ZYX - What am I doing wrong?

[EKron]

Two maiden flights - two maiden crashes.

First flight lasted about 10 seconds. Seemed to be hovering tail-in nicely then did an uncontrolled instant flip inverted and slammed head first in the dirt.

Rebuild time. Normal stuff, shafts, blades, links and this time added a Gryphon Polaris BEC (http://www.gryphon-mall.com/product.php?id_product=80) and ran a ground wire to the tail and confirmed continuity to the motor mount.

Completely went through the setup again twice and chose the "Beginner" setup with a few tweaks. Even had the LHS maestro confirm all my corrections were going the right direction and on the bench things were spot on. Test spooled to full throttle at zero pitch and couldn't detect a hint of vibration or wiggle.

Off to the field a few days later, I lift off and right away notice a bit of a minor shake. Stupid me should have set it back down right then and there but I wanted to see if it would "fly through it". Cautious of giving any sharp commands, I took it easy and let it drift around a bit when suddenly, it went into a violent oscillation and again slammed into the ground. (blades, main & spindle shafts, skids - not too bad really)

This time, I almost have a video. It was my very first try filming with a keychain cam on the brim of a visor and is not aimed correctly but the last second before my poor little heli hit the dirt, you can hear the mega speed wobble that took her down. I scooped her up and flew four packs through my 450 and four through my 500.


(yes, I moved the tail around to make sure I had rudder control but didn't touch the cyclic before lift off)

So, at this point I don't have a lot of confidence without trying something different, but what? I've got my ZYX mounted on a solid platform with my ESC on the bottom. Are they too close? Is my wiring or something picking up interference? I'm clueless and looking for suggestions


Antenna looks close to motor leads in pic but normally sticks out at least 1/2" away


Specs and stuff:
Gaui X2, CC Phoenix 25 fixed end point mode, Gryphon Polaris BEC, MKS Ds92a+ cyclic, MKS Ds95i set as 760µs tail/1520µs digital swash, FrSky TFR6 RX (R617FS quality clone) ZYX (non-s) v3.5 programmed with John_nz's FBL, Futaba 7C TX D/R 80, Expo -40, gyro in HH at 36 gain per instructions. Was in IU1 86.5% flat TC, -50-70-90 PC guessing headspeed around 3850? Don't remember but think I was setup +12/-12 and maybe 7º cyclic or thereabouts. ZYX mounted with HD 3M double sided tape.

[section1]
PitchAgility=30
PitchGain=40
RollAgility=30
RollGain=40
YawAgility=30
YawRight=30
YawGain=70
[section2]
FixMode=1
ServoType=4
SwashPlateType=2
ServoDirCH1=-1
ServoDirCH2=1
ServoDirCH3=1
ServoDirCH4=1
ServoAdjustCH1=0
ServoAdjustCH2=8
ServoAdjustCH3=3
AileronLimit=40
ElevatorLimit=55
TotalCoefficient=-45
PitchDir=-1
RollDir=1
YawDir=1
TailPoint=-22
TailLimitA=85
TailLimitB=77
OptimizationDir=-1
[section3]
Acc1=125
Acc2=40
Acc3=125
Acc4=125
Acc5=20
Acc6=20
DeadBand1=25
DeadBand2=4
DeadBand3=25
DeadBand4=4
PitchGainD=0
PitchGainI=120
PitchGainP=80
RollGainD=0
RollGainI=120
RollGainP=80
SpinSpeed1=30
SpinSpeed2=30
SpinSpeed3=30
SpinSpeed4=30
TailCompsate1=0
TailCompsate2=0
TailGainD=25
TailGainI=25
TailGainP=80
[FBL]

Thanks,
--Elisabeth

[Dr. M]

You cyclic gain is too high (pitch and roll) causing what's colloquially know as the wobble of death (WOD). Decrease the Roll and Pitch gains on the main page of the PC software to 25, which should be low-enough to be safe with those servos. Your helicopter may be drifty or sloppy with gains this low. Once you've confirmed there's no wobble, start increasing these gains 5 points at a time and test fly by giving quick jabs to the cylic stick, observing carefully for oscillations. Repeat until you observe wobble with these tests, or in shallow descents with the disk unloaded, then go back a few points. Do all the tests at the maximum HS that you plan to fly.

Otherwise, I recommend you start with the mild 3D preset, because the "Beginner" and "F3C' have really sloppy tail behavior. Decrease the Agility settings to 30, and use 40% expo on your radio to make the cyclic more docile. If you've not upgraded the firmware to 3.5, do so, but make sure your cyclic D gain (advanced settings) is 10 or lower after the update (preset defaults are 30, which is too much and may cause WOD).

[EKron]

Thank you, Dr. M. This is probably just the advice I'm looking for? The instructions suggest starting out with HH gyro gain at 36 in the TX - any thoughts on that?

Already am at -40 expo (Futaba) and on FW v3.50 so good to go there. WOD is no lie! Both times it happened so fast I'm gonna call it HMWODOC - Hyper manic wobble of death on crack! I've tried to keep up with everything here and the 400+ pages over there but think I'm suffering from information overload, have tripped the breakers and let everything leak out?

