When rotating inverted, Neo struggles to sustain feeling locked-in..

Hi Guys,

An issue I can’t seem to figure out. She is a finely built, very smooth 550 SX swinging RT mains using a Kontronik 80+ HV (not the pro) in governor mode 4. I’m testing at 1,850 rpms.

When increasing collective and flipping inverted (not stick banging it, just nice and smooth) she struggles to sustain that locked-in feel (visibly oscillates) when applying negative collective to soften the decent. Once she’s in an inverted hover, she’s fine. It’s just happens during the transition process.

Basic Settings: Style = 80, Agility = 70, Main Rotor Gain (between 75 and 95 seems fine), currently = 95
Advanced Settings: Heli Size = 50, Paddle Sim = 0, Collective Balance = 35, lightness = 0

What could be causing this issue?

Thanks,
Raz



Edited 1 time(s). Last edit at 09/08/2021 12:55AM by Razmo.

Hi Raz,

can you please post your full setup file (save to disk, attach, or save to radio, retrieve from radio or cloud, attach)?

Could be that you need to zip-compress it because of file types allowed.

This way, we can see more.

Imo it's something more generic than the main menu settings, with the setup, or maybe even with the mechanics, servos, linkage, suspension of the feathering shaft (rubber dampening, stiffness/condition of the o-rings and compression), thrust bearings, or even the tracking on edge, so the blades run out of track more than they do anyway, when you increase the AoA. Could even be a bent feathering shaft.

Is it different at different head speeds?

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddie,

Sure, I'll try to save file to disk and attach over the next few hours.

Regarding the more generic possibilities, all linkage is bind free and properly setup. Although my cyclic servo's are rather dated, they were new for the build. I'm running a set of HV Outrage Torq BL9080. All electronics are 2S Lipo powered. The machine has about 30 flights on it.

The thrust bearings should be fine, very smooth and the feathering shaft is true, checked during the build. I suppose my tracking may be off a hair, but I don't think it could be more than 180 turn on the linkage. It's seems nearly spot on. Dampening sounds more likely and/or not enough grease, but I have no experience understanding the behavioral difference in soft, medium or hard dampening. My 550SX is the latest version, model 5086 with the metal head, built with the included dampeners. I'm not a 3D stick banger, more of a light weight 3D/slower controlled aerobatic pilot.

I've noticed the problem at 1750, 1850 and 2100. At the lower head speed the struggling behavior is more pronounced, like a slower wiggle to find lock-in. At the higher head speed, it just seem to happen faster.

Raz

Another mention here..

I seem to be able to raise the main rotor gain up over 100 even 110 without the machine introducing oscillation during fast forward flight or a bounce after cyclic jabs.

Raz

Let me know if this isn't what you need. My first time. I went to parameter, then saved locally.

Thanks,
Raz

Hi Raz,

thank you for your feedback and the file. Looks all pretty stock to me, only thing I notice is, you have dialed out Expo.
If you are using it instead on your radio, OK, if you feel confident without, also OK.
But the model could also react very directly, even to jitters from your fingers.

If you think you are maybe 180° on a ball link away from perfect tracking, try 360 (the same hair off, but the other side).

About dampening, the rotorhead works in a way so the feathering shaft with the blades attached can move or yield into every direction, suspended and supported by the rubber o-rings. Plus, the blades can swing fore/aft on their bolt (don't tighten too much so they can align), plus the blades can flap a bit length-wise, and even twist the tiniest bit. All this is supposed to help with the changing drag, angle of attack, and balanced in a way so the forces between rotor disc and main rotor shaft are kept in check, and it obviously all dampens the thing.
There are different shore dampeners, softer or harder. You can distinguish them by their diameters. Bigger/harder ones 3x3 ... hardest setup. But you can mix, like hhh or shh or ssh or sss or hsh or ... any combination, but the same on both sides. There is no general rule, whatever works best.
Usually, the included/recommended dampening is good for the model at it's recommended max. head speed and somewhat below, but since it's all dynamic ... what works best can be different.

Very likely such effects come from the whole assembly, not from the electronics, and the electronics (and electro-mechanical actuators, servos) can not check it. In particular if changing the main rotor gain does not change the effect very much or at all.

So basically what you can do is check if your blades balance, length-wise, chord wise, and if they have the same lead or lag if you hang them by a nail.
Then, you can change the dampening, softer or harder, by replacing rubber o-rings, changing the compression (with washers), or even by grinding off a tad to make them go in more flush. And of course, make sure everything's symmetrical, and well-lubed.

Other thing, do the trim flight and optimizer flight, even if you are sure everything's set up properly at 90° angles ... thing is, this is good for a good geometry, but in flight, even in a hover, the model already has to compensate for dynamic things like CoG, tail rotor thrust etc, and they don't adhere to the 90° rule.

Speaking of, CoG. Important, particularly when accelerating into a maneuver, or stopping. If off, the whole (unbalanced) thing will sway, and the servos have to compensate, and the control loop (I, heading hold) unwinding and winding up the other way may just be lagging a bit. This induces what looks like a wobble (if softer) or an oscillation (if harder).

