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HelicopterRadio - Servo - Gyro - Gov - Batt › Is it very common for servos to go bad?? (Warning long post)
01-25-2007 03:01 AM  10 years agoPost 1
7379df

rrApprentice

Branson,USA

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Had my very first crash 3 hours ago. Iv been in this hobby for almost a year. I started with a predator gasser and love it. But now I have lost confidence in my heli.
So about the crash, I hadnt flown for about 3 wks. so weather
was nice today and been dying to fly. First done a radio check
with anntena down and could walk about 50-75' before failsafing.
Done a preflight checking all movement everything looked good and started to bring up RPMs. Everything looked fine and was getting ready to turn on Gov. and noticed the heli jumped to one side, (could see swash plate jump up on one side)alomost like it went in fail safe, so backed off rpms and seem OK so tried it again and
jumped again a few times. It jumped in a way that seemed like something was "hung up" on swash plate and then let loose,
like canopy was catching but it wasnt touching. So I kept
trying and it quit doing it. It only "jumped" about 4 or 5 times
roughly. Then it stopped and did not do it again. So I carefully proceeded a low hover for quit a while. No sign of any problems,
so I started to forward flight and flew a tank of gas (30 min)
with no problems. While flying seemed like something didnt feel right. The previous night I extended my controls on radio (had to show them off, they feel great) and thought it was me getting used to them. Well have you ever had that funny feeling like you
should just land and go home. But no, I had to have one more flight and its always the last one that gets you and it did. I was up about 20 to 30' forward flight with head in and all of a sudden and
I do mean sudden it went to the ground. Well could have been worse.
I have most of the parts to rebuild, mainly tail boom, blades, tail
gear, canopy scratched. Well my biggest problem is I want to know for sure if this is what caused the pile up. I have had alot of confidence in the ole predator and now its gone. This is the first Rc anything I ever had and have put many hours on this machine. I guess after a while you just build up some kind of a trust in it.
I got it home and turned on the radio heli to check the servos.
There is 3 JR 8311s,(The only JRs on the whole machine) on the CCPM and one of the sevos is acting like its stripped out but then you can hold it and its solid. But nevertheless definately something wrong with it. Im not 100% sure it wasnt damaged in the crash but I figured the canopy had protected them. So my conclusion is I think it must have been servo in the first place. And now after this long post, How often do these go out and why ??And also if i replace with Futaba what size would I need and do I need to replace all of them or can I get away with just one ??
Sorry for such a long post. Thanks for any input. Darren

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01-25-2007 03:06 AM  10 years agoPost 2
ESWLFSE

rrElite Veteran

Liberty Hill, TX

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It could have been something as simple as a spread terminal on that one servo connector at the receiver making an intermittent connection.

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01-25-2007 03:20 AM  10 years agoPost 3
7379df

rrApprentice

Branson,USA

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That would be possible. The only thing that puzzles me is you can
move the servo by hand now and it doesnt make the same "gear" sound as the other ones. But the crash could have stripped it out.
Thanks !

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01-25-2007 04:43 AM  10 years agoPost 4
TMoore

rrMaster

Cookeville, TN

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The crash could have put the motor in a bind, loaded the gear train in one direction. The only way to know for sure is to send it back. JR has a 3 year warranty on their stuff. I advise you use it.

TM

Delayed Response Operator Not Engaged

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01-25-2007 04:49 AM  10 years agoPost 5
7379df

rrApprentice

Branson,USA

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Thanks TM, I bought the heli used but it was new to the guy I bought from. He put together and it was to intimidating to fly
so I dont think he ever flew it. Everything looked brand new when I
got it but I noticed tonight that the JRs looked well used. So I just ordered 3 new 9202s from Tower. Thanks for the
advice though

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01-25-2007 05:50 AM  10 years agoPost 6
fritzthecat

rrKey Veteran

Virginia Beach, VA

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Servos, like anything mechanical can and will fail. I've had cheapo serovs survive years of crashes, dunkings and abuse while a U$120 digital failed 10 seconds out of the box.
There is a lesson to be learned here:
The heli tried to tell you 5 times before flying that something was wrong. And during the flight it again tried to show that it just wasn't right. When this happens, strobelights, horns and sirens should be going off in your head while a big red flag appears over the helicopter. Listen to your heli and take heed when it doesn't feel 100%. Nothing ever gets better or fixes itself in flight.

