Vibration analysis...

[zurgxd]

Ok, I'm a noob when it comes to anything rc-related, take it easy.

So, I looked at a vibration log today, and i got pretty confused..
(yes, I've read that "Vibration Analyzing for Dummies")



I can see a peak at ~29600 rpm and another one at ~10000 rpm.

For the huge one, my guess would have been motor or torque tube, but, I dont really know. Anyone experienced here?

[Xrayted]

That image host site you are using is trying to download software on my PC. You can use the file/save screenshot function within the data viewer and simply post of the image file directly here on HF using the Go advanced/manage Attachment function without posting the image to any third party site.

Only one spike at 170hz is shown on the image you posted and it only a small 1.7 magnitude, so your vibes are really low. What size heli and what main rotor RPM? Is this a bench run with any blades missing, or a log from actual flight with both main and tail blades installed?

You can post the actual log itself up as an attachment and we can see everything in our own software if you wish

[zurgxd]

Originally Posted by Xrayted

That image host site you are using is trying to download software on my PC. You can use the file/save screenshot function within the data viewer and simply post of the image file directly here on HF using the Go advanced/manage Attachment function without posting the image to any third party site.

Weird, site works fine for me..

I don't have the option to upload or attach an image or file, it's just not there?

Originally Posted by Xrayted

Only one spike at 170hz is shown on the image you posted and it only a small 1.7 magnitude, so your vibes are really low. What size heli and what main rotor RPM? Is this a bench run with any blades missing, or a log from actual flight with both main and tail blades installed?

There's 2 spikes, I made a new log today however. Same huge spike are still there.

It's some old t-rex 500, not sure which one. Both logs are from flights.

Originally Posted by Xrayted

You can post the actual log itself up as an attachment and we can see everything in our own software if you wish

I wish I could, but the button shown in this post isn't there.



I'll just put the files on my own server until further...



http://zufall.nu/skookum/LOG30.SKV

[Xrayted]

Originally Posted by zurgxd

Weird, site works fine for me..

I don't have the option to upload or attach an image or file, it's just not there?


There's 2 spikes, I made a new log today however. Same huge spike are still there.

It's some old t-rex 500, not sure which one. Both logs are from flights.



I wish I could, but the button shown in this post isn't there.



I'll just put the files on my own server until further...



http://zufall.nu/skookum/LOG30.SKV

Its a lot easier than those steps to post an attachment. First you must click the Go Advanced icon on the lower right of the screen, then scroll down and you will see the Manage attachments icon to load the file. I posted up some screen shots to help locate them.

Its no worry now, as I can see your three main spikes now. The first one down at about 75 Hz is about 4500 RPM, and is likely your head or blades, as it common to see a "double head speed" vibe from this location. I'm guessing your head speed is about 2200-2300 based on this peak. The vibe is very low, but you can check to make sure your head dampers are not worn, and that your blades are properly balanced if you wish to investigate it.

The next one up in the 160-170 Hz range is in the 9500-1000 rpm range, and is your tail. Once again quite low for a flight vibe, and the tail blade balance is the likely culprit since the vibe is primarily fore/aft in nature. Sometimes simply switching the blades in the grips will make things better (or worse)

The last big one way up the scale in the 490-500 Hz range is 30,000 RPM and is classic fore/aft whipping of your torque tube and bearings. Nothing else hits that high of an rpm range, even your motor which will be in the 20,000 rpm range or so.

Are you using only one TT bearing as per the stock setup? If so, you may benefit from adding a second bearing for better shaft support, however do NOT space them evenly on the shaft, or you will get harmonic vibes. Make sure the distance between all spaces is random between the bearings and the ends of the TT shaft.

[zurgxd]

Originally Posted by Xrayted

Its a lot easier than those steps to post an attachment. First you must click the Go Advanced icon on the lower right of the screen, then scroll down and you will see the Manage attachments icon to load the file. I posted up some screen shots to help locate them.

Well, still cant find it. This is all i get.

Originally Posted by Xrayted

Its no worry now, as I can see your three main spikes now. The first one down at about 75 Hz is about 4500 RPM, and is likely your head or blades, as it common to see a "double head speed" vibe from this location. I'm guessing your head speed is about 2200-2300 based on this peak. The vibe is very low, but you can check to make sure your head dampers are not worn, and that your blades are properly balanced if you wish to investigate it.

I know the blades are balanced, at least. Forgot to mention the headspeed, but it should be about 2100.

Originally Posted by Xrayted

The next one up in the 160-170 Hz range is in the 9500-1000 rpm range, and is your tail. Once again quite low for a flight vibe, and the tail blade balance is the likely culprit since the vibe is primarily fore/aft in nature. Sometimes simply switching the blades in the grips will make things better (or worse)

The complete tail assembly, including blades, is pretty new but I guess I could try that or another set of blades.

Originally Posted by Xrayted

The last big one way up the scale in the 490-500 Hz range is 30,000 RPM and is classic fore/aft whipping of your torque tube and bearings. Nothing else hits that high of an rpm range, even your motor which will be in the 20,000 rpm range or so.

