fusion vibration problem

[tntburnett]

Hello folks i am haveing a vibration issue anything over 2000 and 2150. 1953 not vibration. I have change eveything possible, tail blades main blades main shaft torque tube the bearing are good on the heli and the motor bearings are never been crashed. have anyone else have or had this problem. need help. I have also move the vbar senser and no change.

may be could b set up i dont know . my set is 12s 4025-630 ,, cc hv85

[SkinnyMcGee]

what about your motor shaft? and are you mainshaft bearings nice and stright.

[tntburnett]

Originally Posted by SkinnyMcGee

what about your motor shaft? and are you mainshaft bearings nice and stright.

all of that seems fine. i put a new main shaft on

[Gernejr]

Tail grips shaft =.R50N970-SS OUTRAGE Tail Rotor Hub Assembly That it apart it's hollow slide it on small allen driver and spin it . Bet you see little bend on one of the ends....

. not talking about the tail shaft with gear.

[DannyvG]

how would you describe the vibration? could you post a video?

I have had a pretty nasty vibration in my Fusion myself. After taking of into a hover it was stable for a couple of seconds after that the entire frame started shaking left and right pretty fast. I guess the skids oscillated about 1~2cm left and right at a frequency of about 15Hz or so.

Presuming your fusion does the same as mine I suggest the following.
The first thing to try is lowering the cyclic gain of your vbar. I expect that that will do the trick already. If that doesnt help much you should check your mainshaft for any play between the shaft and the top bearing. If you take the main shaft out it is possible that you see pollished rings where the bearings where sitting. If this is the case then the fit between the shaft and bearings is to loose and you should loctite the shaft to at least the main bearing.

I am not 100% sure why my fusion vibrated that much. It seems that the bandwidth of the aileron is close to a resonance frequency of the frame. And this is amplified by the play in the top bearing. When I just give a bit more cyclic gain the heli starts vibrating again.
Here is my topic about it https://www.helifreak.com/showthread.php?t=292033

[tntburnett]

Originally Posted by djamgils

how would you describe the vibration? could you post a video?

I have had a pretty nasty vibration in my Fusion myself. After taking of into a hover it was stable for a couple of seconds after that the entire frame started shaking left and right pretty fast. I guess the skids oscillated about 1~2cm left and right at a frequency of about 15Hz or so.

Presuming your fusion does the same as mine I suggest the following.
The first thing to try is lowering the cyclic gain of your vbar. I expect that that will do the trick already. If that doesnt help much you should check your mainshaft for any play between the shaft and the top bearing. If you take the main shaft out it is possible that you see pollished rings where the bearings where sitting. If this is the case then the fit between the shaft and bearings is to loose and you should loctite the shaft to at least the main bearing.

I am not 100% sure why my fusion vibrated that much. It seems that the bandwidth of the aileron is close to a resonance frequency of the frame. And this is amplified by the play in the top bearing. When I just give a bit more cyclic gain the heli starts vibrating again.
Here is my topic about it https://www.helifreak.com/showthread.php?t=292033

It is doing the same has you describing yours. I change thE main shaft , I check for play and it did have play but I fixed that and it is still there. I had it sittin on the bench and watch it as it spool up a saw the swash was moving back and forth so I scrap down the vbar senser down tight an the swash stoped moving back an forth. Sense.i tried all of this do you think I need to turn the cyclick down.

Thank u
Isaac

[DannyvG]

I understand you havent tried flying it yet?
The fact that the swash didnt stay level on the bench can be deceiving because there can be some resonance and other influences from the bench.

I suggest you just try to hover it with current vbar settings. If you still have the shake just lower the cyclic gain a bit.

I actually use a microbeast but cyclic gain is cyclic gain and in the basics the control loops are alike so just try lowering the gain if you still have a problem.

Only thing I am concerned about is that my cyclic gain is now limited by the frame and not the servo/control mechanics and thus might give me a less stable heli. So I might try increasing the gain a lot to see I can squash the frames resonance frequency. Or I will investigate changing the frames resonance frequency by changing the mechanics.

[tntburnett]

I have already flown it. I justed turn up the head speed and thats when it vibrates. I went from 1953 rpms to 2100 rpms, and this is where the vibration come to play.

[DannyvG]

Originally Posted by tntburnett

I have already flown it. I justed turn up the head speed and thats when it vibrates. I went from 1953 rpms to 2100 rpms, and this is where the vibration come to play.

Have you also flown it after you eliminated the play from the mainshaft?
Even the most minimum amount of mainshaft play will probably make the vibration worse.

But either way, I would suggest turning the cyclic gain down.

[tntburnett]

I just hover it in the yard and it still have the vibration. I will check the main shaft again. I have the cyclic gain down to 70% do you think i need to turn it down more than that.

[DannyvG]

Originally Posted by tntburnett

I just hover it in the yard and it still have the vibration. I will check the main shaft again. I have the cyclic gain down to 70% do you think i need to turn it down more than that.

Sorry cant tell you any balpark number just try decreasing it and see if it the vibrations stop at a certain point, certainly hope so for you. Because to me this doesnt seem like a vibration problem of for example torque tube or blade imbalance but more of a resonance of the control loop.

In theory presuming the problem is in the mechanical stiffness to weight ratio it should be possible to stiffen that part.
I would like to try a cross brace in the frame or push the headblock down further over the main shaft. Perhaps using the first hole gives to much flexibility.

[tntburnett]

Originally Posted by djamgils

Sorry cant tell you any balpark number just try decreasing it and see if it the vibrations stop at a certain point, certainly hope so for you. Because to me this doesnt seem like a vibration problem of for example torque tube or blade imbalance but more of a resonance of the control loop.

In theory presuming the problem is in the mechanical stiffness to weight ratio it should be possible to stiffen that part.
I would like to try a cross brace in the frame or push the headblock down further over the main shaft. Perhaps using the first hole gives to much flexibility.

I will turn down the gain. what do you think about putting a collar on it do you think that would help

[DannyvG]

I will make some videos tomorrow evening of the vibration when I increase the cyclic gain.
After that I will do some experimenting with mechanical adjustments and report back.

Using a collar might help a bit, it would be easier to replace/adjust then using loctite between the top bearing and main shaft.
But first try lowering the gain, I am really interested if that will reduce vibration with your heli like it did with mine.

[tntburnett]

Originally Posted by djamgils

I will make some videos tomorrow evening of the vibration when I increase the cyclic gain.
After that I will do some experimenting with mechanical adjustments and report back.

Using a collar might help a bit, it would be easier to replace/adjust then using loctite between the top bearing and main shaft.
But first try lowering the gain, I am really interested if that will reduce vibration with your heli like it did with mine.

ok i will be looking for it. thanks again. by the way what type of two sided tape you are using. oh forgot to say when i scrap down the senser i dont get viberation do you think it is ok to leave the scrap on it

[millerman]

im running my v-bar at 59% on cyclic gain and im also finding lower on agility better too the Fusion still feels locked in and stable but no longer wobbles on hard stops tic tock and rainbows etc

[tntburnett]

I found out what wrong with my heli. It was the scropion motor. I took it apart foud that one of the bearing had two dents in the dust sheild and they did not have the spacer washer that goes between the inner bearing and the outter casing. Brand new motor and had too replace the bearings already becuz they did not put the motor together right from the start :-(.

Thank the Lord it happen on the ground than in the air.


GisG
Isaac