Arrggghhh! My TT tail gears are ripped off... again!

[pck]

This is my 2nd set of TT tail gears i had changed since converting my 200 to TT and the gears had ripped off again!!! I was testing my gyro settings and then switch my idle1 up. There was a loud sort of bogging sound coming from my main rotor, so i turn off idle1 and landed it. Without doing anything much, i throttle up again and noticed that my tail rotor were not moving. Upon closer inspection, i noticed my tail shaft gear had a couple of teeths ripped off! :(

I am using pretty much stock on everything. Motor, esc and 15/9T pinion gear on my motor for the TT combo.

Looks like i better move back to belt drive.... :(

[Jetleaf]

The bogging sound may have been the gear on the tail shaft slipping and it may have became unmeshed with the gear on the shaft. Mine would have that bogging sound too and I noticed that it was the tail rotor makeing the sound. Also there should be some clearance between the gears, definitely don't have them tight.

[pck]

Thanks for the advice, Jetleaf. :thumbup:

When you say, to have some clearance between the gears, are you referring to the gears at the tail or between the motor pinion gear and the shaft gear in front? (Sorry, i don't know the correct terms for those gears.)

Honestly, are there any difference between TT and belt drives? I must say, both my Trex and my mini titan are belt driven and i have not had any problems so far...

I am contemplating switching back to belt as i can't get any spare parts for TT in my local hobby shops.:thinking

[Jetleaf]

All of the gears, should have play, slop, clearance, or a space between each other, a very small amount of space mindyou. It's measured in thousandths of inches on a lot of things. The 200 is a little more involved because of the dual motor pinion and main drive gear and the shaft umbrella gear all come together. It's to allow for imperfections in the drive train components, gears that aren't perfectly round and basically to freeup the whole system. If every thing is pushed up all tight it has a binding affect and that makes it more stressful on the motor, battery, bearings. You have an increase in heat because of the increased friction, efficiency of operation goes down and wear goes up, uhh not meaning to ramble. It's not good. Any of Finless' vids where he installs a motor he explains it. Differences between the two? Yeah, no belt to deal with period. Did you ever changed the belt on your T-rex? Eliminating a possible cause of static. Assuming one can keep the tailblades from touching anything except air, it's the way to go. That is assuming a lot for several of us, myself included. Beginners aren't encouraged to go shaft drive. I say as long as you have a credit card enjoy, lifes just to short. If your LHS doesn't have parts go online. I haven't had an issue with parts availibility.:smokin:

[psindrup]

You convinced me: I will stick with my belt driven tail for now ...

Peter

[pck]

Been flying the TRex and Mini Titan for > 1 year and i couldn't even remembered when was the last time i changed the belt on those birdies.

I dunno, but the wear rate of the TT gears on them Ep200 just seems so... quick... maybe the it's the meshing problem and maybe i shld just lube the gears.... hmmmm.....:dontknow

Since i got one more spare TT shaft gear left lying around, i will probably try it one more time. Makes no sense to order a couple of these gears online and pay a hefty shipping fee just for them though...

[questionmark]

When I got the SD RTF and uses it for a little while + having issues with crown on the tail ( don't know the name for it) it was not tight arround the shaft (had to CA it couple time) the crown on the motor wear out quite quickly too.. So bought replacement part, including full tail box...but mistake...bought the one of the belt version. Anyway I could modify (grind the stoper in the ring holder) and uses part on the existing tail box. Now it seems I'm fine after a full week using it I don't see sign of wearing. the piple ( don't know the name :-) ) inside the tube moves a tiny bit so there are a bit clearence between crown and motor and on the tail...so far I'm fine.

But I find all this quite complicated. The SD tailbox is a modification of the SE it seems they removed the boom stoper in the holder ring :-) again don't know the name of the tail box and added spacers for making the tailbox wider to accomodate the crown in tailbox...Its a pain to change it.....

I heard people saying TT is more efficient than belt, but maybe more noisy....is that really true?
if more efficient battery wise I keep TT else I go belt as it seems overall more simple....

