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Why digital sevos?

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Old 05-25-2003, 11:28 PM
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DAXX
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Default Why digital sevos?

I see these digital servos, but i still don't get it. Are they really so much better that they're worth paying 5-10 times what a regular servo would cost?
All comments are appreciated.
Thanks
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Old 05-25-2003, 11:56 PM
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Aero330LX
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Default Digi's

Hi DAXX,
I guess it depends on what you are looking for. If you have a plane that you want precision from, such as a 3d plane or precision aerobat or a plane that requires a servo that has holding power than the digitals are the way to go. Simply put, they put the servo where you command it, when you comand it, and keep it there better than their analog counterparts. The reason for this is because the servos is updated 300 times per second verses the 50 of the analog servo. What you get is more holding power or the ability of the servo to hold its commanded position. On the higher end servos, you get more speed and torque for the same size, and some servos that are mini or even micro size put out more punch than standard size analog servo. I've flown the best analog's out there, and there is no comparison to these digitals. They have a precise locked in feel. Do beware of cheap digital servos though if you are in the market for them. The only thing you get from a cheaper servo is lack of reliablity, lack of centering, large amount of deadband, shoddy workmanship, or a cheap motor. There is always something missing with the cheapies...you don't get something for nothing. I learned a long time ago that it doesn't pay to skimp on things with these airplanes...especially airborne radio equipment.
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Old 05-26-2003, 12:14 AM
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Default Why digital sevos?

Really depends what youíre calling a normal servo and the application youíre going to use it for. I fly 35% planes and will use nothing but the DS8411 digital JR has. I even use it on my throttles. To me they are well worth there weight in gold. Very strong, fast, and a very precise center. I have seen standard servos of friendís planes and when moved slightly off center they will sit there. For me anyway that is not an option.
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Old 05-26-2003, 12:19 AM
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Default Digital Servos

Servos are just like anything else electronic, high quality costs a lot more. A high quality DVD player will have progressive scan and several other circuits that the cheap version won't, but the cheapie will still play a DVD. The same with a component stereo compared to a boom box.

A digital servo has very precise centering. You may not need this, or be able to tell a poor centering servo in flight, but some fliers can and like great centering.

A digital servo has great holding power. Forget the torque figures. The holding power is what keeps you controls over during the maneuver. Take knife edge, for example. It is one thing to put the rudder over, but holding it over in on a plane with a big rudder takes lots of power. The circuitry of a digital servo is such that it increases the power to maintain the commanded position. Regular servos tend to lose power as the arm approaches the commanded position, just the opposite.

The newer sport digital servos from JR and Hitech have just over 50 in-oz torque. But try moving them from where ever they are. It isn't unusual for digital servos to have 3 times the torque value as holding power!

Digital servos can also be adjusted as to movement and dead band.

Electronics is electronics and there are all different levels of quality and performance.
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Old 05-26-2003, 12:42 AM
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Default Why digital sevos?

Originally posted by pcm
Really depends what youíre calling a normal servo and the application youíre going to use it for. I fly 35% planes and will use nothing but the DS8411 digital JR has. I even use it on my throttles. To me they are well worth there weight in gold. Very strong, fast, and a very precise center. I have seen standard servos of friendís planes and when moved slightly off center they will sit there. For me anyway that is not an option.
Hi PCM,
I use the 8411's in my 33% 330 too. I also use a digital on the throttle but went with the 9411. It is a lower profile servo, with a little less torque, but still plenty for a throttle. I elected to use that because it gives more precise control over the throttle...just like they do on the aero surfaces, and it's a little lighter. I also have a Morris Knife that I'll be using the 3421 mini digi's on. I've been slowly working on that plane when I have time and it should be ready in a couple weeks if not before. I think anywhere where you want precision these digital's are the way to go.
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Old 05-26-2003, 12:59 PM
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Default Why digital sevos?

Aero330LX,

Sounds like a great setup! I agree with you all the way when you say, "I think anywhere where you want precision these digital's are the way to go."

As Ed_Moorman stated also about the holding power. Digitals have lots to offer to the right applications.
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Old 05-26-2003, 08:09 PM
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Default Why digital sevos?

