Question: Servo noise.

Ok...so I'm starting to go insane! I'm trying to build a 4 channel trainer. I've got everything finished except for the rudder / front wheel servo. Something is wrong with the rudder portion. The servo, without anything hooked up to it works fine. It's nice and smooth and doesn't make any noise. If I attach the control for the front wheel, it still works fine. But the second I try to put the rudder on it starts chattering away. Sometimes I can get it to be quiet when centered, but as soon as I give it any input it starts making the noise. I've heard about it having to try to hard, or exceeding its maximum travel limits etc. I can't seem to figure it out. I've tried using all the different holes in the control arms at both ends and I still can't seem to get it right. Now I'm even trying different attachments at the servo, like a clip instead of just a Z-bend etc. It's driving me nuts! Help.
Jeremy

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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
It sounds like you MAY have either a binding OR tension on the pushrod to the rudder.
The first thing you want to do is swap the servo with a different one to see it the problem persists. On very rare occasions you will get a bad servo right out of the box.
If the servo is still chattering (and the battery is fully charged ) do the following:
Does the pushrod move freely (no resistance - you should be able to move it with a slight motion of your finger tip ) in the guide tube without the rudder attached ?
If it moves freely, check the rudder and make sure the rudder moves freely (rudder hinges improperly aligned and/or CA in the hinge joint can cause the rudder to bind ). The rudder should only require about 2 or 3 times (maximum) the amount of force to move the push rod.
Now connect the pushrod to the rudder and see if everything still moves freely. If it doesn't, the angle of the pushrod where it exits the fuselage will need to be changed.
If everything is still moving freely, check the angle of the pushrod to the servo arm. Is the pushrod and the servo arm at the same angle ? If the angle is not the same, the pushrod inside the guide tube is binding up. You will either need to move the guide tube or the servo to get them both at the same angle. If you move the servo, be careful you do not cause the same problem with the nose gear.
If none of these work, check the information that Alan provided. He is a very knowledgeable person and has a web site that can usually answer any question/problem you may have.
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While I totally agree with the fixes mentioned here, I have found that sometimes you just cant get servos to shut up. I have flown planes with mildly buzzing servos for years with never a problem to my knowledge. Now do not get me wrong if it can be fixed then by all means repair it. Most planes that I have built had the pushrods glued into a certain place long before the radio was even installed so moving that is not always an option. Anyways I do not think your servo buzzing is going to be detrimental to the plane as long as it is not severe and with you description it does not sound that way. Brad
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I think that it probablly is a case of the pushrod binding inside the plastic tube. It seems to be much more difficult to move then the other pushrods are. As also mentioned, moving it will not be a very easy task because the fuselage did come all pre-built. Without doing major surgery I don't know what to do. I tried spraying WD40 down the pushrod even but it didn't seem to loosen anything up.
Thanks for the tips, Jeremy
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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
If it is the tube the pushrod is in, chances are the tube is secured where it exits the fuselage at the tail and on a former near the servo tray only - most ARFS are secured this way. Look inside the fuselage and you should see the tube and where/how it is secured. Some careful use with a #11 blade should free the tube. Try to cut the former away from the tube, rather than the tube away from the former..
If it doesn't come free, your LHS (Local Hobby Shop ) should have pushrod tubes and 24" or 30" long 2-56 rods (threaded on one end ). It would not be difficult to remove the old pushrod and tube and install a new one with the correct angle. If the tube is secured in more than those 2 places, you will most likely need to use the tip of the blade to cut either the tube or part of the former away and a pair of long needle nose pliers (or hemostat) to get at the interior tube mounting.
For the former in the fuselage find a piece of scrap 1/8" lite ply. Make a hole so the pushrod tube will slide easily, and through "trial and error" trim the other end so it will lay against the former with the pushrod and tube at the proper angle. Then use either some thick CA OR 30 minute epoxy to glue the bracket to the former and some medium or thick CA to glue the pushrod tube in place where it exits the fuselage.
Install the pushrod tube, pushrod and connect everything up first to make sure everything is moving freely first, then glue the bracket to the former and the tube to the fuselage with everything still hooked up so you don't loose the angle.
Tip: Leave about 1/2" (or more) of the pushrod tube extending from the fuselage and trim it after everything has dried. For lubrication (if needed ) use POWDERED graphite (lock de-icer). The graphite will not gum up or collect dust and dirt.
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