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Old Feb 25, 2013, 12:01 PM
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United States, NM, Holloman AFB
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Can a receiver get fried by a faulty servo?

I was flying my newly assembled aircraft that took me about a month to build and cover, first one I've ever actually built. I was on my 4th flight for the day (6th total) with it and still breaking in a band new Enya .60 III engine when all of a sudden it stopped responding. Then I got control back and tried to bring her in to land, all the while the engine was throttling up and then cutting to idle without any input from me. Then it started to go sporadic in the air and I lost elevator control, then everything else quit responding and it took a 30* dive into the dirt. When I recovered it, what was left of it, all of the electronics where still on and they all responded except the throttle. The throttle servo was jammed up really good and would not move, and it wasn't making any sounds either. None of the servo's received any damage from the crash and the fuse held up remarkably well.

After I got it all home I decided to test out each servo to make sure they were all ok. Well when I plugged in the throttle servo it made no sound and didn't move. So I took it apart thinking the gear stripped out but to my surprise there was NOTHING wrong with the gears. The motor however was locked up tight. So I tried to plug just the motor back in (had it out of the servo case) and after about 20sec I started to smell an electronic burning smell. Then a few seconds later my receiver (AR8000) started to flash the red light. So I promptly unplugged it, and powered off the receiver. I then plugged in the three other servo's and banged the sticks around to try and draw as much power from them as possible to try and duplicate the brownout warning. It never turned red again and I even took the remote upstairs to try and loose signal but it still didn't flash red at me.

I use Hobbico LiFe 3200mah batteries using both leads directly plugged into the receiver and have never had a problem. I can also get 12 or more flights before needing a recharge, so I know it's not the battery.

So what do you guys think happened that made my plane go down? I'm thinking, faulty AR8000, faulty servo which cause brown out, or a broken elevator (before it hit the ground) and a sporadic engine since I was breaking it in, even though it was running amazingly well before this.
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Old Feb 25, 2013, 12:53 PM
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Well, if a servo fails in a certain way, so that it suddenly draws too much current, it can pull down the entire system then. It is like having a short circuit on the power wires at the servo. That can cause the receiver to lose power. But another situation is where one servo shorts out and the current drain causes the other servos to flake out too. Since Spektrums are seemingly sensitive to voltage fluctuations, a servo shorting out would effectively cause the RX to reset as it loses power, etc.

Another situation is where the servo shorts out just so, causing 5 volts or more to go onto the signal wire line. That could cause the output line on the receiver for that channel to go bad. Usually the RX output lines are open collector driver transistors and are resistant to short circuits to ground, they may not do well if the signal line is shorted to the positive voltage instead. The modern receivers use a microprocessor designed to run off of 3.0v or 3.3v and they have ainternal voltage regulator inside to provide the voltage for the MCU. So if somehow 5v or 6v or 8.4v winds up on a signal wire it may not be good for that channel.

So your thought that the servo shorted out causing a receiver brownout is quite reasonable. But I would test fly the receiver in a clunker or junk test plane first before using it in something nicer. Just to be on the safe side.
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Old Feb 25, 2013, 01:11 PM
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Trust me that receiver will never touch another plane for "just incase" reasons. I'm just so bumbed out about this, it took me a month of about 6hrs a day to get that thing built and ready to fly.
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Old Feb 25, 2013, 04:51 PM
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I have a couple of clunker planes I test fly the receivers in. Both planes are extremely durable planes made with coroplast and aluminum stock metals. So if the receiver goes bad and the plane crashes, it usually isn't a big deal to have the plane going again. But if the RX flakes out in the plane, it goes into the waste bin. I even smash the RX as I have seen guys pick parts out of the waste bin to try and reuse and I don't want them to get ahold of a bad RX as they might try to use it or worse try to sell it on the internet or something.

Many years ago, when radios and servos weren't quite as reliable as they are today (the brand name stuff of course), we used to test fly all the components in a plane. I would run two RX's, one for test and one for flight. The test RX was using the rudder and maybe the throttle servos. Later for servo testing, we'd fly each servo for a while as a rudder servo and ensure it worked OK before using them all in a airplane.

One thought is that the throttle servo may have been stalled out against the throttle stops on the engine. Did you ensure the servo wasn't jamming up against the end of travel on the carburetor? Usually you have to adjust the servo travel on the transmitter to prevent that from happening.
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Old Feb 26, 2013, 08:13 AM
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In the receivers all of the power and all of the returns are bussed together...all of the red wires and black wires are the same circuit. Only the whites are seperate.. If the throttle servo motor shorted out it could indeed pull enough voltage to brown out the system. The problem with a short is that it pulls max amp draw which means heat, that is why you saw the magic smoke. Since you have done a range check it seems that the receiver is ok.
What was the voltage rating of the throttle servo not all servos can handle 6 + volts
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Old Feb 26, 2013, 08:58 AM
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earlwb, I always set the servo travel by way of my DX8 for final adjustments if I can't manually adjust it anymore. I make double sure that nothing ever binds and the servo's are quiet when at rest.

jetmech05, The servo in question was a Hitec A5076HB which is rated for 6v. I've never had an issue with Hitec servos and I run them in all my planes.

