Help needed with my Logo 500's tail wag.

My logo 500 has been in storage for two years when we moved to the UK from South Africa. Before we moved, she had a rebuild caused by a gust of wind pushing her over while spooling up at zero pitch (Kontronik 100lv). Parts that have been replaced - complete tail mechanism with new thrust bearings, tail boom, tail drive belt, tail pushrod and pushrod boom support, mainframe and tailcase, main gear, main shaft, blades (main and tail). We are running Kontronik 100LV and Mikado edition Scorpion motor (stock one), mini vbar with VBC sat, hitec servos all round. She has a one second tail oscillation moving to the left first, then sustained while hovering. It gets worse at changes in head speed and in forward flight goes to WOD. Initially we thought it was mechanical so we rebuilt the tail from scratch and loosened up everything so there is no tail bindingmech falls under its own weight both sides) - we have videos if we can attach or send them to anyone who can help us. Changes in gain (overall, I and P) as well as TPC makes no difference - gets dangerous at high gain as hunts and wags at the same time. We have also switched out servos (her own Hitec, Align DS755 and Futaba BLS256) - makes no difference. We have also tried 3 different vbars - no difference. We have checked that leading edge control is activated and the blades and grips are on the right way around. We are not getting high vibration on our logs, just occasional raised vibration levels on spool up. If anyone has any ideas of what I may have overlooked I would be eternally grateful!

Hi,

don't get me wrong, but that one-liner is hard to read, like Hemingway

Can you please save and attach your current setup file here (with tail wag, I assume), and a couple of clear, bright, sharp pictures showing the main rotor head assembly with servos as well as the tail rotor servo section and the tail itself?

Half way through your text I would have suspected the tail servo, but a Futaba BLS is usually a universal weapon ...

Kind regards

Eddi

Born to fly ...
forced to work.

Thanks Eddi. I have uploaded the photo's you asked for, but I am a bit stupid - how do I retrieve the setup files from the vbc as vbr's so I can upload those - can't find it in the manual - when I copied what I thought was the setup file to my pc it does not have the .vbr extension and I cannot open or upload it - I manually added the .vbr extension, so I hope it is readable!.
Video of Daisy's tail behaviour in hover



Edited 3 time(s). Last edit at 05/29/2020 02:27PM by Trewix.

Hi again,

please excuse the late reply, pentecost weekend :-/

Adding .vbr or zipping the file's the way, well done.

The video looks ugly. But I guess I instantly found the cause, so please lean back, relax, stand corrected , learn, fix it

. you have the wrong swash plate type selected (H-3 instead of HR-3, look at the swash plate from above/behind, the elevator servo points to the rear, not to the front)
. then, you made it work somehow by maybe swapping servo wires, reversing servos and even reversing the direction for positive collective

This together looks right, on the swash plate, but makes the control loop work reverse, at least partially, with the result that tail precompensation works the wrong way, and the gyros fighting back.

What does not help is that you seem to have the tail rotor pushrod at the inner hole of the servo arm (photo 0547 and limits 116/116 tell), and since HiTec-Servos, let's say, are a bit particular, the tail can not do what it could if the pushrod was in the 2nd/center hole of the servo arm, with limits closer to 100.

Things to do:
. make sure the swash plate servos are plugged in where they belong, left aileron CH2 right aileron CH3 elevator CH1) and select HR-3 swash plate from the setup menu
. select leading edge control / swash plate up for positive collective
. reverse servos in the radio so they do what they should do, if you move the sticks as well as if you move the model
. re-trim zero collective if necessary

Do a preflight, especially re-check tail rotor directions and correction, test-fly.
I bet it's already _much_ better.
In a second iteration, you could change the geometry of the tail pushrod at the servo and re-adjust the limits, to further improve.

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi - thanks for coming back to me. We did what you suggested and picked her up this morning - now she is really wagging. The video is with no rudder input at all - we were terrified she would go into full WOD if we touched the rudder! Her new setup file is attached. We've ordered her a new vbar head spindle shaft in case that is causing issues, but her logs from today report no vibration. The second video is of her tail mechanism just to show that there is no binding.

https://photos.app.goo.gl/RLhCsYcyY1CAcayYA

https://photos.app.goo.gl/B5SBUV7P8Edtt39y8

Hi again,

the setup looks OK now, if the VBar is mounted according to it (face up, wires front).

Which tail servo was in it?

Are there any tell tale log file entries?

