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Other › Interesting belt vibration issue
03-09-2006 02:18 PM  11 years agoPost 1
Daniel Wee

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Singapore

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I've been trying all sorts of things to reduce the vibrations on my Heliup T-Rex and have recently swapped out all the bearings for new ones, and to my frustration still found vibrations at certain RPM's.

Finally, upon inspection I made a rather interesting discovery. I had measured the frequency of the vibration and noticed that the vibration on the fins was occuring at an even harmonic of the tail speed - which led me to conclude that the vibration was in the tail system - from the tail pulley and belt downwards. Several tests later, I had the torch light on the where the belt was going into the boom from the front tail pulley and as I pushed up the RPM, I found that at the said frequencies, the belt would go into huge vibrations - it was resonating and the vibrations depended on the standing wave forming. I was partly led to inspect this because the measured frequency of the fin vibration went up as I tightened the belt.

I remember that the idea of the frame resonating was dismissed but I don't recall anyone saying anything about the belt resonating. The vibrations on the belt was great enough so that the belt started hitting the insides of the boom, thus producing a "grating" sound. I would not be surprised if the belt also hit the other side of the belt travelling in the opposite direction. In the past I always wondered what was causing this sound - now I know - and have a video to show this happening. I will post it if anyone's interested but it's basically showing the belt vibrating as I hit various RPM's - ie. boring stuff.

So, now, the question is what was contributing to this oscillation in the belt. In my case, it looks like the MicroHeli CNC pulley which I was using, didn't fit the pulley shaft very well, and was a little larger in size. This resulted in the pulley not turning around it's centre, albeit by a very little bit only. I had in fact tried two of these MH CNC pulleys on a regular Align pulley shaft and they were both a little larger in the bore which resulted in the problem described above. I am now going to try something different and see what happens.

So, in conclusion - the sound of the belt hitting the boom as you spool down sometimes - is just that. This may occur if there is some oscillation in the belt. At this point, it looks like any variation to the length and tension in the belt can result in this kind of vibration. The biggest suspects would be play in the tail shaft bearings or the front tail pulley bearings (defective bearings that don't turn true), or out of true pulleys on either the front or the back end of the belt. These are the most likely suspects. If you are seeing the tail fin(s) go into strong vibration at certain points as you ramp up the RPM slowly - you may want to check to see if your pulleys are turning true.

I thought I'd share this rather interesting discovery. Now I'm going to try the other shaft and see if that improves the situation at all.

Daniel Wee

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03-09-2006 03:20 PM  11 years agoPost 2
Daniel Wee

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Singapore

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Okay, I put in a new pulley that looks "truer" but the vibrations are still occuring at the same RPM so either my tail output pulley is out of true, which I think is a little unlikely (but I will swap out another bearing just to check later), or it's the gear meshing for the reduction gear. When I inspect the mesh, there is one point where the meshing is very tight - with no play at all. I have two of the blue reduction gears and they both exhibit this tight spot in the meshing so right now I'm trying to figure out how to test if it's the meshing that's the problem or something else.

Another thing to note is that while the vibrations are present at the said RPM with or without the tail slider and rotor grips and blades installed, they are much stronger with the slider/grips/blades installed. Adding any mass to the tail output shaft has an amplifying effect on these vibrations - although they may not be the direct cause of it.

Daniel Wee

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03-09-2006 04:36 PM  11 years agoPost 3
Daniel Wee

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Singapore

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I'm using the Heliup frame but I'll give it a try to see if that makes any difference - loosen up the screws to the tail block. I have done what you said with my XL in the past for the same reasons. Will report back here in a few minutes.

Daniel

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03-09-2006 05:29 PM  11 years agoPost 4
gkoutsis

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Athens Greece

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Daniel,

I can tell you that I am also using the MH pulleys front and back with a SS shaft and the one in the frame is not running true. But it doesn't cause any vibrations.

I am also using the blue gears with a MH main gear and the heli flies like a dream. The mesh on my gears is perfect. Frame is the Align CF with the plastic blocks.

George

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03-09-2006 05:39 PM  11 years agoPost 5
Daniel Wee

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Singapore

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Okay, I've loosened the screws that hold the tail pulley block but it didn't make any difference. I think I'm going to swap out another bearing in the Duzi tail.

I'm pretty sure the mesh has a tight spot and don't know how much that's going to be a factor here. This Heliup frame has pretty tight tolerances so even with a few screws loose, the blocks pretty much stay in place, unlike with the Align CF frame.

If swapping out the bearing doesn't work, I'm going to swap out the entire tailset to a Heliup V3 one and see if that resolves the issue. If it does then the fault will fall squarely on the Duzi MT7602 complete tailset.

If that doesn't work, then it's the lower gear mesh. Maybe the tolerance is too tight and I may have to modify the frame to give it slightly bigger tolerance.

Daniel Wee

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03-09-2006 06:12 PM  11 years agoPost 6
Daniel Wee

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Singapore

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Here's a video I made of the vibrations - note that there are two points where the vibrations become especially visible, first at a lower RPM on the horizontal fins, and later at 2700RPM or more on the vertical fins.

http://www.zippyvideos.com/60803820...06/duzi_mt7602/

Daniel Wee

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03-09-2006 06:28 PM  11 years agoPost 7
keyz

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Daniel
i just tried my new setup , same frame as yours but with the v3 microheli pro tail slider and i have no vibes at all from low to high throttle as i said , the heli isnt realy set up propperly either yet
i cant hear any noise that shouldnt be there
what about if you take the tail blade holders completely off and just leave the tail case in situe ?, does the vibe go away then ?

