Tail gear mesh getting loose over time

[Daniel880516]

Hi guys, probably have around 40 flights by now with my xxtreme 700, and noticed this.

You can see the middle gear is wearing out already, and the mesh is getting very loose a little bit more than 1mm for sure.



Thinking I should replace the middle gear and shim the side gear?

[dahld]

This issue has been discussed many times in the past, as it was one of the first things to get attention when the Logo 700 first came to market. We've always had to tighten-up the tail's mesh after the first 10-20 flights when breaking-in a new set of gears, but after that, they last a long time without attention.

The short version of the procedure is (I wish I had the links to the many threads from the past about this this, as they go into a lot of detail), is to remove the tail shaft, remove a small amount (only about a 1/2 mm...you can remove more, but it just takes more shims later) of the gear molding from the right side of the gear (looking from the rear forward). When reassembled, that allows the bevel gear to drift more to the center, tightening-up the mesh. Use shims to get rid of the now present end play on the left side of the gear you've created, and by shifting shims between sides, you can get the mesh they way you want it, with no end play.

Sounds like more of a hassle than it is. Once you do it, then if you ever need to tighten the mesh again, just take one shim off the left side, and transfer it to the right. The mesh tightens, and the end play stays the same.

(-: Dave

[Daniel880516]

Originally Posted by dahld

This issue has been discussed many times in the past, as it was one of the first things to get attention when the Logo 700 first came to market. We've always had to tighten-up the tail's mesh after the first 10-20 flights when breaking-in a new set of gears, but after that, they last a long time without attention.

The short version of the procedure is (I wish I had the links to the many threads from the past about this this, as they go into a lot of detail), is to remove the tail shaft, remove a small amount (only about a 1/2 mm...you can remove more, but it just takes more shims later) of the gear molding from the right side of the gear (looking from the rear forward). When reassembled, that allows the bevel gear to drift more to the center, tightening-up the mesh. Use shims to get rid of the now present end play on the left side of the gear you've created, and by shifting shims between sides, you can get the mesh they way you want it, with no end play.

Sounds like more of a hassle than it is. Once you do it, then if you ever need to tighten the mesh again, just take one shim off the left side, and transfer it to the right. The mesh tightens, and the end play stays the same.

(-: Dave

Thanks very much Dave, really appreciate you taking the time to reply, I knew I've read it somewhere before, but also wondering the condition of my gears if they need to be replaced? Thanks again!

[Highflyer028]

Is this also true for the 800? I have a slight backlash in my tail gears. I'm not exactly sure what part your sanding down and where you are shimming. Pictures would be great.

[rcmarty]

I like to have it still a bit of what i'd consider loose , the inner teeth need to engage some or have the ability to do so.

My 700 has the wear marks on half the teeth also.

I'm going to suggest not shimming to tight.

https://www.helifreak.com/showthread.php?t=544860

I'm also replacing the gears every 100 flights now

Martin

[Highflyer028]

I also just found this.....

[ame]http://youtu.be/j0UsN_OMT7E[/ame]

[rcmarty]

I've seen that one before.

Not overly concerned about that one in the vid.

These gears are trying all day long to repel one another. Clearly the bearings are staying in place as it take a click to get it to pop in/out. Pop it in for mesh setting.

Mine front set on my 800 the entire assembly ( gear , 2 bearings , and spacer sleeve ) would slide easily back and forth. I can assume that the entire assembly could slide back and forth at the tail is loaded and unloaded.
So I set the bearings and sleeve with a little smear of the green retainer locktite.

I do hope we can get a little vid made up of someone setting an acceptable amount of backlash.

My theory ...

Mikado plastic , yes this stuff is tough , very tough. When a tooth fails I can see it making a huge mess ( it did for me ) as the gears provide no give and don't shatter/break/etc. Double edged sword you might say.

Martin

[Highflyer028]

Yea makes sense. Where did you find the shims at?

[rcmarty]

I think my kit came with a little baggie with a few in it.

If those are lost , get the front gear set shaft kit , comes with shims.

http://rcflightstore.com/product_inf...oducts_id=4572

$5 you get the shims and a bunch of bits for the suprize bin

Martin

[Highflyer028]

Is this the place you remove the plastic?

[dahld]

Yes.

[christoffer]

Is there any need to shim the front gearbox? It's quite hard to access the gearbox to check the gearplay whitout tearing down a lot of the mechanics...

[dahld]

In theory yes, but in actual practice, it seems a moot point. Due to the hassle of getting to the gears to do the shimming, we decided long ago when we got the first machines for prototyping to just fly 'em until they strip, and see how long they last...and try to develop a data base over time as to how long they last unmaintained.

