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multiple throttle servo failures

Old 07-21-2011, 07:49 PM
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3daerofly
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Default multiple throttle servo failures

I have had two throttle servos fail on my 50cc Extra 260 (luckily they both happened on the ground). The first was a Hitec MG5245 servo. It was digital, had metal gears, and was a mini size servo. It had 76 oz. of torque. It just stopped working when I was throttling up the engine on the ground before a flight. After I took it out of the plane, I noticed that it's very hard to rotate the arm.
I replaced the broken servo with a standard JR ST47 servo that I had on hand. It has nylon gears. I just installed it in the same spot as the previous servo and flew. It worked for two flights. Before the third flight, it stopped working when I was testing the engine out on the ground. So I took the plane home and decided to try the servo again. When I turned the plane and radio on, the servo didn't move but instead became locked in one spot. (I couldn't move the arm with my fingers.) After turning the plane off, I was able to rotate the servo arm again.
I decided to turn everything off and on again. Weirdly enough, the throttle servo moved for a second when I moved the stick. It then stopped again and stuck.

I think vibration might have caused the servos to fail, but I'm not sure. Any help regarding why the servos failed would be great!
Old 07-21-2011, 08:43 PM
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phantomdriver
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Default RE: multiple throttle servo failures

I use the hitec 5645. I've had throttle servos fail over the past just due to the extreme they are under.
Old 07-22-2011, 03:57 AM
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Default RE: multiple throttle servo failures

Thats one reason I run an optical kill.

I'd suspect as you have, vibration. I use 5625's in my gassers.
Old 07-22-2011, 05:04 AM
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scale only 4 me
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Default RE: multiple throttle servo failures


ORIGINAL: 3daerofly

I think vibration might have caused the servos to fail, but I'm not sure. Any help regarding why the servos failed would be great!
Lets see some picures of your linkage and motor set up
Old 07-22-2011, 07:12 AM
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Default RE: multiple throttle servo failures

I use 5645's also after having several failures. Jerry.
Old 07-22-2011, 08:45 AM
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3daerofly
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Default RE: multiple throttle servo failures

Thanks for the help. I will post some pictures as soon as I get that big cowl off. I do use a smart-fly optical kill and it's a lot faster than having to wait for my throttle trim to completely close the carb.
Old 07-22-2011, 01:50 PM
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Jezmo
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Default RE: multiple throttle servo failures

My 50cc Extra 260 was killing throttle servos so I put one of my spare 7985MG's in her and that was 2 1/2 years ago. Still working like a charm. Two lesser nylon gear servos had already failed (both in the air, one while doing an elevator with the ground getting close fast. Can we say belly flop?) so it was a no brainer for me. Nothing but the best now.

For the question about the linkage on the other gents plane, mine has a carbon fiber rod with 4-40 threaded inserts and heavy duty bolt style ball links at each end.
Old 07-22-2011, 03:23 PM
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Default RE: multiple throttle servo failures

I have been using nylon rod to connect the throttle servo to control arm on the gas engines. The servos are standard futaba ones with Nylon gears. Never have a throttle servo failure.

I think the nylon rod isolates the vibrations well. To prevent the bending, a sleeve tube is added for the rod to pass through.
Old 07-22-2011, 05:16 PM
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GreaTOne_65
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Default RE: multiple throttle servo failures

Hey, nonstoprc, maybe we don't know how lucky we are? All I have ever used is 148 Futabas, on both the choke and the throttle. I can count the failures on one hand, most of those occured after contacting Terra Ferma.
Old 07-22-2011, 05:51 PM
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3daerofly
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Default RE: multiple throttle servo failures

I use ball links on the servo arm and carb arm. They're nylon except for the metal ball bearing. The control rod between is metal, not nylon. Here a some pix of the setup.
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Old 07-22-2011, 06:31 PM
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Default RE: multiple throttle servo failures

Might be that heavy metal rod transferring vibration back to the servo,, why so heavy, what is the a 4/40 rod??
Nyrod supported well at both ends will work fine and transfer much less vibration.. Might be worth trying if the problem persists,,

I've never lost a throttle servo on a gasser,, I almost always use Nyrod

good luck
Old 07-22-2011, 06:55 PM
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Default RE: multiple throttle servo failures

like the strap tie guide,nice!
Old 07-23-2011, 06:01 PM
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3daerofly
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Default RE: multiple throttle servo failures

I took apart the two broken servos and the gears look fine in both. I think that the motor or circuit board must have failed. I measured the voltage to the throttle servo to be exactly 6.00 volts. I ended up putting in another servo from my twist 60 for now...
Old 07-24-2011, 06:12 AM
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Default RE: multiple throttle servo failures

I agree that it "may" be the rod transferring vibration back to the servo. None of the servos that failed on me had gear train issues when taken apart, however, I question why the 7985MG has never had a problem if the rod is transferring the vibration. It would stand to reason the electronics in the 7985MG would be getting the same vibration. I am almost thinking the lower cost servos just aren't built with the same quality materials. It could also be I was just unlucky enough to get several bad servos in row.
Old 07-24-2011, 10:16 PM
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Default RE: multiple throttle servo failures

Friend and I have identical planes and setups. He's burned 3 throttle servos and none for me.

