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Getting tired of wearing-out servos

Old 10-22-2010, 02:56 PM
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R/C Phile
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Default Getting tired of wearing-out servos

Are you guys weraring-out HS55's ?

Today, I retired my second HS55 as an aileron servo on my Little Extra. The 1st one went out after about 1 gallon of fuel's flight time , this one is done after about 3 gallons. I have also worn-out a little Cox servo that was used as throttle, I never thought that Throttle usage could actually wear-out a servo yet it happened.

Is this normal life expectancy for these little guys or did I just get un-lucky?

The failure mode is as follows: The servo progressively looses it' ability to center to the point of causing flutter like chatter with the aileron. This eventually causes erratic moves on the plane.

The Hitec "tech" guy told me it was a bad potentiometer issue on the first one which was replaced under warranty. This one is out of it's one year warranty period so I'll just chunk it.

Would I have better luck with a Futaba 3114 or should I just bite the bullet and buy digital servos? This wearing-out equipment business is getting old..

Thanks,
François
Old 10-22-2010, 03:22 PM
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rmenke
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Default RE: Getting tired of wearing-out servos



Well heck. Guess this is just another reason to fly electric. I have replaced the HS 55's with HXT 9 gram servos at less than 1/2 the price and as good, mabe better performance. With our glow stuff, servos and related equipment take a heck of a beating from the vibration. The electrics also produce vibration, but not as extreme as the glow. I don't think the digital servos are going to cure your problem. More torque and precision mabe. Let us know if you find a better mousetrap. ENJOY
Old 10-22-2010, 04:09 PM
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Default RE: Getting tired of wearing-out servos

Unfortunately, vibration does cause servo pots to wear out. Some faster than others. I can remember changing servo pots years ago, Kraft, Pro Line, Ace, Novak - they all wore out after time.
Old 10-22-2010, 04:29 PM
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Default RE: Getting tired of wearing-out servos

ORIGINAL: rmenke



Well heck. Guess this is just another reason to fly electric.
SHHH ! Holy Smokes, them can be fightin' words 'round here. Do you know what kinds of I/C fanatics lurk on this here forum ?

Just Kidding

Vibration: great point as the failing servo was as quiet as a canary fed cat until I would fire-up the Enya..

Truth to be known I have not been as good as I used to about making sure the prop stays balanced. I have mounted the new HS55 (I had a new one sitting around) using grommets along with the throttle servo I also replaced recently. Also, I'll make sure that prop is well balanced.

It's kind of funny how the micro servos don't even come with grommets these days and you have to cut the grommet in half to make it fit..

Thanks guys.

Old 10-22-2010, 04:53 PM
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Default RE: Getting tired of wearing-out servos

Even digital servos have pots to wear, too bad really. You would think they would have thought of a better way by now. Ihave high hopes for the HXT900 servos, if anything at $4 a piece they are not breaking my wallet. They have earned a very good reputation.
Old 10-22-2010, 04:53 PM
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Default RE: Getting tired of wearing-out servos

Yeah.. HS-55's are great little servos for electric but I hesitate to use them on glow anymore, the gear train is rugged enough for the rated torque values but shock loads and vibration take their toll. I have started using HS-65's on 1/2a now, and HS-85BB on .10-.15 stuff. In fact I recently lost centering on an HS-55 on a lekkie GWS Tiger Moth, the rudder does get nudged on that from time to time and I guess the teeth at center took a ding sometime.
Old 10-22-2010, 06:05 PM
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Default RE: Getting tired of wearing-out servos

Last month's Model Airplane News had a good article about how NOT to crash and one of the items was proper servo & control arm setup. The long and short is not to do most of your flying in a small arc of the servo gears as this will cause slop, fluttering and ultimately death. Start with the connectors on the inside of the servo arm and the outside of the control surface, and set your transmitter for maximum throw then adjust as necessary.

I love HS-65s but have found them to be more unreliable than any other Hitec micro servo. Have sent dozens back over the past few years.

I lost a Little Extra earlier this year to an HXT 9g servo failure. Both the plane and the servo were almost brand new, so my lesson learned was to use HXTs in my foamies but not anything that would cause gnashing of teeth and a stream of obscenities in the event of a cheap item failure...

EG
Old 10-22-2010, 06:30 PM
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Default RE: Getting tired of wearing-out servos

Good Points,

Since my Little Extra weighs in at less than 2 lbs and does not fly very fast (I run a 8 X 3 Prop with my Enya .09 which provides remarkable thrust but not much speed) gears stripping has not been an issue for me on the control surfaces , it's the pots that go bad.

On my control surfaces the linkages are setup Helicopter Style with almost perfect 90 degrees arm at center, mechanical setup good for 100% ATV's, zero slop on the rod ends, etc.. When learned to set my raptor up, I was reading a book on Helicopters (Ray's Authoritative Helicopter Manual) and the author went to great lenghts on the importance of a "Perfect" mechanical servo setup / how it can make the difference between a sweet flying Heli and an un-flyable nightmare, and how to do it. I have since used the techniques for all my aircrafts and seen a noticeable difference in control feel and accuracy.

