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Servos - Coreless or Digital?

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Old 06-23-2003, 03:22 AM
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Holeshot
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Default Servos - Coreless or Digital?

Hello.


What would be the factors in determining whether and where to use coreless -vs- digital servos?



Thanks in advance....................Dave





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Old 06-23-2003, 11:22 AM
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Steve Campbell2
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Default Servos - Coreless or Digital?

Basically, the only factor is how much precision do you want; and are willing to pay for?

Digital servos aren't any stronger or more reliable than their coreless counterparts. They are, however, much more precise.

Some will say that the "average pilot" cannot tell the difference. Bull. I am certainly no more than average in my flying skills, and I could tell the difference big-time.

I have two models, an X-Cell 60 size helicopter and a Kangke CAP 232 Sport airplane (also 60 size), that I flew for years with coreless servos- JR 4131s in the helo, Futaba 9202s in the airplane.

When I got a 9Z, it came with 9252 digitals. I put them in the helicopter, and could not believe the increased crispness and smoothness; especially on collective (main rotor pitch). So I bought four more 9252s and put them in the CAP. Again, the model's "feel" improved dramatically.

The downside to digitals, of course, is their cost, and the fact that you need to use PCM to get the most out of them. They also use more energy than standard servos, so you need to plan your receiver battery capacity accordingly. I've been running a 1650mAh NiMH pack with four digitals and two analogs, and I get 5-6 flights per charge. My helicopter (four digitals, one analog) has a 2400mAh ni-cad, and it is good for four flights- probably more, but helicopter servos get more of a work-out that those in airplanes, and I'm very conservative with my $1500 machine...

I think digitals would be wasted expense in a typical "sport" plane, like a Stik, etc. but if you have a model that can utilize their added precision, then they are really nice. Just don't ruin the experience with Z-bends or some other junk linkage hook-up. Invest in ball links; you'll be glad you did.

Steve
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Old 06-23-2003, 11:36 AM
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Default Servos - Coreless or Digital?

Most digital servos are coreless... only exception that I know of is Hitec's 5600 series servos whiich are 3 pole motors.

Digital or Analog... Coreless or Not... The determing factor is your application and ultimately your budget.

Depending on your application and budget a good analog coreless servo im most cases will do just fine but if your ganging servos you'd be better off to use digitals.

What are you planning to use them in and maybe we can give you a better recommendation based on what you are using them in.
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Old 06-23-2003, 11:43 AM
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Default Servos - Coreless or Digital?

The plane in question rite now is the H9 P-51D .60 with a Saito 100.

It's going to be on the heavy side with air retracts, onboard alternator, onboard glow driver, dual tanks with Perry pump, and maybe an onboard starter.

I don't think that I worry about weight nearly as much as most folks here.



Thanks................Dave
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Old 06-23-2003, 12:32 PM
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Default Servos - Coreless or Digital?

Weight should be everyones concern... the more it weights the higher the wing loading and the easier it stalls. Anything you can do to keep it lighter will show when it's flying.


In a .60 warbird like yours there isn't really a need to go digital. A good set of analog coreless servos will do just fine. If you fly Futaba I'd recommend the 9202's and if you fly JR I'd suggest some 4131's or 4721's.
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Old 06-23-2003, 02:38 PM
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Steve Campbell2
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Default Servos - Coreless or Digital?

I agree with David. I've flown that H9 P-51, and it is a great, docile sport model. But digitals really aren't needed for it; good coreless analogs will do fine.

Steve
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Old 06-23-2003, 03:16 PM
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Default Servos - Coreless or Digital?

Steve,
What does PCM have to do with digital servos?
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Old 06-23-2003, 05:08 PM
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Steve Campbell2
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Default Servos - Coreless or Digital?

The PCM signal has more encoded "bits" of information, which, once all the computer-geek rhetoric is finished, translates into more servo resolution.

The way it was explained to me, running digitals on PPM would be a waste, since you truly could not tell the difference between digitals or analog. That may be where the "conventional wisdom" comes from.

I dunno; I haven't tried digitals on PPM.

