Aileron and flap servo arms in moulded wings.

[sorry]

You are all clever people.

Aileron and flap servos in moulded wings.

What is the best way to attach the arms so that they can be removed/replaced or moved round ?

I have tried making right angled screw drive short enough. Failed.

Tried replacing cross head screws with socket head screws.  Couldn't find any the right size.

Help.

Ta

Robert

[oipigface]

I think these two answers are probably too late by the looks of your picture.....Well, it’s one answer really with two ways of doing it:

Make the servos removeable!

Method 1: Wrap the servos in tape and glue them in, following the detailed instructions on Kevin Newton’s website. These are almost 20 years old, but are still good.  http://kevin-newton.blogspot.com/2001/01/mounting-wing-servos.html.
 

Method 2: More common these days is to use a servo frame glued to the wing skin. The servo can then be screwed to the frame and easily unscrewed again. I don’t know a really good build log for this. Perhaps someone else does? Servo frames can be bought, but can also be cut from plywood that is half as thick as the servo.

It looks as if your servos have been glued to the wing skin without the tape that makes removal easy by cutting the tape. My suggestion in these circumstances would be to disconnect the servo arm, get a pair of pliers and yank on the servo arm. A vertical yank can be good enough, but if this seems to be damaging something, try exerting a horizontal twisting force to the servo. Replace using one of the two methods, being sure to abrade the old epoxy without going through the wingskin. (Can you hear the voice of experience speaking?) It's usually quite easy to see when you’ve got back to the original surface. I use a smallish diameter Dremel grinding bit.

[sorry]

Thanks,  good ideas.

 Nothing glued yet.  Still thinking.

Do some people not screws arms on at all ?  Just push fit.

[Graham Woods]

Servos glued to wing skins are a pain. I have had to remove then once or twice. If this were my model I would un-clip the clevis, then set about removing the horn and not worrying about the screw at this point. I would try to get a Dremel in there to cut the nylon clevis. If I couldn't manage that I would turn to a soldering iron to melt the clevis. I would use my 40watt iron to get the heat to soften/burn the horn. At this point it gets brutal... with a scalpel and taper nosed pliers I would be trying to remove the horn by yanking, twisting etc. That nylon horn has to give way at some point. Once removed I reckon I would be able to get a grip on the servo screw with a pair of pliers. As a seasoned flier you, like me, may have a large collection of spare horns. (That clevis could do with a 2mm locknut btw)

[oipigface]

1 hour ago, sorry said:

Do some people not screws arms on at all ?  Just push fit.

Only idiots like me. I did it once (by mistake), and I will make every effort not to do it again.

[oipigface]

There is another possibility. Earlier versions of external bearings replaced the bolt you are having trouble with with a threaded shaft which ran in the external bearing. Such shafts usually had flats on each side so they could be unscrewed with a small spanner (I made mine myself out of a piece of dural) or with needlenose pliers. Since you haven't glued it in yet, you might consider replacing the screw with one of these shafts. Be warned, though. You might have some difficulty sourcing them. I got some recently from Graham Wicks at rcmetalbitz. They were old stock from the days when Tony Fu used to sell them.

Modern exterior bearings do have the servo arm a push fit, but the exterior bearing housing stops them falling off. Servorahmen.de make these kinds of frames with inbuilt exterior bearings. See for example https://www.hyperflight.co.uk/products.asp?code=SRIDSM-MKS6110. 

 

 

[Stormeflyer]

You can purchase ultra low profile tools like this or make your own to suit specific needs

 

[rc-soar]

 

6 hours ago, pete beadle said:

To me the ultimate bodge to remove the servo arm and retaining screw [...]

You mean like this?

Just need to remove the arm.... 

[oipigface]

Nice work, Mike! What on earth is it?

[Keith_W]

The best way is to make the servo removeable with some sort of mount, buy them or make them.

One way to fix or remove the horn once the servo is in place is to find a long screw that fits the servo shaft and a nut to fit the screw. Screw the nut on to the screw and then screw it into the shaft, when the screw hits the bottom tighten the nut. Loosen the nut and then unscrew to remove.
 

[EssexBOF]

9 hours ago, rc-soar said:

 

You mean like this?

Just need to remove the arm.... 

 

Seeing that picture, I wonder what the rest of the installation looks like

Using a servo mount, has to be the way to go, where this is possible, the flat type of servo being the prime example.

