Servo Buzz
 

hey troops. I have a Sig Mayhem 40. When I throw the flaps or air brakes (really extending but, not full throw for this plane) I get a buzz in the servos. Is this normal? I have dual rates set up although Im not skilled enough yet to try and fly with them. But, when I activate them and move the throws I also get the buzz...?? Im using a Futaba 7CAP with Futaba S3004 servos.. any Ideas? thanks for any help

RE: Servo Buzz
 

With non-digital servos, a buzzing takes place when the servos are fighting to attain/maintain their positions. It's an indication that you've either reached the limit of a surfaces deflection before the servo has reached the end of its travel, or that you have considerable friction somewhere in the linkage. If you don't get it cleared up, at a minimum the affected servos will use quite a bit more battery power and have a shorter life. You may also get some binding in the linkage, which can be bad news.

Check your linkages, and try to resolve the friction points and any misalignment in the geometry or hinge lines for the control surfaces. A good way to feel the problem is to take the servo horn off and move the pushrod with your fingers.

RE: Servo Buzz
 

MikeL hit the nail on the head. Follow his advice.

Ken

RE: Servo Buzz
 

I agree. Disconnect the servo from the push rod and see if the buzzing sound goes away. It should. Try to free up the linkage so the flap goes up and down very easily, and then reattach. If you still hear buzzing, see if you hear it only at full throw of the servo, and adjust as necessary.

RE: Servo Buzz
 

Thanks for the advise. All the linkages seem to be free and smooth and as I said Im not even going full on the throws. Ill do all that was advised. I really appreciate the help.

RE: Servo Buzz
 

What about servo buzz when the servos are at neutral. Whenever I turn my plane on I get servo buzz. How do I get rid of that?

Shane

RE: Servo Buzz
 

analog or digital servos?

RE: Servo Buzz
 

JR 539's

RE: Servo Buzz
 

Can't find 539's, could you have meant 537's?

Anyway, digitals tend to buzz but analogs should not. If they are analog and buzzing they are most likely fighting against drag somewhere in the system.
Disconnect the outputs and see if they still buzz. If the buzz goes away, find and reduce the drag in the controls. Also be sure the TX is turned on but not TOO close to the RX as it could be swamping the RX and causing this symptom.

RE: Servo Buzz
 

They are 539's, the standard servo with the base computer radios here in Australia. I'll give that a try today.

RE: Servo Buzz
 

I disconnected the push rods and the buzz disappeared. It comes back when I tighten the servo arm screw that last bit. It's occuring mainly on the elevator where I do have some sub trim in (30 on a JR XP662). It also appears to be intermittant. Its mainly there but every now and then its gone. Could the sub trim be the problem?

RE: Servo Buzz
 

I have also found that if the hole in the servo arm is a litlle tight for the clevis it was binding at that point. I enlarged it a little bit and the buzz went away.

RE: Servo Buzz
 

Take the pushrod/clevis off the arm and check again. Slowly add components until you fine the cause. The servo sounds like it is fighting against something.

RE: Servo Buzz
 

so to clarify, a buzzing digital servo is not unexpected? I just received one and it buzzes the whole time I have it plugged in, even in neutral, with no load on it. Seems to work OK though.

RE: Servo Buzz
 

digital do buzz. No issues

RE: Servo Buzz
 

Exactly. Digital servos will buzz a little and it is normal. Disconnect the pushrods and listen to the buzz, if it is louder with the pushrods connected then you have something pushing on the servo. But if it stays the same then you are ok.

Ken

RE: Servo Buzz
 

Before you get too concerned, try this...

When the servo is buzzing, lightly touch the servo arm.

Pull it, push it, lift it, etc - all very lightly with one finger.

If the buzzing stops, don't worry about it. When the engine is running, the vibrations will do what your finger did.

RE: Servo Buzz
 

Like Minn said. Sometimes the weight of the elevator or flaps pulling down will add just enough load to the servo to cause it to buzz a little. Sounds silly, but try flipping the plane on it's side, or just gently lift the surface and see if the buzz goes away. I've also found that some servos just like to buzz a little here and there, probably related to the tolerances on the pot, though I'm not sure. But when you stall a servo or really put a load on it, you can often hear a much louder buzz. Try "fighting" the servo by hand.

Another neat trick. If you have a wattmeter used for electric flight, or any random ampmeter, wire it in between the battery and receiver. Then you can watch the current draw. If you think you have an issue, plug the servos in one at a time. Binding linkages, stiff hinges, all that shows up with increased current draw, which is a lot easier to see on a meter than by ear. I found that on one new project, the servos all hooked up with no pushrods connected were quiet and drew very little power. When I hooked up all the pushrods (10 servos in this plane), several servos were buzzing a little bit. But the current draw was the same (to the resolution of my meter). So, no problem there! And deflecting each servo in turn, I could watch the current. For a properly hooked up control, the current at center and the current when holding at full deflection when on the bench should be the same or very very close to the same. (I also found a binding rudder pull-pull setup that WASN'T binding, but was drawing a lot of current when held off-center...)

RE: Servo Buzz
 

Hey Minn, quick question, are you saying if I just litghtly touch the control arm near the servo(on the rudder servo and steering one and the buzz stops or it tends to stop on it's own randomly at neutral then I don't have a problem? If I use the controls and then let it go back to neutral I get the buzz and sometimes it will just sit there for 5 minutes or so and buzz just a little. I have tried disconnecting the rods and even then it will sometimes buzz although it usually quits within 5 seconds in that instance. I've played with the control rods and they don't seem to have much resistance at all. They pretty much buzz anywhere and everywhere when I move the control arms but it seems to move pretty easy and there really is no reason for it.

RE: Servo Buzz
 

Exactly, there is no problem.

As I said, if slight pressure will stop the buzz, then the engine vibration will stop it when the engine is running

RE: Servo Buzz
 

while i seen a whole lot of comments about 'is it digital or analog' that's not the only pertinent question, is it coreless? coreless servos tend to buzz because they don't have the weight in the motor windings to provide a positive position hold and allow for 'over shooting' of neutral so they hunt for center constantly and buzz doing so. touching the servo will stop the buzz because it prevents the over shooting and constant oscillation

kc