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Goblin 280 SAB Heli Division - Goblin 280 Helicopters


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Old 02-06-2019, 11:13 AM   #21 (permalink)
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Ok, will give that a try next.
Thanks
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Old 02-07-2019, 06:14 PM   #22 (permalink)
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I moved the ball back in on the tail servo arm, back to 8mm from 10mm.
I see no change in the way it acts at 3200 or 3500. Worked with gain again, up and down, can`t find the fix.

If there are any more ideas of what to try, please post!
Thanks.
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Old 02-07-2019, 06:54 PM   #23 (permalink)
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Sounds mechanical. Check every bearing and assembly again. If something feels bad you may have a bad part. Odd but it can happen. Unfortunately tail issues seem to be common on <300 size helis. And vast majority of the fixes are mechanical. Just tear the entire tail apart and then reassemble very carefully. I did that mistake on my 420 I had mis-assembly and horrible un-tuneable wag.


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Old 02-07-2019, 08:20 PM   #24 (permalink)
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Will do. The tail movement feels good and smooth, but I will go through it again.
Yes, I am learning that the small heli`s are tail sensitive.
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Old 02-07-2019, 08:55 PM   #25 (permalink)
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does the thrust bearing race, the one with the smaller inner diameter, go easily on the shaft for the tail blade grips? mine barely fit... obviously it has to be apart, but check. mine had very hard to see machine marks that I polished out with 600 grit and a drill.. after that, it easily went on.. if it fetches up when all together, that's what hangs up and could cause a wag. the tail grip assembly should be able to move in and out by hand a little bit.
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Old 02-08-2019, 06:55 PM   #26 (permalink)
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Working on the tail. I have taken both grips off and bearings out. Both of the thrust bearing races slide on the hub with ease.

Two things I noticed; 1) the inner thrust bearing race is a tight fit in the grip.
2) one grip feels really free to turn when assembled on the hub, but barely has any end play. The other grip has a small amount of drag when assembled on the hub and can feel a small bit of notchy when turning it. I also can feel no end play.
Can the shims that are between the outer bearing and inner thrust race be removed?
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Old 02-08-2019, 07:14 PM   #27 (permalink)
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Someone correct me if Im wrong, but I believe you want the same number of shims on both sides. So if you want to remove one from one side, do it to the other. The idea is to keep everything symmetric.

Any non-symmetry in how the two grips feel when installed does need to be addressed. They should have the same amount of play (zero play) and neither should feel notchy.

Your two races have different inner diameters. Make sure the one with smaller inner diameter is toward the outside, away from the hub and toward your blade.
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Old 02-08-2019, 07:45 PM   #28 (permalink)
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both need end play.. or at least mine did.. the thrust races are too tight in the grips. so when you spool up the heli, one grip is tight. I had to lightly sand down the outside of the races on another heli. on these small helis, it doesn't take much to mess up the tail.
I wouldn't take out any shims.
ide be willing to bet a race isn't seating all the way in the grip..
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Old 02-08-2019, 07:46 PM   #29 (permalink)
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Yes I understand the two different races.

There is one shim on each grip installed where I previously mentioned as the manual showed.
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Old 02-09-2019, 07:42 PM   #30 (permalink)
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I have taken both grips back apart, cleaned and looked again. Reinstalled them and still one has a little drag and slightly notchy.
So I swapped the grips to the other side of the hub, and the tightness went with the grip.

All I know to do is to try some of the Lynx grips. Anyone know if they come with all bearings, including the thrust bearings?
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Old 02-09-2019, 08:50 PM   #31 (permalink)
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do the races fit easily in the grips without the shaft? just bare grips? ill bet one is a tighter fit than the other side.
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Old 02-10-2019, 06:26 AM   #32 (permalink)
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Both of the inner thrust bearing races are a light press fit. They have to be pushed into the grip with something and pried out.
I have no means to do anything to the plastic grip and the race is so small and hard, I can't work with it either.
However, I think the problem is with the thickness of the bearing stack or the grip that isn't giving it end play
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Old 02-10-2019, 06:41 AM   #33 (permalink)
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Quote:
Originally Posted by bclark View Post
Both of the inner thrust bearing races are a light press fit. They have to be pushed into the grip with something and pried out.
I have no means to do anything to the plastic grip and the race is so small and hard, I can't work with it either.
However, I think the problem is with the thickness of the bearing stack or the grip that isn't giving it end play
theres your problem..they shouldn't be that tight in the grip. when that tight, once spooled up, they fetch up where they sit and aren't allowed to move out slightly or float.. so their in a bind.. all the time.. lightly sand the outside of the race so it fits better in the grip. most of mine drop right in.
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Old 02-10-2019, 07:17 PM   #34 (permalink)
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Quote:
Originally Posted by tonys-heli View Post
theres your problem..they shouldn't be that tight in the grip. when that tight, once spooled up, they fetch up where they sit and aren't allowed to move out slightly or float.. so their in a bind.. all the time.. lightly sand the outside of the race so it fits better in the grip. most of mine drop right in.
This is not meant to argue with you, this is so I can learn and understand.
So what does it matter if it is tight in the grip if it is against the shim and bearing where it should be anyway.

I`m going to fix them just as soon as I figure out how to sand them down, but just curious so I can understand how the thrust bearing works.
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Old 02-10-2019, 08:30 PM   #35 (permalink)
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when their tight in the grip, they could be offset of the shaft. making everything tight under load. besides, their thrust bearings and shouldn't be tight in there.. theres a diff of tight and slip fit.. the other bearings should be tighter..
I just spin up a dremel with a sanding disk and do it by hand.. very carefully rotating the race. your barely taking anything off.
this is what I do.. done it a bunch of times. I cant count how many used helis ive bought and there was always a tail problem.. one was new and the thrust bearings were forced in and shards of the grip were still in there.
once mr Dremel was used and the junk removed. nice fit of the thrust bearings, nice smooth tail and no wag either.
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Old 02-10-2019, 09:21 PM   #36 (permalink)
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Thanks for the information
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Old 02-14-2019, 06:23 AM   #37 (permalink)
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After reading up on this problem in great detail. I have come to the conclusion that the most probably culprit are the tail blade grips. Even though they may be buttery smooth, it is possible that they are being caught up when being flown.

I decided to replace the stock tail blade grips with the Lynx metal tail blade grips. The wag has completely gone after this.
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Old 02-15-2019, 04:52 AM   #38 (permalink)
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I'm going to try the Lynx grips next myself. Will order this weekend.
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Old 04-16-2019, 06:17 PM   #39 (permalink)
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Been a while, but I finally got the Lynx grips installed. Test hovered today and saw no change in the tail wag at all.
I have looked this thing over and can't find anything mechanically wrong.

Any ideas next?
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Old 04-16-2019, 08:35 PM   #40 (permalink)
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I own a Fireball that is running a Brain2 and the OEM recommended SAB tail servo. Previously I had a kst tail servo in it with an Ikon v2 and that was a bit easier to tune than the current setup.

If you want, shoot me a PM with your email address and I'll send you a picture of my gains.

My Fireball's tail was not easy to tune but in the end I got it to the point where I am very happy with its behavior. It's not perfect, but certainly close enough.

One thing I would suggest is to turn off your governor to see if that makes the tail any easier to tune. If so, then I would suggest turning down the P gain on the governor and/or getting rid of the drivetrain lash between main motor and main rotor.

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