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HomeAircraftHelicopterMain Discussion › Drive gear backlash concern
01-14-2009 06:37 PM  9 years agoPost 1
maveric4

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england

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Hi Guys,

Just built a Trex 600 super nitro pro and need help from the community regarding backlash on the torque tube drive assembly.

There appears to be backlash between the plastic gears in the tail box assembly and also between the plastic gears in the front boom tail assembly. There is also more betwean the main gear where it picks up the drive to the tail unit.
When assembled if you hold the bottom part of the auto unit so it cant move and rock the tail rotor blade assembly there is a lot of movement, I am concerned by how much.
With my raptor 90 there is pretty much nothin but then you shim the gears on that particular model.

Just wondering what you guys have on your models and will this be ok.
I am worried about stripping gears where they dont mesh to well.

Cheers

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01-14-2009 09:16 PM  9 years agoPost 2
TaleGunner

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Deer Park WA

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how much is there?
I have 2 TT on 600s and they both have some slop hundreds of flights with no issue.

CRASH! GLUE! REPEAT!
Spectra-G, Ion X-2

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01-14-2009 09:38 PM  9 years agoPost 3
maveric4

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Hi TaleGunner,

Thanks for the reply.

Its a bit difficult to get tottaly accurate but here is what I did.

Maybe you could check yours and I can use it as a refernce.

I put the tailblades out strait, held the bottom of the auto unit so it could not move then rocked the tail. I put a block just up against the tail tip in one direction then rocked the blade the other way to take up the slop and I had 11mm between blade and block.

Be interesting to see what you have especially if yours has been flying with no problems.
Just seems to be excessive.

Cheers

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01-14-2009 10:10 PM  9 years agoPost 4
Four Stroker

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Atlanta

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You don't have a problem. Anything under 10 degrees or so is fine.

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01-14-2009 10:11 PM  9 years agoPost 5
TaleGunner

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Deer Park WA

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yep yer fine go fly it

CRASH! GLUE! REPEAT!
Spectra-G, Ion X-2

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01-14-2009 10:30 PM  9 years agoPost 6
predatorman

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Falkland Islands

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Better than having it tight, tightness will produce more friction and wear...you will get worn bearings too.

You need some backlash for a healthy drivetrain.

Quality takes........time!

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01-17-2009 12:50 PM  9 years agoPost 7
maveric4

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england

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ok guys

Thanks for the replies, I know that none of the gears in the gear chain should be tight but I have never built any heli with this kind of slop.I have checked and the total is a bit less that 10 degrees and I just cant help feeling that that will put some stress on those gears when pitch pumping.

Suppose we will have to see.

I did expect better from align but they are one of the cheaper brands of heli and I guess I have found why. ( the old saying you get what you pay for springs to mind).

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01-17-2009 01:02 PM  9 years agoPost 8
predatorman

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Falkland Islands

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I wouldnt be too harsh on them

My Century Predator had a few issues with backlash too...but with some filing here and there and some tweaking it runs sweet.

Trouble was the main gear was set quite high...and the flat spot on the tail drive pinion/cog wasnt long enough...the cog can ride up and down the shaft for adjustability...so once the blacklash is looking good and you go tighten the grubscrew for the cog...its sitting right over the end of the flatspot/keyway....go figure?

I suspect that most brands of heli have their weaknesses, my Trex 450 XL had a CRAP main gear setup...now sorted with some common sense.

Rob

Quality takes........time!

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01-17-2009 04:37 PM  9 years agoPost 9
maveric4

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england

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Hi predatorman,

Thanks for the reply bud.

I am not intending to be harsh, But the good old raptor that has been around for years had a better gear train than this one. A shim method was used on them where you moved the output shaft sideway to obtain a perfect gear setup. The same method was used for the front set of gears, of coarse we are talking the 60/90 here as the smaller ones were belt drive.
Now if we look back to when that one came out engineering tolerances were not as good then as they are now. Today the are incredibly good.
So one just wonders what went wrong, I dont beleive there are any excuses today but there we go just my opinion.
Like you said with a bit of work with some filing and some shims the same can be done and we can get a fix. Just a shame to have to hack a new model about with todays engineering.

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