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Old Mar 14, 2010, 03:07 AM
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Gluing servos together is a good idea, but in x-tail fuse, you would want to use different kind of servos elevator and rudder.
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Old Mar 14, 2010, 06:44 AM
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SHV, I knew what you meant, I would not trust servo tape for any use, I want them stiff.

Tuomo, that is opinion, I am trying something to evaluate these for this use. 388 HV's have as much torque and are as fast as JRDS 3421's and are specifically designed for fuse use. It is an experiment, we will see how it goes.

Marc
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Old Mar 14, 2010, 12:21 PM
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Fuse is basically done other than finally packing everything else up front in final assembly and balancing. Weight right now is 13.5 ounces versus 11 empty.

I do realize that using 388HV servos is a step beyond what about anyone has done, but in just set up and checking throws, they seemed to center nicely and after some messaging to get throws where I needed them and everything to fit under the hood, this part is done.

Off for business this afternoon, so wings next weekend.
Marc
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Old Mar 14, 2010, 12:53 PM
isoaritfirst
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I initially put a Futaba S3155 on the tailplane of my Sigma, but the first bump of a landing on hard ground stripped the gears with the backlash from the tailplane.

May have just been unlucky - but changed to a larger servo anyway.
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Old Mar 14, 2010, 08:05 PM
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ISIF, if the stab is aerodynamically balanced correctly, then I would hope that the load could be easily handled. Also, being a Team JR guy, I feel that the construction and guts of this servo will hold up to what is coming. Yap, they are new, and we will find out.

Marc
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Old Mar 14, 2010, 08:57 PM
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Quote:
Originally Posted by OVSS Boss View Post
ISIF, if the stab is aerodynamically balanced correctly, then I would hope that the load could be easily handled. Also, being a Team JR guy, I feel that the construction and guts of this servo will hold up to what is coming. Yap, they are new, and we will find out.

Marc
Yah, since your a team guy JR will buy you a new sailplane if the servo fails

sj
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Old Mar 14, 2010, 09:03 PM
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Yah, since your a team guy JR will buy you a new sailplane if the servo fails

sj
Something like that Joe...
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Old Mar 15, 2010, 01:33 AM
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Quote:
Originally Posted by isoaritfirst View Post
I initially put a Futaba S3155 on the tailplane of my Sigma, but the first bump of a landing on hard ground stripped the gears with the backlash from the tailplane.

May have just been unlucky - but changed to a larger servo anyway.
Robustness is normally not a problem, but minimum slop, high speed & torque and trim accuracy are issues. When choosing x-tail elevator servo, look something very fast, strong (torque & hold power), expensive and at least 15mm thick... Not using the smallest servo is important, because size in not a problem in fuse. Think about small metal gears... Having physically larger gives a mechanical edge.

Those who want ultimate performance, normally choose car steering servos for elevator. They are tight fit, but Tragi 801 fuse looks large compared to F3B planes. Also many helicopter servos are interesting. Most wing servos, also Futaba 3150, are hopelessly slow for elevator. 3155 does not have enough torque for elevator, it is made for v-tails.

In x-tail rudder you can use almost anything. Also analog servos are ok. Metal gears a plus, but my most flown late 2007 Aspire has a 15 euro plastic gear el cheapo servo in rudder. Gears are still ok despite extensive competition work.
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Old Mar 15, 2010, 07:23 AM
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Tuomo, you may want to find out the specs on the 388HV before you compare it to other servos. Here are some comparisons (at max useable voltage):

JRDS368 (JR's original digital)- 60oz-in torque, .18sec/60deg., metal gears, 1.1oz
JRDS3421 (Second generation JR digital)-75oz-in torue, .15sec/60deg., metal gears, 1.1oz
JRDS388HV (Third generation JR digital)- 75oz-in torque, .13sec/60deg., metal gears, .7oz
Airtronics 761-66oz-in torque, .12sec/60deg, metal gears, .8oz

So, on paper, the 388HV seems to meet your criterian for what you are looking for other than the servo not being bulky and heavy. I will admit that I might have put in a 3421 for the stab, but the HV version is not out yet and from what I see, the 388HV is more than up for the challenge.

I am no mechanical genius, but I am going to give this servo a try.
Marc
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Old Mar 15, 2010, 07:53 AM
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Ok I have also some 388's, although branded Graupner DS3288 over here. Specs are very good, but I am afraid of the double centering, which seems to be an issue. It will ruin the elevator trim... I will use the 3288s in wing, where is centering is less critical.

Maybe this is too much fuss over a small detail. Last summer I got two new Aspire's and equiped another one with DS3068 in elevator. 3068 is the duoble BB version of 368. Except of a tiny amount of radial slop, because of small gears of 13mm servo wearing a little, I could not notice any difference compare to the Aspire with faster elev servo.

Anyway, now I have substituted the DS3068 with Graupner DES 658 BB MG. This servo has comparable specs 388/3288, but has the mechanical benefit of 16mm thicness plus seems to free of double centering issue. And it is dirt cheap
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Old Mar 15, 2010, 08:53 AM
Sink Stinks
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Originally Posted by Tuomo View Post
Most wing servos, also Futaba 3150, are hopelessly slow for elevator.
Huh? "hopelessly slow"??? How fast do you need for an elevator servo to be?? I use this servo and it seems to work just fine, so what am I missing?
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Old Mar 15, 2010, 10:25 AM
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Huh? "hopelessly slow"??? How fast do you need for an elevator servo to be?? I use this servo and it seems to work just fine, so what am I missing?
The theory is that faster elevator servo gives an edge at launch, at the moment of release. You get higher altitude... Maybe also other situations, but not so much in F3J, more in F3B.

Anyway, if the speed is close to 0,2 sec for 60 deg, then the servo is slow. Faster ones are at around 0.1 sec, or better. Jeti Box is a very nice tool for measuring servo speed.

Personally I look also for good centering and zero slop. All centering problems are a pain. Double centering spoils elevator trim and if centering drifts with temperature, our lauch trim will come unreliable.
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Old Mar 15, 2010, 10:32 AM
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I have to admit that my skills are not up to the level of being able to discern a speed difference on the elevator servos in my planes. I'm using 3150s and so far cannot feel that they are causing me an issue. Like I said, I am just not at the level where I can feel it.
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Old Mar 15, 2010, 10:38 AM
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Originally Posted by OVSS Boss View Post
JRDS368 (JR's original digital)- 60oz-in torque, .18sec/60deg., metal gears, 1.1oz
JRDS3421 (Second generation JR digital)-75oz-in torue, .15sec/60deg., metal gears, 1.1oz
JRDS388HV (Third generation JR digital)- 75oz-in torque, .13sec/60deg., metal gears, .7oz
Airtronics 761-66oz-in torque, .12sec/60deg, metal gears, .8oz

So, on paper, the 388HV seems to meet your criterian for what you are looking for other than the servo not being bulky and heavy. I will admit that I might have put in a 3421 for the stab, but the HV version is not out yet and from what I see, the 388HV is more than up for the challenge.

I am no mechanical genius, but I am going to give this servo a try.
Marc
I like the 3421 and is a good choice for elevator it's solid and reliable, on 4 cells it's fast if you want faster run 5 cells.

I am using 4 3421's in my 801 Rud, Ele, and both flaps. yes I like the 3421 it has a proven track record

sj
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Old Mar 15, 2010, 03:58 PM
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Bill, I am like you, and in most flight modes, I am flying some expo, so speed is relative anyway.

Marc
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