Swapping out the whole head assembly and mainshaft with an entirely brand new unit and maybe the main bearings too just for good measure then going through my whole setup again this evening. My out of town work got cancelled for tomorrow but we're actually getting some rain here in the great southwest desert so a Saturday test flight is looking iffy? Hoping to report back with good results Sunday afternoon though. (as long as the crappy, tumbleweed infested flying spot isn't too muddy) They say third time's the charm, eh? Wish me luck!

Thank you again for your advice.

--Elisabeth

[Dr. M]

Set your Tx gyro gain to a value such that the output reads 36 on the monitor screen of the PC software. The number on the Tx will depend on make/model. This may be too little or too much, but it shouldn't cause violent wags. Tune it up/down as needed.

Good luck with the maiden!

[LawnDartHeli]

Yeah, you can treat the tail gain in your Tx like any other gyro. The rates on P&R are always too high in default. Like the Doc says, start at 25 and treat it like tail gain (turn it up slowly till it wobbles, then back it off a hair). Once you find a smooth setting to hover, put it in FFF and see if it shutters.

[stevembusa]

It could be bind issue, since you just install new zyx. Try re-bind and do range check.

[EKron]

Originally Posted by stevembusa

It could be bind issue, since you just install new zyx. Try re-bind and do range check.

I use Futaba stuff so it's pretty much bind once and forget it. Guess it wouldn't hurt though?

Believe it or not, it rained here last weekend and I didn't get a chance to do anything. Going through my setup again this afternoon and heading to the field in the morning and hopefully can make it through at least one whole pack without another crash and rebuild. I'm leaving my flybarred Gaui 255 at home this time to have one less thing to mess with - it's not quite dialed in yet either. At least my two bigger birds are working very well and I can only worry about flying them not trying to solve problems.

Thanks all. Fingers crossed!

-- Elisabeth

[stevembusa]

Whenever you change CCPM setup on Futaba radio which I have 7C, you have to bind again.

[peterkjr2009]

Originally Posted by stevembusa

Whenever you change CCPM setup on Futaba radio which I have 7C, you have to bind again.

Is this correct? I never have with my 7c. I used to be swapping receivers from plane to plane, heli to heli. I haven't rebound since i brought it. If its beneficial ill start doing it.

[EKron]

Originally Posted by peterkjr2009

Is this correct? I never have with my 7c. I used to be swapping receivers from plane to plane, heli to heli. I haven't rebound since i brought it. If its beneficial ill start doing it.

I didn't want to be argumentative but I've done some research on the necessity of rebinding Futaba receivers. This sums it up: "If a Futaba receiver has lost its linking data and needs relinking in order to decode the transmitter signal then something is wrong either with the receiver or the transmitter".

In fact, if you ever have to rebind your TX and RX, that's an indication that something is wrong and your equipment needs to be sent in for repair.

I won't go into details yet but as to my test flight after changing settings and going through everything once again, let's just say I'm three for three. Three 10 - 15 second maiden flights, three failures. My latest was pretty disastrous and I haven't even been able to force myself to yet look at the wadded up mess. Took off and things looked and sounded good. Nice stable hover about 10' up for 5 seconds then the fast oscillation noise started again and I knew she was going down. It pitched over and slammed hard into the dirt.

I'm frustrated, pissed and not particularly motivated to immediately rebuild everything and try again so I'm going to let my broken and bent X2 just sit for a while. If I didn't already have a fortune wrapped up in this little heli and it's Hurricane 255 sister and a crapload of spares, I'd consider cutting my losses and selling the the whole lot but I'm sure once I cool off that I'll go back through it again starting from scratch with a total disassembly and do-over from scratch.

I've added a BEC, made sure my tail was grounded, changed the settings as recommended by Dr. M and it still blew up so I'm not sure what to try differently? All I can think of is to maybe use a foam mounting pad instead of 3M tape but the heli seems to be vibe free. I also dumb thumbed my 450 into the tumbleweeds last weekend and have spent two days and $185 putting it back together. At least I know it is going to fly well again if not better whereas I have zero confidence in my X2 with the ZYX since every attempt to fly it has resulted in expensive failure.

This weekend, my 450 and 500 are going flying with me. Maybe in another week or so I'll feel like tackling my X2 and ZYX problems but for now it's just going to sit. Maybe she'll have time to ponder the error of her ways?

-- Elisabeth

[Dr. M]

Sorry to hear about your misfortunes. I hope we can help you figure out what's happening. This delayed-onset WOD is very indicative of too much gain. I think I've spotted the problem and I apologize for not seeing this before. I'm fairly certain your cyclic servo horns are too long, as indicated by your setting for "Collective range"

TotalCoefficient=-45

The absolute value of this parameter should be between 60 and 80 with 12° collective at the top of the stick. A setting lower than 60 (45 in your case) indicates your servo arms are too long (i.e. your system has too much mechanical gain). I recommend you move the linkage balls on the servo arms one hole closer to center (this should be ~10mm center-center). Redo the CCPM setup (collective range and cyclic limits), set the cyclic main gains to 25 and set the pitch/roll PID values to 90-105-10 in the advanced settings. I think you'll be able to increase the cyclic main gains after you confirm the WOD is cured with a test flight. Do it 5 points at a time as explained in my previous post.

Good luck!