[Buzzkill]

Just a thought, I sure wish someone could mill a set of metal gears for the TT. Ya it would make more noise but who cares? The load from the 200 wouldn't be enough to cause concern and they would certainly be stronger, heck I'd even grease the damn things.

What would be the problem with metal gears?

[stoatnchips]

What would be the problem with metal gears?

Not totally sure Buzz but i'd guess it might make the tail EVEN heavier if you replaced both bevel gears in the box... Ali is not as 'Hard' as this plastic so sure, the Ali would "Plastically Deform" on impact rather than break like the plastic, but it would wear out a LOT quicker!! Also remember how fast some head speeds are running and the gear ratios... consequently how fast the TT is rotating!!! With a heavier material such as Ali you would have more inertia in the TT... slower spool up and response and BAD vibrations if the gear balance was just slightly out... There are a couple other minor things but IMHO the trade off of an Aluminum Alloy gear train vs plastic is just too high!

[Buzzkill]

I was thinking the pinion material. But good points.

[Gr4yb3ard]

I'll have to agree with Stoats,

Al will wear badly as a gear material, and if you lube it, you'll sling black gunk everywhere.
What we need is a spiral cut gearset, (like a car differential), made out of Delrin, or similar, and maybe just one hooter larger as well, from what I've seen of the tt set.

Gr4yb3ard
"....considering wenching as an art major..."

[Buzzkill]

Isn't the main pinion brass?

[Gr4yb3ard]

I'm sure it is some brass family alloy.

That's common for the smaller gear to be harder (it wears more and weighs less).
Gears and bearings are commonly made of dissimilar metals to elimate a process called "Galling", where flakes of metal build up, smear, and break away.
Not really necessary with plastics though, most of the stuff is pretty much self lubricating, i.e. the wear material does a good imitation of a solid lube.

Another note, the two gears should have a different tooth count, so that they can "hunt", that is wear against each other in a cyclic pattern. When wear sets in the gears get smoother rather than rougher, but if one tooth goes, it spreads the joy all over the gearset ;-)

Gr4yb3ard

[Buzzkill]

Hmm...I understand all that. At the same time that would be asuming we don't crash. Basicly I think metal gears would out last the current plastic ones because the majority of people will destroy both in a short time anyway.Metal gears may take more of a beating before failure. As in I might get two crashes out of metal gears instead of one with plastic.

[Gr4yb3ard]

Brass and steel would work well, or better, brass and plastic, but bottom line, I think if they'd just make them a bit beefier and with a spiral tooth, this would spread the load and it would not take much more to make them pretty much bullet-proof.

Sorry you're having problems, I *really* want the tt myself, but if Buzz can't make it fly, I'm gonna have to think.

Unfortunately, I think there's not much we can do as far a a mod for the gears themselves short of tooling a mold and getting into the gear busine$$.

But maybe, just maybe, does it look like you could set up a "shear-pin" arrangement???
That's how they used to save gears in equipment back-inna-day.

In this, the (probably front is best) shaft gear is set up so it normally spins on the shaft, but a pin is installed through the collar and shaft. The pin is just a bit stronger than needed to handle normal loads, but shears off when things get hairy. In this case maybe a tied loop of fishing line???

Gr4yb3ard
"...I've done stranger stuff..."

[Buzzkill]

Don't get me wrong, the TT flys great just sucks in a crash. I think the best solution would be for me to stop crashing lol. I wonder if blue locktite instead of the set screw would work? Maybe it would break way in a tail strike?

[Gr4yb3ard]

Yeah, I hear ya, they seem to fly GREAT!

Naw, locktite is too iffy, we'd need a quantified weak link. Back to fishing line, or maybe copper wire chosen from stranded electrical wiring. This would go through a hole going through the gear and the shaft. I'd be a small hole and the line would have to fit pretty good or vibration will eat the link up. BUT, there's lots of diameters of line or wire to choose from, and the drillbits are available, but delicate.

NOW, I'm getting the TT fever!!! Where's my old sliderule???

