Why pricey digitals?

[warpspeed]

Forgetting brand for a moment, is there any real reason why most folks use digitals over standard servos? Seems the common reasoning is response time and holding power, but unless you're a Szabo is the average Sunday flyer really going to notice the difference? Obviously the price variation is significant, but is it worth it?

For example: Futaba 9250-.11/sec, 76 oz-in. @ 4.8v, weight 53g. $99
Futaba 3305-.25/sec, 99 oz-in. @ 4.8v, weight 46.5g. $33

Both are standard sized and have metal gears. The 9250 is faster, while the 3305 can be run @ 6v for more speed and torque. (.20/sec, 124 oz-in)
As you can see, you can get your entire cyclic set up for the price of ONE 9250. Amp draw appears to be higher with most digital servo's as well, leading to reduced runtime.

[overspeed]

IMHO, you will notice the difference between .25 and .11 there are some really nice analog servos out there. I like some of them very much. But they tend to cost nearly as much or as much as the digitals. Case in point: the Fut 9402 is an analog servo that has a transit time of .13 at 4.8 and I think around 89 or so oz of torque. Its a coreless servo with very good centering. But since its metal geared, a replacement gear set is VERY expensive, not to mention metal geared servos can quickly develop slop in a heli. The Fut 9252 is digital servo which can be found for the same price (around $80) has a transit time of .14 and something like 92 oz of torque at 4.8 It however, has plastic gears which are very inexpensive to replace. I'm running a few now and love them. it can be done well with analog, but cheap is cheap, and expensive is expensive.

BTW, the way around the current drain is to run a regulator. I use a Duralite 5.3 volt regulator and a 4300 mah Li Ion batt. Fly all day, no worries!

Dave

[BarracudaHockey]

Analog servos dont produce rated torque untill they have moved quite a bit and back off as they get to thier commanded position.

Digitals produce full torque almost instantly.

[warpspeed]

Overspeed, I've read that before about metal geared servos developing slop, but never any quantifiable evidence as to why. I understand plastic is self lubricating but unless the gears are pot metal it seems they should last at least as long as nylon or plastic gears. In my case I have to use metal geared servos since I crash every time I fly and replacing gears gets to be a real PITA after the 30th time!
Anyway I understand your point about transit speed, but where is it that you would notice the difference? Is it apparent during just 3d maneuvers, or is it noticeable during basics like hovering and FF? 'Cuda's point about instant torque makes sense to me but I'm not sure my dumb thumbs and tired eyes are really going to notice a difference of less than a quarter of a second.

I hope you understand I'm not trying to be argumentative-I guess I'm suffering from wallet-burn and trying to get away cheap on the last bit of electronics I need for my Swift.

[overspeed]

Warpspeed,
I hear you. I've posted this information before, just to make a point that isn't voiced often in the helicopter world. Myself, I use digital servos often (almost exclusively) in my helicopters. I just feel the need to keep us honest. They're not the only thing that will work. BH is right, too, the instant holding power can make a real difference in helicopters. Ok, so we've made that point. Done the typical
(and there's a reason its typical, digitals are better) observance to digital servos.
I can't tell you why I know you'll feel the difference, just that you will. The time difference you described is huge. You can get a lot closer with some other economy servos. How about Futaba 3010's? Transit time .20 Torque 72 oz. Plenty enough for a .50 class nitro. I have a friend who uses them in his Raptor .50 and he likes them. For the loops rolls and stall turns he does to unwind after work they're fine. And these things cost under $30. These servos and others like them will keep you flying in fine form for a long time. Are they as good as high end analogs or digitals? Not even close. But if you're a Sunday sport flyer, why should that matter? The answer to your original question in my opinion is we all go for good quality digitals because they're much, much better. If you want to just have fun and save some money then get something cheaper. Just have fun and do what works for you. Its your helicopter. Do what you want.

Dave

[warpspeed]

O.S., I appreciate your thoughts on the subject, and I'm sure as I get better at flying I will notice the difference. I gave it more thought and my sense of self preservation (I.E. getting killed by the wifey when she finds out I need to rebuild the bird due to a servo failure) overruled my desire to be cheap. So, 9451's are on the way!

You know, it's kinda funny-I know darn well that the purchase price of a new heli is just the beginning, but I still balk at buying everything needed to get it in the air.

