Duho...stupid tail wag

[maddog57]

I need some help w/ my Atom 500. It started with a right side tip over just after touch down of the skids due to dumb thumb of cyclic. The only damage was front skid, tail boom, snapped both tail blades and snapped the link ball off of both tail blade grips.

After making the repairs, I now have a wag that i just can't find the cause of.

Here's what I've done so far trying to find the problem;
fresh grease in main shaft and tail shaft brgs
fresh grease in brg and thrust brg of main/tail grips

replaced the following;
main shaft, feathering shaft, dampers to KBDD lime green, main shaft brgs, tail belt drive gear, main gear, belt,tail shaft, tail hub, main/tail blades...not much left to replace.

I'm FB (I know, I know, ha ha) Align GP750 with Align DS520 servo.

The tail linkage from the servo to the grips is silky smooth. Nice and steady in rate mode, no drift or wag. Replaced the tail servo with a Hyperion DS20x-GCD, to no avail. Tried my trusty GY401 and still have the wag, so i put the 750 back on.

When I spool it up, it hops back and forth (left to right) when it reaches about half speed, then settles out. It didn't do this before. Wonder if this wobble is vibration induced and is messing with the GP750.

I'm at witts end here. I've gone over and over the Atom and am at a loss. I know I'm missing something, but for the life of me, don't know what. Hope you can help!

Thanks and sorry for the length of this post

Chris

[brent.downey]

Not a lot of experience here but have seen my fair share of WAG. LOL

Did you check belt tension after the rebuild?
Also, if your linkages/tail servo position changed it might need a radio
set-up again (refresh) subtrim, etc.

If you took out the main blades in your tip over did you check swash levelling at 0 pitch after replacing your head parts?

Probably double check gyro didn't loosen up/get shifted.

Check tail servo for jitter... this causes wag as well if it's on the way out from the crash.

Or maybe adjust gain setting to be sure.

I'm just throwing a bunch of ideas out there that I have seen or read about.

GOOD LUCK

[leaverus]

Every time i've had tail wag - especially after a crash - it's been a mechanical issue. Apologies in advance if you'll already checked the following:

1) The atom (at least on mine) doesn't tolerate extreme left rudder because linkage to blade grip rubs against hinge arm:



2) Make sure rudder servo arm is not rubbing against bottom of tail case.

[sly the dogman]

Spool up the heli very slowly, put the tail mechanism to the right and very carefully feel the tail shaft (don't beileve you changed it) with you finger you might feel a slight nod on the shaft, to make sure I'd maybe change it.
Just take out the pin and tap the new shaft on top of the old one, don't have to take everything a part.
Hope this helps,

[maddog57]

Thanks for the responces Guys. Atom is my favorite heli and it's been about a month since my tip over that I've been trying to rid it of this crappy wag. So all I've done flying wise, is to test hover after each time I've replaced a part or made an adjustment.

As I posted, I've replaced all the parts you all have mentioned and nothing seems to help.Tried adjusting the TX gain many times and all that does is slow down or speed up the wag.

Leaverus... I'm aware of the linkage bind at full left rudder, so I've adjusted the gyro travel so it stops just a hair before it binds. I will check that again though cuz I forgot about that issue. And I did find the ball link arm seemed bent upward, so i used my heat gun to heat it up enough so it could be straightened.

Brent downey... I checked all that you suggest. Amazingly, the main blades didn't get hardly a scratch in the tip over..I couldn't believe that! They were still perfectly balanced still. But I changed them with new ones anyway, didn't make a difference. GP750 seems OK, but to prove it I swapped it with a GY401 I know works... no change. So the 750 is back on the heli now.

Sly, hey man, how's your Atom flying these days? All's good I hope. I replaced the tail shaft as you said and that too made no difference. I've never had a problem removing the pin. Have read a bunch of threads where people have had a hell of a time removing it.

Sooooooo... keep the ideas comming Fellas. Don't know how much longer I can take it without my Atom. It IS flyable, but I don't want to while it's still wags. Can't believe that's good for things.
I also believe the problem is mechanical in nature. I'm sure with HeliFreak help, I can fix it. Thanks again,

Chris

[skunkworx]

Sounds like you either bent the tail shaft, tail hub or the feathering/main shaft. Sometimes you get wierd little instances where the shafts will get damaged but no damage to the blades.

As to the tail though, if it took out your blades and grips, I would definitely suspect the shaft or the hub. I've bent up tons of Atom hubs but rarely a tail shaft. Bad bearings rarely if ever cause vibration type issues, but you can inspect those as well.

The way you inspect the tail shaft it to take off the hub and spool it up a little (might want to remove the main blades which you'd need to remove in order to check the feathering shaft anyways). Since you'd have the hub off, you can check it for bends either by eyeballing it or taking the grips back off. If it all seems normal but still has tracking issues, I'd go ahead a replace the shaft and hub and see if that fixes it. Same for the head shafts.

