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Replace discontinued servos?

Old 04-18-2022, 06:32 AM
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mikes68charger
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Default Replace discontinued servos?

I sware every time I buy a used jet I'm just blown away by people servos closes.

I just picked up an older 1/5 F86
looking it over and there some very old Futaba BLS351 200oz servos on elevators Gears are tight but 200 oz seems low, even though from my reading 200 oz is what was originally recommended.

I love Futaba but should i replace these? As this jet has flown how much bigger of a servo?

Now the real crazy. Why are there HS 425bb plastic gear 60oz servos x4 on front slats?

This crazy right?

Old 04-18-2022, 07:34 AM
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kevin
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200oz on each elevator half seems ok to me for this. Let's see some pics (skymaster?). Will this make an appearance in Westerville? I'm wanting a 1/5th saber at some point too...


Originally Posted by mikes68charger View Post
I sware every time I buy a used jet I'm just blown away by people servos closes.

I just picked up an older 1/5 F86
looking it over and there some very old Futaba BLS351 200oz servos on elevators Gears are tight but 200 oz seems low, even though from my reading 200 oz is what was originally recommended.

I love Futaba but should i replace these? As this jet has flown how much bigger of a servo?

Now the real crazy. Why are there HS 425bb plastic gear 60oz servos x4 on front slats?

This crazy right?
Old 04-18-2022, 07:52 AM
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LGM Graphix
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We tend to overpower our surfaces like crazy. I've seen all the formulas that say surface xxx requires a gazillion ounces of torque or a crash is guaranteed.

The jmp firebird originally had JR8231's on the ailerons and rudder. Less than 100oz. The last one I built, the owner felt that 400oz was necessary. Not saying having more is bad, that's hardly the case, just saying we tend to believe we need way more than we actually do. Remember when the pica 1/5 spitfire came out? 40oz was about as big a servo as you could get and they worked just fine. Same size spitfire today recommends triple that amount.
the F86 has a pretty small elevator and isn't (or shouldn't) be flown like a rocket ship. 200oz on each half sounds more than adequate imo.
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Old 04-18-2022, 07:55 AM
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As for the slats, they wouldn't be deployed until lower speeds, I won't pretend to know what loads they might see but again for the size, location and intended purpose I'm not sure I'd be concerned about only 60oz of torque. I'd replace them only because I don't trust hitec servos at all and I've seen 425's fail over and over again. I have no issue with non metal gear servos either. I can honestly say that outside of a crash I've never had a nylon gear servo fail. Metal gears seem to develop slop sooner.
Old 04-18-2022, 12:23 PM
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Dansy
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Originally Posted by mikes68charger View Post
I sware every time I buy a used jet I'm just blown away by people servos closes.

I just picked up an older 1/5 F86
looking it over and there some very old Futaba BLS351 200oz servos on elevators Gears are tight but 200 oz seems low, even though from my reading 200 oz is what was originally recommended.

I love Futaba but should i replace these? As this jet has flown how much bigger of a servo?

Now the real crazy. Why are there HS 425bb plastic gear 60oz servos x4 on front slats?

This crazy right?
For the elevator, they seem to be nice enough, but for the slat I would definitely change them…to metal gear maybe some MKS 747, or JR3911….
Old 04-18-2022, 02:04 PM
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George
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Originally Posted by LGM Graphix View Post
We tend to overpower our surfaces like crazy. I've seen all the formulas that say surface xxx requires a gazillion ounces of torque or a crash is guaranteed.

The jmp firebird originally had JR8231's on the ailerons and rudder. Less than 100oz. The last one I built, the owner felt that 400oz was necessary. Not saying having more is bad, that's hardly the case, just saying we tend to believe we need way more than we actually do. Remember when the pica 1/5 spitfire came out? 40oz was about as big a servo as you could get and they worked just fine. Same size spitfire today recommends triple that amount.
the F86 has a pretty small elevator and isn't (or shouldn't) be flown like a rocket ship. 200oz on each half sounds more than adequate imo.
AMEN!!

I wonder how we got away with flying anything years ago when an 8411 was the "biggest" thing available for a very long time, now they are apparently junk!

​​​​​​​And with more powerful servos, people get away with improper set-ups all the time.

Old 04-18-2022, 02:58 PM
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sysiek
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Actually I still have jets with 8411 8611 and the best of them all 8711 and I’m not planning to change them at least until some problems.
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mikes68charger (04-18-2022)
Old 04-18-2022, 05:46 PM
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Thanks guys. I'm going to leave the 2 200oz futaba servos as they seem perfect for elevators.

Took some time to get rudder off but replace the HS5645 servo with a tried and true JR8411 I took of a 2.5m Tomahawk Futura rudder.

I found 4 new S-u400 98oz SBUS servos in one of my drawers, so not a big upgrade over 59oz but mostly because there Sbus and will make radio install easier.

Old 04-21-2022, 04:43 AM
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luv2flyrc
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The worst problem with the older servos is they are all 6v so need to be regulated. If your set up isn't regulated, you can't run Lipo or LiOn.
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mikes68charger (04-21-2022)
Old 04-21-2022, 07:20 AM
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We tend to install way too strong servos. And then a lot of people install the linkage wrongly, where the make a mis-ration and loose a lot of leverage.
In 1988 the Jet World Masters F-15 had one Futaba S9202 on each aileron. I think that had 40Ncm/56oz per inch. Okay, those models were slower, but still...
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mikes68charger (04-21-2022)
Old 04-22-2022, 12:22 AM
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One aspect of servo selection overlooked by many is flutter resistance, its not just about the ability of the servo to overcome aerodynamic loads.
The more powerful and accurate the servo , the sooner, least movement, before it will generate the torque to resist the force of movement initiated by any tendency of the surface to flutter. The higher the speed , the more likely, in general, the likelihood of a surface to flutter , either torsional or flexural.

As for the JR 8411, it was, and is, an excellent servo, have used them, still use them for years with great success. Dont know why some guys rubbish them.

Want more power ? Futaba HPS A 700 is a serious contender for top honours. RC Japans’s top selling servo recently,.
Coffee finished !

Last edited by David Gladwin; 04-22-2022 at 11:01 AM.
Old 04-23-2022, 01:42 AM
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My .02

When you buy a used car, there's certain thing you just...do. Especially if bought from a private individual. Change the oil, check the battery, drain and flush the radiator, check the brakes, etc.

Old doesn't mean bad, but, you also have to think about how many flights those servos have on them. Do you know?
So, you should be able to find specs on voltage, amp draw, etc on those. Put em in a voltmeter. If they check out, don't fix what ain't broke. If they pulling higher amps, they may be worn, dirty, or both.
Make an educated decision. Would you be wrong in upgrading to current tech...no. metal geared in the slats, nobody would fault you.
Its your bird. Do what needs to be done to give you the peace of mind to send it up.
Theres no wrong or right in this hobby. Theres the usual, the normal, the half baked, and the just plain crazy, but none if it is, neccesarily, wrong. We all have our way of doing things thats different from the guy next to us.
If you are comfortable with the reliability of those servos, fly the paint off of it. If not...do what needs done so you are.

There ya go.
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