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Century Radikal - Hawk - 50NX - Predator > Heavy duty clutch in two pieces why did this happen!?
 
 
avator
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Location: New Jersey

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zone8,

You are so right! I have the V2 which is a redesign and it still hits the canopy. I haven't heard yet and wonder if the V3 has the same problem. I wouldn't be surprised. I think the reason that some items are good and some are not is that Century uses different contractors to produce items for the Predator. I was told by a Rep that the carbon frames come from a local contractor in California. Anyway, I'm glad to hear that you found the problems with the frames and corrected them.

Scotter,
I have to agree with you as well with one exception, I've built heli's from Hirobo, Schluter, GMP, MA, Kyosho, and JR and have not experienced so many quality issues as with the Predator. I would go as far as saying I can't remember any quality issues with any of the others regarding parts, only with manuals and maybe a missing screw or nut. I will say, as you did, when you get it right the Predator does fly good. My Predator has also been fairly trouble free for the 8 or 9 months that I have been flying it. I had the clutch to fan button head screws come out even though they were locktited and I had to replace the pitch slider for the tail rotor due to excessive play. Century replaced it, but only after inspecting the old one to make sure I wasn't trying to pull one over on them. Both of these issues showed up within the first couple of tanks.

Funny, I didn't see anywhere in this post where anyone said that the clutch bell failure was caused by torque. Hummm

I think that even though Zone8 aligned the clutch to the bell, as we all know, most of us do this by eye. So there may still be enough of a misalignment to produce a flexing motion that was enough to have caused the bell failure. Just a thought.
01-10-2007 Over year old.
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AceBird
Elite Veteran
Location: Utica, NY USA

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Quote 
The picture shows an exaggeration of the deformed shape, that's why it looks star-shaped. The important thing is the red spots on the border of the holes, indicating high stress areas where a fracture could start.

I don’t really agree with that either. It looks star shaped because that is exactly the way it would fail under a torque load. The red high stress surface that you see in the holes is common for the distortion of a tube or pipe that was crushed in a vice.

I think the model you made is not crude and depicts exactly what would happen under each conditional load. Furthermore I think you vindicated Centuries design although actual numbers would have to be verified for full vindication.

If there are indeed no alignment issues, then I suspect that the bell was fractured when pressing on the bearing or when pressing the bell and bearing into the housing. There is a skill associated with being a mechanic just like there is a skill associated with being a pilot. These R/C helicopters require both although with today’s electronics the required skill of the pilot is much less.

Ace
What could be more fun?
01-10-2007 Over year old.
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AceBird
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Location: Utica, NY USA

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It's right hear. I know you can't read it unless it is spelt right but it surely says TORQUE.

Ace
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01-10-2007 Over year old.
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DS 8717
rrProfessor
Location: Here wishing i was somewhere else

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Gassers also hammer more than nito heli's,this also cause's problems with gyro's and tail wagging and hunting. If the original bell didnt have holes i would say it's just a bad design for gasser engines,because holes dont cause problems with even the 90 size nitro heli's. DOUG

No Es Mi Culpa
01-10-2007 Over year old.
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zone8
Senior Heliman
Location: Ireland

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I've taken another closeup pic as you can see the cut is very very clean, in fact, the two pieces snap back in place like it was a Century upgrade ("heavy duty broken clutch" ) and if you pass over with your finger you can hardly feel any 'lip' on the cuts so I would exclude any vertical movement which would have cause some edges? With the clutch shoe I don't use the button bolts as per manual I use normal bolts and they did not shear - the shoe is fine altogether.

Just out of curiosity the second picture is a standard clutch which I also broke from my first Predator, now that indeed was because of poor alignment, as you can see the bearing ate some 1mm metal from the top of the bell and the shoe is also broken (as well as the bearing). Since that accident I have been more careful when assembling the clutch (yeah right..) anyway, I've been flying with this setup for the entire summer without problems, now I go ONCE in winter to do some gentle figure 8s and bang... fatigue!?

01-10-2007 Over year old.
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avator
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Location: New Jersey

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This was an interesting post with a lot of good information from different sources, that is until the "half gallon expert" chimed in with his usual, "I'm right, you're wrong" attitude. There seems to be no limit to this guy's arrogance.