Steve
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Old 06-23-2003, 07:32 PM
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Default Servos - Coreless or Digital?

I would like to use the digital servos also. I would use them in a 120 size pattern plane.
My radio is an ACE MicroPro 8000 FM ham band with only 512k resolution my receiver is a FMA quantum 8 channel. I am using corless Futaba's now. Will my xmitter even run the digitals?
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Old 06-23-2003, 07:54 PM
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Default Servos - Coreless or Digital?

Originally posted by Steve Campbell2
The PCM signal has more encoded "bits" of information, which, once all the computer-geek rhetoric is finished, translates into more servo resolution.

The way it was explained to me, running digitals on PPM would be a waste, since you truly could not tell the difference between digitals or analog. That may be where the "conventional wisdom" comes from.
I'd disagree with this theory... PCM/PPM only deals with how the signal transmitted from the TX is processed.

I run digitals on PPM and one can clearly see the difference over standard analog servos. The digital servo itself is where you see the increase in resolution.

I'm not saying there isn't any truth to what you've been told but I would like to have a professional explain it more in detail.
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Old 06-23-2003, 07:56 PM
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Default Servos - Coreless or Digital?

Originally posted by turbines
I am using corless Futaba's now. Will my xmitter even run the digitals?
Sure it will...
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Old 06-24-2003, 02:22 AM
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Default Servos - Coreless or Digital?

Steve, I agree with everything you wrote with the exception of:

_______________
Steve's post,
The downside to digitals, of course, is their cost, and the fact that you need to use PCM to get the most out of them.
_____________________

I even agree with the cost part. I disagree with the fact that you need PCM to get the most out of them. The difference in resolution would be at the greatest minimal.


The one thing that has not been brought out is the great holding power that the digitals have, even the newer low cost versions. When you move a control surface x degrees it stays at x degrees till you command it to move again. This is one of the reasons that digitals draw more average current.

One last thought to add, the servo, be it regular or digital has no idea what type transmitter or receiver it is hooked to. The signal strength and level is the same for both.

Ed M.
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Old 06-24-2003, 03:14 AM
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Default Servos - Coreless or Digital?

Digital servos are programable. That is why they are more percise. HOWEVER it is not really your "average pilot" that tells the difference. It is your plane. putting digital servos in a trainer would be overkill. you would never notice the difference from digitals to standard ball bearing servos. If you had a jet, or an ultimate bipe or something slightly faster or more responsive, you just might. I was told not to put a 6v pack in my trainer, as it was a waste of money. I put one in my easy sport, however, and while the other pilots told me i would not notice a idfference, i did. not a huge one. But not a lot. I recently switched from standard servos in the wing of my cap 232 to coreless ones. I was astounded. It reacts a lot faster, and i am able to do things like rachet and 4 point rolls a lot better. It made me look a lot better than i am. Any warbird will have no use for digital servos. maybe your 1/4 scale edge 540T when flying toc.
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Old 06-24-2003, 06:38 AM
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Default Servos - Coreless or Digital?

PPM offers a higher degree of resolution than PCM. It's well documented and proven technology...

PCM is MOST definitely not a pre-requisite for the use of Digital servos.

Digital servos offer several advantages over there analog counterparts. Precision, holding power or torque, repeatable performance and more. The only difference between a Digital core-less and analog core-less servo is the digital amplifier, same motors, same pot's same gear train in comparable model's.

There are only two Digital servos known to us that are programmable (by the user) thus far Hitec and Multiplex.
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Old 06-24-2003, 05:43 PM
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Default Servos - Coreless or Digital?

In case you guys havent seen them yet Hitec just came out with a new line of digital servos. they are the 5400 series. I've been playing with the 5475HB's and so far they have been outstanding. They are very light at 1.4 ounces, have 61oz torque @ 4.8 and 76 @ 6v. transit time at 4.8 is .23 and at 6v it's .18. they are fully programable, have a very heavy duty resin gear train with no backlash, and best of all there only $39.
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Old 06-24-2003, 08:55 PM
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Default Servos - Coreless or Digital?