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi
We have the hi tec servo (her own one) back in. The log just shows normal entries -
This is for the short flight when we took the video

VBar Start -- LOGO 500 -- 03.06.2020 -- 09:54:38
09:54:38;1;Reset Reason: Power On
09:54:39;2;Bank 1 Loaded
09:54:41;2;Calibration Finished
VBar Logfile End -- 03.06.2020 -- 09:55:52

Hi,

nothing special in the log, thank you.

What HiTec Servo type is it exactly? The pic is blurry.

I'm asking because I want to research it's specs (center pulse + frequency), to see if the settings match.
If you have a specs sheet with those specs, please share.

Please do a test, on the ground: remove the blades, let the mechanics run, control the tail—anything obvious? Then same, but move the model in your hands, to check if and how the tail responds to sensor movement.
Careful with the rotating parts!

—Eddi

Born to fly ...
forced to work.

Hi Eddie
The tail servo is a Hi Tec HS-7966HB - she behaves exactly the same with an Align DS655 and the Futaba BLS256. The Futaba belongs to our 800 xxtreme, so we swop it out and change the settings for the futaba (760 etc) just for testing.
Specifications for HS-7966HB:
Modulation: Digital
Torque: 4.8V: 92.00 oz-in (6.62 kg-cm)
6.0V: 111.00 oz-in (7.99 kg-cm)
Speed: 4.8V: 0.10 sec/60°
6.0V: 0.08 sec/60°
Weight: 1.87 oz (53.0 g)
Dimensions: Length:1.57 in (39.9 mm)
Width:0.78 in (19.8 mm)
Height:1.45 in (36.8 mm)
Motor Type: Coreless
Gear Type: Plastic
Rotation/Support: Dual Bearings
Rotational Range: 180°
Pulse Cycle: 20 ms
Pulse Width: 900-2100 µs

When we do the static tests this is what we get.
We spool up with zero pitch to 1600rpm head speed (no main blades!). Left alone on the floor, the rudder did nothing until we increased pitch to about 4 degress positive, then it precomped to turn the heli nose left.

When we picked her up, on spool up to 1600rpm, it moved 90 degrees nose left and then settled down. When we physically rotated the heli nose right at zero pitch without any rudder stick input, it resisted the movement immediately and returned it to the starting position (we could not move the heli nose right against the heading hold). When we did the same to turn the heli physically nose left, there was a very slight resistance to the movement until approximately 30 degrees rotation, where it became a little stronger, but not even half as much as the nose right resistance. It would not allow us to then rotate the heli back to the starting position once we had physically rotated it nose left - it strongly resisted any movement to the right, but was happy to allow further rotation to the left.

I hope all of that makes some sense.
Thanks so much for all your effort to get her going again.

Hi,

to be honest, this sounds like a sensor issue, your ground tests. But if you tried three different VBars, this kind of makes no sense again.

Can you now, with the current setup, try a different VBar, to verify? If it's a Mini, you can just load the setup, if it was one with external gyro, you'd have to check the sensor orientation.

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi
Sorry it took so long - work got in the way! So....with the other vbar, it wags quicker in flight, but did not hunt with the same settings. Static test. Both sides resisted movement with equal strength, but on return to centre it wagged continually about 10 degrees each way - the same happened for both sides. We lowered the overall gain - it made no difference, then we put the overall back to 70 and changed the I gain to 60 and adjusted the coll TC back to 22 and the cyc TC to 8. It made no difference at all to the behaviour of the heli on the static test. We are totally stumped by this.

We also removed the Kontronik's slave cable from the vbar (Rx C) and plugged in a LiFe 2s receiver pack instead. (Previously we were using the BEC from the Kontronik as the main vbar power supply, with Scorpion back up guard connected via a y lead as insurance).
This improved the static test as it no longer wagged when returning to centre after we manually rotated the heli without using rudder input in both directions. When picking the heli up, it now wags a lot less violently. When a rudder input is given, it starts to wag faster through about 15 degrees. It also still wags faster when we increase the headspeed.

The headspeed is determined by the Kontronik at between 1630 (Bank 1) and 1900 (Bank 3). The Kontronik is programmed to mode 4.

We tried swapping the Kontronik ESC for a 100A Hobbywing Pl V3. This made no difference. We also tried swapping the vsat for a known good one from another one of our helis - also made no difference.

Any help would be great, Thanks. We love her dearly, but we are starting to despair.



Edited 1 time(s). Last edit at 06/07/2020 07:29PM by Trewix.