If you can raise up main rotor gain all the way, it speaks for your servos. The point where you would trigger an oscillation is very far off, you might not even reach the point where you trigger that oscillation. That's good!

And since it only seems to happen when you come down and stop inverted, it could also be such a simple thing as the main shaft having axial play. Pull up the rotor head, and re-set and tighten the clamp ring again. Since the bearings can always still settle after a flight or a couple, this can happen. Always check carefully after the first break-in or shakedown flights.

Lots of input to process, hope there's something in it that will help!

Cheers

Eddi

Born to fly ...
forced to work.

Hi Eddi,

Greatly appreciate the information here, thank you! It’s true, I fly precisely without expo. I’m rather sure my fingers aren’t the cause, but happy to try dialing in 10% or so and retest.

Regarding tracking, I’ll try that. But why a hair off on the other side may be beneficial?

Regarding the dampeners, they were certainly a tight squeeze when fitting, notably squeezing the feathering shaft preventing from being easily rotated inside the dampeners if I recall correctly, but I was careful with lubrication, being sure to apply only to the inside of the dampeners. I don’t think there was much lateral compression with the grips attached.

Correct me if I’m wrong. Without the grips attached, should the feathering shaft easily rotate by hand with the dampeners fitted? I assume, by design, the dampeners should remain fixed inside the head, while the feathering shaft easily rotates inside them. Correct?

Looking back at the manual, it calls for two 7x4.5 on the inside with one larger 7x5 on the outside of the feathering shaft. So I assume this would be a SSH configuration, correct? I’m also noticing it includes an 8x11x0.5 washer for extra hard dampening, which I included in the build. I suppose it may be worth pulling the head apart, check the feathering easily rotates by hand and try relieving compression by removing the washers.

About trying different durometers, are you familiar with where compatible dampeners may be purchased if all else fails? I’m not feeling too comfortable grinding by hand if as a last resort I try different dampeners.

Regarding Main Blade Balancing, it’s an interesting suggestion as I’ve always been adamant on balancing the mains on every helicopter build, but I did not this time around as the RT 560’s claim to be quality balanced. I certainly check them, but the chopper sounds/feels smooth.

I’ll give the Trim Flight and Cyclic Optimizer a try. Remind, is there a way to clear the changes to default after trying if needed? My goal, has been to work out what I can with the assembly before trying trim flight and the optimizer.

Regarding CofG. I’m strict about perfect CofG for every flight. Definitely not part of the problem here.

To explain the problem again. The wobbling I’m referring to (as if its fighting windy conditions, when it’s calm) occurs during the transition only, as if it’s trying to find air to hold steady when I’m applying negative collective to slow the decent to sustain inverted flight, then holds once I find inverted hover.

I’ll check the clamp ring, but rather sure there is no axial play in the main shaft.

Thanks,
Raz

Hi,

tracking ... a bit of voodoo. You always assume that everything's symmetrical and balanced and works the same way. But if the blade grips a are a hair untrue, if the blades flex a bit differently, if the balance is a tad off (today's blades are selected and matched, but rarely individually balanced) ... something like that, or even swapping left/right blade does the trick.

The feathering shaft doesn't need to rotate, that's what radial bearings and the thrust bearings are for. But if the feathering shaft moves inside the dampeners (tilts, moves axially (push/pull), extra tension can be of disadvantage.

Right about the dampeners, SSH, and removing the washer could be worth a try.

I'm not familiar with sourcing other rubber o-rings, never tried or felt the urge. And we basically only have what we have, at Mikado.
I also didn't have to grind, for me, it worked all the time. But I'm only using the plastic blade grips, for instance, the full aluminum head is again stiffer, so the dampening has more to do.
uli here flies a 690 SX with 1,000 head speed or below, and he chose to grind the rubber o-rings, to get out of wobbles at such low head speeds.

Optimizer flight and trim flight, copy your current values, then make changes. Optimizer defaults to half Agility (90 Agility = 45 Optimizer, for instance), and it resets if you change Agility. Trim flight defaults to 0/0/0
I set up my helis in a very shirtsleeved way, 90° servo arms, linkages the same length, swash plate level at 90°, zero collective at center stick with folding the blades. All that with low trim values if possible. I only use a pitch gauge (or smart phone) to check for 8° cyclic and +/– 12° collective, w/o paying too much attention to decimals. Then, check tracking, do trim flight and optimizer flight, if the values are not off the chart, job done.

I rarely had reports of such behavior (inverted, w/ collective), and it was always something mechanical. The VBar doesn't know (OK, actually NEO could ...) and (but) doesn't care if it's upright or inverted, it just does the job, with the tools at hand.
Of course, inverted, the the pod on top of the rotor disc, acting as a lever (instead of hanging below) changes things quite a bit, but in reality, not by much.

