SK720 Tail Blade Pitch - Why Zero Degrees

[georgi UK]

=] Gary you are driving me to drink!
It's both because that is the intended result, you can't escape to one or the other and choose which, they go hand in hand....

Make it a double landlord, thanks!....

Edit: Please can somebody answer the following question:

Question: If the heli is set to have the "traditional" counter-torque setup (which has been explained so many times by now, I'm not doing it again) then which of the following two options states the best servo arm position for when clicking "Centre".

This is one for you Georgi my friend and please don't say neither LOL.

Position 1) When the servo arm is at 90 degrees, at which time there will be a few degrees of tail blade pitch counter-torque (offset).

Position 2) When the tail blade pitch is at 0 degrees, at which time the servo arm will be a few degrees away from 90 degrees.

[GaryDT]

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Hi Georgi,

Okay thanks mate, even though Position 1) and Position 2) state different servo arm positions

Cheers,

Gary

[georgi UK]

=] thanks Gary! there is a beer battered fish in the oven, that should do it!

[GaryDT]

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Hi Georgi,

Sorry mate, but I just wanted to finish wrapping up this thread by getting just one final point completely clear and on record with absolutely no doubt whatsoever.

1) The "Centre" button is NOT intended to be used solely as a 'Servo Arm Centre' button, or solely as a 'Tail Blade Pitch Zero Degrees' button. Instead its designed purpose is 100% to be used to set the tail blade pitch to 0 degrees at the same time as setting the servo arm to 90 degrees. In this respect the SK720's design marries these two variables such that if either one is not in place at the time we click "Centre", then this goes against the designed intention of the "Centre" button.

A) Yes the above statement is correct.

B) No the above statement is incorrect.

Please answer A or B.

Cheers pal and I'd just like to say I've really enjoyed this thread and have learnt some very interesting things along the way.



Cheers Gary

[georgi UK]

=]. Yes it's A, and involves a 2 part adjustment, no different from hold cyclic pitch and setting it.

It could be considered a coarse setting as you may have gathered, and gets fine tuned in the tail banks.

Pubs still open for a few more hours.......

Cheers georgi.

[emrekaman]

I have tried both combinations with both Sk720 and ikon, which requires some precompensation at neutral servo position. Here was the results:

- Precompensation with SK720: Bad tail stop behavior, anxious tail even in steady hover. Sounds like too much D gain, right?
- Zero degree tail with ikon: Vibes in FFF, even more vibes when tail gets some direct wind. It looks like too much I gain.

[GaryDT]

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Hi emrekaman,

Thanks for joining in. That's certainly given me something to think about

Cheers,

Gary.

[emrekaman]

Thanks Gary I just wanted to share my experience with this topic. I'm very happy now with my setup, which is zero degrees in tail blades and linkage is prependicular to servo arm. I also think that, this way is easier than finding an unknown offset like ikon and vbar likes.

Cheers
Emre

[GaryDT]

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Hi emrekaman,

I too believe it simplifies the setup, but I'm just very curious, and want to find out if the Setup Wizard is approximating (as I was wondering about/suggesting in my 1st few posts in this thread). It might be approximating, it might be a Skookum preference, or perhaps it is indeed a Skookum method that needs to be followed exactly as the wizard demonstrates to get the very best performance.

The uncertainty seems to be not knowing whether the SK is specifically/fundamentally different to other FBLs, such that it is designed to have a Zero degree setup, or if indeed it is actually just what I've come to refer to as a Skookum preference. The other uncertainty is what does the "Centre" button tell the system? I'm guessing it tells the system where zero degrees is.

Cheers,

Gary.

[emrekaman]

I believe it's a preference. Also spirit fbl wants it to be zero degrees. Like you said, it is the fact that there will be always a compensation when heli is off the ground or even on the ground during spool-up.

I guess this preferences are related to P-I-D gains and their proportional relations with each other, because when you change the angle of the tail blades mechanically, the tail responds like there is a problem with those gain values as I mentioned in my first replay. But as I said, this is only a guess

[GaryDT]

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Edit: Just to clarify, from this point onwards, this thread progressed to me asking questions which related to the maximum cyclic pitch available (the maximum cyclic travel range), which the FBL uses to try and provide your requested rate of rotation in accordance with the agility setting and your stick inputs. This setting is part of the cyclic setup.