Only thing I can say is that I was either unluncky or somehow I was stalling the servo at WOT and didn't know. I was running a cable instead of a push rod but I didn't see any harm in it. It did take a bit more force to move the cable back and forth but no were near the stall torque on that servo.
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Old Feb 26, 2013, 09:27 AM
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I like cables too. They tend to flex a little and thus have some give to them.

You may have had some bad luck in that the servo decided to die on you. It may have been a defect inside the servo. Maybe a little bit of loose solder moved around and got into something. Of course now that it smoked, it likely would be hard to tell for sure. But the little tiny motors have been known to fail every now and then.
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Old Feb 26, 2013, 10:17 AM
Zor
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Quote:
Originally Posted by F16DCC View Post
Trust me that receiver will never touch another plane for "just incase" reasons. I'm just so bumbed out about this, it took me a month of about 6hrs a day to get that thing built and ready to fly.
It is of course YOUR decision to use this receiver again or not use it.

If you make a good range test and it works fine then you have no reason to doubt it.

Zor
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Old Feb 26, 2013, 12:48 PM
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Quote:
Originally Posted by Zor View Post
It is of course YOUR decision to use this receiver again or not use it.

If you make a good range test and it works fine then you have no reason to doubt it.

Zor
I think I'd replace it and not be wondering the next crash if to use it again was a good idea or not, or take it out and put it in a plane you don't have a great fondness for. thats just my .02 cents
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Old Feb 27, 2013, 10:29 AM
Zor
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Originally Posted by rstekeur View Post

I think I'd replace it and not be wondering the next crash if to use it again was a good idea or not, or take it out and put it in a plane you don't have a great fondness for. thats just my .02 cents
I have respect for your .02 cents _ _ _ BUT _ _ _

If we reject everythng we have doubts about it can get out of hand.
We should have a way of checking reliability with all items we use.

I can imagine a fellow having difficulty tuning his engine and discarding it to buy another one and having the same problem .

How about a singing servo (buzzing when not activated) due to a binding linkage? Throw out the servo and buy a new one that will also buzz.

I would not replace a servo connected to a control surface that flutters. I would eliminate the slop on that surface.

The way receivers are built these days I would trust it if it functions well as I said "on a properly done range test".

Note that I am not the fellow that blames all crashes on the electronics

Of course you are free to do whatever makes you comfortable.

Zor
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Old Feb 27, 2013, 10:45 PM
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United States, FL, Delray Beach
Joined Jun 2012
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new Taylorcraft throttle servo burnt up two min before maiden

Last week was going to be the maiden when the throttle servo burnt up ,, thought it was a reciever.. ar8000 spektrum comes installed from factory hanger 9 new 26cc taylor craft. when buy the BNF version. i was kinda surprised you know,, but glad it happened before i took off the ground.. HELLO! ..lol
installed new servo warranty from my LHS.. no issues have 3 flights in so far .
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Old Feb 28, 2013, 05:52 AM
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One thought is if the engine still has the throttle return spring on it or not. Some carbs have a more stiff or strong spring and it can really strain a servo. A stiff spring causes the servo to have to push against the spring the entire time and that can cause a servo to burn out. it is almost like the servo is stalled against the stops while it is pushing against a stiff spring.

I have disabled the throttle return springs on my engines. I usually leave the spring on as a spacer so that the throttle doesn't jiggle around a lot. But usually you can flip the spring end off the throttle arm so it doesn't work as a spring return then.
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Old Feb 28, 2013, 04:24 PM
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Quote:
Originally Posted by Zor View Post
It is of course YOUR decision to use this receiver again or not use it.

If you make a good range test and it works fine then you have no reason to doubt it.

Zor
Zor has a good point about range testing the receiver. A good way to range test and build confidence in it would be to mount in an EPP foamie and start working out in distance. That way if it does fail again it's mounted in a minimal cost airplane, and if the plane dork's itself in it'll probably bounce and everything should be fine.

If the tests are successful, then mount it in a .40 size sport plane, and if that works out, move up in size until you'll confident there will be no issues with it.

Another option would be to send it in to Hobby Services and have them inspect and test it.

Hogflyer
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Old Mar 01, 2013, 02:56 PM
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I didn't have a return spring, it was a stiff cable.

I don't have a "cheap" or "knock around" airframe. So by the time I buy a cheap airframe, build it, install everything, range check it, and see if it fails; I might as well of just bought a new receiver. If it were to fail on said "knock around" airframe and crash, then I would not only be out a receiver but also an airframe and whatever else gets destroyed. AR6210's aren't that expensive, I didn't need a 8ch I just had one laying around from a TX purchase.

But back on topic; I was just trying to find out if an internally failed servo could in fact brown out a receiver even with it being on a LiFe pack rated for a 20A constant drain, and with it having 3/4 charge still in it.
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Old Mar 02, 2013, 07:26 AM
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I answered your question but you can always check with your squadrons avionics gurus good luck....by the way I didn't mean to sound like the blacks and red wires are all bussed together in the receiver....I meant that all the reds are bussed together then all the blacks are bussed together .... That's all the powers to the servos... And all the returns
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