Where did your vibration come from?  
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Where did your vibration come from? - 6/11/2003 8:55:13 PM   
sachin998


 

Posts: 35
Joined: 2/12/2003
From: Cape TownNA, SOUTH AFRICA
Status: offline 		Dear Readers

Vibrations! where does yours come from? How did you eliminate it? We can balance this and balance that, straighten this and straighten that, but we still "sometimes" encounter that strange vibration which may appear to be coming out of thin air, considering we all well know we checked everything inside and out!

So now where is it coming from.

I would like to know from any of you ppl out there; where did your strange vibration come from, and how did you resolve the matter?

It would be nice to have a resource to look up, when we experience the "shakes" so we can all look into it and see if this is our problem. This is something which almost always happens where 90% of the time its the common "stuff", and the other 10% only your dog knows. So this is when we come to rcuniverse.com and look for another baffled soul.

We all are pretty much hooked on this heli and ejoy it thoroughly, so let up your "shaking problem" and let us know.

Kind Regards

Sachin
       Post #: 1

Where did your vibration come from? - 6/12/2003 1:31:30 AM   
N111KX


 

Posts: 87
Joined: 11/20/2002
From: GA
Status: offline 		Get Chris' ball bearinged boom. It helps a lot.
http://www.geocities.com/buckey29/corona.htm
Kip

(in reply to sachin998)
       Post #: 2

Where did your vibration come from? - 6/12/2003 2:16:19 AM   
Spiro



Posts: 335
Joined: 4/14/2003
From: Mesa, AZ, USA
Status: offline 		Here are a few sources of vibration I have run across. Some solutions will be more useful than others

1) Blades out of track
-track the blades well…

2) Blades in track for some portions of the disk, but not for all portions (ie: blade tips line up in the front of the chopper, but a high and low blade are visible in the rear portion of the rotor disk)
-possible bent feathering plate or main hub. Bent feather plate may be caused by blade weight distorting the feathering plate when stored in hot/humid conditions. Check main hub for a bulge near the Jesus bolt. If the Jesus bolt has been over tightened, the hub will bulge out here and will be off center of the main shaft. Either condition most likely requires replacement

3) Blades out of track at some speeds, but in track for other speeds
-possible second order dynamic balancing issue. Balance the blades as per “normal” rc heli guidelines, not just the first order static litemachines recommendation. ie: find the c.g. of each blade along the long axis, weight the tip of one blade with balancing tape to make these match in location. Then match the blades weight by adding balancing tape to the light blade exactly at the c.g. When done the two blades should have the same weight, the same c.g. location, and thus the same polar moment. As part of this the rotor head complete with grips and sub rotor will have to be balanced separately. This often requires adding weight to the feathering plate arm opposite the sub rotor pushrod hole. This can be done by using a longer/heavier bolt through that blade grip, possibly in addition to washers and nuts on that bolt.

4) Main gear mesh too tight
-remesh main gear. If it is impossible to move the lower bearing block forward enough, remove the bearing block and check to see if CA glue “fillet” is preventing forward movement. Grind fillet or bearing block corner. Loosen both upper and lower bearing block when meshing, then tighten lower bearing block first, then upper when proper mesh is achieved.

5) Bent main shaft
-new main shafts can easily be made using 5/32” music wire and a dremel type tool. Simply cut to the same length as the original and grind the Jesus bolt notch and main gear flat in the same locations. Shafts can be straightened through a variety of methods, but will always have some runout even newly made. Just how straight things need to be and how much runout is acceptable is a topic of debate.

6) Clutch shoe cracked/thrown
-install new set of clutch shoes. The clutch shoes should not always drag on the inside diameter of the clutch bell. Good clutch shoes will have a straight/parallel cut separating each shoe from the central body, not a widening V cut.

7) Tail rotor beveled gears (main shaft / drive wire) mesh too tight/loose
-loosen the setscrews holding the beveled gear on the main shaft and also loosen the three screws securing the tail boom to the crutch. Adjust the main shaft bevel gear up and down and the tail boom for and aft to achieve proper mesh as per the instruction manual.

