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Which servos center really well?

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Old 10-25-2005, 09:24 PM
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Edge 540
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Default Which servos center really well?

What servos would you recommended for good centering characteristics? I am looking at mostly futaba and hitec. These would be used on 5-6 lb 3d planes, and a 9lb pattern type plane. Can you tell a big difference between coreless and a 3 or 5 pole motor?
-I would definitely want ball bearing
-standard torque or greater
-good centering
-light, I really want to keep weight down
-possible coreless
-price reasonable... lets say $30<x<$70
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Old 10-25-2005, 10:08 PM
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Default RE: Which servos center really well?

Hi Ultra Stick, could you describe the problems you've been having with centering? In the back of my mind, have a feeling.
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Old 10-26-2005, 07:19 AM
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Default RE: Which servos center really well?

Well, it was mostly with a few 3003 that are several years old and have many (100's) hard flights. There are no long extension, so maybe the pots are wearing out? I have changed the y harness already.
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Old 10-26-2005, 09:34 AM
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Default RE: Which servos center really well?

Its a possibility. 3003/4's are somewhat sensitive to vibration. If it is the pot, they generally, "bounce" around center before stopping. But if the surface tends to stop at a different center depending on the direction, it could be just binding.
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Old 10-26-2005, 10:17 AM
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Default RE: Which servos center really well?

How do you know it is not the pots in your transmitter sticks that are causing the centering problem? I have tested some servos for people that were having centering problems using a computer to simulate the pulse coming out of the receiver to eliminate the transmitter. Doing this I have found that a lot of centering problems are in the sticks of the transmitter not the servos.

In measuring servo centering error I have found a good part of it is hysteresis. So now the centering specs can be part of a game of how it was measured. If it is always measured as repeatability coming from the same side to center it will look a lot better than if it is coming back from center measured from one side then the other.

I know this doesn't answer your question but it is something to look into with servo centering.

Pete
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Old 10-26-2005, 03:25 PM
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Default RE: Which servos center really well?

I have a brand new futaba 9c, so I really doubt it is the TX. Thanks though.
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Old 10-26-2005, 03:52 PM
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Default RE: Which servos center really well?

You might be surprised to find out how much slop is in the sticks...even on a 9C. If you took a voltage measurement at center from the pot after the stick has come back from full left it will not be the same at center after it comes back from full right. There is mechanical slop in the stick and electrical slop in the pot. Now, I am lucky to have played with some expensive equipment to be able to see this in measurements.

A very precise pot is extremely expensive and would never have the cycle life that the pots have in the sticks of a radio...even a 9C

Now add to that the centering error in a sport servo...I think our radios work pretty darn good for what they are.

Pete
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Old 10-26-2005, 07:26 PM
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Default RE: Which servos center really well?

I've been using the Futaba 9650 digitals in my racing planes. Been working good for me, but not sure under the crazy loads of 3d.
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Old 10-27-2005, 03:03 PM
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Default RE: Which servos center really well?

If you are interested in determining the merits of your system get one of the Vespa ServoXciters. This has the capability of measuring the deadband of your servo and also measuring the output pulse width of your radio. See it at www.vespacontrol.com
PS I am in no way connected with Vespa.
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Old 10-29-2005, 08:09 AM
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Default RE: Which servos center really well?

Most small digital servos would give you the accuracy you're looking for. I'm not familiar with Futaba servos, but I have used the JR DS9411s and JR DS3421s they are both very accurate and powerful. Look for something similar in a digital futaba and you will be impressed. You can blow on the control surface and here the servo start!

Slop in TX pots? [&:] I can see how it would have an effect with some cheaper radios, but I would EXPECT the 9C to have no problems of this sort.
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Old 10-29-2005, 12:51 PM
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Default RE: Which servos center really well?

I would too. I am very pleased with the radio.
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