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30% Sbach - Are these servos sufficient?

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Old 01-18-2011, 06:48 AM
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Capt Cash
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Default 30% Sbach - Are these servos sufficient?

This is my first 30% size plane and I just want to make sure I'm not missing the ball on what servos to get. It's an 88" Sbach 342 with DLE-55.

I'm definitely not one to go cheap and save on servos, but I don't want to spend more than I need to either. I've decided fornowonHitec and plan to use:

1 - 7955TG - rudder
4 - 7985MG - ailerons, elevators

My flying style can sometimes be pretty hard butI'm hopingthe 7985s are still sufficient on the ailerons and elevators?I'll also be using unregulated A123 batteries so I'm hoping torquewill remain high with a steady 6.6v.

As always price is somewhat of a factor. The 7985swould save me $100 over getting all 7955s. I never plan onmoving up larger than 50cc planes so I'd rather not get all 7955s unless absolutely necessary.
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Old 01-18-2011, 07:17 AM
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Default RE: 30% Sbach - Are these servos sufficient?

That'll work fine.........
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Old 01-18-2011, 07:39 AM
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Default RE: 30% Sbach - Are these servos sufficient?

Capt
I looked at AirWild and the servos are $89 for the 7955 and $79 for the 7985. $10 difference each. So...about $40 total.
If it was me I'd put at least 2 more of the 7955s in the plane. I'd put them on the elevators. This makes it so much easier for hovering, waterfalls, etcs. I think the 7985s are fine on the ailerons. As they generally don't seem to need the torque at least the way I fly (3D). For $20 I'd certainly go with a couple for 7955s. You won't ever be sorry.
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Old 01-18-2011, 07:41 AM
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Default RE: 30% Sbach - Are these servos sufficient?

BTY,
I had that airplane and thought it was a great plane. Mine was the black one from Pilot RC. One of the most complete ARFs I've seen. Almost everything was done...including the fuel tank, hinges, rudder cables, etc. Very nice. Mine came in right at 16lbs and flew very nice there. I think you'll enjoy yours.
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Old 01-18-2011, 08:08 AM
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Default RE: 30% Sbach - Are these servos sufficient?

Thanks for your reply. I priced the servosat Tower Hobbies,

After member discount and shipping:

4 - 7985s - $306
4 - 7955s - $403

Prices are all over the place on the internet, but it looks like 7955s are pretty much around $100 apiece.

I'm still on the fence about it. I do like to do high speed/ high rate aileron rolls, so maybe the7955 would be a little more insurance here too. Just don't want to lose a plane because of a darn servofailure.

I wouldv'e never bought this plane but Tom at Wild Hare lives 5 miles from me andofferedme his last onenew inthe box for $300.He said the box was extraordinarily long to shipfor customers withoutcosting an extra $50 on top of the normal shipping rate, so he's no longer carrying it in his line up of planes. Surfaces prehinged withRobarts, pre-hinged rudder cables, nice smoked canopy. I assume the flying characteristics of the various brandsof 50cc Sbachs arerelatively the same. I saw a PilotRC one at my field recently andsome of the experienced3D guys really loved it after trying a hand at it. Can't wait.

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Old 01-18-2011, 08:30 AM
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Default RE: 30% Sbach - Are these servos sufficient?

Yup, I'd marry my PRC 50cc SBach if it were legal in FL

Mine has 7955's all around.
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Old 01-18-2011, 03:05 PM
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Default RE: 30% Sbach - Are these servos sufficient?

Capt.
If you want to buy the 7955 for $89 each....you can do that all day long at Air Wild Pilot Shop. Nice company to do business with.
$300 is an outstanding buy for the Sbach. Is that for the 50CC version? Mine was $650 + shipping. I almost wish I hadn't given it away. It was that good.
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Old 01-18-2011, 04:11 PM
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Default RE: 30% Sbach - Are these servos sufficient?

Thanks, I'll look at Air Wild.

It is the 88", 50cc mermaid color scheme version.At the time Icalled Wild Hare since they are local to me, looking aroundfor a used 50cc and heoffered me the new Sbach so Itook it. I probabably wouldv'e never chosen the plane otherwise. My first choice was a MX2 butI alreadyknew most all 50cc size planes are around $500-700. After researching both the full scale and rc versions of this aircraft I've found nothing but good things about it.
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Old 01-19-2011, 07:26 AM
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Default RE: 30% Sbach - Are these servos sufficient?