The data output in milliseconds from my PPM setup indicates it is resolving to at least 1200 positions, which is nearly 20% finer resolution than a 1024 position PCM and let's not mention 512 position PCM! PCM is not a requirement for digital servos. The company that "invented" them, that first gave us programmable digital servos, doesn't even make PCM!

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Old 06-25-2003, 12:09 AM
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Default Servos - Coreless or Digital?

I have never heard about higher resolution, what I have heard is that PCM updates its signal more frequent. I don't know if this is true, just passing on RC lore!
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Old 06-25-2003, 12:12 AM
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Default Servos - Coreless or Digital?

Originally posted by mglavin
There are only two Digital servos known to us that are programmable (by the user) thus far Hitec and Multiplex.
Hitec owns Multiplex and will have a new line of Multiplex radios released later this year
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Old 06-25-2003, 12:27 AM
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Default Servos - Coreless or Digital?

same here. I have never heard that ppm has a higher resolution than pcm, but i do know that for every one time a ppm reciever updates it's signal, pcm does it like 5 times. Wouldn't that mean that pcm has a higher resolution?
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Old 06-25-2003, 11:02 AM
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Default Servos - Coreless or Digital?

That's the way it was explained to me, Spaceclam. More signal updating = higher servo resolution.

Guys, I didn't say that PCM was a REQUIREMENT for digitals. I said I was told it was better. That may not be the case, apparently.

Whatever; I still prefer PCM for my "good" models because of the failsafe feature.

You think this discussion is spirited? get on a heli board and mention PCM/failsafe...

Steve
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Old 06-25-2003, 12:18 PM
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Default Servos - Coreless or Digital?

Originally posted by Steve Campbell2

Whatever; I still prefer PCM for my "good" models because of the failsafe feature.
I'm just the opposite. PCM doesn't solve radio problems it just hides them and the failsafe... well I've seen more plane go in lately from a total lockout than from just jumpy servos.

I will say that PCM does have a shorter freq wave that helps elminate outside noise but I'm not one for the lockout feature. Even if you set it at a slow idle, with neutral controls or even with a little up elevator if you lockout in a knife edge or inverted your still bumming.

Now as for the servo resolution... resolution is the measurement, usually in ms, of the smallest distance the servos arm can move. I don't know how or if PPM/PCM can relate to that but it might.
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Old 06-25-2003, 02:11 PM
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Default Servos - Coreless or Digital?

Originally posted by WreckRman2
I'm just the opposite. PCM doesn't solve radio problems it just hides them and the failsafe... well I've seen more plane go in lately from a total lockout than from just jumpy servos.

If you have enough interference to lockout a PCM long enough to lose a model, then you have enough to knock out a PPM one as well.

As for the digitals, in many cases now they are only a couple bucks more than the analog versions so why not buy them?
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Old 06-25-2003, 02:45 PM
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Default Servos - Coreless or Digital?

I only have pcm becaus i fly at the basin on occasion. those of you who live in los angales know why. However, I have figured out how to kick my gyros on heading hold when i get locked out. i haveo ne on my tail, jsut in case i am turning or in a kife edge
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Old 06-25-2003, 06:12 PM
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Default Servos - Coreless or Digital?

<<...PCM doesn't solve radio problems, it just hides them...>>

Well, I'm not opening that can of worms, except to say that, while technically true, that statement does not tell the whole story. This issue has been beat to death among helo pilots, with every possible pro and con argument you could imagine. After a lot of thought and study, I decided that the advantages of PCM out-weighed the drawbacks.

This is one of those topics that has very few middle-of-the-road types.

Steve
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Old 06-25-2003, 06:28 PM
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Default Servos - Coreless or Digital?

Ity also eliminates some radio problems. There was a guy with a trainer, using a futaba ppm reciever. That means, automatically, that it was negative shift. We did a test. He turned on his plane and radio, I turned on my plane and radio. His plane went Whacko, but mine was unnefected and i still had full control, not evel lockout. Less people (or so it seems) have pcm than do ppm, so it is just that extra litle bit of insurance.
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