The post that refers to low cost digital servos not being any good what servos are bad ones? I hope not Hitec I jest ordered some 5625s.
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Old 05-26-2003, 09:48 PM
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Default time to use the "Search" function...

Originally posted by ronk1
The post that refers to low cost digital servos not being any good what servos are bad ones? I hope not Hitec I jest ordered some 5625s.
There were some widely reported failures of 5625 and 5645 servos when they were first introduced. If you ran your ATVs up to 140% the servos would freak out and lock at their travel limits.

(It also seemed to occur primaily to people using Futaba transmitters.)

This problem has been resolved through software updates - servos with the current revision software work quite well.

FYI - the higher-end Hitec digitals (the 5925, 5945, 5745) are well-liked, and perform as well as their 'name-brand' counterparts.
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Old 05-26-2003, 09:49 PM
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Default Why digital sevos?

Digital servos should not cost more then the analogues. The lack of competition makes it so and the fact the people are willing to pay the price, me included.

As a matter of fact, the digitals should cost a bit lest because there are less components on the circuit board. And everything is automated. I beleive Hitec is leading the way in making the prices of digitas come down.

The servos are exactly the same as the analogues except for the amplifiers.

What could make these servos cost more are the ballbearings, high quality motors etc.

Look at Hitec's low cost digitals, they use 3 pole motors which are about as cheap as they come.

Next time any of you have the inclination, open up a digital and an analogue servo and compare....
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Old 05-27-2003, 12:41 AM
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Default Why digital sevos?

Originally posted by ronk1
The post that refers to low cost digital servos not being any good what servos are bad ones? I hope not Hitec I jest ordered some 5625s.
Hi ronk1,
I'd recommend you do a search here on RCU. There are lots of threads on the hitecs already here, and anything I would say would basically just be repetitious. The ATV issue was not one of the issues I was referring to. It's the issues with hard-overs (servos that go full deflection and stay there), and what looks like a trend of amps burning out. There have also been a bunch of unexplained crashes where the date code issue (ATV issue) was up to date, but guys still had failures. Most of these seem to happen at 20 flights or less. I don't wanna get into too much detail here as plenty has already been written, and don't wanna be in the middle of a brand war which is why I left the brand names out of my original post. If you look through the majority of the posts you will see the trends...yes there are a few that look isolated, but some of these issues are just happening too much, and one of them I have seen myself. Hope this helps you some though.
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Old 05-27-2003, 01:09 AM
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Default Why digital sevos?

I never tried digitals until last year and once I did I will admit it is hard to go back to analog. Once you try just one on a rudder or whatever you will see exactly how precise and powerful the digitals are.

After my first digital servo, I've used them in just about everything I've flown since. My Wild Hare Giles has JR DS8411's throughout for all control surfaces. Caliber 30 heli has Futaba 9252 digitals for everything except throttle. Venus 40 has Futaba digitals on elevator and rudder. Modeltech Magic has the JR mini digitals on rudder and elevator.

The only downside right now to them is cost (I feel they will become less expensive each year as the component cost is not high) and current draw. Digitals will draw more battery current than a standard servo. However with the newer Ni-mh and Li-Ion capacities being used this is less of an issue now.

Try a digital and you will see why. I wasn't a believer until I tossed that 1st one in a plane They get my vote.
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Old 05-27-2003, 01:14 AM
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Default Why digital sevos?

Originally posted by RCadmin
I never tried digitals until last year and once I did I will admit it is hard to go back to analog. Once you try just one on a rudder or whatever you will see exactly how precise and powerful the digitals are.

After my first digital servo, I've used them in just about everything I've flown since. My Wild Hare Giles has JR DS8411's throughout for all control surfaces. Caliber 30 heli has Futaba 9252 digitals for everything except throttle. Venus 40 has Futaba digitals on elevator and rudder. Modeltech Magic has the JR mini digitals on rudder and elevator.

The only downside right now to them is cost (I feel they will become less expensive each year as the component cost is not high) and current draw. Digitals will draw more battery current than a standard servo. However with the newer Ni-mh and Li-Ion capacities being used this is less of an issue now.

Try a digital and you will see why. I wasn't a believer until I tossed that 1st one in a plane They get my vote.

Marc, in your Giles, did you ever install the Fiber Optic extensions on throttle and choke and if so, how is it going??
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