[sly the dogman]

Do you set your gyro in rate mode before HH, with the servo rod ajusted and all ?

[maddog57]

Usually trouble shooting my heli problems is part of the fun of helis for me, but this wag is getting frustrating. I'm really glad you guys are here to lend a hand. Gotta love the HeliFreak community.

Skunkworx, thanks for your input. The first thing I started looking at was the tail mechanics.. I've bent a tail hub more than once, always resulting in a wag. I have replaced both the tail shaft and hub, ( did a test hover after each piece was changed), and niether made a difference. Also have changed main and feathering shaft along with changing the OEM dampers to KBDD lime green ones (had lots of slop there and thought that was creating a vibration). No change in the wag. Changed out the main shaft bearings as well... nothin' !

Sly... yeah I've set up the GP750 in rate mode, as with any gyro I've used. Tried a spare GY401 that I know works well, but no change. I've been up and down with the gain settings and it only changed the speed of the wag. Tail linkage is silky smooth.

I'm bound and determined to find the problem and won't stop til I do. I'm gonna keep going over and over Atom and eventually I'm sure I'll figure this out. It's a great learning experience...

Anyone think of anything else to look at?

Chris

[sly the dogman]

Just a shot in the dark here ; have you tried strapping the gyro down with a strap of velcro or a ty-wrap ?
Sometimes the way the gyro is placed can result in a tail-wag, maybe also turn the gyro 45 degrees on the tray......
I have that Kyosho double pads under mine, DS760, yea man I got paddles too, isn't great.

[rc-bender]

Lurking here because I'd like an Atom!

I know it's not an Atom, but I'm searching for a vibration on my 600 that's causing issues and it's coming down to bearings. Everything else is new and true. I'd go through it and check for any that aren't totally smooth, despite the greasing you've already done.

I've compared used bearings that I thought were good to brand new ones in the package and was surprised how much smoother the new ones were.

[maddog57]

Sly...yeah I love the paddles too. Maybe someday I'll go FBL. As far as strapping the gyro down... no I haven't because the GP750 manual says not to. But hey, I'm desperate now and will try anything .

Mr. Bender...I do think I'm generating a vibration that's messin with my gyro. I replaced the main shaft brgs, but no others cuz i don't have any for the tail shaft. When I was inspecting all brgs when I greased them, one of the main grip brgs felt just a wee bit "gritty", I don't know if that could cause a problem or not. Maybe i should buy/change all the brgs and see what that does? I hate to keep changing parts that don't seen to help, but am at a loss as to what else to do.

Won't be able to work on it anymore til Sat., so I'll post again them. Thanks to all for your input.

Chris

[skunkworx]

I fly with pretty gritty bearings all the time. Never caused any issues other than it's a little noisier than usual or a little rough. Never got a wag from anything other than incorrect gyro gains, crappy gyro tape, or bent parts.

It's possible that you simply had your gain too high and when you replaced a lot of the parts it won't need as much? I've seen this a few times throughout my career, so even if it's a rare chance, try dropping a couple points and see if it goes away but still holds rock solid. If it starts to feel weak though, you definitely know it's something else. Did you change tail blades by any chance? Did you check them for balance and COG?

How does your belt look? Almost sounds like it could be a chewed up tooth/teeth, but that would likely be a little on the intermittent side. Is your driven gear bent or wobbling? Is your tail boom bent and/or the belt rubbing inside or on the tail case? Maybe tail gear/pin?

Small chance of it happening, but is your motor shaft straight? A tiny wobble there would send vibes like mad through the whole airframe. It would be more evidenced by white flaking of the main gear. If you notice any, check the gear itself, the motor shaft as well as the pinion.

Did you bend up and of the head parts in the crash? (usually you take out the grip arms, but it's possible to have bent a grip or the head itelf or the yokes).

Unfortunately, that pretty much goes over what's left of the whole heli. Not much else could be causing it. It's probably something really superfluous. I chased a wierd vibe for almost a year on mine. I ended up crashing it a replaced a few parts and it flew great after that. No ryhme or reason to it.

[rc-bender]

My buddie's logo 600 (w/ Skookum FBL) was suffering from a tail wag w/ bad radial bearings in his blade grips. I've never had vibes from bearings shoot me in the foot yet, but it's a direction worth looking at once you've ruled out all the blades, shafts, tail servo and motor.

My vibes only show up when the main blades are on, otherwise it's smooth as silk. It has to be something in my head that only blades can exacerbate. Could be a blade grip bent ever so slightly.

Look at it this way maddog, you'll have a great crash kit replacing parts one by one until you nail it down.

[maddog57]

Skunkworx, I've changed just about all the tail drive parts you've suggested to inspect. Belt, main pulley, boom, tail shaft, tail shaft pulley, tail hub, tail grips and blade (tho didn't balance them, but will).

