Wicked Tail (?) Vibration Sk-720 Trex 600 DFC

[jamisonchang]

Good Evening,

I am getting a wicked tail vibration in my trex 600 DFC. It is hard to tell if it is up or down or side to side but I can hear it at speed. The vibration analyzer shows it off the charts. There seems to be something right around 200 Hz and 400 Hz. Is this the tail and the torque tube? Log 24 is with tail blades on, Log 27 is without. Any thoughts on what might be causing this? Tail blades balanced, grips seem fine.

Thanks. I know folks don't have a lot of time to be looking at vibration logs-- I guess I have been lucky not to have many bad vibes for the 4-5 years I have been in the hobby.

[mrultralite]

are you using the gov.?

[jamisonchang]

No. Mostly flat throttle curve. Thanks

[Xrayted]

Originally Posted by jamisonchang

Good Evening,

I am getting a wicked tail vibration in my trex 600 DFC. It is hard to tell if it is up or down or side to side but I can hear it at speed. The vibration analyzer shows it off the charts. There seems to be something right around 200 Hz and 400 Hz. Is this the tail and the torque tube? Log 24 is with tail blades on, Log 27 is without. Any thoughts on what might be causing this? Tail blades balanced, grips seem fine.

Thanks. I know folks don't have a lot of time to be looking at vibration logs-- I guess I have been lucky not to have many bad vibes for the 4-5 years I have been in the hobby.

That is a wicked tail vibe! Classic fore/aft and up/down pattern, so its classic unbalance situation. Further proof is that it goes completely away when you remove the tail blades.

Either ditch those blades and try for some others, or you can spend some time doing a full static and dynamic balance on them, and even do a balance of the entire hub with blades attached while off the heli. Also, where is your FBL unit mounted? The spot right on top of the tail gear box at the frame will pick up a lot of vibes. I always had much better luck on my Align helis mounted down inside the frame on the lower skid mount.

The other vibe is your motor. Pretty much all side to side indicating a slightly out of balance can, but focus on the getting the tail sorted first, and then we can recheck and go from there on the other parts if needed.

[jamisonchang]

Wow, thanks so much for your help. I really appreciate your time.

I tried two different sets of plastic blades and the same thing. The gyro is mounted on the front mounting area by the motor. Should I use CF tail blades? I'll take the hub off first and try to balance it. Many,many thanks

[Xrayted]

Originally Posted by jamisonchang

Wow, thanks so much for your help. I really appreciate your time.

I tried two different sets of plastic blades and the same thing. The gyro is mounted on the front mounting area by the motor. Should I use CF tail blades? I'll take the hub off first and try to balance it. Many,many thanks

Hard to say on the blade material......plastic can sometimes flex and vibe more than CF, yet the plastic blades were better on my 500 than CF.

It comes down to weight, and the lighter blades will vibe less. Large heli plastic blades can be very heavy compared to CF, and can vibe more. I had a set of plastic 700 size KBDD blades that were heavy and had high vibes

[jamisonchang]

I believe the tail rotor hub was mostly balanced when I put it on the Dubro. Still vibrating like mad.

Any thoughts?

[Xrayted]

Originally Posted by jamisonchang

I believe the tail rotor hub was mostly balanced when I put it on the Dubro. Still vibrating like mad.

Any thoughts?

Do you have any other blades to try? No slop in the grips or anything?

Make sure the CG of the blades is also good, and not just a static balance. Static will balance fine using the teeter test, but different CGs can vibrate like crazy dynamically once spun up. Weigh each blade on a gram scale and make sure they are not way off from each other

http://www.skookumrobotics.com/wiki/...lance_the_Tail

[Colin Broughton]

Originally Posted by jamisonchang

I believe the tail rotor hub was mostly balanced when I put it on the Dubro. Still vibrating like mad.

Any thoughts?

Are your blades on backwards or have you modified your tail rotor to be trailing edge controlled?

[jamisonchang]

Thanks X-rayted.

