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Old Nov 19, 2014, 03:34 PM
hot air rises...
jfinch's Avatar
Pleasant Grove, UT
Joined Jul 2005
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Analog vs. Digital Servos

I have always put digital servos in all my DLGs, because... well, that's what I've been told to do and what I thought everyone else was doing. By everyone, I really mean most folks... I'm aware that some are still enamored with D60/4.7. But I've never personally tried analog servos in a DLG. I've recently notice a couple guys using analog servos (Oleg's CX4 build and Kristoff) and it has me wondering.

I've assumed that digitals were used because of their resolution and maybe because of their holding power (during launch). But if this is not really the case and that extra resolution/holding power isn't really needed, maybe I should be looking harder at analogs (and their reduced power consumption and cost)?

What do you think?
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Old Nov 19, 2014, 03:55 PM
Do it AGAIN! This time BETTER!
ThermalThief's Avatar
WA
Joined Jan 2005
476 Posts
Never have I felt disadvantaged running analogs. A servo with centering issues can happen with either. Find a servo with good power for your application, test it for slop and if it's good strap it in. I have Futaba 3114 in my Snipes. I recently bought one used with MKS 65's. These now reside in my spare parts bin.

Ken
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Old Nov 19, 2014, 04:15 PM
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United States, CO, Berthoud
Joined Mar 2006
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I use digital servos in all my DLGs because I use a ATX SD10G Tx and FHSS3 Rxs. Digital servos work better with the FHSS3 Rxs. If I deflect the Tx sticks and let them go, the slight bouncing of the stick to either side of neutral is reflected in the movement of the control surfaces. This may not make the plane (or me) fly better but I like the absolute, positive connection between Tx stick movement and surface movement.

Bob
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Old Nov 19, 2014, 04:31 PM
Mickey from Orlando. Really.
Joined Nov 2004
3,517 Posts
I use S3154's and S3114's somewhat interchangeably (rudder and elevator, pull string). It's impossible to tell the difference in flight. Power consumption favors the analog S3114's.
I stick to digital on ailerons (S3156) because they do have better holding power and I feel like the insurance against flutter at launch is worth the extra battery usage.
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Old Nov 19, 2014, 04:36 PM
Will fly for food
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Bellevue WA,
Joined Dec 2003
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Digitals consume more power but deliver better accuracy and holding power. Now with the current use of single cell lipo's can anyone notice the difference?
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Old Nov 19, 2014, 04:55 PM
agnotology
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Joined Jan 2007
3,654 Posts
Does anyone actually have measurements showing digitals consume more power? From my own testing, some that was on QuietFlight, and Servormances, digitals don't seem to take more power. It does depend somewhat on the servo. D47s have very low power consumption, but make up for that in other ways.

I've attached some Servormances data for some Futaba analogs, a digital, a Hyperion DS09AMD, and a MKS DS6100. The digitals show better speed under load (Vitesse), lower power consumption (Consommation) at zero torque and under load, much better centring (Precesion du neutre), and basically no deflection (Fleche) under load until quite high torque values.

The analog servos show about 2 to 3x the centring error, higher power consumption, and deflection even under small loads that increases with torque.

My own crude testing shows the same thing.

Kevin
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Old Nov 19, 2014, 05:14 PM
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Mr. Finch

I ran MKS 6100 servos in my Snipe, then replaced them with JR188HVs. The result is increased battery endurance (1.5hrs+, versus 0.4hrs), reduced weight and more space. I assumed (perhaps incorrectly) that increased battery endurance meant reduced power consumption, but electricity has always been a sore point with me.

I ran Hyperions for the ailerons in both my trusty B3s - and wound up replacing all four before both airplanes went to others. I no longer use Hyperions, preferring Dymond D60s. The D60s fit in the same space, and with proper setup give the same resolution, centering, repeatability and travel as Hyperions.

I have been using Futaba S3114 serovs for elevator/rudder duties for several years, and not until the JR188HV servos came out, have I been tempted to use any other. They work with either push rods or pull/string, no sweat. JR285 servos work well, but the Futaba S3114 is easier for me to obtain and is lighter.

