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Duel elevator pushrod problem

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Old 05-06-2008, 03:07 PM
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pumbadog
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Default Duel elevator pushrod problem

I keep running into a wall in getting the elevator system set up right. First I tried running a Y down to the elevators using a singe servo to Y pushrod configuration. I wasn't satisfied with the flex I was getting. Then I went to graphite in sleeve pushrods running down the sides of the fuselage from dual servo's. much better push but I was getting binding problems where they exit the fuselage and both elevators weren't always moving exactly the same.

New system is to try and cross staight graphite tube from dual servos to the elevators so they have a straight shot. Now, new problem... you guessed it, they meet down towards the end of the fuselage and can't occupy the same point at the same time. Physics can be inconveniant some times.

Here's my potential solution but I'm going to see what you all have to say before I overcomplicate a simple solution.

I'm going to try and cut one of the rods and make a piano wire loop for the other pushrod to pass through or use some scrap tube and bridge it across the top and the bottom allowing the other to pass through.

Is this a good solution or is there an easier way? Will it hurt for them to possibly rub or vibrate on each other? This is central hobbies graphite tube. I know they make a bellcrank system for elevators, put my fuselage is too wide.







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Old 05-06-2008, 03:53 PM
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JohnBuckner
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Default RE: Duel elevator pushrod problem

I often avoid split elevator halfs as redundant anyway and frequently reinforce the tie between the halfs expecially for my higher performance pylon airplanes.

If What you are suggesting is some sort of loop for other rod to go through seems totaly counter productive of what the carbon rods are for in the first place (a flex free system with zero potential for any aerodynamic blow back of the surfaces).

If you are going to use two servos as in your drawing then the solution is to not mount the servos on the same rails but one deep within the fuse and the other higher towards the access. This should allow clearance where they cross.

I always do this with my warbird pylon racers except If neccessary I convert to a single servo and make sure the connection between the elevator halfs are diving board strong and will not twist. The rudder servo and elvator servos often just behind the wing are crossed as in your drawing and one servo is deep in the fuse the other higher up. Allowing arrow straight carbon pushrods from servo arm to surface horn. The differance in how much better the airplanes fly and handle is amazing compared to the wet noodle pushrod systems so common today.


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Old 05-06-2008, 04:33 PM
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Default RE: Duel elevator pushrod problem

That's worth a shot. I just hope I don't have to alter the exit holes in the fuselage too much more to allow for the difference in exit angle. I'm an ok builder, but I hate mounting radio gear.
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Old 05-06-2008, 05:45 PM
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Default RE: Duel elevator pushrod problem

I would move the servo horns to the inside and take the X out of the set up. Just run the right pushrod to the right half and same on the left.

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Old 05-06-2008, 06:34 PM
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Default RE: Duel elevator pushrod problem

I wish it was that easy. If I do that, they would exit the fuselage about 6" ahead of the horizontal. I'm mostly stuck with the exit slots I've already made in the fiberglass fuselage. Hindsite being 20/20 I'd have joined the elevator halves prior to install and use one pushrod. I made the mistake of following an already poor set of instructions. Thanks though.
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Old 05-06-2008, 07:13 PM
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dbacque
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Default RE: Duel elevator pushrod problem

I've had problems with "Y" pushrods too. Lost a nice plane to elevator flutter because the pickle fork pushrod just had too much flex in it. But there's nothing wrong with a Y pushrod setup if you have good straight runs. And the only way to achieve that is to split the pushrod at the other end.

What I do is run two 4-40 pushrods from the elevator halves up to just behind the servo. Cut one here and solder it to the other, wrapped with wire of course. Both pushrods have full length outer sleeves to just behind the fork with supports on each end and more if you can do it. Done correctly this gives two perfectly straight pushrods that have no flex and no intereference problems. Also works with carbon pushrods, just substitute JB Weld for solder.

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Old 05-06-2008, 07:38 PM
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Default RE: Duel elevator pushrod problem

So maybe instead of duel servo's, go to one servo and run both pushrods off that servo in a V configuration instead of a Y. I'll have to see how well that works and figure out if it'll interfear with the rudder and tail wheel pushrods. right now they cross so far into the tail that it's a non issue. If they cross up at the servo tray, it could be an issue.

Thanks though. It's a good thought worth checking.
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