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Servo 'hum' that operated Robart Valve - 1/9/2013 2:13 AM   
newflier1


 

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I cannot get rid of a 'hum' in my servo that Iam using to operate a Robart air valve.  Hum is probably not such a good description, but what is happening is that my volt-watch is lighting up like a Christmas Tree when I turn on my transmitter and plane.  If I unplug the retract servo, the volt watch just shows one steady light and you don't hear any 'hum'.  I've tried both a Futaba S3004 and a HiTec 325 servo and I get the same results. I have my throws set really 'short' so I know I'm not attempting to move the valve past its operating range.  I think I have some sort of 'tension' problem between my valve and the servo.  I'm using a clevis to attach to the valve and a screw lock push rod connector on the servo arm.  When I turn everythin on and 'jiggle' the servo arm, the humming will stop.  But when I flip my transmitter switch back and forth, the servo hums and many lights on my volt watch all illuminate.  Everything seems to be lined up nice and straight and the distance from the valve to the servo is only about an inch and a half manybe even an inch and a quarter.  I know this is a problem as this will drain my receiver battery if I dont find a remedy.  I am at a loss as what to try next. Any suggestions?



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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 2:30 AM   
Gray Beard


 

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Status: offline 		Does it go away when you remove the servo arm? Sometimes all it takes is the weight of the control rod to get one to hum. Then any tension at all will also make it hum. Usually not too big of a deal. It can be the weight of the control rod or just a slight amount of tension.

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 3:01 AM  1 votes
Scar



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Status: offline 		Both the servos you mention are regular servos. Set it up with a retract servo, and that hum all goes away.

The transmitter's retract channel doesn't have any proportional at all, it's all the way one way, all the way the other way. The retract servo must be set up to turn 180 degrees without bottoming on either end. It can't respond proportionally, it goes all the way either way and stops.

Good luck,
Dave Olson

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 4:41 AM  1 votes
DavidAgar



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Status: offline 		I am betting you either have a bind between the valve and the servo or you need to adjust your servo end points. The Robart air valves need very little throw to work and I cannot ever remember not having to set the end points to get the servo to quit acting up. I also use ball joints for my ends. Good Luck, Dave


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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 10:27 AM   
TomCrump



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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 12:07 PM   
scale only 4 me



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quote:

ORIGINAL: newflier1

I cannot get rid of a 'hum' in my servo that Iam using to operate a Robart air valve.  Hum is probably not such a good description, but what is happening is that my volt-watch is lighting up like a Christmas Tree when I turn on my transmitter and plane.  If I unplug the retract servo, the volt watch just shows one steady light and you don't hear any 'hum'.  I've tried both a Futaba S3004 and a HiTec 325 servo and I get the same results. I have my throws set really 'short' so I know I'm not attempting to move the valve past its operating range.  I think I have some sort of 'tension' problem between my valve and the servo.  I'm using a clevis to attach to the valve and a screw lock push rod connector on the servo arm.  When I turn everythin on and 'jiggle' the servo arm, the humming will stop.  But when I flip my transmitter switch back and forth, the servo hums and many lights on my volt watch all illuminate.  Everything seems to be lined up nice and straight and the distance from the valve to the servo is only about an inch and a half manybe even an inch and a quarter.  I know this is a problem as this will drain my receiver battery if I dont find a remedy.  I am at a loss as what to try next. Any suggestions?




My first thought was you were in hi resolution mode with analog servos, but don't know what your equipment is,, so that just guessing
also
Could quite possibly be this connection, if it too tight in the plastic servo arm, I've had those connectors cause buzzing too, sometimes they are just too tight and won't pivot freely enough.

good luck

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 1:33 PM   
newflier1


 

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Status: offline 		Here is what happens.  If I leave everything connected, but just loosen the allen screw on the "screw lock push rod connector', the hum goes away.  It appears only to 'hum' when I tighten down on the allen screw.  It appears that when the push-rod is in its 'locked' position and I activate the switch, it is adding some tension and the servo hums.  I can't use a retract servo as one person mentioned, as I only need to move this valve less than 3/8".  Somehow, I am not getting a nice pivot and I think that is what is causing tension and thus the hum.  As you asked, if I hook everythig up and lift the the servo arm off the servo, the hum stops.  That is telling me its a 'tension' problem, but I don't know what to do to eliminate it.  Maybe try ball joints as someone mentioned.


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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 2:03 PM   
JohnBuckner



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Status: online 		In this case the very shortness of the pushrod itself is agrivating the situation, this is especially so when an EZ Just is used on one end of the rod or other.

