Bizzarre Behavior

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I"ve been struggling with the CGY750 for the past couple of weeks. I installed it on a fresh build Compass ATOM 500 thinking that it would be a good fit. Nothing could be further from the truth. In fact, it is unflyable. I set up the heli mechanically as perfectly as one can. All the measurements are factory specific, Swash is perfectly level, set up on the shops granite surface plate using CMM. All links have been sized and adjusted for free movement. (While I don't particularly care for the ATOM's Tail arrangement, the blades are fairly secure in their holders). I may add spacers to tighten them up as I don't particularly like a floppy tail)

I set up the CGY750 according to the manual, double checked with videos from Nick Maxwell, Bobby Watts and others on Youtube University. At first glance, it looks fairly straightforward and simple to setup. The first test flight was a disasterwith the heli shaking in the air. Lucky to land with no damage. I went over the setup again, added expo, reduced gains, all the things you would normally do. The next flight was better, but still not 'locked in' by any means. It reminded me of my Hirobo Shuttle in the 80's flying with no gyro.

Today, I took it out again to see if I could make some adjustment and I find that the tail is reversed. On spoolup, the heli spun like a top. I checked the tail direction and it was correct, but the Gyro was reversed (even though it was 'correct' in the OLED screen)

I switched it around to no avail. So at this point, I'm thinking that I must have a defective unit. For all the hype and all the other people claiming this is a fabulous unit, I can't say that I've had that experience.

If anyone has any suggestions, I'm all ears, but it seem that I may just have to admit that this unit has me beat.

Just for some background, I have setup over 20 helis of my own with controllers from IKON, NAZA, BAVARIAN DEMON, SKOOKUM (The Skookum gave me some moments, but guys here on HELIFREAK set me straight) and others and never had this much trouble. I own a machine shop so when I set up my helis mechanically, I am using micrometers, CMM and Surface plates to insure that everything is level and accurate.

[dchekas]

Which Firmware version are you running?

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Version 1.4 which is the latest as far as I know.

[dchekas]

Not certain why the Gyro would reverse from one day to the next, that certainly is odd....

Just to clarify, have you solved your shaking by reducing gain? Where did your cyclic gain wind up?

A few suggestions based off the information posted:

-Try reducing Stab. Gain a few points. This should allow you to increase the overall main gain. You should end up between 55-70% on the cyclic gain.
-Increasing response style parameter will increase the "locked in" feel. You may want to increase this 2-3pts. It's fairly sensitive, so adjust in small increments.
-CNT.Gain can be increased to increase locked in feel aswell, but I would typically look at the first two suggestions above before toying this.

[hrefab]

I put the heli back on the setup table and have gone through every step. I believe that I have the tail sorted out, how it changed is a mystery to me. I downloaded the updated manual and am re-reading it to see if I've made any mistakes.

The heli spools up smooth as can be, and as it gets to be light on the skids, shows no indication of shaking. My problem today was that it would spin (with gyro reversed that would be expected). I rechecked the mechanical setup and found that it was exactly the same numbers as originally built. I have +12° - 0° -12° as that is the easiest to analyze. I usually don't fly that much negative (I'm not a 3D pilot) but for setup, it's probably a better choice to have equal throws.

I'll give the gain reduction a try and see if that helps. You've helped me out a number of times before so I want to thank you. Helifreak has proven to be one of the better places to get information and support. It's much appreciated.

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I posted this in teh Compass ATOM 500 forum but think that it's still a CGY750 issue
My recent Compass ATOM 500 build has been a real headscratcher for me as the previous posts have shown.

YOu all are aware of my initial problem,s and after going through the software and hardware and making sure everything was exactly as it should be, I'm now trying to sort out this problem

I can get the heli into the air and it's relatively stable. Nothing that some tweaking of gains won't fix. However I get a persistent tail wag regardless of the settings in the radio (Futaba 14Sg). I have changed the gyro from AVCS to NORM, 80% (as recommended) down to 30% and the tail still wags. The tail mechanism is free, the links have been sized perfectly and the tail belt is secure.

Personally, I still think it's an issue with the gyro, but hope that someone here might have a suggestion or have dealt with the same problem. It may be a peculiarity of the ATOM 500, but if so, the post in that forum might find someone to set me straight.

Almost there! Just have to get this last little bit sorted out.

Thanks in advance for any ideas.

[gouki74]

did you check the bearings on the tail rotor if they're ok?

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Yes, brand new, perfect. I tool the Blade holders apart to see if they were assembled properly. Noticed that the bearings weren't greased (from factory) so proceeded to grease them and reassemble them. Going to change the tail blades as well and see if CF blades will work better. Just grabbing at straws here at this point.

Also made sure that the taiul boom was secure and the belt properly tensioned. Going to run a ground wire from tail boom to frame although I doubt that will have any effect.

[marc8090]

Did you pick the correct freq for your tail servo? I have seen an unfixable wag more than once when this was set incorrectly.

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Hi Mark:

Yes, I'm running an Align DS520 which has a 1520us pulse rate and a 333hz frequency.

I'm beginning to think that it's simply a matter of the absolutely awful Compass Tail. For such a nice heli, that's so well made, I'm shocked at the absolute CRAP of a tail that this thing has. The blade grips wobble, move in and out and are in general, something that you might find on a really cheapo heli. The tail on my Trex 250 is more robust than this piece of junk. I wonder if I can swap out a tail from another heli that would be more solid?

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I've been chasing this thing for over a month now and I finally have it down to a slow tic. I haven't changed the controller which is one of the things I wanted to do, but at this point, it's "flyable" using the term loosely.

If I can get some free time I still want to change controllers and see if the tail still wags. I have a good selection of controllers to choose from, Bavarian Demon 3sx, Skookum, 720 Black, Skookum 540, Naza H with GPS. so any of those should be able to pinpoint whether it's a software or hardware problem.

At 50% Gain AVCS the tail wagged Tic..Tic..Tic

I bumped it to 60% and it now wags Tic.....Tic....Tic.... (I hope that makes sense)

Starting at the recommended 80% just doesn't work and will crash the heli (Way too violent).

So I think I'm on the right track, but it's like splitting hairs.