X5-lite tail driving me BONKERS

[sp00fman]

I intended this as my hop-up to larger helis, but instead it is going on and off the workbench with only test flights for nearly a year now, and still unable to get the tail issue fixed.

Problem is the tailrotor starts to give massive vibrations as it approaches 8000rpm.
This interferes with the gyro making it unable to hold properly and giving a wide slow wag in hover. The ZYX was reasonable with it, the V-bar "type" not so good. Log shows some high vib warnings and on some test flights extreme vib warning.

I must confess, its an belted Gaui Hurricane, With the tail hub and grips switched to the X5 parts. Essentially a complete X5-lite tail now. Attempting to run 520mm blades at 2200rpm. Without the tailrotor and mains V-bar shows <80 vibration points.

I hope someone can relate to my issues and know the trick to get right.

First off, the tail never even bumped the ground, let alone crash. Trex600 landinggear takes care of that.
I have a spare kit and ordered a lot of spare tail parts over the time to sift out any faulty part. I went with the X5 tailhub and grip because of the sturdy construction and the thrustbearing. The Standard hurri grips are a p.o.s. , ready to explode or binding up..

Stuff i did to make it as good as i can get it:
Play with belt tightness. more loose and pretty tight.
Running 80mm hurri550 tailblades. got a second set to be sure, no difference, dynamically balanced the tailblades, and experimented with extra tape on the center point of it. Extra set of X5 tailhubs in case it was bend/drilled wrong. Switched the tail rotor shaft 4x with a new one (one of them real X5 part....but they are identical). Spare bearing pack, shimmed the bearings so they have sideways pre-tension on them, making the shaft wobble in them much less.
Glued the bearing ID to the tailrotorshaft, making the shaft feel really solid on the tailcase.

Rebuild the entire tailcase and pitch assembly with my spare kit parts, new belt, loctited on ABEC-5 bearings on the shaft, shimmed the bearings, loctited the tailhub on the shaft..... now it can finally spool up with 120 vibration points....BUT when i reassembled the tailhub to locite the grubscrews it went crazy again. I now notice the tailhub is not a precision fit on the shaft like my MiniProtos.

In what order do i have to screw it down to make it work correct? Is the play intentional and do the grubscrews act as a pivot point for the tailrotor? and thus am i messing things up by using loctite between the hub and tailshaft?

Here some pictures of my bird and all the brand new "only flown a few times" spares.

[kgd1]

I swapped the plastic tail out for the metal tail (after crash). I always used the second grub hole in on the tail shaft with both plastic & metal with no vibe problems.
Good luck.

[wis1]

Make sure the thrust bearings in the tail grips are in correct as some of the x5 grips had the thrust bearings installed backwards. I started with the x5 lite(belt) and had nothing but problems getting the tail right and went to the torque tube tail with align v2 grips, problem solved.

wis1

[sp00fman]

I noticed the thrustbearing wrong on the X5 tail, but corrected that right away. TT is not an option with a plastic frame as i read elsewhere. I kind of like belt drives as i land on uneven ground.

What difference would Align tailgrips make?

[milliotseb]

I have to say that I have the same kind of slow wag with my Gaui 425 (belt, plastic tail case and X5 plastic tail grips)
I already change the tail servo. There was a small improvement but not much.
Now I am installing tail servo with straight tail link to see if it help.

I also have checked the correct orientation of thrust bearing and everything was fine.

I will try to keep you updated of my progress

[wis1]

Originally Posted by sp00fman

I noticed the thrustbearing wrong on the X5 tail, but corrected that right away. TT is not an option with a plastic frame as i read elsewhere. I kind of like belt drives as i land on uneven ground.

What difference would Align tailgrips make?

Don't know why but I was trying everything and that combo worked for me.

wis1

[czynot]

1) is your belt tension correct? Possible the belt too loose and flapping inside the tube?
2) try different HS and see if vib is related to HS.
3) check tail blades for balance.
4) spin the tail slowly by hand and keep eye on belt riding on the tail and main pully. You want to make sure the belt are sitting in each teeth correctly. Some belt teeth can be thicker or taller causing it not to sit in the pully correctly.
5) lower the tail gain. if still there? check your I-gain.
6) remove control rod from servo and check tail for binding.
7) what tail servo you have?
8) this may sound stupid. but check make sure tail blade is spinning correct way. Main clockwise, tail counter-clockwise.

[Himilou]

More mechanical gain on the tail servo? ( i.e. move the ball link out on the arm away from the servo gear )
Preload the tail with ~8 degrees of angle to counter initial hovering torque?

[sp00fman]

1) is your belt tension correct? Possible the belt too loose and flapping inside the tube?
-chk
2) try different HS and see if vib is related to HS.
-It is all relatively smooth untill 1800rpm on the head.
3) check tail blades for balance.
-yes, a few attempts and also different blade set.
4) spin the tail slowly by hand and keep eye on belt riding on the tail and main pully. You want to make sure the belt are sitting in each teeth correctly. Some belt teeth can be thicker or taller causing it not to sit in the pully correctly.
-I think i would have noticed. Replacing both pulleys and belt should have eliminated that.
5) lower the tail gain. if still there? check your I-gain.
Gain 14% to 60% it slowly wags. above 60% the tail stops get bouncy and a few more aggressive wags.
6) remove control rod from servo and check tail for binding.
-It is smooth when spooled up and i push the slider by hand. Perhaps some binding in the control rod.
7) what tail servo you have?
Hyperion DS20GMD at 5,5V BEC. Spec: 4.0kg/cm @6.0V 0.05s => 3.2kg/cm @4.8V 0.07s
8) this may sound stupid. but check make sure tail blade is spinning correct way. Main clockwise, tail counter-clockwise.
-quadruple checked already Actually everytime i look at the darn thing.

