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Old May 05, 2004, 06:09 AM
Will work for planes
omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
1,783 Posts
Help!
violent corona shaking from subrotor. :(

Tracking down the shaking in my corona I found the feathering plate "titer-toters" on the hub. With everything except the subrotor off I can see the subrotor wobble. Can the feathering plate and hub be taken apart and the bad one replaced? The pin that holds them together seems like it isn't coming out with out some coaxing. Or should I replace both together? Even with out the main blades on, it doesn't seem that a loose feathing plate should cause so much vibration or could it?
Here is a vid of the vibration.
http://f1.pg.briefcase.yahoo.com/bc/...uments&.view=l

Here is a pic of the feathering plate/ hub. The section that is loosest it the side opposite the subrotor pushrod.
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Old May 05, 2004, 06:11 AM
Will work for planes
omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
1,783 Posts
oops forgot the pic.
red arrow indicates the spot between the subrotor and hub, blue arrow indicates direction of play.

the green arrow is the side that has movement in every direction on the feathering plate.
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Last edited by omega blood; May 05, 2004 at 08:04 AM.
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Old May 05, 2004, 07:20 AM
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corey's Avatar
Canada, MB, Winnipeg
Joined Oct 2001
998 Posts
Bent main shaft perhaps?
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Old May 05, 2004, 07:48 AM
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omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
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I tried three different shafts. The old one (that was bent) and two new ones that I cut myself from harden steel. I rolled the two new ones one of those supper strait/flat grannit tables and they were as strait as I think a shaft can be. The same problem is exhibited in all three shafts.
One more thing that I noticed is that where the subrotor sits in the hub via a pin there is play. I don't know if this is normal but I can slide the subrotor about a sixtyfourth where it is pinned to the hub.
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Old May 05, 2004, 08:04 AM
Logo 20/Corona pilot
MikeStammer's Avatar
Chicago!
Joined Jun 2002
271 Posts
You can get a real nice carbon reinforced feathering plate from heli mod man (Matt). The pin will come out, but you do need to tap it out of there with a thin rod or something. Cost is about 25 bucks. Check http://www.ballistictechnology.com for more info
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Old May 05, 2004, 08:15 AM
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denver, colorado
Joined Nov 2003
243 Posts
is this a used machine ??
if it is you need to obtain a builders manual if you dont have one (pdf file at LMH) and completely disassembe it down to the smallest part. Inspect the drilled holes which the pins fit thru and insure that the pin did not go thru cock-eyed, causing an elonggated hole, allowing the pin to wobble, along with the part it holds. Check the head to insure that it has not been clamped onto the shaft too tight; this will cause perm. damage and deformation of the head and allow the entire head to wobble. Check that the lower main shaft bearing is not worn fore and aft; hold the spur gear on its circumference, at the machine center line, aft and try to move it in a fore and aft motion - if it wiggles then the spur is not tight to the main shaft and/or the lower main shaft bearing is shot. check the main shaft bearing blocks to insure that they are tight; but before doing that slightly loosen the main shaft bearing blocks and hand spin the rotor head to allow the main shaft to align in the bearings then tighten down the main shaft bearing blocks.

good luck

oh, by the way, re your gy240 comment: the video really shows the tail rotor servo responding to the vibration.

CAVU
roger
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Old May 05, 2004, 10:47 AM
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393 Posts
My subrotor seems to wobble if you look at the center round disc as it rotates. Not sure if I have the same amount of play in the feathering plate but I can check -however I know my Corona head is on the loose side compared to my cp helis.
I've never run mine without blades so I can't say what amount of vibration I might see if run without blades and grips - perhaps some vibration is normal because there's no load on the feathering plate? I've found that blade grip tension is very important and improperly set can cause a LOT of vibration.
I first set mine tight enough to hold the blades from falling when I tilt the heli on its side, then I position the blades off center (to make sure they have centered) and spin them up slowly into a hover (to center them) and then slowly reduce rpm and set down. (I don't over rev the motor at this point because it will cause the blades to shift position) I then carefully tighten the grips very snug and mark the positions with a silver sharpie and test hover again. The sharpie marks allow me to return the blades to the same position later because the tighter blade grips will not allow the blades to auto center in flight. I've found if you leave the grips on the loose side the blades will shift in flight depending on the flight conditions and engine rpm causing vibrations to come and go.
Also, I've been able to remove any remaining vibration by applying small amounts clear tape to the underside of the lighter blade across the blade cg point (using the trial and error method).
Hope this helps.
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Old May 06, 2004, 03:07 PM
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omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
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Thanks for the help guys.