Fritz


'Send Money, Women and Guns!'

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01-25-2007 12:25 PM  10 years agoPost 7
perfesser zero

rrKey Veteran

Dublin, VA., USA

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7379df...

Servos, like anything mechanical can and will fail. I've had cheapo servos survive years of crashes, dunkings and abuse while a U$120 digital failed 10 seconds out of the box.
Which just goes to show you that price alone is not a determining factor in how good or bad something is. Remember that even Bentley motor cars have repair facilities. Do as TMoore has recommended and send it to Horizon and have it repaired/replaced.

Later...

Scott!

Tiger 50 - OS 50SX-H
Hawk Sport - OS 37SZ-H
Raptor 30 - OS 37SZ-H
JR 10X/R950S

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01-25-2007 01:06 PM  10 years agoPost 8
7379df

rrApprentice

Branson,USA

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Fritz, I believe you hit the hammer right on the nail. I should have quit when I had that funny feeling like something wasnt right. I wish I could rewind and start over, I would have went home when I
felt something didnt feel right. As for the JR servos are they worth sending to JR and I have no way of knowing how old they are.
By the way would i send them directly to JR or another web site.
Is it very expensive to repair ? Thanks for all the replies guys, much appreciated !!! Darren

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01-25-2007 01:40 PM  10 years agoPost 9
Tday

rrKey Veteran

Needham, MA

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It's a good lesson to listen to the heli, but what would you have done to check it out? Sometimes I find myself not listening because I don't know what it's saying. Well servos do fail regardless of price---though I will say that you usually buy expensive servos for performance not longevity, so to say an expensive servo didn't last long may be like saying your ferrari idles badly. Anyway---I have this thing called the servoxciter which let's me check the servo out. I can let it run a servo through the full pulse range and see if it's hopping and jumping at any point (and know it's not the radio or anything else in the control loop), see if it has dead spots, and feel the torque all along the way. You can also check to see if you're extending your servo past the pulse limits it's designed for---that will burn out these suckers *fast* but that's not likely your problem after a year unless you just changed your servo throws.

Anyway---servos do fail and quickly too. You'll know their warning signs from here out.

Tom

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01-25-2007 03:30 PM  10 years agoPost 10
whirlyspud

rrKey Veteran

USA

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If the servo is in a machine that gets flown alot, Gas or glow, I would go no more than 2 seasons before replacing them. If it is an electric machine you can go longer. Vibration kills. Thats what I have been doing for about the last 20 years. Works well for me. As for sending them in for repair, I only repair them if it is stripped gears or a broken wire at the circut board. Anything else and they get filed in the little green can. I've had way too many just returned from service servo's die within a couple flights. Granted this was a few years back, and maybe the service is better now, but I tend to doubt it, and to me it just isnt worth the risk.
The above is only for my helicopters, on planks I go much longer mainly because they don't see the vibration levels that those in the helicopters see. That also depends on the specific model.

Mike

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01-25-2007 10:22 PM  10 years agoPost 11
7379df

rrApprentice

Branson,USA

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As I said earlier, i looked at the servos on the ccpm a little
closer and they seemed to be on the well used side. When I got
the gasser it looked brand new and had not been flown all that much.
A very nice and well kept machine. So back to the "old" servos I was thinking about having the one fixed but then what about the
others, they could go out as well. Then after giving it some thought figured it would be safer to buy all three new. I gave around $148 for 3 new 9202s. I figured this would be better insurance and in the long run cost less. Like Mike said probably a good idea to replace every 2 seasons, at least on the CCPM. If the tail servo goes it wouldnt be quite as bad as having the ccpm servos go out. When the crash happened it was so fast I didnt have time to hardly react and it went into a nose dive. It felt like the servo "jumped" or let loose and instanly headed down. Tom I was wondering if you could tell me where to get that servoxciter. You could at least check them periodically and have a little more confidence.
Thanks again !!
Darren

