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Do I need stronger servos?

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Old 04-12-2002, 03:03 PM
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DeadMeat
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Default Do I need stronger servos?

I am finishing up a TF Contender. I am using a couple of Hitec HS-425 servos for the elevator and rudder. The servos work the control surfaces just fine. But when they return to neutral they keep buzzing.

I know my HingePoints are a little stiff. But should that be happening? I will have to grease and tweak my pushrods some. Where they exit the body, they do not exactly line up with the horn. So I will probably have to put a bend there. But if that does not fix the buzzing, what else should I try? Worst case scenario I guess I will trade up to some HS-605s.

Tom
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Old 04-12-2002, 03:39 PM
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Dazzler
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Default Do I need stronger servos?

Servo's buzzing at center is not a result of not having strong enough servo's, but rather as you mentioned the binding that you have is more than likely the culprit. Your pushrods should move very freely, if not redo them until they are all free from any binding. Also, servo's buzzing is not as big of a deal as many would think, I dont like buzzing servo's either, but after you free up your pushrods if you get a little buzzing, dont worry about it. Daz...
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Old 04-13-2002, 08:04 PM
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Default Do I need stronger servos?

If you are using the Robart style hinge points they are known for causing binding right at neutral. It is imperative that all the hinge pivots be perfectly aligned and that can be hard to achieve.
The difference in hinge pin centerlines causes an over center action as the surface moves through neutral . While the poor servo is trying to maintain the neutral the spring action is trying to put it anywhere BUT neutral.
This can also make for tricky landings etc where it is next to impossible to make real small movements.
Hingepoints are used every day with excellent results,don't take me wrong. Problem is it only takes one twisted in it's hole or in too deep or a hole drilled at an angle to create trouble.
Try taking the pushrod off and move the surface slowly through neutral. If ther is no hint of springing through neutral ,that part is OK and you can check the P'rods etc for drag.
Also if you have access to a Milliammeter you can (should) check the servo current draw. It is amazing how well you can fine tune linkages just by watching how much current it take to drive.
Digital meters are fine for checking static drain at neutral . Analog are needed for watching drain while moving controls ,and work well for neutral testing too.
The new digital servos,5 pole servos and coreless are not always a concern when buzzing slightly. The 3 pole motored analog can draw too much at idle and tell you they are by buzzing.

The only way to know is to take a current draw reading .one servo at a time. Better safe than sorry.

Let us know what you find.
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Old 04-17-2002, 03:03 AM
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Default Thank you...

For your help.

I figured it out. It was my pushrods. I am using a rod-in-tube setup. When I first put the rods and bushings in everything worked just fine. But when I glued the bushings to the rods the CA hardened the bushings and the rods started binding. A little sandpaper action plus lubricant and the pusrods work like a charm.

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