I highly recommend the book to anyone, even if you don't fly 'copters, the portion on how to setup servos is the best I have seen anywhere.

I have however had an issue with a sticking throttle barrel which I think caused the demise of the little Cox servo controlling it. This one's gears got out of mesh and the servo seized at Full Throttle Since I have the aformentionned setup for "Speed" (Or lack thereof) it was no sweat to simply finsh-up the tank at full chat and land it dead-stick..

Of all the servo failures to have in flight, the throttle is definitely my 1st choice, I'm sorry you lost your Little Extra to a bad servo

EDIT
One more thing, has anyone tried those Futaba S3114 servos? The specs seem awesome and I have never had a Futaba servo go bad on me before

Old 10-22-2010, 09:09 PM
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Default RE: Getting tired of wearing-out servos

HS55's are the worst servos I have ever seen along with futaba micros.

This are the best you can find at 1/3 the price.

http://www.hobbycity.com/hobbycity/s...?idProduct=662

I always replace std gear with metal one's
.
http://www.hobbycity.com/hobbycity/s...idproduct=6760

Been using HX900 with glow engines for almost 3 yrs with no failures caused by vibration.
Old 10-22-2010, 09:55 PM
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Default RE: Getting tired of wearing-out servos

ORIGINAL: jeffie8696

Even digital servos have pots to wear, too bad really. You would think they would have thought of a better way by now. I have high hopes for the HXT900 servos, if anything at $4 a piece they are not breaking my wallet. They have earned a very good reputation.
They have thought of something better. http://www.hitecrcd.com/products/new...s-m7990th.html They are using magnetic encoders. I've been waiting for this to show up in servos.
Old 10-22-2010, 10:58 PM
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Default RE: Getting tired of wearing-out servos


ORIGINAL: eroc144

Last month's Model Airplane News had a good article about how NOT to crash and one of the items was proper servo & control arm setup. The long and short is not to do most of your flying in a small arc of the servo gears as this will cause slop, fluttering and ultimately death. Start with the connectors on the inside of the servo arm and the outside of the control surface, and set your transmitter for maximum throw then adjust as necessary.

I love HS-65s but have found them to be more unreliable than any other Hitec micro servo. Have sent dozens back over the past few years.

I lost a Little Extra earlier this year to an HXT 9g servo failure. Both the plane and the servo were almost brand new, so my lesson learned was to use HXTs in my foamies but not anything that would cause gnashing of teeth and a stream of obscenities in the event of a cheap item failure...

EG

Yep, computer radios have made a lot of us lazy builders. It's not just the flutter that is hard of a servo, but vibration when attached via a high leverage ratio and a heavy aerodynamically unbalanced control surface. I know several guys who fly small high performance airplanes with servos like these and have "trim problems" with the airplane, when in reality they aren't taking up enough of the servo's stroke to get good centering resolution so the airplane never flies straight, particularly on the elevator.
Old 10-22-2010, 11:48 PM
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Default RE: Getting tired of wearing-out servos

I've had a handful of 55s fail as well. No crashes yet. I've just had to replace them when they got jittery at or near center. Not sure which direction I'm gonna go in the future.
Old 10-23-2010, 03:41 AM
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Default RE: Getting tired of wearing-out servos

There are plenty of other servos from Hitec that are a lot more durable than the HS55. The HS 65HB for instance are great with carbonite gears.

If cheap servo's can make any move to electrics, then you where not really in the right hobby to start with....
Old 10-23-2010, 07:56 AM
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Default RE: Getting tired of wearing-out servos

I have lost faith in all my HS-55's as well. Just last week I had an instance I was sure was a reciever problem. But I could put the reciever in another plane and eliminate the issue. Even with the reciever outside the plane, the servo's would twitch (all of them) just like a bad reciever. So I started replacing servo's one by one. About half way through I just replaced all the servos (HS-55's) with GP B-8's. Suprise! Rock solid flight at 3 times the range. This was with a Hitec reciever too. It seems they set up some kind of interference when they go bad. Either that or they just get posessed after a while. At this point I am having better luck with the Chinese knock offs than the HS-55's. It's a shame as I have about 15 of the HS-55's. I have 30 year old Futaba S-28's that I trust more.

