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Digital or Coreless...

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Old 12-19-2004, 07:31 AM
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a65l
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Default Digital or Coreless...

I'm building a Zen 50 and am having trouble decicing which way to go with servos. I fly Futaba stuff, and I'll probablly wind up going digital as Servocity.com has the S3151's in a buy one, get one free sale. Tower's price is cheaper, but overall I'll save quite a bit going with servocity. I don't really think I need the extra speed from coreless on this plane, and I'm trying not to make any compromises. I'm going to stick with and FM receiver, don't feel any need to go PCM just yet. But I'd appreciate any input about the servos...


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Old 12-19-2004, 11:45 AM
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Default RE: Digital or Coreless...

It's a good deal but those servos are very slow. If that's ok with you I'd get them for the money savings. But that could hinder your response time in manuevers. I looked for others that were faster in the Futaba brand but they are too expensive. Take a look at these Hitech servos. They plug right into Futaba receivers so no problem with compatibility.

http://www.servocity.com/html/hs-525mg_high_speed.html

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I'm building a Zen 50 and am having trouble decicing which way to go with servos. I fly Futaba stuff, and I'll probablly wind up going digital as Servocity.com has the S3151's in a buy one, get one free sale. Tower's price is cheaper, but overall I'll save quite a bit going with servocity. I don't really think I need the extra speed from coreless on this plane, and I'm trying not to make any compromises. I'm going to stick with and FM receiver, don't feel any need to go PCM just yet. But I'd appreciate any input about the servos...


Andy
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Old 12-19-2004, 03:12 PM
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Default RE: Digital or Coreless...

I bought some of the S3151 servos and yes, they are quite slow, even though the official specs claim 0.21 seconds for 60 degrees (the same as an S3001). In fact, I believe these are an S3001 with a digital amp.

Several members at our club are using them without problems and they seem fine.

Are they worth the extra $ over the S3001? I don't know -- they certainly don't seem to be as nice as the Hitec digitals -- but they cost almost twice as much even for the cheapest.

If people are worried about speed they can always use a 5-cell pack -- that's what I do when using cheap standard servos and it provides a very useful improvement -- allegedly speeding the S3151 up to 0.19 seconds for 60 degrees rotation (just 0.02 seconds slower than the HS525 on 4-cells).

The issue of servo speed is an interesting one.

If you look at someone's thumbs while they're flying, you'll note that (other than 3D fliers) most of the inputs are actually quite slow, meaning that the servos are seldom called on to travel at speeds anywhere near their maximum. This is probably why the average sport flier would never notice the difference between an ultra-fast servo and a slow one. What's more, lots of people are now using expo on their transmitters and this has the effect of further reducing the speed servos need to move most of the time.

I use Hitec 5925 servos (0.08 sec) on my 3D ships and find the extra speed really useful -- but I'm doing stupid things like pulling out of vertical dives at 3 feet above the ground, so a servo that takes 0.13 of a second longer to go to full deflection *does* have quite an effect in such cases :-)
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Old 12-19-2004, 06:22 PM
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Default RE: Digital or Coreless...

For a 50 size plane I would recommend 9001's to someone who prefers Futaba. I would probably opt for a 9202 on the rudder. Both servos are coreless and faster than you're going to need. There is really no need for a .08 speed servo. Hope this helps.

-Kelly Gerber
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Old 12-23-2004, 09:01 AM
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Default RE: Digital or Coreless...

I used to buy Futaba 9202 servos but have had a 50% failure rate on the pots. They wiggle finding or trying to hold center. The S-131 was much better. I just bought some Hitec 6635 karonite digitals and really like them. The 6635s are smooth, strong and seem to be a good digital replacement for the S-131/9202.
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Old 12-23-2004, 04:42 PM
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Default RE: Digital or Coreless...

Well, I wound up going with the digitals from servocity. They arrived today, and I'm sort of suspucious. I thought all the digital servos had larger gauge input wires, but these look like the same as are on all my other Futaba servos. They're also listed as having dual ball bearings, but I pulled one apart and can only find one ball bearing, although there is a metal bearing on the bottom of the output shaft. I was afraid it was an uncaged ball bearing, but if the balls went everywhere I can't find them, and the fit is too tight to allow any in there anyway.
I also thought that digital servos "buzzed" at neutral, but these are completely silent. They even sound the same as the standards, but what was I expecting. But I am very puzzled about the wires...


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Old 12-23-2004, 04:47 PM
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Default RE: Digital or Coreless...

Which model of digital did you get?

Not all digitals buzz or sing, it's generally only the high-performance ones. I have some some of Hitec's entry-level digitals (HS5475) and they don't buzz, neither do the Futaba S3151 units. My coreless HS5925 digitals however, sing like a bunch of banshees :-)

Why did you pull your servo apart? There's a lot of wisdom in the old adage: "if it works, don't fix it."
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Old 12-23-2004, 08:37 PM
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Default RE: Digital or Coreless...

I got Futaba S3151's. Apparently they came out of a 9C set, because they were in individual plastic bags, and the hardware was all in one bag. So I would guess Servocity sold just a transmitter, and put the servos/receiver up seperatly.

I was curious because I thought digital's had larger gauge wire than regular servos, so I wanted to take a peek inside and make sure they weren't just 3001's with a new upper case! Suspucious *******, aint I?

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