Another idea would be servos: I once had a customer with an HV servo on the tail, which I could hold with one finger (!) in one particular position, where in others, it would have broken my bones. Result were inexplicable tail kicks in tic tocs, parameters didn't help, everything was mechanically sound, adequate tail blades and angles and speed ... just the servo (known brand, not no-name) was somewhat unwilling at one position.
He replaced the servo, heard of him no more after that.

If even one of you cycle servos was not playing ball, inverted, at a certain position, it would disturb the whole thing.

Lastly, just to rule that out, too, if you have the chance to try a different NEO on the same helicopter, with the same setup.

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddie,

Greatly appreciate your dedication and depth of detail here, very helpful.

Some interesting news…

I too do my setup in a very shirt-sleeved way, with a perfectly level swash at center stick (requiring very little trim, a couple clicks only). After thinking some more, I decided to be sure both grips were exactly zero when parallel to the boom. Meaning, with the helicopter on the bench, blades off, nose in (facing me) I measure what I call my master grip first (the grip closest to me). Making sure this grip is 0 degrees at center stick. I then rotate the opposing grip into the same position and remeasure. Both grips register 0 degrees.

I then decided to measure collective travel in the same way. Here is what I found. My master grip measured 0 at mid stick, 11.5 at full positive collective (exactly where I want it) and 11.5 at full negative stick (exactly where I want it). I then rotated the opposing grip into the same position. It measured 11.9 degrees at full positive collective and 11.3 at full negative collective.

I know the metal grips are a two-piece design, but I was very careful to piece them together properly, as was designed. These are factory new grips, no damage or a crash what so ever. My thinking here, my opposing grip must be the problem. Causing the mains to spread further out of track (you can hear it) at every progressive position outside of mid stick, forcing the NEO to struggle.

Thoughts? What next?

Thanks,
Raz

Hi Raz,

to be honest, IDC

Technically, in a perfect world, with no slop or play, with no possibility for the chassis or skids or servos or anything to budge or flex, and with everything running true, if the swash plate is level and if the main shaft is exactly upright, one swash plate ball will not move up or down during a full rotation, so the output angle is always the same.

Ergo, one blade grip connected to it will have the exact same angle(s) all around.

With two control rods to the blade grips of exactly the same length, and with the blade grips true to size and exactly the same, the other one will have exactly the same angle(s) all around.

With that in mind, I go with eyeballing the swash plate, adjusting equal control rods to the same length using calipers (not an exact science, no precision-cut threads), adjusting 0° collective with blade folding (good enough), and max. angles w/ a pitch gauge or smartphone to _one_ blade grip (level surface there), the one over the tail boom at that, then go fly.
If I find tracking to be off, I do try and error, and that's that.

The result is, in itself, the assembly is symmetrical, and it also requires the servos to be at equal center positions, it's simply geometry.

I don't care very much about absolute angles, especially since the center in flight (if there is one, but let's take hovering at zero wind) is also off level, a slight tilt against the tail rotor thrust and a slight tilt to compensate for the CoG as well as for effects the tail boom and tail rotor have in the downwash.
Here comes trim flight, because it can sense it where it happens, if left alone (no stick inputs) and center the servos in a way so the control loop is unloaded (like adjusting the tail in normal mode, back in the day).

20+ years ago I also tended to spend several evenings per new or newly set-up model, chasing decimals, adjusting angles. But I found for myself that the model doesn't fly any noticeable bit better that way, so I went for the shirt-sleeved way and started spending more quality time (flying) than messing with measuring

If I'd fly F3C, I'd probably notice a difference, and I'd probably spend more time on it, but I dare say, for the majority, average sports- and 3D-pilots as well as stick bangers and scale model pilots, it is just fine this way

My opinion.

Best,

Eddi

Born to fly ...
forced to work.

Hi Eddie,

All I can think of here, is the grips need to be replaced with a new set. Hoping the tolerance of each are true, providing symmetrical collective travel.

I don't know what else it can be. Are there no known manufacturing errors with the Mikado metal grips?

Thanks,
Raz

Hi Raz,

to be honest, not really.

Main rotor yokes have been reported to run untrue (very rarely), but you'd notice right away when taking her out for a spin, not only in particular maneuvers.
Feathering shafts can be bent, and if they rotate inside the head, the tracking can be arbitrary. But that wouldn't cause what you reported initially, either.
Then, there were two generations of blade grips, one with the bolt head sticking out, the other one with the bolt head sunk all the way in (most obvious difference). I guess you would notice it's not subtle, and it only came up when one replaced only one original one with a later one, not both.

The struggling inverted, in my opinion and by my experience, is very likely something else.

To rule it out, replace the blade grips, even with plastic ones, just different.
Or if you have another LOGO with a similar sized head, replace the whole assembly, including blades if they fit.
Just to have a comparison, to ID or rule out components or assemblies.

Kind regards

Eddi

Born to fly ...
forced to work.



Edited 1 time(s). Last edit at 09/22/2021 09:05AM by Eddi E. aus G..

Hi Eddie,

I've ordered a set of new metal grips and a set of plastic grips. Going to try the metal grips first, see what I get. I report back soon.

Thanks,
Raz