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Jef Ott

Wing Servos - making them easy to get out

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Jef Ott

When installing servos in brand new Calypso Contest wingtips a while ago, I gave a lot of thought to being able to get them out again.

Using 1/8" liteply and plastic blocks to screw the servos to, I made frames to fit the servos.

When I fitted the servos, instead of putting them where they would naturally go, but where you cannot see the screws (mounting and arm), it seemed a good idea to mount them further into the wing.

The horn alignment still had to be right, but the bulk of the servo is the 'wrong' side.

After sticking masking tape to the frame across the servo aperture, to prevent the servo from being stuck in too, I used a smear of Araldite Rapid to stick the frames to the skin.

When after a few months I crashed the model (it was only a matter of time), one of the frames became unstuck again, but where the smear of epoxy had made a 3D female mould of the frame on the top skin, it was obvious when the frame was in the right place and I simply stuck it back in with cyano.

Here is a pic of the remounted servo, taken through the clear pvc servo cover. As you can see, a normal screwdriver can be used to remove and replace the three servo screws.

Servo cover.jpg

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satinet

Is the servo sitting on the 1/8th ply?

 

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Jef Ott

Tom,

The servo is sitting inside the frame and screwed to the plastic blocks that are stuck to the liteply.

The shape of the servo is cut out of the Liteply.

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Jef Ott

Currently need to make some servo frames (similar to the one in the picture in the OP) for a pair of new centre panels, for the XantEa.

Is there any doubt as to what this entails?

If so, I can do a step by step photo "How to" in this thread. Happy either way.   

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Brett82

Hi Jef

I would appreciate it if you posted some pics. I've never built my own servo frames before so I would be interested to see how it's done for future reference. Thanks.

Brett 

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Jef Ott

OK Brett.

What I do may not be the best way, it is just what I have done a few times. Others will probably have better ways of doing it, so I will benefit when they put me right.

Will do some work on the frames and post some photos tonight.

Jef

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Brett82

Thanks Jef

There may be 100 ways to skin a cat so I'm happy for you to teach me one of them.

Brett  

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isoaritfirst

See December 16 in the ncfm moth build thread. 

There is a bit there about how I build frames. 

Dead easy if you have a band saw and belt sander. 

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Brett82

Thanks Mike, will have a look. 

Brett 

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Jef Ott

Thanks Mike.

Using my recently inherited fretsaw would make life easier, but I will just use handsaws, drills and files so that everyone can copy the technique, if they have just simple tools, as that is the way I have done it in the past.

Probably won't win any prizes for looks.

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Jef Ott

This will do for now, will post some more tomorrow...

001 Four roughly square pieces of plywood.jpg

002 Find the centres of two of them.jpg

003 scribe lines 6mm either side of a diagonal and drill on intersects.jpg

004 screw four together and file off unwanted poke throughs.jpg

005 position servo.jpg

006 mark round edge of servo with a ballpoint.jpg

007 Drill holes right through all four inside lines.jpg

007a making sure you miss the screwheads on the other side.jpg

008 ignore the servo tabs at this stage.jpg

009 Using a strong knife cut through the holes.jpg

010 cutting downwards on a surface that won't get you shot.jpg

011 Cut through from both sides.jpg

012 You should have four of these now.jpg

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isoaritfirst

Just to make the making easier thats where I now differ. If you cut that plate straight down the middle and make two U shapes then cutting out is much easier, Then cyano them back onto a base plate or just fix them into the wing as two pieces. It makes no difference when they are stuck down they become whole again.

end result is no better or worse - just a little easier to achieve.

 

 if you cut along the line of the servos lugs then glue back with the space for the lugs -- 

 

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Jef Ott

Mike the whole point is that this part - the base - is kept strong and light, and all one piece to minimise adhesive. You have taken me out of context (easily done), I never said making the frames this way was easier - What I said was getting at the servo screws, and getting the servos out, was easier on the Calypso Contest installation, because of where I had stuck the frame, wasn't it? 

Anyways, thanks for your comments.  

Oh OK then just a few more tonight, then I will do some more work on them tomorrow after work...

013 needle file the aperture to fit the bottom of the servo first.jpg

014 Mark with a needle file the ends of the tabs.jpg

015 this gives you something to aim at with the flat needle file.jpg

016 using both marks to align filing.jpg

017 then start shaping the top using the servo as a reference all of the time.jpg

018 keep referencing the servo fit on both sides of the sheet.jpg

019 When it gets to this stage make one left and one right.jpg

020 File an angle around the output bearing support.jpg

021 the servo arm will sit in a recess so use a half round file to make room for it.jpg

022 a larger file will be needed.jpg

023 check against the light for tight spots when it is getting close.jpg

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oipigface

There's another way detailed on my Graecalis build. (Episode 8, I think) Essentially, I fitted rails that grip the servos on each side - finger tight - then screwed a G10 strap over the top. The tops of the rails are a tiny bit lower than top of the servo, so the servo is gripped tightly by the strap.

Easy to build, and easy to remove the servo. Probably wouldn't work so well with thin servos.

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Scram

One thing I think you have not pointed out, Jef.

For the servos to be removable from this frame, sited between both wing skins, the gap between the skins must be at least equal to the sum of the frame and servo thicknesses.

i.e., the servo must be as thin or thinner than the gap left between the frame stuck to one skin and the other skin.  Yes/No?

A situation unlikely for most F3F mouldies, I suspect.

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Jef Ott

That's quite right Jerry. I don't fly F3F models though. Anyway I still have a fair bit of work to do before the frame is finished, so I had better crack on!

 

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Jef Ott

Finished...

024 keep filing until the servo will go fush with the back.jpg

025 make sure the arm will clear the frame.jpg

026 Shape the frame avoiding sharp corners.jpg

027 make plastic side supports.jpg

028 2 little screws.jpg

029 drill holes for side supports.jpg

030_prepare_to_stick_side_supports_to_base_of_frame.jpg

031 let the glue set.jpg

032 with any luck the servo will come out again.jpg

033 mark and drill pilots for the servo screws.jpg

034 drill through and countersink holes for side screws.jpg

035 fit servo screws.jpg

036 you may have to alter the screwhead shapes once they are in.jpg

037 pop a bit of masking tape over the aperture before gluing in place in the wing.jpg

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Jef Ott

@Scram 

You could (if you wanted to use this method) thin the portion above the tabs, down to the difference between the servo thickness and the gap between the skins, and mount them as I did on my Calypso Contest in the OP of this thread.

Just because I like to keep the frame base thick there, in the interests of solidly supporting the (rather cheap servos) output bearing as much as possible, to keep the surfaces slop free, it doesn't mean that you have to. Indeed you could chop it off at the tab line. 

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Brett82

Thanks Jef.

Always interesting to see how others do things. I'm know there will be other ways of doing it but the more ways you see the more you can take from each and adapt them into your specific application or model.

Thanks again mate. 

Brett 

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Jef Ott

Brett,

The side supports are made from a low density plastic, which signmakers use.

I use it because I am screwing to the base (perpendicular to the sides) and screwing the servo to them (inline with the side strips), so using any wood would be a compromise (due to wood having grain).

If you want some, PM me your address.

Jef

PS it has a strong affinity with wood and superglue too!

PPS To quantify the density of the plastic I use, it is about 9.6g per cubic inch. Water is about 16.4g per cubic inch. Sorry for using the units that my brain can process!

 

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