Hi Georgi,

I hope you've recovered from last night

Apparently this is a Bacon Dance

I've Googled "It could be considered a coarse setting" (see #45), but I can't find out what this means, but it doesn't matter, and I have another question which is written below.

"no different from hold cyclic pitch and setting it"

I'm not exactly sure what you mean by this, but it reminds me of setting the cyclic pitch reference point in VBar, which is the stage that we're teaching the system where a known point/cyclic pitch is, to allow the algorithms to function correctly.

Question: Please can you tell me if the SK cyclic setting is teaching the system about the geometry of the heli like the VBar setting does via an 8 degrees reference point (Also BeastX uses a 6 degrees reference point)? See Links Below.

https://www.helifreak.com/showthread.php?t=309696 (#4)

http://www.rccanada.ca/rccforum/showthread.php?t=206987 (#2)

I'm slightly confused about what this setting is for. Please listen to the guy in the video who tells us to set the cyclic pitch setting to 10 degrees. This has got me wondering whether this is the equivalent teaching step that I've described above. But I guess it can't be since the guy in the video and the instructions very clearly (apart from there being no reference to any other value than 10) show that it's related to the cyclic pitch range.

The onscreen message states "Ten degrees is a good starting point for most sport fliers". This onscreen message is displayed from 4:10 to 4:33

This suggests that it isn't a reference point at all, and in fact the setting is related to the cyclic travel, such that a higher value (for example 12 degrees) is a good starting point for most 3D pilots.

I realise that for more aggressive flying more cyclic movement is required, so perhaps that is why it implies the value will need adjusting to suit your flying style (assuming it isn't a reference point).

SK 720 Swash and Cyclic Setup Wizard Walkthrough (6 min 17 sec)

[georgi UK]

Originally Posted by emrekaman

I have tried both combinations with both Sk720 and ikon, which requires some precompensation at neutral servo position. Here was the results:

- Precompensation with SK720: Bad tail stop behavior, anxious tail even in steady hover. Sounds like too much D gain, right?
- Zero degree tail with ikon: Vibes in FFF, even more vibes when tail gets some direct wind. It looks like too much I gain.

=] more details please, you have (combined) control of Integral and Derivative in the tail gain setting, the SK pid is perfected, it just doesn't like working with 'things' it wasn't designed for!

[georgi UK]

=] Gary, yes I'm on the mend!

V-Bar tried many (clever) methods to setup pitch and cyclic ranges over the years, I remember talking with Ulrich when my mechanical setup didn't meet their requirements, and was told it would fly fine, which it did.

As for SK we have the advantage of self tune bell gains. These indicate if the heli is over-pitched with unrealistic SW control rates.

10 deg cyclic pitch these days is achievable, some guys reduce to 8 deg to avoid bogging etc.

[GaryDT]

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Also, just in case there's any doubt here, when I'm referring to the maximum cyclic pitch available (the cyclic pitch range), I'm Not suggesting that this is the same thing as the agility setting, most certainly not. The FBL/Gyro will work within this available cyclic pitch range and attempt to achieve your requested rate of rotation. Your requested rate of rotation is determined via the agility setting and your stick inputs.

The question still remains: Is it a reference point or not (teaching stage)? I guess not, but a clear yes/no answer would be great.

The other question still remains below (assuming it's not a teaching stage):

What does "Ten degrees is a good starting point for most sport fliers" mean in respect to it connecting "Ten" with "sport"?

I also have a few more questions below:

1) If the setting is used to set the maximum cyclic pitch available, then please explain if the instruction is either incorrect, incomplete, or out of date?

2) If the value is actually a reference point (which I doubt as I've stated before), then is the ideal value 10 degrees, and should it NOT be used to try to set or manipulate the roll and pitch rates?

3) Assuming that the setting/value is for setting the available cyclic pitch range, then if "some guys reduce to 8 deg to avoid bogging" and 10 degrees is right for sports flying, what type of flying is 8 degrees more suited to?

Cheers.

[georgi UK]

=] You will find with SK they tend to be generic so as to avoid inflexibility with their system. So they prefer to give run of the mill settings. That should cover 1)

1) If the instruction is either incorrect, incomplete, or out of date, then please explain?