Hey genius, the word is spelled, not spelt.
01-11-2007 Over year old.
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pschurter
Senior Heliman
Location: La Serena - Chile

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Thanks for stating it, Avator, I completely agree.

Good flight, good night!
01-11-2007 Over year old.
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SteveH
rrProfessor
Location: Texas

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Quote 
the second picture is a standard clutch which I also broke from my first Predator

Avator,

Don't know what it is, but there is definately a common denominator somewhere here. To have two different clutches fail in the same manner is just too much evidence, IMHO, that something is wrong, possibly with your setup or alignment.

I have many flights on two different Predator Gassers, with both the original gasser clutch and now the HD clutch, with no failures like you have had. I also have not heard of any other failures like yours.

Can you tell me the amount of flights on this clutch, and also measure the clearance between the clutch shoes and the lining?

SteveH
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AMA76186
01-11-2007 Over year old.
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zone8
Senior Heliman
Location: Ireland

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Steve, the two clutches did not fail in the same manner, as you can see from the pictures, which I posted in fact, to show how differently clutches may fail. Also, they failed on two different helis, and while one failed this week the other one broke almost two years ago. On my current Predator I have been enjoying over a year of trouble free flying i.e. zero crashes with the heavy duty clutch that recently failed. That, the very clean cuts, and the fact that the bearing is fine make me think that the fault MIGHT not be caused by poor alignment. I also think that if the heavy duty clutch bell had 5 holes like the standard clutch, maybe this wouldn't have happened.

The amount of (sport) flying on this h.d. clutch is 120 liters = 240 tanks = over 100 hours.

When I installed the clutch I used two feeler gauges at the same time to make sure that the bell is parallel to the frames. The clearance is 1.23mm (0.048in).
01-11-2007 Over year old.
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avator
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Location: New Jersey

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Sorry Steve, it is Zone8's clutch bell that failed, I was just adding my .02 trying to help figure out what the cause might be.

pschurter,
Believe me when I say it was my pleasure.

Regarding the clutch bell failures, Zone8 seems to have his act together as far as assembly and setup. Since this has not happened to anyone else that we know of, there has to be something unique about Zone8's heli that is causing it. I for one am very interested in what the cause is. Whether or not the cause is ever determined is another matter. One thing I know for sure is that critisizing other members for their opinions as to the cause and making speculations based on nothing more than bolstering ones own ego is not helpful.
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AceBird
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Location: Utica, NY USA

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“Spelt”, past tense of “spell”. It’s a grammar mistake not a spelling mistake, the “is” should be “was”.


Quote 
To have two different clutches fail in the same manner is just too much evidence, IMHO, that something is wrong, possibly with your setup or alignment.

Sorry to be so arrogant, I was only trying to help the guy out. As long as he thinks it is the holes or a design flaw he will NEVER solve his problem. It has to do with mechanical skill and understanding the rigid coupling of two independent shafts. I thought he was asking for ideas. If all he wants to do is beat up on Century then I guess you found a buddy.

Have a happy.

Ace
What could be more fun?
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SteveH
rrProfessor
Location: Texas

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Avator,

Sorry about the mistake.

Zone8,

Again, can you measure the clearance between the clutch shoes and the inside of the clutch bell on the HD clutch that recently failed, as it is today? What I want to know is the amount of wear on the lining.

SteveH
Magnum Fuel
AMA76186
01-11-2007 Over year old.
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zone8
Senior Heliman
Location: Ireland

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Acebird I don't quite get your comment, in the same post I think you're quoting Steveh and talking about me (Zone8 the guy with the broken clutch). Anyway, yes I am reassembling the heli right now and would like very much a final advice from someone - an engineer possibly since experience in this case doesn't count much since this has never happened before - on what to do to avoid a repeat, IF in his/her opinion the failure was caused by poor assembly skills. To recap, right now on the bench I have: clutchshoe dial indicated within 0.002 inch, bell within 0.004 inch, bell perfectly parallel to the frames, no vertical play whatsover, zero pinion/gear mesh but if I turn the gear 180' there is a slight play. Now what else should I check?

IF, on the other hand, you think that it MIGHT be a problem with Century and the HD clutch design, prone to 'fatigue', I would also love hearing about this, since as said I do sport flying with a Predator for fun but can also imagine guys flying over residential areas with a fully featured Condor and $4,000 of AP equipment and the very same clutch as me, that might be a little worried.
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avator
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Location: New Jersey

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Quote 
“Spelt”, past tense of “spell”. It’s a grammar mistake not a spelling mistake, the “is” should be “was”.