If you need to get high , go and fly !

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03-09-2006 06:29 PM  11 years agoPost 8
keyz

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also what belt is that your using ?

If you need to get high , go and fly !

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03-09-2006 06:37 PM  11 years agoPost 9
gkoutsis

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Athens Greece

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I think you need to remove the Duzi tail and sell it to me

George

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03-09-2006 06:43 PM  11 years agoPost 10
Daniel Wee

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Singapore

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I've tried it without the tail grips, slider - only the shaft is in place. In that condition, the vibrations are very very much weaker but you can still see the belt vibrate at the same points. I will post a video of this later.

I'm at a point where I'm almost giving up on this Duzi tail although the design is very well thought out and I really like it. The belt is a custom belt because the Duzi tailcase is shorter than usual (and thus lighter too - 15g for the whole tail) and requires a shorter belt when used with the Heliup frame.

RCHover doesn't have the Heliup V3 tail in stock, although the website says they have it in-stock. As such I have to wait and am giving this Duzi tail my best shot at making it work before giving up completely - which would be such a waste of money since it's just about the most expensive tail in the market.

I have e-mail Martin about this and made the video specifically for him. So far he's offered to examine the tailset if I would send it back but that's going to mean more waiting time, more postage, and I already have spent money on new flanged bearings to replace the ones in the tailcase. To be honest I'm preferring Corrado's service much much more than Martin's at this point.

Video coming up shortly.

Daniel Wee

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03-09-2006 06:44 PM  11 years agoPost 11
zrdcorp

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Caguas, PR

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DO you have a carbon fiber boom on?

Roger's Law: If it is worth doing it, it is worth exceeding it.

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03-09-2006 06:56 PM  11 years agoPost 12
keyz

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daniel
how much tension has your belt got on it ?
you said it makes a slapping scrapping sound ?
just an idea that may be worth a try , i put a cable tie (the flat end) between the belt and tension pulley and pull the whole thing taught , then after removing the cable tie i seem to get a near perfect tension on the belt
i dont want to make it sound like you dont know what your doing , you obviusly do
worth a try maybe ?
i can push my belt 1/2 way in , which maybe a little tight , but ive never had probs with this method

just throwing ideas at you mate

If you need to get high , go and fly !

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03-09-2006 07:17 PM  11 years agoPost 13
gkoutsis

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Athens Greece

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Daniel can you upload the file on RR?

I cannot see it either.

George

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03-09-2006 07:37 PM  11 years agoPost 14
Daniel Wee

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Singapore

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RR does not accept videos I think. I have uploaded it here though so maybe this will work (same video as above):-

http://www.daddyhobby.com/gallery/s...=500&ppuser=954

And the video for the belt vibrations is here:-

http://www.daddyhobby.com/gallery/s...=500&ppuser=954

In both videos you see the MicroHeli CNC pulley. I have swapped that out with an Align CNC pulley with no improvement to the problem. The vibrating belt is a little hard to see in the video but in real life, it is actually very prominent. It's just that he video shutter speed is a little low due to the low light conditions.

Daniel Wee

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03-09-2006 09:17 PM  11 years agoPost 15
gkoutsis

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Athens Greece

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Daniel,

Have you tried the Align belt?

George

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03-09-2006 09:57 PM  11 years agoPost 16
Andyn_uH

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Calgary, AB, Canada

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Daniel Wee,

Reading your entire post and watching your video closely couple times, I have a thought about what cause this high frequency vibration (HFV):
-Suspect on your tail blades and tail grips area, both tail blade might not have equal pitch or unbalance somewhere on the grips and tail blades. To prove this, you need to remove your both tail blades and run up again, if the HFV is gone, then you need to work on this area, there are coupld things to check on this area, we will go futher details on it.
-The "GRATING" sounds you heard is from Tail Push Rod and parts attached onto and arount it. This is telling you the HFV appears on your tail system.

On my heli, i use 2 tail push rod guides to eliminate this noise, please take a look on this picture for more detail: http://trextuning.com/phpBB2/album_pic.php?pic_id=1299

Others will have better ideas to fix your HFV problems.

Thanks,

Andy Nguyen,
Microheli.com

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03-10-2006 10:55 AM  11 years agoPost 17
Daniel Wee

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Singapore

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In the video with the belt vibration, it was done with no tail grip/slider/blades installed, and the main rotor blades were off too.

I'm not sure where the push rods come into this picture but I can take that off as well to eliminate it as a source of problems or noise.

I think my next course of testing would be to try some new bearings, and then to try a slightly different length of belt. I can't use the Align belt because it requires that I pull the boom out so much that one of the booms grips will lose contact with the boom.

Daniel

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03-10-2006 01:52 PM  11 years agoPost 18
keyz

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daniel
try getting hold of some carbon tube and cut your own length to suit
or get a long boom and short belt to try it with standard align belt
may be worth a try

If you need to get high , go and fly !

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03-10-2006 06:04 PM  11 years agoPost 19
Rick McWilliams

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Ventura CA USA

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gritty noise during spool up

I used to have a peculiar gritty sound that would occurr at low speed during spool up of a stock TRex XL. This went away when I loosened the belt tension and added a bit of WD40 to the tail tube. It may be that the Q of the resonance is higher with a high belt tension.

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03-19-2006 08:25 AM  11 years agoPost 20
keyz

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daniel
did you manage to sort out your vibe issue ? im interested to know your outcome

If you need to get high , go and fly !

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Other › Interesting belt vibration issue
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