10 deg coupled with 12 deg collective is a hefty load to deliver, we don't fine tune the cyclic throw or consider this as a performance enhancement. We use the control rates in the cyclic banks for this.

2) Is the ideal value 10 degrees, and should it NOT be used to try to set or manipulate the roll and pitch rates?

Some scale multi blade heads and larger heli's benefit from reducing the cyclic throws....

3) If "some guys reduce to 8 deg to avoid bogging" and 10 degrees is right for sports flying, the what type of flying is 8 degrees more suited to?


I'm ready!

[GaryDT]

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Hi Georgi,

Somehow your post is missing some of the content in my post, but I guess it doesn't matter, even if it makes me look silly

The direct answers relating specifically to my questions seem to be evading me

My Guess: The setting sets both the reference point and the maximum cyclic pitch available, by using the maximum cyclic pitch as the reference point. On 2nd thoughts, if the 10 degrees is not a Fixed value, then perhaps this isn't it then

Here they are again (reworded)

1) Is the setting a Reference Point like VBar and BeastX has (see link at the bottom). Yes or No?

Answer please:

2) Does the setting set the maximum cyclic pitch available for the control loop. Yes or No?

Answer please:

3) "Ten degrees is a good starting point for most sport fliers.". Does my quote below explain this Wizard instruction reasonably well. Yes, No, or (N/A - answer to question 2 must have been No)?

"I realise that for more aggressive flying more cyclic movement is required, so perhaps that is why it implies the value will need adjusting to suit your flying style?"

Answer please:

4) Is My Guess correct. Yes or No?

Answer please:

Cheers mate
Gary.

A useful reference: https://www.helifreak.com/showthread.php?t=309696 (Please see #4)

Another interesting link: http://www.rccanada.ca/rccforum/showthread.php?t=206987 (Please see #2)

[georgi UK]

=] Top of my list for tomorrow!

[emrekaman]

Originally Posted by georgi UK

=] more details please, you have (combined) control of Integral and Derivative in the tail gain setting, the SK pid is perfected, it just doesn't like working with 'things' it wasn't designed for!

Yes, I completely agree with you. My intend was saying just the same thing, fbl units want to work with correct mechanical setups as they designed for it.

It's friday 9PM here, it's pub time!

[GaryDT]

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Hi Georgi,

Whilst I'm waiting for you to soba up my friend I've decided to have a go at answering my own questions. Just for fun

1) Is the setting a Reference Point like VBar and BeastX has (see link at the bottom). Yes or No?

Answer please: No

2) Does the setting set the maximum cyclic pitch available for the control loop. Yes or No?

Answer please: Yes

3) "Ten degrees is a good starting point for most sport fliers.". Does my quote below explain this Wizard instruction reasonably well. Yes, No, or (N/A - answer to question 2 must have been No)?

"I realise that for more aggressive flying more cyclic movement is required, so perhaps that is why it implies the value will need adjusting to suit your flying style?"

Answer please: Yes

4) Is My Guess correct. Yes or No?

Answer please: No

[georgi UK]

=] Here goes Gary!

1) Is the setting a Reference Point like VBar and BeastX has (see link at the bottom). Yes or No?

Answer please: No.

2) Does the setting set the maximum cyclic pitch available for the control loop. Yes or No?

Answer please: Yes.

3) "Ten degrees is a good starting point for most sport fliers.". Does my quote below explain this Wizard instruction reasonably well. Yes, No, or (N/A - answer to question 2 must have been No)?

"I realise that for more aggressive flying more cyclic movement is required, so perhaps that is why it implies the value will need adjusting to suit your flying style?"

Answer please: We need to differentiate here as it's being assumed or implied (I think?) the only/best way to improve the flip & roll rates is by increasing the cyclic pitch range. Where in fact we just turn up the gyro's using higher control rates.
No different to using blurred piro, the mechanical setup remains the same.

4) Is My Guess correct. Yes or No?

Answer please: I forgot the question??!

We must also consider there are other 'hidden' / 'inaccessible' settings at play here also, cyclic ring being one of them. You proved that by setting higher cyclic pitch!