Getting tail gain right

[Wargamer]

I'm finding that the Oxy tail wags slightly in a hover, I would say no more than an inch to either side, with a freq of 1-2 wags/sec. Have taken the tail gain gradually up to 30 and I would say it's only slightly better. How high would you go, or is it possible something else is going on?

It seems solid in forward flight and modest pitch pumps.

EDIT: More info after more flying...
Have played with tail gains from 20 to 40. There is slight reduction in the wag by 40, but it's still there. On the other hand, piros go from smooth at 20 to very choppy at 40. Although they actually seem rather slow considering the piro rate is set to 400/sec.

I have over 30 minutes on it at this point so I'm going to check over all the mechanicals. Would appreciate any thoughts on possible config or other issues that might be causing this.

[myxiplx]

A couple of questions:

- Is the tail mechanically smooth?
- All the bearing parts on the tail are definitely in the right order? (Reversed thrust washers can cause binding under load)
- Have you done a trim flight, or set the tail neutral position in rate mode?
- What's your overall travel on the tail (the total of the two endpoint numbers)?

[Wargamer]

Tail seems smooth to me, although I have no other experience to go on since the 230 is driven. As I was sitting here typing, however, the tail servo suddenly developed a very odd shudder that I have never seen in a servo before. Of course I moved the stick before thinking to check the exact position, and I can't get it to repeat.

All the main tail components are factory assembled.

Did a trim flight.

Tail travel is 120 + 120

[Shogun71]

Tail travel should be 200 total. If one number is slightly higher it's ok like 110/90.

You may need to adjust your throw or look at a faster tail servo.

Please post a pic of your tail servo arm and linkage and the exact model of your tail servo.

From my recollection you will need to lengthen the ball out a little on the arm. That should get you closer to 200 total.

I really prefer the mks ds95i or something similar.

That servo got rid of a lot of tail issues on my Trex 250 that has a known nasty tail.

[HEXAHYDRATE]

Originally Posted by Wargamer

Tail seems smooth to me, although I have no other experience to go on since the 230 is driven. As I was sitting here typing, however, the tail servo suddenly developed a very odd shudder that I have never seen in a servo before. Of course I moved the stick before thinking to check the exact position, and I can't get it to repeat.

All the main tail components are factory assembled.

Did a trim flight.

Tail travel is 120 + 120

To check how free your tail is, just pop the rear link off of the tail control rod. Operate the mechanics of the tail pitch assembly by hand. It should be completely free with virtually no effort to move it, and make sure there are no sticky spots.

Also make sure your tail control rod is lined up nicely and move through the guides smoothly.

And +1 on the MKS.

[numbermonkey]

What does tail travel have to do with a slow wag? Sure if its absurdly short it would be an issue but wags happen around mid point so the ends are irrelevant.
Don't be afraid to be bold with gain raises but be ready with the TH. You'll know during spool up if you've overshot the sweet spot and if the tail is wagging before the skids leave ground then don't even attempt to fly it. I go up by 5s typically when I'm hunting for the magic number.
Another test for your tail. Hold the slider still and try turning a blade grip. Ideally, there should be zero wiggle. Any slop here can translate into hunting since the FBL is trying to get to a spot but the blades overshoot slightly which causes it to react and try seeking back. But it overshoots slightly which causes it to react and trying seeking back. And so on.

[Wargamer]

Very much appreciate all the suggestions. Let me try to respond here:

1. On tail travel, the Studio language indicates that the goal is to have total travel > 200. I don't think it needs to equal 200.

2. Running 4 x 215MG. Seems quite common on the Oxy with no other folks reporting issues. The fact that I had the one-time strange shudder on the tail servo might mean a bad servo, so need to at least keep that on the table. Thanks for the 95i suggestion.

3. Tail mechanics do seem quite smooth with finger pressure. And with the ball popped free, if I flip the Oxy on its side, the slider will move down under gravity only.

4. There is VERY slight rotation (~0.5mm) possible by twisting either grip while holding the slider in place. Everything seems as tight as it can be, so I would interpret this as the minimum play necessary for smooth function. But shout if that seems excessive.

I need to go back and confirm the correct ball distance on the tail servo, but I know I double checked it when I set it up, so I don't think that's an issue.

I can try raising the tail gain a bit more, but the fact that higher gain is giving me serious stutter in piros seems odd, or at least indicates that gain may not be the only problem here. I will post this over in the Oxy forum when I get a chance, since it seems more than likely there is some kind of mechanical issue I'm not seeing. Any other thoughts are obviously welcome here as well though!

[Shogun71]

With those servos tail ball distance is crucial. They just don't seem fast enough. Any minor issue makes finding a happy tail challenging. If you don't have a lot of build experience/OCD/flawless parts, little things like this are maddening. I spent hours trying to get my Trex 250 to fly properly, it taught me a lot!!!!

We were working on tail issues on one Oxy3 with exactly the same setup as yours. If we got rid of the slow wag we got oscillations in flight stressing the tail. If we got rid of the oscillations we got the wag.

Mine with a dedicated tail servo never exhibited those types of behaviour.

A slightly longer ball and dedicated tail servo should make your tail rock solid in all conditions.

[sutty]

Originally Posted by numbermonkey

What does tail travel have to do with a slow wag?

It has everything to do with it. It is nothing to do with the fact that it is only in the middle, it is to do with the resolution with which the gryo operates with.

You had no idea what number he was going to come back with, and they don't need to be absurdly out anyway.

Too high and the servo is effectively slowed so much it cannot react in time to the Vortex's wishes, and the helicopter's responses, especially if the servo isn't the fastest to begin with, and too low and the granularity is insufficient for accurate positioning. In these circumstances no amount of gain tweaking can get a good hold.

Honestly, before looking too far for mechanical faults I would try again with the numbers closer to 200 overall, not 240.

If you go out a hole and get nearer to 200, and still can't tune it, then it's true that slow lazy wag issues are very often mechanical, and a common cause with small helicopters is binding or tightening of the grips under load.

Don't worry about that until you try with lower numbers by going out a hole, reset your ends, and see what happens after another trim flight.

[myxiplx]

I do think it's worth lengthening the tail servo horn. With a total throw of 240 you're effectively making the tail servo 20% slower than it would be with the travel in the 200 range, and the smaller the model, the faster the tail has to react to keep it steady.

It's an easy thing to try at least, and remember to repeat the trim flight after making the change.

[Wargamer]

Really helpful discussion. Even if this turns out not to solve it you guys have shared a ton of useful info. I may not actually get to fly again until Sunday, but I'll post when I do.

EDIT: After playing around with a couple of servo horns, I ended up with 105/107 vs. 88/89. We'll see how the first one flies.

[Wargamer]

Update...

Moving the ball out a bit (to get 105/107) made a big difference. Tail wag gets much better with some gain, and the piro stutter at higher gain is gone. Just need the wind to die down for a trim flight and fine tuning the gains. Then I can start to play with the governor.

Thanks all -