Another thing I completely forgot to mention, the 2 bearings inside that plastic tt drive "box" isn't really in a good condition. One is a little notchy and the other one felt sluggish/unsmooth. New bearings are on the way however.

Could this be the cause?

Originally Posted by Xrayted

Are you using only one TT bearing as per the stock setup? If so, you may benefit from adding a second bearing for better shaft support, however do NOT space them evenly on the shaft, or you will get harmonic vibes. Make sure the distance between all spaces is random between the bearings and the ends of the TT shaft.

Planning to put another bearing in there once I start to pull apart things.

[zurgxd]

I seem to be getting nowhere..

I replaced 2 "front drive gear" bearings and the tt bearing, inside the boom, and now I'm getting this:

[Xrayted]

Have you tried a different TT shaft? Also, dont press the tail box all the way up hard onto the TT. You want to engage the TT on both ends, but leave a small amount of float.

That spike is about 30,000 RPM and is pretty much all up/down which looks like classic TT whip to me unless its your motor. You would need to be running 3000+ rpm head speed for motor rpms to be that high up which, would be really high for a standard T Rex 500 ESP model and would likely blow your tail apart at some point. I would expect your motor to be in the 20,000 rpm (320-340Hz) range on that model

One way to rule out the motor and be 100% sure we are dealing with the TT would be to disengage the motor from the main gear and do a bench run of the motor only and see if the peak persist.

[zurgxd]

Originally Posted by Xrayted

Have you tried a different TT shaft? Also, dont press the tail box all the way up hard onto the TT. You want to engage the TT on both ends, but leave a small amount of float.

Yes, I replaced the shaft and bearing. I put the shaft into the boom and then the boom into the box. I ran a test without main blades (on a folded towel) and there were no huge spikes then..

Originally Posted by Xrayted

That spike is about 30,000 RPM and is pretty much all up/down which looks like classic TT whip to me unless its your motor. You would need to be running 3000+ rpm head speed for motor rpms to be that high up which, would be really high for a standard T Rex 500 ESP model. I would expect your motor to be in the 20,000 rpm (320-340Hz) range on that model

Shouldn't be the motor then, I've never been above 2200 rpm headspeed

[Xrayted]

Originally Posted by zurgxd

Yes, I replaced the shaft and bearing. I put the shaft into the boom and then the boom into the box. I ran a test without main blades (on a folded towel) and there were no huge spikes then..



Shouldn't be the motor then, I've never been above 2200 rpm headspeed

Def not the motor then. Im not exactly not sure where to go from here. In my experience, the umbrella gears themselves turn turn at or about a 1 to 1 ratio with the tail rotor itself, and wouldn't be near that high rpm, but bearings are a different story as the balls or chipped races can create very high vibe rpms.

My last resort when Im not sure where the source is would be to do what I call "layering"

That is, to disassemble and start making bench vibe runs adding one part at a time until it shows up again. In your case I would remove the tail box and TT, leaving the front gear box in tact, and go from there.

Add the TT back in alone, then add the tail gears and tail shaft only without the tail hub, and see at what point the that massive spike shows back up.

I would also be suspect of all tail bearings, as they have high rpm vibe signatures like that. Sometimes the peak can be smaller until you start adding mass from other parts which makes the bearing issue much worse.

[zurgxd]

Originally Posted by Xrayted

to do what I call "layering"

Yea, will try.

But one thing, I ran out of the original skookum adhesive pads so I used the thicker ones included in this kit (between metal plate and frame)

http://www.amain.com/spartan-rc-vibr...ion-kit/p25452

They are much softer than the skookum pads, could this have any negative impact on the vibrations?

[Xrayted]

Originally Posted by zurgxd

Yea, will try.

But one thing, I ran out of the original skookum adhesive pads so I used the thicker ones included in this kit (between metal plate and frame)

http://www.amain.com/spartan-rc-vibr...ion-kit/p25452

They are much softer than the skookum pads, could this have any negative impact on the vibrations?

Yes, too soft especially with the heavy metal plate on top of them can mean that vibes can be increased to the gyro, as the mass can be moved around on the mount. The SK metal plate is much thicker and heavier than the plate made for the Spartan.

I tried some of the soft Spartan pads based on someone here saying they reduced vibes the most compared to other methods, however I found them to be much too soft and no better than anything else.

Your other vibes are low though, so this isn't the main source of your issue. That high spike of 12 may improve with a different mount setup, but it isn't going to just go away.

[zurgxd]

Well, "bench" run, all blades off, and that spike isn't even there anymore. Only a 0.33 mag tail spike..

As for pads, thinking about trying these
http://www.amain.com/align-aps-gyro-...foam-6/p239975

Edit: I put the blades on, took it outside and the vibes are back.
It went down a little (10-ish) after changing tail blades

[Xrayted]

Originally Posted by zurgxd

Well, "bench" run, all blades off, and that spike isn't even there anymore. Only a 0.33 mag tail spike..

