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Old Nov 18, 2012, 01:35 AM
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South Africa, GP, Pretoria
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Originally Posted by 4stripes View Post
Thanks for the feedback!
The sound of this fan has caught the attention of many modelers at our field, including a couple turbine fliers! The performance is just right for the Venom. Thanks to the flier who made the video I can share the sweet sound.
Cheers
You have done really great work on that combo. We are lucky to be flying now with all these changes that make edf flyin a lot of fun.
Keep up the good work!!!
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Old Nov 18, 2012, 03:48 AM
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Germany, SH, Neumünster
Joined Dec 2011
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Originally Posted by 4stripes View Post
I personally will not use any more of my 45g rotors as they are too much work to dynamically balance and then have them destroy the shroud and possibly motor shaft as well. Had one blow at only 1800watts on 6S even though it was perfectly dynamically balanced.

The very early 45g rotors are still working for me but the ones sold this summer were duds.
Thanks for your feedback! I am fully agree with you and will wait for the replacement rotor.
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Old Nov 18, 2012, 03:37 PM
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Thomas Nelson's Avatar
Calgary, Alberta, Canada
Joined Sep 2002
2,898 Posts
Ok ...

Earlier I posted that I was done with this particular fan. Well .... addictions are hard to overcome, and I caved in and bought yet another CS12.

From HobbyKing.

So it was the weak version.

And last week I had yet another failure. The third failed fan in 121 flights on this airframe.

But this time I caught the failure as it was occurring. I was able to hear the subtle bzzz as it was happening and landed safely. This allowed me to disassemble the unit and see just what was going on.

Yep, the shaft had shifted off center - aka runout - just like I theorized a while back. So what I was hearing was the vibration of an imbalanced unit, plus the contact of the rotor with the shroud. Surely this weak rotor would have failed imminently under such circumstances.

Anyway, way too much to type to explain it all so I took a vid of the damaged CS12, along with some thoughts for the next one.

A bonafide glutten for punishment, I know. But the SOUND ....

tn

Another CS12 Failure (4 min 54 sec)
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Old Nov 18, 2012, 03:48 PM
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United States, TX, Grand Prairie
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Don't know if you can call that a failure of the fan, I think what 4S was describing earlier was there was a batch of bad blades that would come loose from their base tossing the rest of them.

Shroud rub would no doubt cause the lighter blades to fail fast.

Are you able to bottom out the motor shaft adapter onto the motor shaft?

Also what thread lock are you using on the grub screws?

regards
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Old Nov 18, 2012, 04:06 PM
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Canada, ON, Burlington
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There should be no "runout" on the adapter/motor shaft fit but of course there are loose fitting adapters. That is corrected by putting some epoxy into the adapter hole as you put it on the motor shaft. No wobble or shifting possible then. My catastrophic failures were not caused by any runout as my adapters were made solid. Whole blades would come out of the hub, breaking the front tabs that were supposed to hold them in.
The plastic simply couldn't hold the blades in.
Cheers
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Old Nov 18, 2012, 04:40 PM
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Calgary, Alberta, Canada
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Hi erh - answers to your thoughtful questions below. Thanks for the feedback!

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Originally Posted by erh7771 View Post
Don't know if you can call that a failure of the fan, I think what 4S was describing earlier was there was a batch of bad blades that would come loose from their base tossing the rest of them.
I am thinking that the busted blades might the the result of contact with the shroud. IOW, the root cause of the failure is the adaptor shifting. Everything else is an effect. If the adaptor shifts even after the significant effort I went to prevent this ... then failure is imminent:
  1. adaptor shifts, followed by
  2. severe imbalance, followed by
  3. contact with the shroud, followed by
  4. busted blade roots.
Shroud rub would no doubt cause the lighter blades to fail fast.
Agreed. And this is why I'm labeling it a failure. No way it could have survived more than a few seconds of rubbing. Case in point, my previous fans both made the "same" noise for only a ~second or so before exploding.
Are you able to bottom out the motor shaft adapter onto the motor shaft?
I pushed it on (was difficult) as far as I felt prudent? The resistance simply increased until I didn't think I could go any further, but there was no distinctive 'bottom' as far as I could tell. To remove the rotor I used allen keys like pry bars from the back of the unit. There needs to be some clearance between the back of the rotor and motor holder to wedge something in there to pry the rotor off. It was tight!
Also what thread lock are you using on the grub screws?
During initial assembly I put serious torque on those grub screws. Upon disassembly, it was clear they did not move at all - they were clearly still "locked" and left distinctive marks on the shaft. And those marks show no rotational movement either. I truly don't think they are the issue. But to answer your question - it was Blue Loctite as pictured in the vid.
regards

If I can "play" with the runout of the adaptor during assembly, simply by varying which grub screws I tighten & how much, does this not suggest that the adaptors are too loose? If the only thing keeping the adaptor runout in check are those four grub screws, can we honestly expect that it will not shift due to vibes or rough landings?

