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DIGITAL SERVOS?

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Old 09-19-2003, 11:06 PM
  #1  
wheels
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Default DIGITAL SERVOS?

I'm FINALLY gonna put together the H9 edge I bought TWO years ago and I'm at the point of selecting servos.

An add in RCM caught my eye and the hitec hs-5475hb is had about the tourqe I want on elevator halves and ailerons and isn't much more than a comparable analog so ................... Can someone explain to me what exactly the advantages of digital are, are they worth the extra cash? What about servo programming, do I NEED a programmer if I'm going digital, if not what can a programmer do for me?, What about power requirements? Do digitals draw more power than analogs, if so what size of a pack would be reqired to run four of these and a large single servo for rudder (100 + oz)?

I know it's alot of questions but I'd like to know, this isn't gonna be my last large airplane and if digital is the way to go I might as well start with it.
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Old 09-20-2003, 12:19 AM
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Default RE: DIGITAL SERVOS?

I just made the move to digitals and went ahead and bought the programmer as well.

It was worth every penny "to me" anyway!

The biggest difference between digital and analog IMO is holding power, they are also very precise and fast. Here's a test, turn on your plane with analogs and move the stick to deflect the elevator, next apply pressure with your hand to the surface moving it back against the servo's torque. If your going for max throws, out as far on the servo arm as possible and in on the horns, you will probably be able to push the servo back against it's torque pretty easily. Do that with a digital with comparable torque and it locks into position like a rock! Both types will "fight" to hold position but the digital wins the battle hands down.

As for power usage I think it's a good idea to go to bigger packs but it really depends on your airplane and flying style. If you "work" the plane hard the bigger packs really save on having to recharge a lot. I would think that for that Edge a 1200-1600 pack would be plenty beg enough and if weight is an issue I wouldn't have any problem putting a 1100 in the plane, I would just make sure I checked my packs often for state of charge and piece of mind.

The Hitech programmer is a gem and is really the only way to set up multiple servo installations like dual servos on a single surface or for getting dual servo'd elevator halves to match up DEAD ON. Yeah I know you can do this in many transmitters but if you match the servo's out of the plane you will find that they are right on the money once you install them. If your running a single servo per surface I don't think you need the programmer YET but to get the most out of these gems it's really a great tool to place in your box. I just set up my UCD 60 with HiTec 5625's on the elevator and all I did was match them on the programmer, because the DIDN'T match each other out of the box and no amount of fiddling with my 9C seemed to get them to match to my satisfaction. Now they are perfect and I don't mean close I mean dead on perfect.

Try that with analog servos!
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Old 09-20-2003, 10:44 AM
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Default RE: DIGITAL SERVOS?

I agree with Scott on many points....But I've had success with high torque analog futaba servos as well as digitals from hitec and futaba.

If you have the cash, go for the digitals. If not, then go for the analogs.

My flying is such that I can't tell the difference in the plane when I use digi's as compared to analog.
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Old 09-20-2003, 12:37 PM
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Default RE: DIGITAL SERVOS?

I have the Hanger 9 Edge 540 with Hitec digital servos all around.

Ailerons are using Hitec 5645MG Digital Servos

(2) Elevator servos using again, Hitec 5645MG servos

Rudder, (1) Hitec 5945 Coreless Digital


The performance of these servos is down right awesome! Precision, speed, and torque sums it up.


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Old 09-20-2003, 12:52 PM
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Default RE: DIGITAL SERVOS?

I know digitals are very powerful, and precise, but what is different on the inside? More powerful motor obviously, but what else. Also why are they soooo expensive. Will the cost drop eventually as tecnology progresses, and better servos are offered?
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Old 09-21-2003, 12:32 PM
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Default RE: DIGITAL SERVOS?

I think there is a misconception about torque with digitals

Digitals are not more powerfull because they are digitals. If you take the same servo, one with a digital amp inside and one with an analogue amp, the torque will be the same.
But the one with the digital amp with have more torque from the starting point and will have more holding power.
It will be a bit more precise, but again not necessarily so. If you have a digital with a 3 pole motor, it will not be very precise,but a digital with a 5 pole motor or a coreless will be much more precise just like with the analogues.

Don't forget, Pattern flyers were flying very precise maneuvers back in the 70's with AM radios, and analogue servos which weren't even as good as the Futaba 148's..

I love the digitals and wouldn't go back to analogue unless its an insignificant airplane, but not because I MUST have be rather because I simply want it.
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Old 09-21-2003, 12:37 PM
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Default RE: DIGITAL SERVOS?

Also why are they soooo expensive. Will the cost drop eventually as tecnology progresses, and better servos are offered?
That's another thing, they are so expensive because people are buying them.

Electronically speaking, they should be less expensive. But as long as they sell, the prices will stay up.

Look at the Harley Davidson Motorcycle, do you really beleive they worth the price they are selling for, I don't think so, but they sell everything they are making so why should they lower the prices.

When you have a chance, have a look at the amplifier of an analogue and digital servo and you will understand what I mean.
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Old 09-21-2003, 06:17 PM
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Default RE: DIGITAL SERVOS?

First of all, thanks for the input, much appretiated.

big_stik_40 do a search for a thread called "needed, servo class 101" in this forum, it has a really great explaination if what the difference between digital and analog servos is as well as cored vs coreless motors

Shortman, looked up the specs on those servos, wow, that's ALOT of power for these surfaces isn't it? What are you powering your edge with?
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Old 09-21-2003, 06:59 PM
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Default RE: DIGITAL SERVOS?

I agree with Roger, digitals give more accurate and quicker response with more holding power because the error signal has more effect on digitals compared to analog. I went to digitals and converted back to Analog. I may try them again on another plane but I prefer coreless analog servos on my PW Extra.
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Old 09-21-2003, 08:00 PM
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Default RE: DIGITAL SERVOS?

Wheels - I got a Moki 180 (30 cc) for power
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Old 09-21-2003, 10:55 PM
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Default RE: DIGITAL SERVOS?

Guys, I am just now going through the same choice of deciding between $80 Digital servos V.S. $78 analog servos. I am new to big planes as well.

Have you seen the exreme price drop in Futaba servos that Tower has just offered?!! I guess they've finally got tired of Helihut cutting in on them with rock bottom prices. Geeees...it's obscene to know the profits that were being made when these same digital servos were being sold by Tower for $120 just a few months ago, and $100 last month!

Anyway, is there any reason why I shouldn't go with three Futaba Digital 9252 "all purpose"servos which are 92 Oz torque @.14 sec., (for $240), instead of three 9402 "coreless 2bb metal gear" servos which are 89 oz torque@.13sec (for $232) ?

They are going in an 84" Big Bingo, or, a 85" Top Flite P-47 I plan on building in another month or two.
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Old 09-22-2003, 08:44 PM
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Default RE: DIGITAL SERVOS?

yeah, good prices on Tower's site... definitely a step in the right direction/
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