Who says???It may be that way in your hillbilly dictionary, but, in the real world:

Spelt noun

Hardy Wheat

a hardy variety of wheat of inferior quality, sometimes grown in mountainous regions.

You just know it all, don't you?? It must be wonderful to never be wrong about anything.

The past tense of spell is spelled. ex: Ace spelled another one incorrectly.
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avator
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Location: New Jersey

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Zone8,

Your setup sounds good to me. The main gear on the predator does have a little runout, maybe a few thousandths. I would turn it to the tight spot and adjust for a slight amount of play. You will still have adequate mesh on the loose side and you'll eliminate the stress and vibration of running tight on half of the gear. Could this be the reason for the clutch failure??I guess it could be a possibility.
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SteveH
rrProfessor
Location: Texas

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Zone8,

First, you state "bell perfectly parallel to the frames"...the most important thing is that the clutch AND clutch bell are parallel to each other.

And, did you get me the clearance between the clutch shoes and the clutch bell that broke?

SteveH
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AMA76186
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zone8
Senior Heliman
Location: Ireland

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Avator, I will leave a bit more play, but, the day the clutch failed, assuming that the mesh was probably a bit tight (no play on the tight spot, little play on the other side) how could this possibly cause such a disaster - I thought the teflon would wear before a clutchbell broke that way. I've read many posts where this kind of mesh is recommended.

SteveH, yes of course the bell is parallel to the shoe, this is done by eye there is like 1mm of shoe visible under the bell looking from every side and slow turning the engine doesn't change. I don't know how to check this if not by eyesight. The clearance was the same as now 1.20 mm.
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avator
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Location: New Jersey

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Zone8,

I've read about individuals who run the gear tight and wear it in, but I don't agree with that philosophy. I always thought the gear was made from Nylon. I have found that, generally, if you have a nylon gear meshed with a steel gear, the steel gear seems to wear out first.
I'm not saying that the tight mesh definately caused the clutch failure just that it might be a possibility or maybe a contributing factor. Not being an engineer I can't say for sure how or why this could happen, however, if the clutch is being driven by the engine that is in turn driving the bell which is meshed through the pinion gear with the main gear and the mesh between the two is tight on part of the rotation, then the sudden application and subsequent release of the load caused by the tight mesh would cause stress on all of the components including the bell. If you got your clutch aligned with the bell then what else might have caused it? All I'm saying is it's a possibility. If you get the mesh right from the start you eliminate that as a possibility.
Since your last bell lasted two years before the failure it might be awhile before we know if your problem went away. MHO is if you have the alignment good and your gear mesh is not tight and based on the fact that no one else experienced this kind of failure I believe that you won't see another clutch bell failure like this.

At least I hope you don't.
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AceBird
Elite Veteran
Location: Utica, NY USA

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Quote 
To recap, right now on the bench I have: clutchshoe dial indicated within 0.002 inch, bell within 0.004 inch, bell perfectly parallel to the frames, no vertical play whatsover, zero pinion/gear mesh but if I turn the gear 180' there is a slight play.

Stop right there you are already in trouble. I am going to say this and I am sure I will get a lot of flack. There is no way of indicating the clutch shoe on the face of the shoes. Anyone that puts the indicator on the face of the shoes is kidding themselves. You need a plug gage that will fit tightly in the one way bearing and then indicate that plug. This will tell you where the center of rotation is. That’s all you care about.

Now .004 on the bell is too much. This is also what is causing the change in backlash on the gears. I have to go back to how that bearing was pressed on the bell. Never mind the lining for the time being, there should be less than .0005 in. runout on the outside of the bell to start with. As a check the lining thickness including the aluminum should not vary more than a thou (.001). Now I am talking new parts not ones that are used. I would be concerned with how the outside of the bell runs rather than the inside lining because the outside in more of an indication of the center of rotation although it is best if they both are concentric.

Ace
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AceBird
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Language has a way of changing over time. Page 813 in a Webster dictionary. It has a few years on it.

Ace
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Century Radikal - Hawk - 50NX - Predator > Heavy duty clutch in two pieces why did this happen!?
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