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jetpipe

SERVO ARMS IN MOULDY WINGS

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jetpipe

Has anyone found a way of removing a servo arm from a servo in a moulded wing?

   I have bought a second hand mouldy and need to change the position of an airbrake servo arm. The servo seems very secure and I am worried that I will damage the wing skin if I remove it.

    I suspect it can't be done but thought I would ask before I take a hammer to it!

       John.

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pete beadle

Hi John

Your problem is the servo retaining screw

If you bend the shaft of a small Phillips screwdriver through 90 degrees near the point you should be able, with some jiggling, to get the screwdriver into the cruciform head of the servo screw, undo it little by little using the shaft of the screwdriver, quarter turns are usually enough, until you unscrew the servo retaining screw far enough up its spline to move it round

You may have to cut a small slot in the servo well edge to do this but it won't show when you refit the servo cover

It's VERY slow and fiddly but I've done it a few times now

Good luck

Pete

BARCS1702 

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Phil.Taylor

Ive done it with a cross-head bit (from an interchangeable bit driver) and a small spanner or pair of pliers to turn it - very fiddly but can be done

if you end up having to de-glue the servo it can be done without damage

Phil.

 

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jetpipe

Thanks guys, the trouble is the servo is at the edge of the box and I don't want to enlarge the opening because it would mean cutting into the carbon spar flange, so I can't get a bent screwdriver to it

     The servo hasn't been fixed with epoxy but something thin and transparent, maybe cyano and has not responded to some "gentle" persuasion.

          John.

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Jef Ott

Can you take a photo John?

 

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Scram

This is my take on the tool needed.  I seem to have collected lots of interchangeable crosshead bit so don't mind sacrificing the odd one.

IMG_3839.JPG

IMG_3840.JPG

I cut a bit of ally flat and drilled a hole in the end such that the bit could be driven in tight and then cut off the back bit with my dremmel cutting disc.  Works a treat.  Just need to be sure you have selected the best size bit for the servo screw.

 

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RamJam 53

Have you tried gripping the servo with pliers and applying a twisting motion?

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Redbird

Haven't tried it myself yet but I heard that CA can be released quite easily by putting a drop of petrol ( I think ) or surgical spirit to an edge. I may be remembering wrong though, perhaps that trick is not for CA.

If you are lucky and the screw is not very tight, perhaps you could mould a piece of plastic to the actual screw head to form a driver something like Scram pictured.

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Scram
16 hours ago, jetpipe said:

     The servo hasn't been fixed with epoxy but something thin and transparent, maybe cyano and has not responded to some "gentle" persuasion.

When it comes to removing a servo which is glued in, I prefer to use a right-angle flat blade screwdriver.  Put the blade under the output shaft and apply slow but persistent pressure against the wing skin.  Have to be careful not to break the skin.  This works really well if the servo was wrapped in sticky tape, then glued.  Remove as much tape and glue that is accessible first.

I have never been able to get any grip with pliers.

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satinet

You can make a loop in wire and put it round the output shaft. Twist the end and pull with pliers

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f3fman

I apply pliers or grips to a mounting lug and pull like mad. The epoxy has always broken away before the wing skin has broken.

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Reggie Perrin

If it's been cyano'd then the de-bonding agents that are available work very well..

Providing that the rest of the structured is epoxied and not also cyano'd.....

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jetpipe
7 hours ago, Scram said:

This is my take on the tool needed.  I seem to have collected lots of interchangeable crosshead bit so don't mind sacrificing the odd one.

IMG_3839.JPG

IMG_3840.JPG

I cut a bit of ally flat and drilled a hole in the end such that the bit could be driven in tight and then cut off the back bit with my dremmel cutting disc.  Works a treat.  Just need to be sure you have selected the best size bit for the servo screw.

 

You the man, Scram. I made a tool like that but with thinner aluminium and was just able to get it onto the screw and the arm is off.  

    Thanks to everybody for the plethora of excellent ideas. I am sure they will all come in useful in the future,

                Cheers,

                                  John.

 

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thermaldoctor

Although this doesn't help in this particular instance; if you replace the usual cross head phillips servo horn screw with an appropriate allen bolt instead you can then use a small allen key with the 90 deg bend in to get the screw out easily.

Regards

Neil

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jetpipe

My woes continue! The servo arm I got off is not the correct one and was jammed on by a previous owner. When I replace it ,it slides off as it is too tight and I can't get the retaining screw back on.

     Does anyone know where I can get servo arms for MPX POLO DIGI 4 servos? I believe these are out of production now and I have tried other MPX arms but they don't fit. Slough RC and Mike Ridley haven't come up with any yet.

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Phil.Taylor

I seem to remember reading that the MPX Polo Digi shared the same mechanics as the Hitec HS85 - so try a Hitec servo arm on it ?

Phil.

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thermaldoctor
1 hour ago, Phil.Taylor said:

I seem to remember reading that the MPX Polo Digi shared the same mechanics as the Hitec HS85 - so try a Hitec servo arm on it ?

Phil.

Totally correct. The MPX Polo will accept any standard Hitec 24T horn

Neil

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jetpipe

YOU GUYS! What are you like? Hitec arms do fit, at least 85 and 325 do. 

   Another problem solved, thanks,

         John.

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