Gr4yb3ard
"...Wilbur: It could work!!... ...Orville: It's just not possible that an engine could suck itself along whilst shooting fire out the back, think clearly Wilbur!!!..."

[Gr4yb3ard]

No, I take that back, never say never.

It's the application of the locktite that would be the variable.

As long as it gives up with pretty much the same torque every time, it's the same thing.


Questions: I would assume that the second gear in the chain, (the one on the front of the tt) is breaking. I also assume that this is one is easier to get at than the far forward driving bevel gear. (yes/no?)

Are either of these gears pressed onto a splined shaft, like the tail rotor shaft? Or is the shaft smooth and a set screw is used.

Can't tell from the detail of the pictures I've seen....

Gr4yb3ard

[Buzzkill]

Mine didn't really "break" the teeth on the crown gear got chewed down or if you will wore off. There is still remnants of teeth on the gear, small rounded nubs left on it.

What we need is some type of clutch for lack of a better term, Something that will hold at a predetermined amount of presure but would give in the event of tail rotors being stopped. something like this maybe? (will post sketch in a few)

[Jetleaf]

Gr4y, the tail shaft is not splined. It looks like somebody gripped it real tight with a pair of vise grips and left some angular cuts in the shaft. They are not deep enough to secure the gear on the shaft hince the gear slipping issue. The gear is pressed onto the shaft but the bore in the gear is smooth. On the driven end of the shaft the crown gear, as Gaui calls it or umbrella gear as Align calls it, is held on with one set screw. There is a flat on the shaft for the set screw. Interestingly there are two set screw holes 180 degrees opposite each other in this gear but only one set screw and one flat on the shaft. I have installed an additional set screw in mine which seems to have elminated an eccentric wobble of the crown gear.

[Gr4yb3ard]

Exactly!

The shear pin, or shear material, is just that, it gives up at just the right moment before the expen$ive parts break. Sorta like a clutch, but lighter and cheaper, a one-shot item.

Can you send some pictures of the damage in a gear-"thrash" on the tt?
Again, which gears are involved exactly. I'll bet you a Starbucks, it's on the front set, and the one on the boom shaft is the one with the most damage! ;-)

Gr4yb3ard
"...gotta get more GAUI's!..."
"...the defrayment of material is a natural, and inevitable consequence in the course of combat..."

[Buzzkill]

Here's what I meant. See pic. The sheer pin is a good idea but the gear material is so soft it would be hard to get a pin that wouldn't break the gear before it broke itself.


I have too much time on my hands lol. I should get back to doing canopys. :thumbup:


I'll upload some pics of the damage ASAP.

[Jetleaf]

I wonder if a oneway bearing would work?

[Gr4yb3ard]

Jetleaf,

Excellent description!

All's not well in shaft-flat land, but I'm thinking....

Awwright, I gotta go play like I'm at work soon. Shall we call this the "tt initiative" and go from here?

Gr4yb3ard
"...Orville: "There're at it again".... ...Wilbur: <pulling bedsheets, rubbing eyes> "Who, what"... ....Orville: "Those voices about the free refrigerators with every meat purchase"... ....Wilbur: "What the %$#*@ is a <refrigerator>!!!"..."

"...Good afternoon sir! Please make a selection from our Airway Bistro!".... ...."M'am, why is this sandwich green?".... ...."I have no freeking ideal bozo, just sit the *&#^ down and pray that Boeing puts a couple more toilets in the next version...."

[pck]

well, i kinda lost track back at post #15 and couldn't really understand the rest of the discussions after that. But don't mind me, please carry on your discussions here as i am sure it will benefit many others and me as well, eventually.

For me, the crown gear in the front where it interfaces with the pinion gear has been good so far. I haven't had to change that yet. It's the little bevel gears at the end that has been loosing it's teeth, especially when i switch to idle up. The sudden spool up in headspeed seems to generate too much torque to these gear meshings and increases the wear rate tremendously, that any hard landings would rip some of the teeth of bevel gears off at the tail.:shock:

The idea of using metal gears sounds really good but then the additional weight, especially right at the end of the tail might be an issue for getting the CG right.