Only difference? I unhook the throttle return spring so...try it - might work He did and hasn't burned any more throttle servos..
Old 07-26-2011, 07:35 PM
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3daerofly
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Default RE: multiple throttle servo failures

I made sure there was no binding when settin up my throttle servo again. I did take that spring off from the throttle arm when i first got the engine. I also used the heavy metal rod for the throttle because that was what was supplied by Aeroworks. I think a nylon rod would have been better but I don't know why that wasn't supplied instead. Thanks for the help guys!
Old 07-27-2011, 06:46 AM
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Default RE: multiple throttle servo failures

I have used the 5245 from hitec in my 35% yak... burned 3 sevos one of them to the point that smoke came out from it. I was told that that servo doen´t like the 6 volts.
I tried two more on a smaller plane with a 50cc engine at 4.8 volts and they have been working for two years. The ones on the 6 volt plane burned after 2 to 4 flights.
Now I use hitecs 645 on throttle and choke, three and a half years latter no problems.
Old 07-27-2011, 01:36 PM
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Default RE: multiple throttle servo failures

juanes, that may be the answer because I am running 6 volts. I know the 7985MG's are OK with 6 volts so maybe that's why I'm good now after putting one on the throttle. I know in my case it wasn't the spring.
Old 07-28-2011, 09:49 AM
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Default RE: multiple throttle servo failures

I've always used Hitec 5745 digi standard servo, Karbonite gears if I remember right, never had a problem with several different 30% to 35% planes & 1000+ flights. I do place the servo way back in the fuse and use Great Planes grey (nylon like) push rods(similar to the yellow nyrod but far stronger). 2/56 threaded rod ends screw in nice & tight(plus a little Gorilla glue) on each end, the flex-rod is in the middle. 2/56 ball links or Sullivan locking clevis on the ends. This is "old school" when 2.4 wasn't around but works great, no vibration or electronic interference to servo from ignition. Some of my throttle servos are over 4 years old, in 2 planes & still work fine. I remember way over 10 years ago some of the first "gassers" here had throttle servos fail quite often.
Old 07-29-2011, 03:26 PM
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Default RE: multiple throttle servo failures

Awhile back there was, I believe, a short artical by Quigue Somenzini explaining that digital servos have problems with heavy vibration transmitted back through the throttle because they are trying to hold position to accurately which over time causes them to burn out. I'm pretty sure he recommended a coreless servo such as Futaba 9001 for the throttle to prevent this. The idea that the linkage may give a little and keep the servo from being damaged may very well be true.
Old 07-31-2011, 05:15 AM
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Jezmo
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Default RE: multiple throttle servo failures

.
Old 07-31-2011, 06:37 AM
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Default RE: multiple throttle servo failures


ORIGINAL: Jezmo

Coreless servos ARE digital. The difference is in how the motor is designed. Sounds like QQ was talking marketing garbage. Saying digital servos are having a specific problem then recommending one is exactly that, marketing speak. Once again, just for clarity. I am currently using an HS-7985MG, which is digital, and it's been in the plane for about 2 1/2 years without any trouble. Nothing else was changed, not linkage, mounting or anything else. My original servos, which failed, were nylon geared analog servos.
Sorry Jez but there were coreless motor servos long before digi's came in vouge. The 9001 and 9202 come to mind.
Old 08-01-2011, 12:28 PM
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Jezmo
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Default RE: multiple throttle servo failures

Fair enough Andy, my bad, I'm not familiar with that particular servo. What I do know is the switch to a digital servo solved my particular problem. Although I must admit it could have been the lesser servos just couldn't handle the 6 volts even though they were rated for it. The throttle servos that failed were Futaba but they weren't expensive ones. (They weren't junk cheapies either, just middle of the pack analogs.)
Old 09-22-2011, 09:13 AM
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Default RE: multiple throttle servo failures

ivae had several 225mgs and a 5245 fail on me on throttle and choke servos... i discoverd i was over driving the servo trying to get every last bit of RPM, or every last bit of choke...i later discovered that after 80% throw to WOT it makes no difference in RPM... i now use 5625s,5645, 7985s and 2721 no problems yet, plus i readjusted the throw and not let the throttle arm bottom out at WOT
Old 09-22-2011, 09:20 AM
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Default RE: multiple throttle servo failures

A device like the Hangar 9 Inline Amp meter makes quick work of this. Tick up the end points till you see the current start to bump up, back it off till its stable and voila perfect throw, no binding, no stalled servos.

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