I have been having good luck with all my B-8's though. They are just a Great Planes version of the Futaba.
Old 10-23-2010, 12:09 PM
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Default RE: Getting tired of wearing-out servos

I have two of the HS-55 servos in my little .049 plane, 21 oz. weight. 38 X 7.5 " wing. I mounted the servos with a 3/32" slice of fuel tubing under and over the servo 'ear' on each end. I tighten the servo mounting screw just enough to see the fuel tube 'bulge' a little. I have 72 flights this year... one ounce tank and 15 to 17 minutes per flight. No problems. I flew all last year with the same servos, same set-up, but don't know how many flights. I guess I'm just 'easier' on equipment because I don't doubt what others have written.
Old 10-23-2010, 12:20 PM
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Default RE: Getting tired of wearing-out servos

I admit, I do push mine, especially the rudder ones. Most of the ones that have stripped did so in the middle of a blender or something equally retarded to do with a 1/2A plane and light gear. But I haven't had the problems with other small servos. And for the price you would think they would stand up better. Those are also the only ones I break ears off the cases too. Seems like the plastic is more brittle. I guess the best thing I can say about them is the plugs on the end of the wires do hold up well.
Old 10-25-2010, 09:57 AM
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Default RE: Getting tired of wearing-out servos

I had yet another one go bad, this time on the elevator.

Like the others, it progressively lost its ability to center and was doing a little "Flutter" at rest as the engine was started. It became pretty bad on Friday evening's last flight(Would not settle down until about 1/3 stick travel) . I got lucky as It was not enough to cause anything serious, just enough to ground the plane until it's replaced. This one also lasted a little over 3 gallons.

I like the "Tubing Bushing" idea. Lately, I have been using 1/2 grommets but I was not entirely satisfied with the solutions as the screw's head was still in direct contact with the casing.

I looked around and saw the HS56 and HS65HB (Like Mr Cox says). The guy at my LHS says the HS65HB is also significantly thougher (Indirect pot) and he's never worn one out. I'll try it and see.
Old 10-25-2010, 10:56 AM
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Default RE: Getting tired of wearing-out servos

At this point I think they would make a great $3 servo for full contact combat. I've had better luck with them mounted in the tail, way away from engine, battery, reciever, and vibration.
Old 10-25-2010, 12:51 PM
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Default RE: Getting tired of wearing-out servos

Howdy Gents. I allways use a braided cable on the throttle. It does not transfer the vibs to the servo gears. Keith.
Old 10-26-2010, 04:42 AM
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Default RE: Getting tired of wearing-out servos


ORIGINAL: Yuu

I have two of the HS-55 servos in my little .049 plane, 21 oz. weight. 38 X 7.5 '' wing. I mounted the servos with a 3/32'' slice of fuel tubing under and over the servo 'ear' on each end. I tighten the servo mounting screw just enough to see the fuel tube 'bulge' a little. I have 72 flights this year... one ounce tank and 15 to 17 minutes per flight. No problems. I flew all last year with the same servos, same set-up, but don't know how many flights. I guess I'm just 'easier' on equipment because I don't doubt what others have written.
The HS55s were intended for electric as they didn't provide for grommets. I don't doubt they're wearing out if they're hard mounted to the airframe. I've been flying for over 40 years and have rarely seen pot failure to any significant degree. That's with servos with grommets.

THERE IS NOTHING WRONG WITH HS 55s. On electric they will last a long, long time. On glow, as Yuu shows us, they MUST be isolated from engine vibration. But most of the fault lies with Hitec. Any servo could be made to take grommets and be suitable for electric or glow. Hey Hitec, grommets ain't that expensive.
Old 10-26-2010, 09:27 AM
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Default RE: Getting tired of wearing-out servos

That is true Andy, my B-8's all come with grommets, same with Futaba. What is even more sad, is that the $3 9g Chinese servos come with grommets. But for $15 to $17 Hitec can't manage to squeeze it into the budget?

But I've even had issues with hs-55's that were double-sided taped into airframes. I just expect more for that price.
Old 10-26-2010, 11:49 AM
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Default RE: Getting tired of wearing-out servos

Yes, they could have included grommets. But it is not that hard to place a bit of rubber under the servo when mounting it.
Another good servo from Hitec is also the HS-45HB (8grams), with Karbonite gears and ball bearing.
Old 10-26-2010, 02:21 PM
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Default RE: Getting tired of wearing-out servos

That's a good thought and would help but rubber under the mounting tab doesn't entirely isolate the servo from the frame. Vibration will still get at the pot and motor brushes where the head of the screw contacts the tab. A proper grommet is a donut of rubber that takes the servo out of the vibration equation entirely. When I got my first, HS 55s some years ago, I shelved them until I found use for them in a glider. They were intended for electrics and were never meant to be used in aircraft using real engines.

For the HS 55s to be used with engines, the tab design must be changed to accept proper grommets. Are you listening, HiTec?
Old 10-26-2010, 02:33 PM
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Default RE: Getting tired of wearing-out servos

The flutter you describe sounds a lot like an issue I had where castor oil had gotten in my servo and disturbed the poteniometer. I don't know how oil could mess it up that bad but that seemed the culprit. It follwed the throttle linkage all the way back inside the plane.

I also had the same exact problem with water BTW but that cleared up after I dried it out well.

I have gears strip all the time though in my 55's. I don't buy them any more for that reason.
Old 10-26-2010, 03:07 PM
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Default RE: Getting tired of wearing-out servos

I'm guessing the small Cox servo's Bernie sells are made for at least 50% castor

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