8) Bent tail rotor drive wire
-buy a new drive wire or straighten the old one. This usually results from a boom strike. The carbon fiber tail boom and bearings would also be an excellent solution for this problem and perhaps others.

9) Tail rotor gearbox bevel gears mesh too tight
-loosen the gearbox retaining bolt and pull the gearbox aft. I usually run the gearbox as far aft as the tail boom slot allows.

10) Tail rotor poorly balanced
-remove the tail rotor (on its hub) from the rest of the tail section and rebalance. The instruction manual does not call for balancing this item, but it certainly can’t hurt. It is possible to use a short piece of music wire of the appropriate diameter and use the “fingertip” prop balancing technique. Cut a length of the music wire 1/2" longer than the hub. Chuck the music wire in a dremel or drill and grind a point on each end. Put the pointed wire through the center of the tail rotor and hold gently between two finger tips. The heavy blade will fall. Light sanding on the tip of the heavy blade may be enough to correct small imbalances, otherwise use balancing tape on the light blade.


I am sure there are quite a few more, but these all seem to be easy to check and fix. All of these have in one way or another bitten me in the past.

For what it is worth,
Spiro

(in reply to sachin998)
       Post #: 3

Where did your vibration come from? - 6/12/2003 2:58:42 AM   
grimlock


 

Posts: 23
Joined: 3/6/2003
From: Ontario, Canada
Status: offline 		How does the CF boom stand up to tail boom strikes?

(in reply to sachin998)
       Post #: 4

Where did your vibration come from? - 6/12/2003 6:04:34 AM   
N111KX


 

Posts: 87
Joined: 11/20/2002
From: GA
Status: offline 		I have had 2 crashes with it. One was inverted, the other was a very hard landing after the loss of a mixing arm that slowed the rotor the the point where it hit hard but level. The blades had to have contacted the boom. The boom is unscratched. The blades are undamaged also. The cf boom would have paid for itself had I got it initially.
Kip

(in reply to sachin998)
       Post #: 5

Where did your vibration come from? - 6/12/2003 10:48:31 PM   
davensocal


 

Posts: 9
Joined: 6/5/2002
From: riverside, CA, USA
Status: offline 		Also, out of balance main spur gear has caused some high frequency vibes. We tried to balance it, but eventually replaced it with the Belt Drive. Some of the stock gears seem to be worse than others..

We also went so far as to orient MR shaft collars so that the set screws are 180deg off each other.

Not sure how to quantify it, but everyone says it is a real smooth heli, so I guess I did something right.

BTW- uneven blade tracking (only tracks on one side of the disk) can also be caused by having slop in the mixing arm links (between the swash and mixing arms). 1/2 turn in on one arm only took care of my uneven tracking.

(in reply to sachin998)
       Post #: 6

Where did your vibration come from? - 6/13/2003 9:44:21 AM   
Spiro



Posts: 335
Joined: 4/14/2003
From: Mesa, AZ, USA
Status: offline 		Two more things.

As davidhnsocal mentioned, rotating the various set screws to be 180deg apart can help. I keep mine all lined up on the main shaft, since the sub rotor balance job should take care of this and it makes it easier to realign in the future. Putting the set screws 180deg apart on the tail rotor can, however, make a big difference. My latest attempts to balance the tail rotor ended up with the thing balancing perfectly once the set screws were 180deg apart. With the two collars and all the set screws lined up it was well out of balance. Of course, now with the two colloars 180deg appart and at opposite ends of the hollow tail rotor shaft, this is about the worst thing to do for the 2nd order case. I will have to see if that makes things better or worse.

The second thing was an interesting one to me. I took apart my rotor head in order to change out the main hub and feathering plate. When I slid the long pivot wire out of the sub rotor, I discovered that it was very noticeably bent. I would go so far to say it was badly bent and in several places! I imagine that putting the heli into the pavement so many times had something to do with this, but the bent up wire was completely unnoticeable with the rotor head fully assembled. I do not know what difference this may or may not make, but I cut a new piece of piano wire to replace the 7 year old bent up pivot.

For what it is worth,
Spiro

< Message edited by Spiro -- Jun 17 2003 4:46PM >

(in reply to sachin998)
       Post #: 7

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