Main drive parts changed are main shaft, main brgs, feathering shaft & dampers to KBDD lime greens, and main blades (did balance them). Can't find any bad parts in the head, as far as i can tell.

I was really surprised at how little damage was done from the tip over, probably due to the fact that TH was on and the heli just kinda slowly rolled over on the right side. main blades didn't have a scratch and didn't even bend the fly bar.

You mentioned the motor shaft as a potential problem and I had thought the same. I've taken it out and pulled the pinion off, ran the motor to see if the shaft is bent. It looks good as does the pinion. Is there a certian way to detect a bent motor shaft besides visually? I could put a dial indicator on it if you think I should. Don't see any flaking/dust off the main gear either.

I also adjusted the gyro gain too many times to count. From 52 (goes to rate at 51 and below) to 95, which by that point the wag was crankin'. I did it in 5 point incraments and the only change was in the speed and amount of travel in the wag from L to R. Berlow 60 the tail control gets mushy.

When the heli is in the air in HH, I can hear the motor surging in sync with the wag, In rate, there's no drift, no wag.

Is it possible for the problem to be electrical/electronic in nature? I even tried removing the BEC leads and tried the BEC of the CC Ice 75 with no change.

I can't find a thing wrong mechanically with Atom, though someone like yourself with much more experience might.

rc-bender, thankfully I have a pretty good stock of spare parts. Any part I've changed out has looked fin to me. No bent shafts, no missing teeth, nothing.

I'll find the trouble if it kills me! I just know that when I do find it, it'll be some small, dumb little thing that'll make me go !!!

Thanks guys

Chris

[maddog57]

Forgot to mention... I removed the main blades and while holding the boom, spooled it up to feel for excessive vibration. Had read about doing this in another thread. Can feel some, but just like a little"buzzing" type of feel, if that makes sense.

Chris

[skunkworx]

Things that make you go hmmm...

Well, I hoped you saved all your swapped out parts as a lot of them are likely still good (if you swapped them for troubleshooting anyways, if they were damaged, toss 'em).

The motor sounds to be ok. Dial indicating certainly won't hurt to try, but couple be an excersize in futility (or at least peace of mind!). If you don't have any flaking or areas of significantly raised friction on the gear in certain spots (sometimes the gear goes out of round in the moulding process but will usually flake off during flight as the pinion wears into the plastic) then you'r emost likely in the clear for a bent motor shaft. Besides, it'd take one heck of a hit to bend the sucker. I've only ever bent up one on a 6HV and it totalled the bird if that's any indication?

Your Gyros gains sound right on the money. Your mechanical is perfect if it gets mushy below 60 and wags like mad above about 75% to 80%. I set up one once that need like 92% to get it locked in which simply meant the mechanical gain was way too low (servo ball spacing was incorrect) so your diagnosis there sounds good to go.

Electrically I could believe. If the motor is surging at all, something isn't right. I know sometimes they have little hiccups, but if there is a pretty sizable fluctation in motor rpm, you might have something amiss in your settings or your governor is wigging out on you. Any possibility of getting a quick video of it showing the symptoms? I have to admit, this one is starting to kick my butt. Unfortunately, I can almost guarantee it's something simple we're missing. Probably something I should've thought of from the start so hopefully we nail it soon!

[maddog57]

Yeah it's been kicking my butt for like a month now. I posted about it as a last resort.

I did keep all parts that were changed out for trouble shooting purposes as they apparently aren't the problem/bad.

I'll work on getting a short vid posted. I've never done any recording so it may take a day or two to get one up.

Today will be devoted to my Atom.

thanks again,

Chris

[leaverus]

i realize you want to find the source of the problem and you know, i understand this may not be an option for you but sometimes it's not worth the time spent chasing down a problem; it's time that could be better spent doing other stuff - spend time with your wife, kids, whatever. otoh, maybe this is time spent well for you, i dunno. but if it isn't and money isn't a concern, i say just replace the entire tail with new parts and have done with it.

[maddog57]

That's a good point. Money isn't limitless, but I'm lucky in that I can afford what I want. I have two 400 size and a 6HV (STILL in the build phase) that haven't been played with for a while cuz with my life being really full (grand kids, work, wifie time...) I have squat for free time, hence my crappy flying skills, LOL. but yeah, this is quality time for me.

I'll keep at it with Atom...#1 cuz I truely love this heli, (am a big Compass fanboy), #2 I will not let this wag best me! Plus this is great learning experience foe me. #3 it's awesome to talk with other Freaks... I don't post a lot, but am on here multiple times just about every day.

Chris

[sly the dogman]

Had the exact same problem a while back changed everything you did on the heli. Then got tired or pissed tried another gyro and after carefull settings, wag is gone but a slight drift that I can live & fly with. I had a GY520 changed for a DS760.
Real bummer, hope you get it right soon.