBAR / LOGO 600SE vbar

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01-21-2011 10:01 PM  7 years agoPost 30
Paul Gleeson

rrApprentice

Bonn, Germany

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Running at 1900 RPM as I'm using 470mm blades

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01-21-2011 10:56 PM  7 years agoPost 31
clayboy

rrApprentice

phuket thailand

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i found this problem

blades where balanced and cog perfect

changed to a pair of half chipped original blades and problem solved

and had a closer look at the blades

Post

i started with nothing and still got most of it left

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01-23-2011 12:58 PM  7 years agoPost 32
Bugcatcher

rrApprentice

Perth, Australia

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Just a quick follow up to everything.

Firstly, want to thank everyone for there input into this thread. There's some really great info for anyone trying to nail down vib issues on the Logo 400. I think it has been a very informative thread.

Ok, after getting my Logo 400 running near vibration free at around 400 without main blades on, I had what I can only describe as Vbar glitch occur doing forward inverted circuits sending the heli into ground. I nearly saved it and ended up only damaging main/tail blades, undercarrage. Afterwards I have no end of vib issues again with my tail all over the place doing rainbow punch outs and alike.

I though I would recheck a few things and thought I would make sure the main/counter gear mesh angle like mentioned here and it was way way out. I fact I could get it even closeer than 3 deg difference. Had a closer look to realise my boom had bent very slightly from the last crash. I replaced it and aligned the meshing to within 0.1 deg.

Along with that, after asking Mikado about some movement or the Vbar pcb inside the case, I opened up the mini-vbar and harmounted the pcb with a small amount of silastic in each corner. Along with this I re-did the mounting gyro tape between the gyro mount plate I bought off ready heli and used some futaba gyro tape to fix the vbar back in place.

I can safely say it's like a different heli now, completely locked it with no tail issues and no weird stutters when I switch into idle up.

Okay, without knowing which one or even the combination of everthing, the heli was completely transformed and now flying totally awesome. Amazing how just some small changes can make such a difference.

I haven't re-checked the spectrum analyzer again yet and will put up a screen shot if I do. All I can say is once dialled in and vibs sorted, it is an awesom heli to fly. Currently building a second one as a nightflyer so will see how that goes.

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01-24-2011 07:17 PM  7 years agoPost 33
Paul Gleeson

rrApprentice

Bonn, Germany

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Just for fun I tried this to visualise any vibrations

http://www.youtube.com/watch?v=s3iHHq3bRtI

Kind of a competition between a friend of mine to see how vibe free we can make our machines.

Paul

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Logo 400 › Logo 400 vibration level on vbar5 spectrum analyser
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