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03-25-2006, 01:46 PM | #1 |
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I am: Mike Gyger
Join Date: Jul 2005
Location: Chilliwack BC
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Pushrod input please (fixed now!)
My King Kobra is flying after 10 years of construction. The only problem I have is the pushrods are slapping together at certain RPM's (may be prop out of balance still) and in certain combinations of inputs.
The servos are mounted in the fuse. The rods are Carbon Fibre ones and I think it's just the nature of them when they tap each other. (the fuse at the rear is really tight, maybe 1" square or less). I'm thinking of changing them out to just a hardwood dowel, maybe 3/8 or 1/4 diameter. I'm looking at all the plans etc I have on hand, and they all use Balsa. I'm wanting to use dowel, as it's stiffer IMO. I'm just wondering if I'm asking for problems by doing this. Pull Pull has been suggested by a guy in the club, but I don't think it'll be easy to do, I'll need to hog out holes inthe rear of the fuse, and there is not enough room. I'm looking for a simple fix, that will stop the clattering I hear. It's not a problem structurally, or anything, I just need to eliminate the noise. It makes the plane sound much more annoying than it already is. Thanks guy's Mike |
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03-25-2006, 03:34 PM | #2 |
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I am: Dave
Join Date: Jul 2004
Location: P.River,Alberta
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Get Shafted
Mike,
The carbon fibre rods should be just fine. You may want to use ball links at either end of your connections. The binding can usually be adjusted by moving servos around to avoid the criss crossing of rods. Also I remember using about 3 1/2 to 4 inch threades rods off the pushrods at the tail end. Dave |
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03-25-2006, 03:41 PM | #3 |
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I am: Ken Currell
Join Date: Jun 2004
Location: Whitby, Ontario
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Hi
Get a small mirror and look inside the fuse to see where they are hitting together. You might also need a tiny flashlight. Do the rods cross over each other inside the fuse? If that is where they hit it may be as simple as a tiny bend in the wire or raising up one of the servos by adding a 1/16" piece of plywood under both ends of either the elevator or rudder servo to separate the rods. Cheers |
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03-25-2006, 04:05 PM | #4 |
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I am: Wayne MIller
Join Date: Aug 2004
Location: Kitchener/Drumbo, On
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Pushrod noise
Hi,
I'm making the assumption you do not want to replace the current pushrods, or replace them with nyrods. The following are old tricks, and may not be acceptable today, but I thought I'd pass them along for you to evaluate and hopefully they may be of some help. Many years ago I had an old Ugly Stick that had the same problem, when I looked into the fuselage, I noticed the pushrods dowels just touched each other when they crossed inside the fuselage. What I did was take the pushrods off at the servo arms and slid one "O" ring (just the right size of both rods together) over both the dowels down to the crossing point. This held the rods together, allowed them to move freely but did not allow them to "slap" into each other under vibration. I continued to fly the plane for another year until the fuel soaked firewall gave out. I really liked that plane. If the push rod dowels are hitting the sides of the fuselage, the above won't work. However, you can get a block of light foam about an inch or so thick. Cut it the same shape as the interior of the fuselage, cut holes for the pushrod dowels to go through at approximatel the same place where the dowels would go through when in the fuselage (make the holes just a little larger than the pudhrod dowels to allow free movement). Take the pushrods off at the servo arms, put the pushrods through the foam and gently slide the foam down into the fuselage. The foam will dampen the vibration and stop the pushrods from hitting the fuselage. Let us know what the final fix was. Fly4Fun, Wayne Miller |
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03-25-2006, 04:59 PM | #5 |
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I am: Mike Gyger
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First attempt, test fly tomorrow
Alright guy's
I had an engineering moment there. I have tried to keep everything on this plane as simple and robust as I could. The control surgaces have Robart Ball link control arms. The servo end has soldered on Dubro clevises. Servos are only futaba 3004's, but they should be fine. The control rods are Carbon (1/4" tube) with 6-32 rods on each end. When I installed the rods originally, there was only about 1/16th of an inch or so space between the rods and the fuse formers. They do not cross. So far, I've put a 1/4" or so offset at the servo end of the rod. Being 6-32 (I'm thinking I went overkill) it shouldn't cause any issues. The offset is over 2 or so inches. This gives me 1/4" clear at the servo closest to the servo, and around 1/8 or so towards the rear. Hopefully this will be enough. I'll find out tomorrow. Now, I need to go balance some props. I'll let you know if my rattly plane is better tomorrow. Thnks Mike Wayne, I avoided nyrods, as I have a Cub with them in it. I battled them for a year. They were always flexing in different spots. I eventually was able to get enough attachment points along the outer sleeve to stop it, but nothing is worse than trying to bring a largish Cub in for a landing with the Elevator oscillating about once every 2 or 3 seconds. I know it was my fault not the rod, but it still worries me, especially with my flying style. |
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03-25-2006, 05:11 PM | #6 |
RCC Supreme Contributor
I am: Wayne MIller
Join Date: Aug 2004
Location: Kitchener/Drumbo, On
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Pushrods
Hi Mike,
Great pictures. I think you probably have it fixed. Let us know how tomorrow goes. Fly4Fun, Wayne |
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03-27-2006, 10:13 PM | #7 |
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I am: Mike Gyger
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Thanks everyone for your suggestions.
Although they were all excellent, and would have worked, I took the easy way, and just installed the offset (as I've already said). For once, the easy way worked out. I forgot I'd change the trim though, and thought I was having something else go wrong when I had to start dialing in a bunch of elevator and rudder trim. Once I landed, and started to look for the cause, I remembered I'd changed everything on the tail (more or less). Problem solved and the plane came home in one piece!! I'm off to find another problem to fix on another one! Mike |
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03-28-2006, 06:24 AM | #8 |
RCC Supreme Contributor
I am: Wayne MIller
Join Date: Aug 2004
Location: Kitchener/Drumbo, On
Radio of choice:
Hitec A9 JR 9303 # of RCs: 19
Feedback: 11 / 100%
Posts: 2,169
Total Props: 9
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Thanks got Follow Up
Hi Mike,
Thanks for the follow up. Glad to hear your in the air again and all is well. Sounds like your getting everything dialed in for the summer flying. Fly4Fun, Wayne Miller |
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