As for pads, thinking about trying these
http://www.amain.com/align-aps-gyro-...foam-6/p239975

Edit: I put the blades on, took it outside and the vibes are back.
It went down a little (10-ish) after changing tail blades

I would expect TT whipping to still remain with the tail blades off, as the TT still has to spin the tail rotor hub. The fact that is dissapears completely with the blades off now has me second guessing.

The RPM is way higher than the tail rpm would ever be for an out of balance tail, so Im still thinking its bearings back there that really show themselves when you load up with the tail blades.

Make sure the thrust bearings in the tail grips aren't worn out and are greased properly, and check the radial bearing supporting the tail shaft, making sure they aren't notchy or loose and spinning in their mounts. They are cheap and easy enough to replace just to make sure.

[zurgxd]

So, this is the result after (in addition to the above) re-greasing thrust bearings, adding 2 more tt-bearings and straightening the boom..



..not much better. Damn, apparently this thing is expensive to own. And I haven't even started crashing yet... guess I should have bought a quad instead like everyone else does..

[zurgxd]

So here we go again. This is from a machine that was supposed to replace the previous one. New/unused airframe, worked great the first few months but now vibrations are starting to show up on this one too... shouldn't have bought another align...

Any idea here? It's not the blades (factory balanced), it shouldn't be the TT (almost new with like 3 bearings). Maybe I should just give up and shelf it like the other one.

[Xrayted]

Originally Posted by zurgxd

So here we go again. This is from a machine that was supposed to replace the previous one. New/unused airframe, worked great the first few months but now vibrations are starting to show up on this one too... shouldn't have bought another align...
Attachment 627494
Any idea here? It's not the blades (factory balanced), it shouldn't be the TT (almost new with like 3 bearings). Maybe I should just give up and shelf it like the other one.

Those values are extremely low and excellent. My own values on my 700 are higher than that for individual components, yet my overall vibe score is 1 or less on scale of 1-10.

You will always have some vibration on any spinning part, so don't obsess just because you see something......it will never be zero unless sitting on a shelf, and your highest peak which is your tail is barely above 1 which is fantastic!.

Connect up to the software and look under the View/Voltage,RPM and Vibe score drop downs.

There you will see you overall vibe score ranked 1-10. Anything over 7 will trip the self level feature off and is considered too much. Your score likely won't even register as low as those values are, so just fly and enjoy

[zurgxd]

Originally Posted by Xrayted

Those values are extremely low and excellent. My own values on my 700 are higher than that for individual components, yet my overall vibe score is 1 or less on scale of 1-10.

Ok, sounds promising but the thing is, 2-3 months ago, those first 2 spikes weren't even there. I've always thought that increased vibes meant that something is going to fail very soon..

And the second thing. I got 3 different headspeeds setup. The log above was done with the lowest, 1550rpm. As soon as I increase to 1650 these vibes gets even worse. Haven't even tried 1950 for a long time. That said, I've been flying the last months only at the lowest speed, afraid of something to fail even faster if I turn it up higher...lol.

<- an older log, with the "slightly higher" headspeed.

Originally Posted by Xrayted

You will always have some vibration on any spinning part, so don't obsess just because you see something......it will never be zero unless sitting on a shelf, and your highest peak which is your tail is barely above 1 which is fantastic!.

I thought it should be under 1 if everything was functioning properly, but maybe I'm expecting too much.

Originally Posted by Xrayted

Connect up to the software and look under the View/Voltage,RPM and Vibe score drop downs.

There you will see you overall vibe score ranked 1-10. Anything over 7 will trip the self level feature off and is considered too much. Your score likely won't even register as low as those values are

I tried self level one time, several moths ago. It started doing some weird small wobbling/shaking, looked weird and unstable. Never touched it again after that.

Originally Posted by Xrayted

so just fly and enjoy

Will try to

[georgi UK]

=] what's not helping here is an uploaded vibe log, it's all well and good to grab a view that says nothing on its own, the pro's in here will spend a good 20 mins analysing and trying to correlate the source.

Your heli looks sound as said upstream, so please include a flight log next time.......

[Luvmyhelis]

Vibes under 1 overall are outstanding. Go fly. Various kinds of vibe layering tend to aim at specific areas of frequencies we deal with. No one seems to be the best. I have played with about 60 or more combos. Each damped out different vibe frequencies better and allowed others through. Layering works well for most but adds in a tendency for 3d guys as the gyro tends to over shoot slightly in hard moves. Sounds like you have this sorted! SL should work fantastic if the regular flight modes also do and the vibes are reasonable. If the vibes are way high, it simply shuts off the SL feature and flies like normal.

[zurgxd]

I replaced a few suspected parts and seems like I actually got rid of some vibes. This is at 1750 rpm now:


That large peak is still there though and I guess bumping up the hs would make it go over 3. I'm still curious about what the cause of this peak could be. Log or not doesn't matter as the peak stays the same.

Well, I'll just keep flying and hope it doesn't explode in mid air.