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01-25-2007 11:18 PM  10 years agoPost 12
Tday

rrKey Veteran

Needham, MA

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Here you go. I'm surprised how useful this has been--I use it all the time. I've also had a lot of servo types of failures from not understanding what stresses them beyond hard flying. At least my set-up isn't hurting the servos anymore, and I can check some important aspects of how they're working easily enough. Tom http://www.vexacontrol.com/

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01-26-2007 12:38 AM  10 years agoPost 13
7379df

rrApprentice

Branson,USA

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Thanks for the address Tday, just got one ordered. That will come
in very handy. Darren

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01-26-2007 01:12 AM  10 years agoPost 14
JKos

rrProfessor

Redondo Beach, CA

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Sorry to say, but 9202 servos are too weak for a 90-size bird. 9252s would have been a better choice. You can find them for around $69 each.

- John

RR rules!

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01-26-2007 02:45 AM  10 years agoPost 15
7379df

rrApprentice

Branson,USA

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JKos, Thanks for letting me know. I wasnt for sure what to get so I looked in the predator manual and seen a picture of 9202s on the
CCPM and assumed they would be alright. Where would you recommend
purchasing those at $69.00 ? I found them at Tower Hobby for
$79.00. Im new at this and dont know alot of decent sites.

Thanks for your help ! Darren

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01-26-2007 03:21 AM  10 years agoPost 16
JKos

rrProfessor

Redondo Beach, CA

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Well, it seems I'm wrong. The RC Universe servo database has wrong info for the S9202 servo. That was the first hit when I searched for S9202 specs. Every other source shows a much higher torque rating than what I first looked at. So, S9202 do seem to be ok. Sorry about that.

That being said, 9252s are still better for centering accuracy and holding power.

Check your PM for shop recommendations on the 9252.

- John

RR rules!

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01-26-2007 03:37 AM  10 years agoPost 17
7379df

rrApprentice

Branson,USA

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JKos, Im going to stick with the 9252s. Ive seen alot more of them
on helis than the 9202s and there probably a bit better. Id rather not skimp when it comes to CCPM servos. Im glad you said something though cause I wasnt real sure. Tower is pretty good about returning and they had the 9252s. And also got $25 off of price. Thanks, Darren

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01-26-2007 03:46 AM  10 years agoPost 18
perfesser zero

rrKey Veteran

Dublin, VA., USA

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JKos...

Aren't the 9252's digital and the 9202's coreless analog servos?
Just curious.

Later...

Scott!

Tiger 50 - OS 50SX-H
Hawk Sport - OS 37SZ-H
Raptor 30 - OS 37SZ-H
JR 10X/R950S

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01-26-2007 04:09 AM  10 years agoPost 19
JKos

rrProfessor

Redondo Beach, CA

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Scott,
Yes, the 9202 is a coreless motor analog servo and here are its specs:

76 oz-in @ 4.8V - 98 oz-in @ 6V
.26 sec/60 deg @ 4.8V - .21 sec/60 deg @ 6V

And the 9252 is a coreless motor digital servo with specs of:

92 oz-in @ 4.8V
.14 sec/60 degrees @ 4.8V

There is, of course, the classic debate of running 9252s on 6 V. There are those who have done it on regulated 6 V for a long time and those who still say you shouldn't.

And for completeness, the 8311 which was in Darren's PG is a coreless motor digital servo with specs of:

130 oz/in @ 4.8V
.18 sec/60 degrees @ 4.8V

Again, plenty of folks using the DS8311 on regulated 6V (or close to it) for even better performance.

- John

RR rules!

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01-26-2007 04:34 AM  10 years agoPost 20
7379df

rrApprentice

Branson,USA

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Looks like the Jr 8311s are a little more powerful.
Are they as dependable as Futabas equivelant? Opps, maybe I shouldnt ask. That would be like opening one big can of worms around here. Maybe I should have went back to 8311s ?? HMMM.

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HelicopterRadio - Servo - Gyro - Gov - Batt › Is it very common for servos to go bad?? (Warning long post)
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