----

More mechanical gain on the tail servo? ( i.e. move the ball link out on the arm away from the servo gear )
- Yes, tried 10mm and 13mm. now at 13 and V-bar limits are at 100.

Preload the tail with ~8 degrees of angle to counter initial hovering torque?
-Yes, it is actually build into the bladegrips. think more like 5 degrees.

-
Mike suggested to ditch the Z-bend control rod. Build one with 4mm hollow CF tube and cut the weight from 16g to 7g. Steel seems to be heavy metal

Looks nice also.


The V-bar log picture is from yesterdays flight..... Grrrrr


Hope to try again tomorrow.

[Himilou]

don't have a vbar. Are you sure its a tail vibration? Maybe its a head vibration manifesting itself in the tail?
dampers?

[sp00fman]

Without main head the tail does start to vibrate on the bench near target RPM. The whole problem is that i just cant get the tail assembled to rotate without imbalance somewhere. If then take the tail blades off i can spin it up as fast as i can without a problem. (not 100% throttle, don't want to kill my motor)

[Langelus]

As you say it's fine without the tailblades on(?) and I only gathered that you dynamically balanced the tailblades, have you actually tried i different set of blades?

[sp00fman]

Yes, i did try a second set of tail blades. same problem. I also tried the smaller blade type (69mm) and it can spool up a lot faster, but the problem then manifests itself around 2500rmp on the mainshaft.

[mverhorst]

Originally Posted by sp00fman

Yes, i did try a second set of tail blades. same problem. I also tried the smaller blade type (69mm) and it can spool up a lot faster, but the problem then manifests itself around 2500rmp on the mainshaft.

Did you check your thrust bearing orientation in your tailgrips. Could be that the grips bind when loaded up by the weight of the blades at set RPM...???

[sp00fman]

These grips are smooth when spooled up. Tested by pushing the slider by hand while holding the tail tube really tight with my other hand. Blew all kinds of stuff through the room

Just tightened the belt a whole lot and more force on the tailbox screws. Bearings start to complain slightly now, but vibrations seem lower now.
Dropped the I-gain from 60 to 40.

Im afraild doing that is just masking the problem, and it will be back over time.
The tailblades are super noisy when spooled up, but i dont have any reference to what should be normal. Even a 450 tail spooled up inside sounds scary.
Might shoot a vid of that inside.

Here is my flight vid of today and the log.
Seems better, but not near as well as my other helis.

[ame]http://youtu.be/gy6zWEW5QE8[/ame]

Headspeed tached at 2235rpm, or 9750rpm on the tail. Exactly what i was aiming for. When i switch the 425mm to 520mm blades it should give me the performance i'm looking for.

CW piro stops seem mushy at times, will have to look into that.
I have quite firm and thin tape on the gyro now. i might try the other stuff i have at hand. Also got some 3mm thick foam from HK. worth a shot?

Also i will try again with governor disabled. I dont see any headspeed changes in the audio file, but who knows....

[sp00fman]

Put the tail hub on the inner holes on the shaft, reducing overall pitch range a little. Feels reasonable, but will have to put the vib analyzer on to see if it is any better.


[ame]http://youtu.be/HMiqQpU3lSc[/ame]

update. not so good yet, 400 vibes.

[sp00fman]

I've almost had it with this tail. Got it rotating reasonably steady, but in flight you see the tail go in and out of vibrations with the associated wag. some visible tailfin vibrations come with that also. When it is steady in between the tail seems to hold pretty nicely.
On the bench i felt a high vibration area around the frame just on the front tabeltpulley bearings. I dont know if that is just resonance from the tail, or i killed the bearings by running the belt too tight. Will also try a different maingear to make sure that is not messing the the auto gear,

Getting pretty fed up with the thing again. Ordered a set of trex500 tail grips + 550 blades, Really hope it will work out.

[Himilou]

long shot here, you say that without blades its no issue. You've tried different blades, same problem. How about the bolts? If they were different weights for some reason that would cause a vibe.
also while I think about it are your tail blades tracking evenly? Never had to check this before but maybe you have one slightly out of spec grip to slide length.

[Integrity Handywork]

When i have that much trouble with something, i replace all the possible components that could be the issue. In this particular case i would get the CNC integrated tail box and switch to shaft drive if you can on the hurricane model. Otherwise get the CNC integrated belt drive tail box. Since the CNC tail box comes with the tail shaft, that replaces your old shaft as well. If that didn't fix it, i would go and get the X5 CNC tail grips and the CNC pitch slider too, why not? Also since i'd be placing the order anyway. I would get a set of CF tail blades of your brand choice and maybe some KDBB plastic blades. See which ones you like best and keep the other as a crash backup.

Anyway, that is what i would do. Keeping in mind i don't make a lot of money either. But when a problem like this occurs and i can't "fix" it. I just end up throwing more money at it till it works right. But getting the same old parts that aren't working now isn't what i would do.

Good luck, hope you get it worked out.

PS, replacing bearings couldn't hurt either. If you did in fact ruin any or had bad ones from the start. They can cause vibes too.

[sp00fman]

Thanks for all the input!

For the time being im completely broke. The >$50 CNC hub is just too much. I have seen plenty of hard 3d videos of the stock hurri with the plastic tailcase, I just cant imagine it is the cause of it all. It locks together tightly and is nice hard plastic.
Torque-tube is not an option on the plastic frame.

I'm just waiting out on my HK shipment of the CNC trex grips + trex550 tailblades. Its clone parts so at least no align logos on it

Shipped yesterday so 2 more weeks. In the meanwhile i will check all bearings again, and see if the thing does in fact still run smooth without tailblades.