On ailerons, the servos have to be smaller, due to the wing thickness at that point being thinner. This leaves little choice, but to use smaller servos, in which the mounting lugs, are vertical when the servo is laid on it's side.  I use a test rig to set the servos up to determine the position of the arms. Important to make sure the arms are at the same rotational position, at their neutral or start position, as if they at different positions, the ailerons/flaps will not move at the same rate/positions through travel.

I tried many ways of glueing servos in,whilst at the same time, having the ability to be able to get them OUT.  I have used the following for some time now. Remove servo  arm. slide a piece of heat shrink tubing over the servo, leaving a small excess over the ends where the lugs are. Shrink SLOWLY with a heat gun. If you blast it with to much heat you will blow hole in the heat shrink . Where the splined output spindle is, carefully cut round it, to expose splines.  On the side to be glued down onto wing. rough up the heat shrink, to remove shiny face. I use Rapid Araldite to glue in, as I find this does not set hard & brittle. Check position does not move whilst setting.

To remove the servo if needed, just cut through the heat shrink on top of servo exposed, servo can then be popped out. To , remove old glue, with a Dremel tool which no modeller should be without.

[rc-soar]

1 hour ago, pete beadle said:

As OPF says though, the specimen you found, "What on earth is it?"..........I hope you didn't buy it!

It was the handiwork of an ex-member of the ISA (you'll remember him Pete!),  well known for his use of glue as a structural material! And no I didn't buy it, I suspect it wouldn't have lasted long enough to complete the transaction

[rc-soar]

I use a custom extractor to remove MKS servos from their frames. Slide under the cam and lever off gently. It's designed around the cams provided with the Stribog, but could no doubt be modified.

Attached STL and Fusion 360 files in case anyone is interested.

MKS servo removal tool.stl.txt MKS servo removal tool.f3d.txt

[oipigface]

The Baudis system (which is the basis of my attempts at making home-made frames) doesn’t require anything so fancy - just a screwdriver. Looks to me as if the external bearing housing is glued into the wooden frame in the Stribog setup. The Baudis system has it screwed in, so it can be removed by taking the two screws out. The servo itself takes 2, 3 or 4 screws, so the whole lot can be taken out by unscrewing somewhere between 4 and 6 screws, all of which have their heads pointing upwards in the wing aperture. 
 

There’s a photo in my thread called “Homebrew servo frames with exterior bearing” on this forum. 

[isoaritfirst]

You are all looking at this the wrong way round. 
servos should be installed very carefully and complete with equal length pushrods on each aileron and equal length push rods on each flap. 
servos should be set/programmed into correct position and glued into position when everything is connected and servos set to the correct rotation point. 
 

do it right from the start. Never any need to remove until you break something. 

[oipigface]

1 minute ago, isoaritfirst said:

You are all looking at this the wrong way round

Just answering the question asked, Mike, which was a very sensible one. Your comments about fitting them carefully in the first place are also sensible, but it is only prudent to look ahead and ask what happens if things go wrong. I bet even you sometimes strip gears, or break servo arms, and when you do, I’m sure you would rather be able to do the repair as easily as possible.

[satinet]

Mike is right in that servos should be sub trimmed to match the arm angle in pairs and the pushrods made to the same length in pairs.

 

[thermaldoctor]

Bear in mind control surface horn position plays a very big part as well and just getting servo horns at the same angle and pushrods the same length doesnt always guarantee success. 

Using a commercial servo frame or making your own mount up to allow quick and easy removal of the servo will really help set your linkages up to match.

And  also as per your initial question will really help to make altering and trying different servo arms and positions a doddle rather than a chore. 

[isoaritfirst]

The point  is, that they shouldn’t need taking out. The OP’s question although answered by others does have a deeper problem, that is highlighted by their requirement to remove servos for correction of installation problems. 
It is completely possible to calculate/ guesstimate or even mock up installations so that once installed there is no reason to remove or adjust. 
LDS installations are non adjustable. Fitting rods and clevises are no different. 
When I do an install of this type I solder the clevises to the rod at both ends. I use a rough guide of 7/10 servo arm to horn ratio and take great care in ensuring all horn positions / lengths are equal. 
To the OP I would suggest that they spend some time researching or just considering what they are trying to achieve. 

[Andy_B]

And when you buy a model second hand and put a new rx tx combo on it you dont have a chance to install as you want , and as we know not all centres are born equal .