E5 Tail Transmission Failure: sorry Matt it was clearly my fault

[ChrisW]

Hello,

Since the relevant parts of my unfounded rant have been quoted, I think it's safe to replace my initial post with just an apology to Matt for my incorrect evaluation of the cause of my crash. I of course admit full culpability for it, and really I should have asked for help investigating what happened first, instead of making certain assumptions.

After rebuilding I see why you have done what you have done in regard to the pin retention and it is a valid solution to the design problem.

Best Regards,
-Chris Wuester
Chandler AZ

[Darren Lee]

Third : You should not be relying on the plastic-to-pin interference to retain the pin.

As a matter of fact, there is already a pin retention feature in place.  Please refer to the manual, page 39.  A set screw is inserted into the shaft which presses against the pin.

Sorry about your crash but this is a builder error, not a design error.  Don't feel too bad though, you are not the first to overlook this! 

[flyalan]

Yes.  I caught one on some else's E5.  I was helping him with a damaged tail and boom after a crash.  He managed to take out the bevel gear in the tail.  I had him do much of the work.  I watched as he tried to push the pin out and chuckled a bit and asked if he had loosened the set screw.. Reply.. What set screw?... Needless to say it wasn't loktited...

Cheers

Alan

[Rodney Kirstine]

I'm not Matt (the designer) but I have done extensive first-hand destructive testing on all Synergy models  and here's my take on your second suggestion.  For reference, the TT design is shared between the E5, N5C, E7, and N7.  I have crashed all but the N7 multiple times in pretty much every way imaginable.

Second : You really should not be relying on just the pin to transfer torque. There should be a spline, a square drive (like you used on the torque tube itself), a square key and keyway, or a flat on the shaft.  For DFM reasons I would recommend the spline (or really just a straight knurl), and pressing the gear onto the shaft with a healthy press-fit wherein the spline teeth deform the plastic. Then add the pin as a torque holding back-up, and to keep the gear from sliding on the shaft (which is what a pin should really be used for).

Every time I've had a bad enough crash to break parts in the transmission, it's always been teeth broken on the mushroom and/or bevel gears so I'm 100% sure that there is plenty of surface area on the pin-to-gear interface to handle the torque.  Keep in mind that not every single tooth on those gears is engaged at the same time.  For torque transfer, the surface area of the engaged teeth isn't very large.

Third : You should not be relying on the plastic-to-pin interference to retain the pin. Either you need to change the hole in the 320-408 shaft to create a metal to metal interference fit with the pin, or you need to add a metal or plastic ring collar pressed onto the outside of the gear's OD to retain the pin. If you make the change in my first suggestion this may become less necessary, but I recommend doing it anyway.

As Darren and Alan note, the design does not rely on an interference fit of the pin in the gear and there is a retaining set screw, as noted in the manual.

Please also note that a very similar set screw retainer design is used for the ball link adapter on the swash followers and, if the instructions in the manual are not followed when you disassemble it, you can damage the ball link adapter.

http://synergyrchelicopters.com/forum/index.php?topic=1510.0

[ChrisW]

Hi All,

Thanks for pointing the set screw out because the trans box apparently has a similar set screw, and because now I'll check the tail end also.

I wish Synergy had just put the parts in sub-assembly step separated plastic bags and eliminated the dis-assembly portion of the build. It's too easy to not see something that needs to be taken apart.

If the set screw had been loose in a bag of parts needed to build the transmission, I would have been 99% sure to put loctite on it and tighten it down...

Best Regards,
-Chris

[curmudgeon]

Sorry about the crash.  It's a shame it was due to a loose set set screw.  Don't forget about the other pin retaining set screw on the tail end.



About pre-assemble parts vs parts in a plastic bag, it would also be my preference to have the parts not pre-assembled, but it seems pre-assembled parts won that battle.


Hope you get the bird back in the air soon.

[Rodney Kirstine]

Chris, that's a really easy one to overlook, for sure. Get that thing back in the air soon!

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[ChrisW]

Thanks for the loan of a crying towel guys : )

IMO there should not be "easy to miss" critical items in a build. So to reiterate my position, if it's pre-assembled it should be pre-assembled completely and correctly so as to not cause a crash. Otherwise it should not be pre-assembled at all.

To make it not "easy to miss" there could be a physical red tag attached to the pre-assembled sub-assembly that says "look for the set screw that holds in the pin and loktite and tighten it down or you will crash this helicopter" ; ) The little box in the instructions didn't get my attention, probably because I was using an iPad mini and it was a little small...

