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Old Apr 11, 2012, 03:50 PM
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jojoen's Avatar
Norway
Joined Dec 2003
1,444 Posts
I have a friend that lost a plane after failure of one servo. Another friend lost one servo on ground and it drained the battery in 20seconds.

My solution is cut either positive or negative wire and install 5A car fuse (the small ones). This will protect the rest of the system but stay intact no matter what the servo pulls in normal use.

Electronic solutions only makes even more electronic that can go wrong. We have seen solutions for this in scale gliders. Specially the landing gear that can get stuck. The solutions have been a switch that cuts if the current is higher than programmed but tries again after 1 second before it cuts for that flight.
Emcotec OCP
http://shop.rc-electronic.com/e-vend...&t=6&c=17&p=17
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Old Apr 19, 2012, 05:49 AM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
1,976 Posts
Replacing the gears on a 6125 Mini

Anyone tried replacing the gears on a 6125 mini?

The replacement gearset comes with ballraces attached. Interference fit.

The problem is the servo case has a death grip on one of the ballraces. Again, interference fit I guess.

Tried to push it out from underneath but there's no access.

Before I try heat and expletives I was wondering if anyone has had success.
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Old Apr 19, 2012, 10:45 AM
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Thousand Oaks, CA
Joined Mar 2004
2,381 Posts
Use a heat gun to quickly heat the red case, avoid heating the bearing and it should loosen its grip substantially. Often the shaft is the best tool for working the bearing out but you may be able to make a little hook from music wire.

Alternately, you could put a little loctite on your old shaft and glue it back in.
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Old Jul 26, 2012, 01:11 AM
Glasson Master
f5mmx's Avatar
France, IdF, Breuillet
Joined Sep 2004
47 Posts
I'd like to suggest anyone using the MKS DS6125 mini to have them run in static during some 100's cycles before installing them into their model.
As an example I mounted a pair of them in my Maxa wing and one of the two behaves has it would have two neutral positions depending on where it is moving from.
centering issue on MKS DS6125 Mini servo mounted on a Maxa wing (0 min 16 sec)

I'm lucky this happened on the wing tips, a friend of my had the same issue on one of his Xplorer V tail servos...
J'm
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Old Jul 30, 2012, 04:29 PM
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Alvaro Silgado's Avatar
Madrid, Spain
Joined Sep 2004
229 Posts
Quote:
Originally Posted by DrFragnasty View Post
Anyone tried replacing the gears on a 6125 mini?

The replacement gearset comes with ballraces attached. Interference fit.

The problem is the servo case has a death grip on one of the ballraces. Again, interference fit I guess.

Tried to push it out from underneath but there's no access.

Before I try heat and expletives I was wondering if anyone has had success.
I had the same problem. I finally removed the bearing attached to the gear instead of removing the one on the case.

Just apply some heat to the gear and use a small flat screwdriver to slowly remove the bearing. Apply a little preasure between the bearing and the gear, then on the opposite side, then on the original side, and so on. With a little patience, it will be out after some minutes. Be carefull not to damage the pinions of the new gear.

Good luck!

Alvaro.
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Old Aug 20, 2012, 10:20 AM
Glasson Master
f5mmx's Avatar
France, IdF, Breuillet
Joined Sep 2004
47 Posts
Hi there!

I nearly crashed my Maxa due to a defective MKS 6125-H elevator servo ... it looks like the motor gear is loose on it's axis:

Defective MKS 6125-H servo on MAXA elevator!!!.3gp (0 min 25 sec)


A month ago I had an issue with a wing 6125-mini and now this issue, do I have bad luck or does MKS face a serious quality issue?

J'm
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Old Aug 20, 2012, 11:21 PM
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SoaringDude's Avatar
near Sacramento, CA
Joined Aug 2010
692 Posts
Quote:
Originally Posted by f5mmx View Post
I nearly crashed my Maxa due to a defective MKS 6125-H elevator servo
I did crash. In mid April I had a 6125-H fail on my X4.0 elevator. Been busy so I had not reported it here yet. Major fuselage damage, wings luckily survived (with strapping tape holding the tips on).

Failure mode was the servo remained centered but ignored the servo signal in either direction unless you manually pushed the servo arm in the right direction, then it jumped to the correct position. In the air it just stayed centered, no movement.

