The Importance of 100% with the Tail Servo.

[A VIKING]

Georgi/Omer,

I hear you guys always stressing the importance of achieving 100% in the Tail Servo Tab and with the geometry of my 770 and the shape of my tail servo I was never able to get 100%. The best I could get was 71%. The control rod ball end would hit the servo limiting throw.
So in the spirit of making things perfect I drilled an extra hole inboard on the horn and repositioned the ball on the servo arm from the top side as required by SAB instructions to the bottom side. This gave me the needed throw of the servo arm to easily acquire 100% for servo travel , left and right, in the setup control panel.
With my adjustable control rod guide I was able to unscrew the end to line up properly with the rod, now that is lower, and still be strong and ridged in it's support.

Given I am a mild 3D pilot on wheels, what is the advantage of the corrected 100% throw on the tail servo compared to the old 71% throw?

With the 71% I seemed to have plenty of tail authority in all flight envelopes I am able to fly.
Is the 100% available throw easier for the SK in coming up with a yaw correction?

The photo shows my new control rod arrangement on the Goblin to get the left and right 100% throw of the servo. I could actually go to 110% now with the system now but I guess 100% is the target.

[Digger1973]

I have run less than 100% with no issues. As long as your travels are not highlit yellow in the software indicating the sk unit isn't happy then it really shouldn't make a difference. I am basing that off several posts made by georgie and others that do support on here.

[A VIKING]

Now that I have thought about it a little while, my real question is this.

With a long tail servo horn length I can get stop to stop tail blade pitch angles.
This happens with a short stroke of the servo motor because of the length of the horn.

With a short servo horn I can get stop to stop tail blade pitch angles but with a much longer stroke of the servo motor due to the short horn.

It seems that a short horn with a longer stroke of the servo motor is preferable to having a long horn and short stroke of the servo motor.

I totally understand arm length influencing distance traveled but why would a shorter horn be better than a longer with our controls.

What's the science behind that?
Just trying to understand the logic behind it all.

[DaveHolland]

What you just explained about the servo throw changing is resolution. You want a good amount of resolution for the FBL to be able to make correct adjustments. As you do harder and harder moves you tail will require different inputs to hold the tail or keep it piroing at a constant rate. The higher resolution give the FBL more steps to find this perfect spot. That being said, too much resolution is bad because then it will have to many spots to sort through and feel like its lagging behind in commands.

The head works the same way. If you give the system a little more resolution you can raise the gain and it will help the system lock the head in better, but you can end up hitting servo travel limits. Like what was mentioned earlier, keeping the number out of yellow is best. I usually end up running a little higher than 100% on my tail and that because of the provided servo horns. My tail holds well enough with the slightly higher resolution.

[A VIKING]

I believe I understand now.

So I can compare servo resolution to turn buckle style P/C links.
Without the turn buckle style links you are limited to one half turn adjustments which can get you close but not exactly perfect in track. With the turn buckles you have infinite points to adjust track and so you can achieve perfection.

With higher resolution of the servos they can get that perfect adjustment in trim but at a lower resolution they can only get close, not perfect.

Good analogy?

Thanks Dave and Digger!!

[gitbse]

Originally Posted by DaveHolland

What you just explained about the servo throw changing is resolution. You want a good amount of resolution for the FBL to be able to make correct adjustments. As you do harder and harder moves you tail will require different inputs to hold the tail or keep it piroing at a constant rate. The higher resolution give the FBL more steps to find this perfect spot. That being said, too much resolution is bad because then it will have to many spots to sort through and feel like its lagging behind in commands.

The head works the same way. If you give the system a little more resolution you can raise the gain and it will help the system lock the head in better, but you can end up hitting servo travel limits. Like what was mentioned earlier, keeping the number out of yellow is best. I usually end up running a little higher than 100% on my tail and that because of the provided servo horns. My tail holds well enough with the slightly higher resolution.

This.

Good explanation.
100% is not required to be dead on, but it's best to keep it under +/- 10 each way. If you can get between 90-110, it will be good.
Do some experimenting one day. Move the servo ball in or out on the horn, set the end points and try to tune the tail. Move it to extremes, see what happens when the boxes turn yellow. You could even do it with the cyclics as well. You will notice remarkably different flying results, and it will be impossible to tune. Then set it back to as close to 100% as you can, then see how it differs.
IMHO, the best way to learn about tuning FBL's is to experiment. As long as the control and comp directions are proper, you really can't hurt anything. (Within reason.)

[DaveHolland]

With older servos you had to find the perfect balance. New HV servos are so fast it really doesnt matter to place the ball closer. Reducing mechanical gain will decrease servo speed. This factored in with the older 0.10 or 0.08 servos. Todays 0.03 tail servos can loose some speed and still maintain a good lock. So for instance if you moved the ball in one hole on the servo it may slow the servo down to 0.04, but that is still fast enough to respond.

I use fast HV tail servos and I shoot for a little more tail resolution when setting up my helis. It may not be the proper way but it works well for me. When I say more resolution I am saying 110% or so.

[A VIKING]

Good stuff Guys. Thanks!!
I have also done a lot of experimenting going up and down the adjustment scale on everything in the SK control panel which really teaches you a lot in terms of how the ship reacts to all those variables....except tail servo end points.

Thanks for sharing the knowledge!

[DaveHolland]

Now to confuse us all after all this. I set up my TSA 600N with a longer horn and was running around 70-80 tail end points. I didnt notice any odd behavior from it but I have since switched to a shorter horn and have about 110 and 115 travel. Also no odd behavior from it.

[georgi UK]

=] Martin although this was some time ago, after a firmware release half the pilots who voted couldn't fly their heli, because of a severe tail issue. SK addressed this. From memory I was grounded for about a month, the patch which was released required a servo distance that gave equal 100% travels, the tail is designed to make a non~linear tail, linear.

I would say this setting up still holds correct today, nothing in the tail has been changed significantly since then to ignore it. Many users issues we see have deviated from this lack of understanding, if you read the thread there is evidence there to confirm what I'm saying, have a good read!

https://www.helifreak.com/showthread...highlight=Poll

[A VIKING]

Originally Posted by georgi UK

=] Martin although this was some time ago, after a firmware release half the pilots who voted couldn't fly their heli, because of a severe tail issue. SK addressed this. From memory I was grounded for about a month, the patch which was released required a servo distance that gave equal 100% travels, the tail is designed to make a non~linear tail, linear.

I would say this setting up still holds correct today, nothing in the tail has been changed significantly since then to ignore it. Many users issues we see have deviated from this lack of understanding, if you read the thread there is evidence there to confirm what I'm saying, have a good read!

https://www.helifreak.com/showthread...highlight=Poll

Interesting.
Thanks for the insight Georgi.
I have a pretty good grip on the concept now...and feel better that I modded my tail achieve L100-R100 in range. At a setting of L71-R71 I was on the fringe of the dreaded yellow box.

I realize that I may not see much change at my level of performance but it is very important to me to be completely accurate in the setup.