-Chris

[Kevin Feil]

 In regards to the red tag, I think its important and always a Great Idea to read the Manual at least twice to get a better understanding of the build steps but also a clear vision of the parts that make up each component of that assembly. You have to understand that these kits are the highest quality you can buy, along with the Best support the industry has to offer, and in my opinion houses the Most enavative designer the hobby has to offer. I can assure you based on the Millions of kits sold, this issue has only come up 3 times, and those three times were due to not reading the manual thoroughly. These are surely not beginner helicopters but do require a clear understanding of the build process and accountability regarding the parts and quantity of parts used.

I always hate to hear when someone has an unfortunate accident that requires us to rebuild, but this is also expected. As far as the design aspect goes, It won't change it is well proven and even more been tested by some of the worlds greatest pilots.. The design is fine  . Good luck with the rebuild, read the manual as well as build "Tips and Tricks" and buy some Loctite and go have fun..

Best Regars,

Kevin

[ChrisW]

Attached is my submission for example updated pages for the E5 manual. Here is how you could make it -completely obvious- what needs to happen to make sure the model does not fail in flight due to incorrectly pre-assembled sub-assemblies. The wording is maybe a little sarcastic; sorry, but it could not be helped.

Mr. Botos : please feel free to use these updated page versions, and propagate the new text boxes to all pages describing the re-building of already incorrectly-pre-built sub assemblies, no thanks or royalties needed 

Hi Kevin,

In a perfect world, yes. In reality you open the kit, all excited, start ripping screws out of the pre-built assemblies and putting them back in with blue loktite... You refer to manual only when something is not obvious. I looked at the top of the pre-assembled gear box and saw a nylock nut, "no loktite required on that!" I thought, so that's as far as the dis-assembly went. Oversight? Yes.

The manual needs to have big bright red boxes to get your attention while in a state of building frenzy . And I bet there are many of these kits flying around like whirring ticking time bombs with non-tightened / non-loktited set screws not holding in those two pins.

-Chris

[flyalan]

Well I do like the "you will crash statement".   

Cheers
Alan

[Rodney Kirstine]

Chris, when you built your kit did you disassemble all the pre-assembled parts and reassemble, using loctite?

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[Kevin Feil]

I refer to manuals regardless of how obvious something is. I'm in the full scale helicopter business and my guys are required to have manuals regardless how many times they have done something. I have built an astounding amount of Rc helicopters as well as Full scale helicopters and I can assure you I still reference the manual. These kits like others require common sence and a lot of "Patients" you will not convince me otherwise Chris. These things are not toys by any stretch. I think based on this summers current events and the loss of a Great Pilot and Friend proves that.  I understand being excited about building a kit or repairing one, we have all been a victim of that and will continue to be, however a clear understanding of how everything goes together in its proper form and is correct " That's your responsibility" the manual is there, if your not an avid builder of heli's and in this case Synergy's then you need to read the manual how ever many times it takes to get the full grasp of what your doing. Mistakes happen, over sites happen, we are all guilty.. If someone says they aren't, they are lying! In the real heli world you miss something and it crashes or god forbids kills someone, you go to jail !   There are a lot of things happening with a helicopter and require even more skill than one who builds Airplanes... If your unsure or have questions, ask one of us. I'm sorry if I come of like an ass but Brother I don't want to read a post were someone lost a limb or hurt someone else due to Lack of Product knowledge because they didn't read the manual or the "Tips and Tricks" section under each Model Synergy Sells. Pay Attention Brother. Your learning and I assure you , you will learn more if you choose to stay with this brand and hobby for that Matter. Ask a lot of questions Chris, Synergy has a army of people that are more than willing to help you regardless what that question is.  I think we have talked about this enough and need to move on. Get that heli fixed and get your butt back in the air and be sure to let us know how it goes.. Welcome to the Synergy Family and enjoy. Again sorry If I offend you or anyone else, I have seen first hand what can happen do to Negligence....

Best Regards,

Kevin

[matt_c_25]

sorry to high jack this thread but I'm so glad I read this as I overlooked that screw set on the tail shaft.


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[Greg Jackson]

I agree with Kevin.  I studied the manual for weeks while I was away last year for Christmas before I did the build because I wanted to make sure I had everything covered.  Sorry you had a bad experience, I have been there with other brands.  But try not to get too disappointed yet, I made some very dumb errors at the beginning with this helicopter and almost gave up, but they were my mistakes.  Even though you are soon to be an engineer with a degree, it is still a good idea to have someone look over the helicopter.  Same way someone looks over a paper before turning it in.  Another set of eyes will catch something you didn't like Alan said. 

Also I recommend watching Chris Sexton's videos as I recommended to someone else earlier.  Guess it is just me, but when I make an expensive purchase I read up ahead of time so I know what I am getting into.  That is only because I have made so many mistakes to learn from.  Please don't give up yet!