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Servo Humm....Any ideas?

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Servo Humm....Any ideas?

Old 02-05-2008, 09:57 PM
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rjp
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Default Servo Humm....Any ideas?

Need some advise gents. My rudder/ nose gear servo hums about 70% of the time, when in the null/neutral position. I've tried to adjust the clevises by a few turns to release any strain/load with negative results. I can remove the push rods from the control horn and the servo acts normally (indicates a loading problem I believe). I've swapped servos, same results. I'm using the following gear:

Thank you in advance.

Futaba 9001 analog servos
4.8v 1500ma battery
2.4GHZ 7 channel receiver
Sullivan fibergalss pushrods / 2-56 rod
GB Skylark 70

Old 02-06-2008, 01:03 AM
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Tired Old Man
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Default RE: Servo Humm....Any ideas?

Probably more of the angle the push rod is at connecting to the servo. It's pretty common when the push rod is acting like a prybar against the servo arm.
Old 02-06-2008, 03:25 AM
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perreback
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Default RE: Servo Humm....Any ideas?

Many servos tend to hum even with the slightest amount of binding present. Of course you should try to make the pushrods move as smoothly as possible, but sometimes it's really tricky to remove the humming altogether. Make sure there isn't excessive binding, because that might drain your rx battery quicker than you want. Don't lose any sleep over the occasional humming, though. If you think about it, most of your servos will be under load all the time in flight anyway. For instance, if you have to trim your ailerons a few clicks during your maiden flight, then your aileron servo(s) will be under constant load in flight from then on (think about it, and you'll see what I mean). They'll be humming up there, but you won't hear it. I'll probably be flamed for this, but...
Old 02-06-2008, 07:07 AM
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Default RE: Servo Humm....Any ideas?

No flame from me perreback, I agree with the logic.
Old 02-06-2008, 08:43 AM
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Default RE: Servo Humm....Any ideas?

I have some Futaba 9202 in a Cap and they will hum without any linkages connected. It used to worry me but I've not noticed the battery draining quicker so I stop worrying about it.
Old 02-06-2008, 11:12 AM
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BadSplice
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Default RE: Servo Humm....Any ideas?

Heres my theory on humming servos. I try my best to get the best and smoothest pushrod connections I can, but sometimes I get those humming servos also.
My test is: if a small twitch of the stick, or a small tap on the rod makes it fall into place and stop humming, then I dont worry about it. I figure that, in flight, the vibrations from the engine and the motion of the plane will always be jostling the pushrods around a bit, so they will naturally fall to the neutral position..

If I cant get it to stop humming by twitching the sticks, then I disconnect the pushrod from the servo and push it with my fingers, trying to find whats making it bind any, till I get a smooth connection.

The point about flight loads is great also
Old 02-06-2008, 12:32 PM
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bhole74
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Default RE: Servo Humm....Any ideas?

Losen the scews on the bottom of the case 1/4 turn and see if it stops. Too tight of a fit in the case will cause them to hum.
Old 02-06-2008, 01:03 PM
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js3
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Default RE: Servo Humm....Any ideas?

So is it a specific tune that they are humming or is it just sort of random notes * la John Cage?
Old 02-06-2008, 01:17 PM
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bla bla
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Default RE: Servo Humm....Any ideas?

I like to address these type of problems using highly advanced technical equation. [sm=bananahead.gif]: F'iT!

Let 'em hum. Once the engine is on... you don't hear it anyway.
In the air, your servos are humming continually anyway. As soon as you input even the slightest command, the air pressure is forcing the surface in the opposite direct.
Your servos have to fight against this.
Old 02-06-2008, 09:53 PM
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Default RE: Servo Humm....Any ideas?

Gents thanks for all the advice, I should get an opportunity to try a few solutions tomorrow night.
Old 02-07-2008, 06:25 AM
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Default RE: Servo Humm....Any ideas?

Servos that hum are usually drawing more current than necessary.

If you really want to analyze the problem put an ammeter in the servo line and observe the current draw. Observing the current draw is a positive method to test and correct servo binding. Listening for the hum is a very crude method of testing. I am always surprised at the difficulty to achieve linkage that does not have some binding. Servos will sometimes bind and draw too much current and no hum will be observed.

Bill
Old 02-07-2008, 10:57 AM
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Default RE: Servo Humm....Any ideas?

When you are checking for smooth linkage, also check for any excessive "up or down" force (perpendicular to the normal servo arm motion). A pushrod pressing down on the arm can cause the humming.
Old 02-08-2008, 09:13 PM
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Default RE: Servo Humm....Any ideas?

Do you have a FM set-up with Nicad batteries? If you have a PCM set-up and NIMH batteries,,will alleviate a lot of the humming,,,this is just a minor aggrevation using NICADs. Iswapped all of my stuff to PCM and NIMHs. I noticed a huge difference.

TAZZZZ
Old 02-08-2008, 09:34 PM
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Default RE: Servo Humm....Any ideas?


ORIGINAL: tazzzz

Do you have a FM set-up with Nicad batteries? If you have a PCM set-up and NIMH batteries,,will alleviate a lot of the humming,,,this is just a minor aggrevation using NICADs. Iswapped all of my stuff to PCM and NIMHs. I noticed a huge difference.

TAZZZZ
Please explain to me how battery type will produce servo hum? I just don't see it. Servos and rx's shouldn't care what type of battery it is as long as they are getting the correct voltage and amps.

To the OP:

Digital servo's will hum all the time. Analog servos should not hum. A humming analog servo indicates binding somewhere. The binding can be anywhere in the circut, control rod hooked the the servo arm at an odd angle, control rod binding at some point in the fuselage, even the binding can be caused by the hinges being too stiff ( I've never cared for ca hinges for this reason).

Vance
Old 02-08-2008, 11:21 PM
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Default RE: Servo Humm....Any ideas?


ORIGINAL: bla bla

I like to address these type of problems using highly advanced technical equation. [sm=bananahead.gif]: F'iT!
Agreed!

Once the plane is 3 feet away and the engine, do the servos still hum? WHO KNOWS!??? As long as there isn't any excessive binding in the linkages, you are good to go.
Old 02-09-2008, 08:41 AM
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Default RE: Servo Humm....Any ideas?

OK,,,in my experience,,it cleaned up my act right off the bat. TAZZZZ
Old 02-09-2008, 05:44 PM
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Default RE: Servo Humm....Any ideas?


ORIGINAL: tazzzz

OK,,,in my experience,,it cleaned up my act right off the bat. TAZZZZ
I think it's more likely the change from a regular ppm signal to a pcm signal had more to do with the elimination of your servo buzz.
Old 02-10-2008, 10:03 AM
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Default RE: Servo Humm....Any ideas?

YUP,,thats it.

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