I'm thinking adding some kind of adhesive to the "end" of the shaft after final assembly should prevent shifting of the adaptor on the shaft.

Sill wide open to other thoughts naturally.

tn
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Last edited by Thomas Nelson; Nov 18, 2012 at 04:56 PM.
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Old Nov 18, 2012, 05:32 PM
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Calgary, Alberta, Canada
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Gotcha

Interesting that my weak-gen rotor was able to handle a bit of contact with the shroud without instantly grenading. However, I'm next to certain that the last two failures I had were directly related to the adaptor shifting.

Can't say what took out the first one though. I never weighed the blades, but am assuming it was one of the tough ones 'cause I bought it just after they came out.

Oh - just to be clear - my adaptors seemed solid once all tightened up too. It's just that I could "adjust" the runout during intial assembly via the grub screws.

tn

Quote:
Originally Posted by 4stripes View Post
There should be no "runout" on the adapter/motor shaft fit but of course there are loose fitting adapters. That is corrected by putting some epoxy into the adapter hole as you put it on the motor shaft. No wobble or shifting possible then. My catastrophic failures were not caused by any runout as my adapters were made solid. Whole blades would come out of the hub, breaking the front tabs that were supposed to hold them in.
The plastic simply couldn't hold the blades in.
Cheers
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Old Nov 18, 2012, 05:54 PM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
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Nice work Thomas. What was the cell count/watts?
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Old Nov 18, 2012, 06:12 PM
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Newton, Ks.
Joined Feb 2004
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I agree with the thought of not being able to change run out with the grub screws. I think a collet type adapter would center better. My .02
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Old Nov 18, 2012, 07:17 PM
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Quote:
Originally Posted by Thomas Nelson View Post
Gotcha

Interesting that my weak-gen rotor was able to handle a bit of contact with the shroud without instantly grenading. However, I'm next to certain that the last two failures I had were directly related to the adaptor shifting.

Can't say what took out the first one though. I never weighed the blades, but am assuming it was one of the tough ones 'cause I bought it just after they came out.

Oh - just to be clear - my adaptors seemed solid once all tightened up too. It's just that I could "adjust" the runout during intial assembly via the grub screws.

tn
This makes total sense, I have seen it happen on other fans, and this is why I mount all my adapters the following way. I don't like flat spots on motor shafts and if there is one I usually fill is with jb weld. When I mount an adapter I drop 3 or 4 drops of red loctite in the adapter hole. Then I press it against shaft until it bottoms out and quickly start going at the grub screws to get the best run out, then let it dry 24hrs.

This way my adapters never shift, but if it has to be removed it will have to be heated.
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Old Nov 18, 2012, 07:25 PM
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Canada, ON, Burlington
Joined Jan 2009
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TN It appears your motor shaft is rather short compared to most of my motors. I have one that was that short (EMAX 1650 that came with my HTG L39). It was impossible to get dynamically balanced until I used the epoxy trick. Once the shaft was supported, it was easy to get balanced as there was no more shifting.
It seems some "5mm" shafts are also not exactly the same as other "5mm" shafts. Slight variations in size doesn't help when adapters also have slight variations. I have a bag full of adapters that I go through to match up to whatever motor I am setting up. Usually I end up using some epoxy as it is rare that the adapter fits as tight as it should.
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Old Nov 18, 2012, 07:27 PM
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Canada, ON, Burlington
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In order to allow the possibility of removing the glued on adapter, I usually apply some wax to the motor shaft before installing. One easy way to remove the adapter is to get a long spinner bolt and just turn it in while holding the adapter from turning. The spinner screw will push the adapter right off.
Cheers
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Old Nov 18, 2012, 08:22 PM
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Nashville TN.
Joined Mar 2006
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Why aren't you guys just using a dremel cutoff wheel to make a flat on one of the grub screw marks when you are adjust the adapter for run out?
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Old Nov 18, 2012, 09:58 PM
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Thomas Nelson's Avatar
Calgary, Alberta, Canada
Joined Sep 2002
2,898 Posts
Hi Kevin

I'm flying on 6S at 2100 watts. Wish I could keep these fans together

Quote:
Originally Posted by Kevin Cox View Post
Nice work Thomas. What was the cell count/watts?
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Old Nov 18, 2012, 10:04 PM
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Thomas Nelson's Avatar
Calgary, Alberta, Canada
Joined Sep 2002
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Good tips 4stripes!

I'll wax the shaft before epoxying the adaptor in place. Carnuba car wax what you have in mind?

BTW I've had three of these HET motors and the each had shafts of the same length. I agree that longer would be more desirable.

tn
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