I did a detailed post mortem after disassembling the servo. The servo electronics were working fine i.e. both the servo motor control IC (FR6461) and the dual FET drivers were working fine. The motor itself had gone bad.

I was running the servos at 6.0v from a linear regulator. I replaced the 6125-H with a JR 3241 and am now running a 5.4v linear regulator. Still have a 6125-H on the rudder and 6125 full size on the flaps. No idea if the 6.0v added extra stress but I do know this: in Nov last year MKS said to "keep the voltage below 6v" and that they recommended between 5.5-5.8v for "maximum performance." I don't know if voltage played a part in the failure or not.

I had promised MKS I would send the servo to them for analysis but as I said I've been very busy.

Chris B.
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Old Aug 21, 2012, 02:24 AM
Glasson Master
f5mmx's Avatar
France, IdF, Breuillet
Joined Sep 2004
47 Posts
Thank you for your feedback Chris, I'm using a 4 el NiMh pack on the Maxa so the supply voltage shouldn't be the problem.
The Graupner DS3288 seems to be a more reliable solution.
J'm
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Old Aug 21, 2012, 03:35 AM
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Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
2,382 Posts
Quote:
Originally Posted by SoaringDude View Post
I did crash. In mid April I had a 6125-H fail on my X4.0 elevator. Been busy so I had not reported it here yet. Major fuselage damage, wings luckily survived (with strapping tape holding the tips on). .
It happens sooner or later if you fly long enough... Just 2 weeks ago saved my
Aspire. Elevator servo went dead while I was far downwind in strong thermal. In the limits of vision. First I did not believe I had a servo problem, thought that it is just bad piloting because I could no see the plane very well.

Fortunately the elevator servo jammed close to central, in not so steep dive. When I started come home I first let the plane dive to gather speed, then went to series of loops by using just a little landing flaps. Did this over and over again... It took 7 minutes to get the plane back to the field

The moral of the story? If you loose elevator servo, use flaps to control plane. Usually it can be done. More or less...

BTW I would not use DS3288 in elevator. Reason: the notoriously bad centering. Nice servo for the wing, though.
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Old Aug 21, 2012, 04:26 AM
Glasson Master
f5mmx's Avatar
France, IdF, Breuillet
Joined Sep 2004
47 Posts
Thank Tuomo, what servo would you suggest to use instead of the DS3288?
J'm
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Old Aug 21, 2012, 04:46 AM
Registered User
Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
2,382 Posts
Quote:
Originally Posted by f5mmx View Post
Thank Tuomo, what servo would you suggest to use instead of the DS3288?
J'm
DES 658 BB MG is what I use. Gaining popularity. Cheap (35e), robust and accurate. Try it!

The elevator servo that failed had been in a plane that dived in direct to ground in launch, line still attached. So cannot really blame the equipment...
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Old Aug 21, 2012, 09:41 PM
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near Sacramento, CA
Joined Aug 2010
692 Posts
Quote:
Originally Posted by Tuomo View Post
It happens sooner or later if you fly long enough...
Perhaps, but I don't expect an essentially brand new servo (2 months old) to fail like that. But I appreciate your comments Tuomo. Hope your flying season is going well.

Chris B.
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Old Aug 21, 2012, 11:51 PM
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PDX Slope Pilot's Avatar
Portland, Oregon
Joined May 2002
3,922 Posts
Ugh. Reading some of these problems is not making me feel particularly comfortable about using my new MKS servos in my plastic fantastic. What feedback, if any, has anyone gotten from MKS to these problems?
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Old Aug 22, 2012, 01:31 AM
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Australia, QLD, Gold Coast
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4.8V and your fine ....
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Old Aug 22, 2012, 01:51 AM
Ja9
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Norway
Joined Dec 2004
149 Posts
I have had 2 MKS 6125 Mini going bad on me lately, fortunately not in the air.
First one of the flapsservos in my brand new Pike Precision was dead.
No reaction what so ever in this servo.
Got a new one, from a friend, to install in the Precision wing.
This one has some very strange behavior.
When running the servo towards it endpoint, it first goes a bit beyond the endpoint before returing and stopping at the point where it is supposed to.
It seem to center as it should, but does this strange things at the endpoints.
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