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HelicopterMain Discussion › What happens internally to a boom mounted tail servo when it fails?
09-16-2007 10:03 AM  10 years agoPost 1
AnnihilaT

rrKey Veteran

The Netherlands

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Is it fuel and oil which has fouled the brushes and contact points in the motor? Would using a brushless motor servo eliminate the need to worry about this happening? Anyone else thinking along the same lines?





A day without sunshine is like, well, night.

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09-16-2007 10:13 AM  10 years agoPost 2
Furious Predator

rrProfessor

Kitchener, Ontario, Canada

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well, i know this doesn't answer your question really....but i just avoid tail mounted servoes all together.

when i got my Predator, it was sold to me with a tail mount for a servo. the first...seriously....the FIRST thing i did to that heli when i put it on my bench, was rip the mount off, and order a conversion kit to mount the rudder servo in the front.

also notice....

The Align 600E has a tail mounted servo, while the 600N has it safely under the canopy. someone out there is thinking.

Shawn
Team Leisure-Tech
Team HelixRC

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09-16-2007 10:38 AM  10 years agoPost 3
AnnihilaT

rrKey Veteran

The Netherlands

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Shawn,

Im totally with you here... Ive always had my tail servos under the canopy on nitro ships which in my opinion is exactly where they belong.

The problem is that im forced to mount it outside of the canopy with the VMAX conversion so my thinking is either to figure a way to move it back inside with a custom mount or else switch to another type of servo which wouldnt be susceptible to failure due to exposure to fuel and oil.





A day without sunshine is like, well, night.

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09-16-2007 11:52 AM  10 years agoPost 4
ppridday

rrKey Veteran

Detroit Lakes MN

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Where does the fuel/oil tend to migrate into the servo? The only places it could be are the case halves, wire inlet or at the servo horn gear. Wouldn't it be fairly easy to seal these points up better to stop any possible ingress of fuel/oil?

I've had a few tail servo's apart & have never seen fuel or oil inside. Usually just broken gears. Not saying it doesn't happen as it obviously has been a problem in the past with others...

Paul

"There's someone in my head, but it's not me..."

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09-16-2007 12:04 PM  10 years agoPost 5
SteveH

rrProfessor

Texas

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Most all of the high quality servos today are sealed with rubber seals at the case halfs, where the bolts go thru the case, and also where the gear exits the upper half of the case. I just wipe them off at the end of the flying day along with the rest of the heli and have never had one fail.

The government cannot give you anything without first taking it from someone else.

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09-16-2007 12:12 PM  10 years agoPost 6
9387ASH

rrElite Veteran

UK

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It is difficult to totally seal a servo. If fuel etc gets inside, it can migrate inside the motor (again almost impossible to seal).

This will eventually get onto the paper former (on coreless motors) and will cause the paper to expand. Once this happens it then starts rubbing against the magnets. The friction will increase until the motor seizes solid.

The entry points are not just the case halves but the case screws, and the servo output shaft.

If the servo can be shielded then this goes a long way to mitigate the effect.

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09-16-2007 12:17 PM  10 years agoPost 7
AnnihilaT

rrKey Veteran

The Netherlands

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Well i have personally never had one fail either... just heard quite a few stories and as this is the first time i will be boom mounting a tail servo (Futaba 9256) i was thinking to take preventative measures now... especially with the rest of the tail problems ive already been trying to sort out on this particular bird.

Im aware that any decent servo for the tail these days are sealed with rubber and at the points where the case halves meet and where the screws are but the one point that isnt sealed (on futaba servos) is where the servo horns meets the main output shaft of the servo itself. I suspect this is how/where the oil gets in.

I also just realized that the pot itself is still a failure point as fuel and oil can get between the contact point of the pot as well. And actually when i think about it... it seems much more likely that a failure due to oil and fuel would be more likely caused by a failed pot than fouled brushes as the motor casing itself is better sealed. hmmm... just speculation tho...





A day without sunshine is like, well, night.

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09-16-2007 01:42 PM  10 years agoPost 8
Leif

rrElite Veteran

USA

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the one point that isnt sealed (on futaba servos) is where the servo horns meets the main output shaft of the servo itself.
That isn't a problem since the output shaft is typically sealed with an o-ring to the top of the case. Also, the hole in the output shaft doesn't go through the gear so any oil that seeped past the screw would not reach the pot.

I run tail-mounted S9254 servos on both my Evos. They get oil on them all the time but I've never had a problem. I just wipe them off when I get the heli home. I've had both of these servos apart for gear changes and there isn't any oil in the servo.

The biggest factors in tail rotor servo damage is high gain and vibration. Both of these cause the gyro to drive the servo excessively causing the motor to overheat.

Leif

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09-16-2007 01:53 PM  10 years agoPost 9
z11355

rrMaster

New England

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re: futaba servos

even w/ the O-rings, I've lost a number of 9253/4's to oil when
mounted on the boom.

It somehow slips past and what really happens is that the paper
insulator/form inside the coreless motor absorbs oil and swells slightly. that creates drag on the motor and it slows down and/or
eventually burns out.

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09-16-2007 02:19 PM  10 years agoPost 10
Torkroll

rrApprentice

Bakersfield Ca

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The way a person flys has a big effect on this.

Tank after tank of inverted hover will soak them.
An active routine or a new flier doing FF won't get that much oil on them.

Anyone who says it's a small world never tried to walk to Zimbabwe.
Jerry

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