No, I just had the grips on my apparatus and threw the blades back on incorrectly -- they are still leading edge control on the machine.

Appreciate all the help

[jamisonchang]

Found some old plastic tail grips from my 600 N and swapped out for the metal ones that I used in the previous tests.

Tail vibration a lot better, right?

Still very pronounced vibration at 400Hz-- motor or torque tube?

Feedback appreciated.

[Xrayted]

Originally Posted by jamisonchang

Found some old plastic tail grips from my 600 N and swapped out for the metal ones that I used in the previous tests.

Tail vibration a lot better, right?

Still very pronounced vibration at 400Hz-- motor or torque tube?

Feedback appreciated.

Much better, so its the blades just as we suspected!

That is your motor with an out of balance can. There are several vids around showing how to balance the can on your own using tape or similar, and member A VIKING balanced his using dots of epoxy on the outer can. Let me guess.......this is an Align motor We see out of balance issue a lot with them for some reason.

Just do a search on balancing brushless motors if you want to tackle it on your own, or you can choose to fly the heli as is and see what your overall vibe score will be. Its not going to be all that bad really, even with that motor spike.

[jamisonchang]

Xrayted, thanks again!!

I actually changed the grips out and kept the same blades-- so, instead of the metal align grips that I had this morning ( with the high vibes), I had an old set of plastic tail grips from by 600N. So, this leads to me believe that the align metal grips are the problem? I really don't see much play in the metal grips so I am not sure what is going on...

I was going to buy a new set of tail grips (metal).

Thanks for the tips on the motor... yep, Align 600 MX. Probably will put a KDE motor in now.

[Xrayted]

Originally Posted by jamisonchang

Xrayted, thanks again!!

I actually changed the grips out and kept the same blades-- so, instead of the metal align grips that I had this morning ( with the high vibes), I had an old set of plastic tail grips from by 600N. So, this leads to me believe that the align metal grips are the problem? I really don't see much play in the metal grips so I am not sure what is going on...

I was going to buy a new set of tail grips (metal).

Thanks for the tips on the motor... yep, Align 600 MX. Probably will put a KDE motor in now.

Very interesting.....at least its solved one way or the other. I would have expected to see a vibe spike on the no blades run you already posted originally if the grips were the culprit, but I've learned that anything is possible.

[jamisonchang]

Thanks again Xrayted. Yea, that makes sense about the vibe spike.
If you have any other thoughts about what might be going on, feel free to share but I won't keep harassing you : )

[Xrayted]

No worries at all

[A VIKING]

...and yes I did balance my motor can with small dots of epoxy. That was a year ago and I am proud to report the epoxy is still holding on after hundreds of flights...although a little dizzy turning at nearly 20,000 RPM.
It was interesting in that during my recent first bearing change on the Quantum, the epoxy drops that I placed on the exterior of the can were in the exact same location as the putty installed on the inside of the can by the factory for balance, they just came up short by just that little bit.
See the photo: I didn't know if the epoxy would stick for very long on the painted surface of the Quantum so I sanded the paint off for one epoxy dot as an experiment. Didn't matter, the epoxy stuck equally as good on the paint as it did on the bare metal.

Vibes are still low.
I won't go through how it was done but if anyone would like to know how I did it, post a note and I will elaborate.
I don't know if this process would work good on the ribbed cans as I don't own any of those.

[jamisonchang]

Thanks A Viking. You are much better man than me--- I have a KDE motor waiting to be put in my 600

[A VIKING]

Originally Posted by jamisonchang

Thanks A Viking. You are much better man than me--- I have a KDE motor waiting to be put in my 600

...not a function of being better than, just a function of sharing ideas and discoveries. I bet you know plenty that I haven't even thought about with these ships.
I believe you'll enjoy the KDE. I have heard no bad comments only good from those who have them.

[jamisonchang]

Fair enough. Thanks for taking the time to respond. I am interested in how you did this-- if you have it written down, please pm me. Happy flying