Hello! I've been finishing dialling in my Goblin Black Thunder and the only thing left before it's perfect is a very short, rapid tail wag when I come out of a loop or FFF at speed and load the head with collective. You can barely see it with the eye but it's audible- the blades bite and release rapidly.

I've dropped the gains to 1.2 multiplier and 54% on the diagnostics gyro channel from over 62-63 before. However that twitch just won't go away.

I'm using the BK 7006HV at 7.5V. It's rated speed is 0.32sec / 60 degrees. I'm using 2 as the rudder delay, 170 as piro consistency and 6 as rudder dynamic. Also running the governor at 6 response, 3 holding performance. End points are reasonable at 90-110 or so.

What is puzzling me is that the tail gains are actually lower than the ones I'm running on my G500 with the much slower KST525mg servo. Both have 170 piro consistency, same rudder dynamic and same rudder delay (2). Both have counter torque applied at debater rudder. The tail does seem t hold well during pitch pumps. However on my G500 no matter what I could not get the tail to wag. On the black thunder it's much more twitchy and sensitive.

Any ideas on how to tune this out? The tail seems to hold ok, even though today with the wind on the side of the Heli it did appear to be "catching" it , sort of like pushing the tail around a bit and causing a slight low amplitude, low frequency wag.

Should I reduce rudder delay? Could this be causing it? Or drop the multiplier to 1.1 and increase the gain in the TX? What's your recommendation?

What Tail blades have you got?
On my SOXOS 700 with new 115mm Tail and 696mm Main, I had to reduce Gain down to 42% with 1.25 = 56% on max Head speed 2100.
This would equal to 56%/1.2 = 46 % for you. Might be worth to try. For low rpm 1600 I have got 55% on gyro.
I had the problem on fast Funnels, now its fine. Tail holds solid on speed backwards loops just fine.
Delay 4 with 0.04Sek/60° Servos / Piro 155 / Dynamic 6 / slightly higher endpoints 110,120 / The remaining tail kick on full pitch I killed with Revomix of 1

Just an other tough, as you describe, it happens on adding load to Head, eq. loading ESC. Might Governor cause this? Maybe Gov Respond performance tuning required.
I discovered solid Governing is the key/solution to tail problems as well. I run Respond at 8 and Holding on 4 with latest FW 2.1. I used new Channel mapping feature on TX Knops AUX 3/4 to tune Respond and Holding and did end up with 8.

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I'm using 105 tail blades, it's a 650 size so not quite a 700 yet however it's using the new thunderbolt SAB tail blades which are quite wide chord toward the tip and they grab really well.

I could bring in the ball in one hole in the servo but not sure whether that would make a difference?

Well you might try to reduce Piro consistency as well, I've got the following out of tuning guide:

4) Piro Consistency parameter:
**snip ** You shouldn't set the parameter too high if not necessary, else tail oscillation in high extent can occur. You can verify it in Fast Forward Flight or Pitch Pumps whether the value is too high and if you can see a tail oscillations.
viewtopic.php?f=20&t=378

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Oxy4max SpiritPro + HW // SOXOS 550, SpiritPro, HW120A V4, 920KV // SOXOS 600, SpiritPro, HW160A, Pyro650 // SOXOS Strike7, SpiritPro, HW160A, Pyro750 // Skywing Spirit Aero // FrSky Horus X10S + Taranis X7 /

Weird numbers you guys have.

I have a protos max v2, align 855 tail servo (12kg, 0,03 sec at 8,4V, but im runnig it from 7.5V so it is slower and weaker) tail ratio on the protos is 4,8 and im running rail 116 blades withrapid 710 mains at 1950-2050 rpm.

Tail multiplier is 1,3 tail gain is 70%, piro consistency 200, delay 0, tail dynamic 6, Revomix, or tail precomp 0.
No matter what i do with it, no wag, and the tail is rock solid, stops are really hard, tail barks, no bounce back at all. Literally. (FW 2.0)

Try delay 0, and increase piro cons to 190.

This is my protos with the setting above, but with 760 blades, at 1850 rpm, with 760 blades at slower headspeed the tail is not as agressive, but as you can see it holds great. And with 700 blades around 2000 rpm, it goes really agressive, i like it.

https://www.youtube.com/watch?v=21BQZBLuZ30

I agree I would be expecting higher gains with this machine, higher than my goblin 500 that is running piro at 170 and gain at 68x1.1.

So I've gone through the manual again and I probably have too much mechanical gain. The manual recommends 15-16 mm on the servo horn but I was using the 18mm hole on the sab servo horn. I've moved it back to the 15mm mark and will test fly tomorrow.

This should definitely let me increase gains. Also maybe the servo just did not have enough resolution to precisely hold the tail requiring less gain.

I'm keen to see whether it will affect the tail holding speed as the servo now would need to travel farther to get the same blade deflection. However the BK servo is quick so I'm hoping this will balance things out.

Hi,

you can try to reduce Governor Response, if it is too high, it could induce tail oscillations as well.

What are limits of the rudder?

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Spirit System developer

So I've put the servo ball one hole in (15mm vs 18mm) and my limits now are 110 - 130. Before they were 95-110 or so. I've reduced rudder delay to 0, increased piro consistency to 175 from 170 and bumped up the gains by 15 points or so (60 x 1.2) for my first flight today. Gov gains are 6-3 which are holding well but not too tight. 7-3 is the one that would hold the RPM tight. As I was doing sport flying when the mini-wags where happening I was flying with 6-3.

I've seen tail wag with BK servos before on my 450L whereas the (much) slower 520M was working fine. Putting the ball one hole in fixed it there so Im hoping for the same here.

I have also re-checked my 500 sport end points and its running at 105-119 so its closer to the new ball placement on the Black Thunder. Looks like this was the culprit, at least from reviewing the settings and the manual.

Ill retest today and let you know how it goes!! Thank you!

So I've put it up this morning, with 7-3 gov gain the tail is twitchy, I could hear it doing "micro wags" during FFF. With 6-3 it works well in FFF. I've dropped gains to 70 & 1.1 multiplier.

However I have a slight kick when loading the head in the first part of the pitch pump. When unloading on the top of the pump it's perfect and when reloading on the bottom it holds perfectly. That's with 6-3 gain.

I can live with that unless you have any suggestions on how to tune out? I'm guessing I can't have it all fully solid tail in pitch pump while also no twitch in FFF?


Ps. My rpm sensor filter is set to 8, however j do get signal is noisy errors every so often in the log.

Tomas any ideas? Would increasing piro consistency further make the kick on the start of the pitch pump go away?