[DavidH]

Most people put too much servos in the helis that are smaller than a 90 size. The 9451's are overkill in anything less than a 90 sized engine heli. As for servo failure, any of them can fail at any time no matter the brand or price. So don't let price be a determining factor that the more it costs the less likely it is to fail.

David

[overspeed]

WS,
those will be really nice, top drawer servos that you will really enjoy. Only thing is, the metal gears will get pricey if you have to replace a set. That's why I go with the 9252's. Unless its a hot .90, I (opinion) don't think you need to go with them (metal gears). But like I said, they're really nice and you love em.

[warpspeed]

Hey David ya coulda said something BEFORE I pushed the "buy" button! :arggg: Like I said earlier I still crash quite a bit and the set (9451's) I have in the T600 have held up very well. I tried plastic gear servos (hs56) in the 450 but replacing gears got old REAL fast-since switching to the 65mg's I haven't had to pull a servo once. It's hard to determine what's overkill in a heli since the manufacturers don't publish a minimum spec. The Swift instructions, for instance, don't even specify what 'size' servo's let alone a minimum torque or speed rating. Guess I decided to err on the side of caution for once. :wink:

Just out of curiousity is there a generally established set of "rules" for heli servos? Something like "300 to 500 size require a minimum of X torque & X speed, 500 to .90 require this much, big gassers require that much, etc etc"? I searched the forums for "Servo guidelines for cheap S.O.B.'s" but came up with nothing.

[DavidH]

Basically 90 size helis need servos on the swash with at least 90 ozs of torque.


50 size helis today need about a 60 oz torque servo.

30 size can use a 50 oz torque servo.

The Trex 400 series type electrics can use servos that have 25-30 ozs of torque.

The rest of the specs for servos such as transit time is irrelevant in most cases. Torque spec will affect transit speed, transit speed can make torque seem less than it is or vice versa. For example I have used servos that had more torque and more transit time. They replaced servos that had less torque and quicker transit times. The servos with more torque seem to move faster in the model , than the servos that had less torque but a faster transit time.

David

[BarracudaHockey]

Unfortunately if the plastic gear doesn't break, something else will and a gear set for a 9252 costs about 8 bucks I think.

[archiebald]

Well, when I bought my 9C last year, it came in a very reasonably priced package with 4 x 9255's (metal geared) I probably would have chosen the 9252 if given the choice, but there it is.

Up to now, I've had well over 200 flights on them, 3 crashes with one being a real showstopper and not a hint of slop or damage yet.

But then, I also run a boom mounted 9254 which some people don't recommend but that has now had over 250 flights and 4 crashes but still not a hint of a problem from fuel residue or physical damage.

I'm not qualified enough to state conclusively but based on what I have experienced personally up to now it seems to me that there is a little too much unsupported opinion floating around the internet on matters related to servos.

But coming back to the original topic, I started out on analogs then changed to digitals. Even to a relative newby, the difference was like chalk and cheese. Just hovering the thing in one place became so much easier.

Just my 2 yen's worth

[overspeed]

Archie,
good points well stated.
The analog servos I mentioned (fut9402) have been my favorite servos for 3D fixed wing for quite some time. They are metal geared and over the many flights I put on them in airplanes they stayed nice and tight. I needed some servos for a heli, as my hanger was growing faster than my radio box could handle. So I stuck these servos in and once again really enjoyed the speed and centering. One of them however, became sloppy pretty quickly. I had read that that could happen so, oh well. Then I had a crash and checked into the price of a gearset. Sheesh! Really expensive. That was the time I invested in 9252's. I reall like them too. What I like best, however, is how cheap the replacement gear sets are. So, just like you, I'm stating my opinions based on personal, first hand experience. Thanks for writing your flights achieved on the 9254. Its nice to know they can last awhile.

Dave

[warpspeed]

Over 200 flights with only 3 crashes? Man I am obviously not doing something right! I've gotten into the habit of bringing a large cardboard box with me so I've got something to put all the broken carcasses into for the trip home.

In any case my extensive crash research proves the necessity for metal gears. I actually like tinkering on these things so rebuilds don't bother me, but for some reason I just hate replacing servo gears. With the metal geared servos, I don't have to.

[archiebald]

warpspeed,
one word.......

"Simulator"

Initially AFPD and now Phoenix. Both have paid for themselves 50 times over.