Hi again,

I'm kind of stumped. Any LOGO should fly with the default settings (as in: create new setup) if all the requirements are met. I mean, nothing accidentally reversed and then corrected by reversing something else. The only thing you need to adjust is overall gain, like 90 for good tail servos (Futaba BLS class) or like 20 points less for more budget class servos, and then, the latter don't even feel much inferior.

The only thing you could see would be a slow wag in a hover, or a fast wag or hard oscillation in ff or fff, if the overall gain is set too high.

The ESC interfering could intensify a slow wag, but not induce a fast wag or oscillation.

I did check your device list: your legacy VBars are from 2013 or earlier (Minis and at least one full size), one of the full sizes 2014 or earlier.
Although there is no best-before or expiration date, it would be possible that the older units have sensor issues. But again, it's not likely that all are the same. But like us, they get older, and might get tremors sooner or later, figuratively speaking.

The sats have no hands in this, they work, or they don't, the deliver a digital signal to the NEO, from the radio, without processing it.
The power supply _could_ if it was fluctuating (I mean, they all do, with load, and the electronics can cope with much of that, but still ...).
But with a charged and resilient battery, it should then be OK.

You seem to have one NEO registered to one of your two accounts. Could be worth a try with this one, trying to narrow down the cause.

Kind regards

Eddi

Born to fly ...
forced to work.



Edited 1 time(s). Last edit at 06/08/2020 09:15AM by Eddi E. aus G..

Hi Eddi
So - I eventually got the time away from work to have another go - we put the logo 500 onto our Neo - we also gave her a set of brand new thrust bearings (a second set since this problem started!) and a new vbar head feathering shaft. She seems more stable in hover on the Neo (not solid, but better), but the wagging starts up as soon as any rudder input is given - it seems less pronounced, but very much still there. The video link is for a short hover with the Neo installed.

https://photos.app.goo.gl/jAHEAEP6zepfGbHu6



Edited 1 time(s). Last edit at 06/21/2020 11:09PM by Trewix.

Good morning,

this is not how it's supposed to look. I mean, a slight wag around center, in a hover, OK, but not to that extent, and it's usually gone if you fly circuits, aerobatics or 3D.

What servo were you using in that latest video? Would you mind sending the setup again?

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi

Thanks for looking at the video. I have uploaded the NEO setup file she was flying on in the video. She is flying on her original hi-tec tail servo.

And good morning again

thank you for sharing the file. Looks all default but some high trims on CH3, which you could lower significantly if you rotated the servo arm one notch on the servo.
But that wouldn't affect the wag, it's just an observation.

Next step would be trying the Futaba Servo again. Although I have nothing against HiTec, I have made my experiences myself, and Futaba is still on top of almost all other servos in my personal opinion, when it comes to performance especially on the tail.

Like, no issues, use what you want or like, issues, try a Futaba

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi changing the servos did not help. What I did find was an old thread from 2014 regarding a similar issue with a 550SX. The thread was titled 550SX tail assembly/wag issue, dated 22 June 2014 by a user named RotorWheels. In it, he mentions having a similar issue to ours. He notes that there appears to be two different types of tail spindle, a "flat nose" spindle and a stepped spindle. If I understand it correctly, the flat nose version is supposed to come with thrust bearing sleeves. I have attached a photo of my spindle with the bearings and spacers that came with it laid out - I am not sure what the sleeve is meant to look like, but I can confirm that if we tighten the bolt up properly, then it definitely feels as if the thrust bearing is not quite smooth anymore - almost as if it is being compressed too much. Could this perhaps be our problem and, if so, what do we do about it. The tail grip assembly was bought earlier this year as part no 4069.

Hi again,

the spindle has been updated at some point, what you have seems to be the current one.

One thing you might try, seeing the parts, is: leave out the outer thrust washers (to the socket head screws).
They are meant to help with production tolerances (thread length of the bolt vs. thread depth in the spindle).
In general, this washer should not add any extra pressure, because it sits where the bolt head would sit, otherwise.
But since they are stamped parts, they may be warped ever so slightly, or have burrs, and this might make a difference, adding a tiny bit of extra pressure.

Next thing is, there is no need to tighten the bold with force, if you turn in the bolt until it locks, and secure it with loctite, all is well.
If you overdo it, you can also deform the thrust washer, causing it to no longer lie flat but add the tiny bit of extra pressure.

Kind regards

Eddi

Born to fly ...
forced to work.