Well...we've never stripped one! I don't know if it has something to do with the idea that the further back along the tail's drive train, some dynamic requires more need for the mesh to be maintained, or something about the mechanical design of the front gear box that makes the gears more immune? I don't know.

The front gears seem to get worn up to a point, and then the wear slows way down. They eventually of course must fail, but we haven't found that point yet.

So I'd say for being on the safe side, take it apart over the winter and check / shim as needed, and they should be good for the whole flying season.

(-: Dave

[Highflyer028]

Hey Dave last question. I think haha. So the main focus is on getting very little backlash on the tail gears to prevent failures. Have people reported or have you had the back tail gears strip in flight? And as far as the front tail gears go, does Kyle fly them in the stock setup per the manual and no shimming? In the end you say it might be advisable to shim them also but I think it's pretty safe if Kyle can fly it as hard as he does and never had one go out on him.

I am simply looking for piece of mind to gain confidence in the machine again.

[dahld]

As I mentioned in my last post above about letting the mesh on the front gears loosen-up during prototyping to see just how long they'd last to determine a data base, we did the same thing on the rear gears. And, we did eventually experience a failure by letting the rear mesh get too loose, and I've heard of a few others as well. But as I said, never the front gears...go figure?

So since then, we fly a new set of gears for some flights (10 flights maybe, whatever), keep an eye on them, and when they start getting loose and get some play in them, we shim 'em back to just enough play to feel. They then last for quite some time without re-setting them. But checking them is always part of the pre-flight.

They of course over time loosen-up some again, but they are pretty resilient, and some play is OK. It's hard to describe how much is OK, and what might be considered too much. Kind-of like trying to answer the age-old question, "How tight should the belt on a Logo 600 be?". How do you describe that? You can show someone, but to describe it on the forum is hard

So anytime we have the front gear box out of the heli for any reason, we check and shim the gears back to "just enough play to feel" status, and forget about them until the next time we break a frame and have access to the front gears. During the initial build, we of course check the feel of the mesh, but it's usually pretty good new. Can't remember having to shim anything new. Just after some wear.

(-: Dave

[Highflyer028]

Anything special with the front gears? Any trimming of plastic or is it simply putting a shim or two in???

[dahld]

Just shimming...no plastic removal necessary with the front gears.

(-: Dave

[rcmarty]

I'm assembling the front gears as per manual.

I did shim them ( took 1 shim from top to bottom ) and ~20 flights later they melted

( after shimmed there was still backlash , smooth all around with no high spots. I had all align machines previously so gear shimming/setting expert ..lol)

https://www.helifreak.com/showthread.php?t=544860

Funny thing was I working it hard on the previous flight , but the flight they failed on was a mellow flight. My allergies were acting up so I was doing a discharge flight. FF quick elevator 1/2 flip to inverted.

I did move 1 shim on the vertical gear previously and green loctitied the TT drive gear bearings to the housing ( they would fall out under its own weight) and got ~20 flights before the failure.
Grand total 117 flights on heli.

I've got it all rebuilt now ( about $ 1200 ) and I went with the stock shimming as per manual.
It makes a rattling sound on spooldown again. This time I won't be shimming to remove rattle , same with 700

I'm suggesting not to goto far on the shimming.

I make sure the inner teeth have the ability to mesh with one another even if they don't engage fully all the time.


Dave ..

Do you have a pic of the gears you stripped out ?

Some speculation about the Mikado plastic. Yes it's tough , to tough ? My gears are melted , still stuck together melted ( even after getting those darn bearings and sleeve off)

My next question is do they strip ? Or just melt ? I can see a fighting chance of saving it with a tooth chunking out and making a thunk thunk racket. My front gears just loaded and loaded up motor and lost all headspeed , no small feat for a 14s powered system !!

Martin

[Highflyer028]

Well I think I will let the front gears go. Keep my fingers crossed on them. I watched some videos of kyle's flights tonight and thought damn if they can stand that abuse then I can probably have a little backlash in mine. As for the back I did the process and got minimal backlash. Not as tight as mr.dahl explained (atleast I don't think so) and am going to go with that. Give it some room to change with temps and what not. I could probably take a tiny more off and add one 0.1mm shim to make it like suggested but kinda nervous to keep taking more off. I feel it's pretty damn close now. Hopefully it will work flawlessly for the next 500 flights and I will be happy.

[gadawg58]

Interesting ... Have over 300 flights on my 800 and have never shimmed anything. Think I'll check the gear mesh in the tail again the in the morning to make sure I'm not moments from disaster! Have new 700 and also nothing shimmed and after about 20 flights all seems good.