Curiosity got me about running digital Hitec servos on my 2.4g Futaba 617 Receiver. I would not think there would not be any compatibility issues would there? I posted this in the Radios section also but figured I'd put it here also for anybody that might could comment on. I'm no expert so please correct me if neccessary but here is what I've concluded so far:

After some internet research I found some older threads about this scenario where Hitec servos were misbehaving or locking out due to the signal output voltage of some Futaba receivers being lower than the required voltage oftheservos. This would not be good, and even worse the problem would not present itself until the servo reached about a 120F operating temp (which could easily be done on a hot summer day) or is continuously under high loads at which point the servo would require a higher voltage than the receiver signal would put out. So you could easily have apotiental latent failureand never even know about it! This is one choke point I wouldn't want to have.

Good news is I think this is not a problem anymore. Some 2.4Futaba receivers would put out a max of 2.7v to the servos, while some Hitec servos required a minimum 3.0v when at max operating capacity therefore resulting in servo malfunction. If anybody knows any more or can elaborate on this please chime in.

Another similar scenario to this is not in compatibility of components but in using long servo leads, lighter guagewire,and/or y-connectors.In this casethereceiver signal voltage drops over the long leads to the servo and the result is jittering, twitching or lockout thatinmanyinstances will not be present under nomal range checks. Apparently aneasy fix for this is an in-linebuffer-amplifier; cheap insurance for boosting the voltage to the servos. I assume the Smart-Fly power boards will do this also.

So I've now given a lookand am leaning towards Futaba servos again. I don't want to start a war on the perfect servohere but the Futaba 9156 seems to be an awsome servo and comparable in perfermance and price to the Hitec 7955, yet you just don't see many Futabas on large scale aircraft? Heck, many of the larger well known internet RC retailers don't even carry Futaba servos but instead push Hitec hard. I think over the years Futaba was passed by Hitec in the large scale market due to pricebutit seems theyare catching back up. Futaba dosen't push the infamous "Titatanium Gears" like Hitec followers, but for those that have used this line ofservos,theyhave reported very long life spans with little slop ever developing and better centering over the Hitecs.
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Old 01-19-2011, 08:18 AM
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Default RE: 30% Sbach - Are these servos sufficient?

The servos in question are the 7950TH's. I have 'em in my PRC 29% S'bach on 7.4v lipos unregulated.

The servo issue is on the signal side of things, you're right, but only with long extensions. Any length over 24"(even 20awg twisted) unregulated they will glitch/twitch. I had the glitchy problem first hand with my elevators on 36" extensions. I got their signal booster for those channels and it solved the issue. I didn't like the set-up and tried a different Rx placement/config eliminating both the boosters and the 36"s. Problem solved permanently. Rock solid and they move the plane around with authority with the unregulated 7.4v power supply. I would do it again, but try a 6.6v LiFe supply, only for the safety offered by the different battery.

If you are going the digital route, they are power hungry but worth every penny, imo.
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Old 01-19-2011, 03:16 PM
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Default RE: 30% Sbach - Are these servos sufficient?


ORIGINAL: Capt Cash

Thanks for your reply. I priced the servosat Tower Hobbies,

After member discount and shipping:

4 - 7985s - $306
4 - 7955s - $403

Prices are all over the place on the internet, but it looks like 7955s are pretty much around $100 apiece.

I'm still on the fence about it. I do like to do high speed/ high rate aileron rolls, so maybe the7955 would be a little more insurance here too. Just don't want to lose a plane because of a darn servofailure.

I wouldv'e never bought this plane but Tom at Wild Hare lives 5 miles from me andofferedme his last onenew inthe box for $300.He said the box was extraordinarily long to shipfor customers withoutcosting an extra $50 on top of the normal shipping rate, so he's no longer carrying it in his line up of planes. Surfaces prehinged withRobarts, pre-hinged rudder cables, nice smoked canopy. I assume the flying characteristics of the various brandsof 50cc Sbachs arerelatively the same. I saw a PilotRC one at my field recently andsome of the experienced3D guys really loved it after trying a hand at it. Can't wait.

you can get he hitec from chief for 89 bucks.... i use 7955 all around and 7985 on my throttle on my 50cc, on my 30cc and 100cc i use Power HD servos, really nice and the price is awesome.
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