I took out the pin(s) that hold the feathering plate in the hub and found that it had snapped in half in side the feathing plate. So I cut me a new pin put it back together and the massive shaking is gone! There is still vibration but is very small, acceptable to me.
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Old May 06, 2004, 11:28 PM
the other, other dave
S.F bay area
Joined Sep 2002
795 Posts
indicate the main rotor hub , common error is over tightening the nut and screw that attach the m/r hub to the shaft, it will easily distort.. good luck
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Old May 07, 2004, 07:00 PM
Will work for planes
omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
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Thanks for that tidbit dave, I think I tighten it too much when I screw it in then. I'll be sure to make it snug.
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Old May 07, 2004, 10:24 PM
Registered User
Pasadena, CA
Joined Jun 2003
3,182 Posts
The feather plate should not move in a titer-toter fashion. Only rotate in axis with the blades. If it does, either the head or feather plate must be cracked.

I second the recommendation, for Matt's CF reinforced feather plate. Makes a NOTICEABLE difference in handling and tracking.

I also recommend his shaft kit, oversized Ti rod, that fits the stock bearings, just leaving out the bushings. It uses a drilled out stock head, (included), and crown gear, and a stock main gear. Lighter, much truer - less vibration, and stronger, than stock. Again, a really good improvement.

(The TR belt drive ain't bad either, when you get sick of replacing the stock TR drive gears and parts.)

Don
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Old May 08, 2004, 06:08 AM
Will work for planes
omega blood's Avatar
Fullerton, California, United States
Joined Jan 2002
1,783 Posts
Thanks for all the suggestions guys. I finaly got some real stick time on the corona. That GY240 kicks ace. I was able to get it at head hight and bing it down with out crashing. Yayy. I even got brave and flew forward and backward, cool. FINALY THE BLOOD HAS RETURNED TO HELIS. CAN YOU SMELL WHAT THE BLOOD IS COOKIN'?
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Old May 10, 2004, 07:17 PM
E-Flight Addict
Silicon Valley, CA
Joined Apr 2002
846 Posts
Well I found this from a search.

Trying to solve some shakes on my corona that has been shelved while I fly my ECO, & hornet & hornet2..

Stock corona, has been put in once on purpose when a cyclic servo went beserk, once from a low battery..

I removed the head & found a bent shaft- straightened this in the crutch as I would my Hornet.. Spin up with the tail intact is smooth, when I put on the head it looks like it (the head) is lopsided- I wonder if I didn't tighten too much.. It appears like the subrotor center part is spinning off center. Oh it does shake with the head on no blades.

Is there a good test to tell what part is off? If it is the hub can it be fixed if it was too tight?

Thanks guys,
Steve
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Old May 10, 2004, 07:26 PM
E-Flight Addict
Silicon Valley, CA
Joined Apr 2002
846 Posts
BTW Just for the heck of it I installed the mains & spun it up- most of the shaking is gone from straightening the bent shaft. at least in a quick hover with the battery dying,
I just like to keep em running smooth. So the question still stands.
Thanks,
Steve
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Old May 10, 2004, 09:14 PM
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denver, colorado
Joined Nov 2003
243 Posts
I don't know about the head - i think the plastic has a memory; there is some elasticity but the point at which permanent deformation occurs is fairly low on the hysterisis curve.

basically, no; once it has deformed there is no brining it back. Maybe with a little heat applied here and there, but it is easier to just replace it.

How do you tell which part - in some cases all you can do is black box it - replace it and see if it is better.

roger
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