My happiest combination so far: D60s for ailerons (servos in the wing); S3114s for tails. A 350mAh LiPo will get me well in excess of 1.5 hours of flight.

About D47s: I've installed over forty over the years. Yes: 40+ D47 servos. Not one, not ever, has failed in an airplane. They do come to me dead in the box, but once installed appear to have charmed lives. I prefer D60s for ailerons now, however, because the D60s have more reliable arc of movement.

Hyperions are the only digital servo I've had much experience with. I will install them for others, and they appear to have out-lived the poor failure rates I experienced in my B3s. The MKS 6100s performed well, but sucked down batteries like there was no tomorrow - twenty minutes was not enough for me. Maybe I'll use mine in the wings of an F3J ship.

Yours, Greg
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Old Nov 19, 2014, 05:21 PM
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the reason i use and recommend d47 on the tails is for these following reasons:
-low power consumption on spring loaded tails (spring loaded is they key here , never did measurements but read reports about digitals consuming xx% more multiple times , tried digitals on pull spring and the ones i used drained the battery very noticeable (springs build according my manual with supplied material are rather strong (which is preferred )
-d47 has been around for very long and I'm sure some people occasionally had a bad one but overall they are very reliable which is proven over many years now.
-centering is good.

on 2s pull-spring setup i think they're strong enough, have good center and resolution and are reliable , (that's all i ask)

on pushrod tails i would not recommend them as they have flex in the horn and gear train (for spring setup not an issue, it takes it away)
on 1s they are to weak for spring setup , they need 5-8 volts.

for ailerons (not spring loaded off course) i never used analog servos.
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Old Nov 19, 2014, 06:10 PM
Mickey from Orlando. Really.
Joined Nov 2004
3,517 Posts
Quote:
Originally Posted by kcaldwel View Post

I've attached some Servormances data for some Futaba analogs, a digital, a Hyperion DS09AMD, and a MKS DS6100. The digitals show better speed under load (Vitesse), lower power consumption (Consommation) at zero torque and under load, much better centring (Precesion du neutre), and basically no deflection (Fleche) under load until quite high torque values.
Not sure I buy the comparison, the DS09AMD and 6100 slow compared to the others. It's easy to get more torque at less current if you give up the speed.

Maybe a better comparison would be the s3154 and s3114 as they are the same mechanicals and gearing, just one with a digital amp and one analog.
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Old Nov 19, 2014, 07:03 PM
Team JR
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San Diego
Joined Feb 2002
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The simplest explanation for why I use digital over analog in most cases is the resolution, and holding power off of center. An analog servo develops max torque at about 17 degrees deflection, whereas a digital reaches max torque at about 3 degrees. So in general, a digital servo is more accurate.
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Old Nov 19, 2014, 07:09 PM
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United States, AZ, Arizona City
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I don't understand the relationship between max torque and resolution that you referenced?

My understanding is that resolution is a function of how repeatable the servo is (deadband) , which has nothing to do with power?
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Old Nov 19, 2014, 07:56 PM
Team Hong Kong F3K
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Hong Kong
Joined Sep 2010
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As far as I know, most analog servos can only reach a resolution and deadband of 7us, and with the best ones at no lower than 4us.
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Old Nov 19, 2014, 09:56 PM
M Seid
Solana Beach, Ca
Joined Sep 2006
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EFF YEAH FINCH!!!!!



Welcome to winter people!
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Last edited by M Seid; Nov 19, 2014 at 10:01 PM.
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Old Nov 19, 2014, 11:41 PM
Sink? Circling now to confirm.
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United States, UT, American Fork
Joined May 2002
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So let the games begin......
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Old Nov 19, 2014, 11:52 PM
M Seid
Solana Beach, Ca
Joined Sep 2006
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Did someone just call you Mr. Finch?

I need to start a new RC Groups handle called "Stifflers Mom" just so i can call you Finchy.
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