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HelicopterGasser Model RC HelicoptersOther › Don't use any servo arm but metal or discs on a​gasser...
12-03-2011 05:45 PM  5 years agoPost 1
flyinfriend

rrApprentice

North American​continent

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Hi,

I was flying my Spectra last week and flying fast circuits. On my second tank I was just entering a turn and the engine just quit. I had to complete the turn and then autoed in toward myself. The auto wasn't hard, the heli was quite a distance from me and once on the ground she tipped a little to one side causing the blade to hit slightly which caused the other other blade to come around and strike the tail boom. Damage was tail boom, torque tube, main and feathering shaft, and main blades.

The cause of the engine quitting was my throttle servo arm, a plastic Futaba cross. The arm had cleanly broken off at the root of the arm. I will never use anything but a metal arm or full plastic disk on my gassers. I thought since there was not 'real' stress on the arm it would be fine. This is the same arm I had on it when I was having problems with the engine seals leaking causing it to run lean.

I currently have the plastic cross arms on my tail servos and will be changing those out too.

Just thought I would put this out there for anyone else using plastic servo arms with 'arms'.

Tom

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12-03-2011 09:19 PM  5 years agoPost 2
toejab

rrApprentice

Buffalo ,New York​area

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question

did you leave all the arms on or trim off the unused ones? i have seen many cut way back and completely off....weaking the disk.maybe this wasnt your problem,but it is a concern to be aware of.

IF I AIN'T FLYIN' - I'M PROBABLY BUYIN'

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12-03-2011 09:29 PM  5 years agoPost 3
flyinfriend

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North American​continent

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Hi toejab,

Thanks for the post. It was a complete arm, I left all four on. I use to cut them off of my nitro helis but hadn't on this one.

Thanks,

Tom

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12-04-2011 07:22 AM  5 years agoPost 4
Justin Stuart (RIP)

rrMaster

Plano, Texas

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JR makes some nice metal servo arms which have two socket head cap screws to tightly clamp onto the servo output spline. In a crash you'll strip your servo gears, but I suppose it's better than the alternative which is a servo arm falling off or breaking.

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12-04-2011 02:17 PM  5 years agoPost 5
kogibankole

rrKey Veteran

albuquerque/ibadan

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metal arms are over kill

i use the white plastic jr ones, because in a crash they snap before the 8717 strips

if im not blade bogging youll find me pack puffing

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12-04-2011 02:35 PM  5 years agoPost 6
GyroFreak

rrProfessor

Orlando Florida​...28N 81W

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Good thing the throttle body has a light spring or you may have gone full throttle. The reason I recommend a light safety return spring in case the power fails or throttle wires break.

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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12-04-2011 07:44 PM  5 years agoPost 7
Justin Stuart (RIP)

rrMaster

Plano, Texas

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Anti-chicken dance spring.

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12-05-2011 02:16 AM  5 years agoPost 8
bwarkent

rrApprentice

Houston Tx

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If the ball link is not spaced off of the servo arm properly it will cause the arm to twist and snap. I had this happen twice on my spectra g. I checked for binding both times. The only way I figured it out was when a friend watched the servo arm in the air with a telephoto lens and watched it snap. I was using JR servo arms. Had the same one on my 1005 and was never an issue. check your geometry

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12-05-2011 02:25 AM  5 years agoPost 9
Carey Shurley

rrElite Veteran

Orlando, FL - USA

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fwiw, I always use the plastic cross (4 arm) servo arm on gas helicopter throttles and have never had an issue over 15 years. Sometimes I have to cut 2-3 of them off

somebody else here suggested making sure that the travel is right. Make sure there isn't a low idle or engine cut off or full throttle position
that can twist the arm.

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

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12-05-2011 02:53 AM  5 years agoPost 10
flyinfriend

rrApprentice

North American​continent

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Thanks again for the ideas guys. I had no binding on the high or low. I'll check when I get it back together to ensure there was/is no twisting. I had never noticed it and I always check throttle/arm travel during setup.

bwarkent,

What do you mean by 'make sure the ball link is spaced off of the arm'?

Thanks again guys,

Tom

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12-05-2011 03:07 AM  5 years agoPost 11
Carey Shurley

rrElite Veteran

Orlando, FL - USA

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when you get out to the throw extremes its possible that the flat side of the ball link can bind up against edges of the servo arm and twist it. If you use a longer ball or space it out that can't happen.

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

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12-05-2011 12:28 PM  5 years agoPost 12
RojoalfarrApprentice - Punta de Mata,​Monagas-Venezuela - My Posts: All  Forum  Topic

Servo arm not fail... servo did!!!

/
/

I decided to used futaba s9451 servos... It was supposed to be strong enough on my spectraG...

After 15 flights... servo gear failed...

I still don´t get it... metal servo gears failed!!! on a place were you don´t have enough forces to do that!!!

Vibrations ?... I pull the carb spring out... so, now it is free...

Run an Anti-chicken dance spring ?... oh my...!

/

Saludos cordiales,

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12-05-2011 12:35 PM  5 years agoPost 13
Carey Shurley

rrElite Veteran

Orlando, FL - USA

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just to clarify, you were running without the return spring or you removed it after you saw this?

because of its location, the throttle servo on this model is the most prone to vibration

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

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12-05-2011 04:11 PM  5 years agoPost 14
Rojoalfa

rrApprentice

Punta de Mata,​Monagas-Venezuela

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just to clarify, you were running without the return spring or you removed it after you saw this?

because of its location, the throttle servo on this model is the most prone to vibration
I removed the spring AFTER this failure... a lot of vibe and this spring also make force to damaged the servo, I presume...

I am thinking about reinstall the spring, for security reason...

/

Saludos cordiales,

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