Which end of the rod is the EZ Just being used and what kind of connection is being used on the other end of the rod?

Sometime in this situation just reversing ends with an EZ Just will solve the problem. They have the least give and flexability of all and yes using a ball type connector will definately help.

John

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 2:08 PM   
da Rock



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quote:

ORIGINAL: newflier1

Here is what happens.  If I leave everything connected, but just loosen the allen screw on the ''screw lock push rod connector', the hum goes away.  It appears only to 'hum' when I tighten down on the allen screw.  It appears that when the push-rod is in its 'locked' position and I activate the switch, it is adding some tension and the servo hums. 


Sounds like you have a fair grasp of the situation. At least you have a very good test of it.

So consider a couple of things you see.

When you unscrew the allen screw while the system was turned on, if the push rod was pushing or pulling the servo arm to cause the hum, that pushrod should move when you unscrew the allen screw, right?

If you can't see that movement, then mark the rod and do the test again. If the rod isn't moving, then something about tightening the allen screw is introducing that push.

You might consider removing the allen screw and filing it's contact point flat. Also might simply try a different screw. It sounds like the twisting screw pulls or pushes the rod as it tightens down and introduces tension into the servo arm/push rod connection.

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 2:11 PM   
newflier1


 

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Status: offline 		I should probably take a picture, but here is how I have it currently set up.  On the valve end I just have a scew-on plastic clevis, that is the threaded part of the push rod.  The other end I have nothing - it is just going through the hole in the 'screw lock push rod connector'.  Now the 'screw lock push rod connector' is attached to the servo arm and is a 'little' loose so that it will pivot.  The entire length of this set up like I said is about one and a half inches.


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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 2:18 PM   
JohnBuckner



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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 3:15 PM   
scale only 4 me



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quote:

ORIGINAL: newflier1

Here is what happens.  If I leave everything connected, but just loosen the allen screw on the ''screw lock push rod connector', the hum goes away.  It appears only to 'hum' when I tighten down on the allen screw.  It appears that when the push-rod is in its 'locked' position and I activate the switch, it is adding some tension and the servo hums.  I can't use a retract servo as one person mentioned, as I only need to move this valve less than 3/8''.  Somehow, I am not getting a nice pivot and I think that is what is causing tension and thus the hum.  As you asked, if I hook everythig up and lift the the servo arm off the servo, the hum stops.  That is telling me its a 'tension' problem, but I don't know what to do to eliminate it.  Maybe try ball joints as someone mentioned.


Sounds to me like the servo arm is not rotating on the same plane as the in/out motion of the valve. just a little twist of the servo arm can cause buzzing

A ball link on both ends would surely cure any misalignments

good luck

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 3:21 PM   
newflier1


 

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Status: offline 		I have not checked to see if the 'control rod' moves when I loosen the allen screw, I can do that and see what happens.  I agree with you that if there is tension, then I should see the rod move when I loosen the screw.  I can answer your second question.  When I do tighten down on the allen screw, I do see the control rod turn - there is not doubt that is happening.  I have NOT filed a flat spot on the rod where the allen set screw tightens down. 


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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 6:56 PM   
Gray Beard


 

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Status: offline 		If you have the room then using the ball joint type of clevis may work for you. Last air/air set up I did took a lot of aligning to get it right.

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RE: Servo 'hum' that operated Robart Valve - 1/9/2013 9:28 PM   
dasintex



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Status: online 		+++ on the use of Ball Joint Connectors, I put one on the Air-valve, and a nylon quick connect on the servo side, a nylon clevis on the servo would work as well, or better yet, ball joints both ends on a fully threaded push rod, that way it articulates fully, will adjust on both ends to get the end points and travel adjusted mannually, as well as using your radio, should take care of the buzzing, something you don't want because it will draw on your battery.


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RE: Servo 'hum' that operated Robart Valve - 1/10/2013 3:31 PM   
newflier1


 

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Status: offline 		Dasintx - I think I may be in luck.  I picked up a dubro ball joint at my LHS last evening.  I put that on the Robart air valve.  I was just able to get a nylon clevis onto the other end (I'm only dealing with about 1.25 inches here - which is part of the problem).  The hum has been greatly reduced.  I think I just have to add a little 'shim' under my servo, as the ball on the 'ball joint' added some height and now I am not on the same plane between the servo arm and the valve.  Granted the ball joint makes up for some of that, but I think once I raise the height a little, I will be set. 


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