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Old 11-10-2012, 11:02 PM   #1
bugjam1999
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Default Construction related question - advice please,have pics :)

Hello all,

Been a while since I posted in this forum... hello again

So, a construction related question... advice please. I was in the middle of building an ultrafly F16 and nearly finished, but a small spanner has appeared :o the rear elevators are connected to each other and controlled by a 2mm rod passing through the fuselage. A collet with an M3 threaded hole in it is on that rod. A special fitting control horn goes over the collet, screwing a screw into the hole holds the special control horn onto the collet and the screw grips the rod.

It might be easier to look at the photos to see what I mean... the first photo shows the rear of the plane, the second shows the broken special fitting control horn (black) and screw and what i bought to replace it with after I broke it (white), the third shows the collet up close.

So, what's the problem? well, the special control horn broke when i screwed the screw into it, meaning i was left with a collet but nothing to fit over it. I bought what i thought would work as a replacement, the screw with the white plastic piece on it (i was going to cut the screw down in length) and screwed it into the collet and... found that the collet's thread is stripped. Damn.

So, suggestions please? I've got a collet on a rod that I want to securely fix it to. The elevators are made of two layers of depron sandwiched together with the ends of the rod in them, so to get the rod out would be a wrecking job on one end... added to which there are two bends in the rod after it exits the fuselage so to extract the rod it'd have to be bent straight... basically meaning it wasn't useable again as refitting it and bending those bends again would result in very weak points in the rod.

Thinks i have thought of are:
-drip some epoxy down the hole and see what happens
-cut the rod and remake the elevators - not the end of the world, but annoying to redo the making of them
-cut the collet off with a dremel and fit some other fitting that could be put on the rod in place, if such a thing exists...
-retap the collet to the next size up, M3.5 if that exists?

all suggestions appreciated!

Thanks,

S.


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Old 11-11-2012, 12:00 AM   #2
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How about drilling through the collet and the rod just large enough the fit your screw, fill the hole with epoxy and glue the screw in?

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Old 11-11-2012, 02:07 AM   #3
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your idea is a great fix,use the screw you bought and cut it to the finish size you want the pc to be. then silver solder it into the the collet. with a little flux in the hole of the collet the solder will not only fasten the bolt in place securely,but it will also seep into the collet around the rod making it one very permanent fix.just try to heat the area with your soldering iron and use wet paper towels to keep the lengths of the rod from overheating ...and apply sparingly as you don't want to overheat the rod, heat travels quickly and foam hates heat. not sure if this idea will work around foam but would sure work else where.

looks like a nice build,can you post some more pictures when your done....i'd like to see it.

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Old 11-11-2012, 04:25 AM   #4
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I had a similar dilema on a F15 scratch I built recently ... how to link to a central elevator pivot rod.

I decided not to in the end and fitted external control horns and did it conventionally. With a couple of tiny servos instead of the single larger - I ended up with similar weight and CoG and easily maintained control system.

With yours you could leave the rod passing through as your axle ... fit control horns on each elevator at the axle pivot line ... small servo each side ...


TBH - would never trust the collet in there with repairs ... and epoxy would be near useless I reckon. Only way would be to get hold of a bottom thread tap to re-thread the collet...

I still think external modification ! The other point also is that the F16 ... F15's etc. are far better controlled with combined aileron / elevator system ... the roll rates are amazing !! and pitch authority is awesome.

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Old 11-12-2012, 12:52 PM   #5
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Originally Posted by pmullen503 View Post
How about drilling through the collet and the rod just large enough the fit your screw, fill the hole with epoxy and glue the screw in?
Thanks for the suggestion, but the rod is only 2mm steel... So the most I could drill put would be 0.5mm perhaps, and that'd be a tricky job!
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Old 11-12-2012, 12:55 PM   #6
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Originally Posted by stuart View Post
your idea is a great fix,use the screw you bought and cut it to the finish size you want the pc to be. then silver solder it into the the collet. with a little flux in the hole of the collet the solder will not only fasten the bolt in place securely,but it will also seep into the collet around the rod making it one very permanent fix.just try to heat the area with your soldering iron and use wet paper towels to keep the lengths of the rod from overheating ...and apply sparingly as you don't want to overheat the rod, heat travels quickly and foam hates heat. not sure if this idea will work around foam but would sure work else where.

looks like a nice build,can you post some more pictures when your done....i'd like to see it.
Thanks for the suggestion... There is a lot of foam in that area, I can see the potential for disaster, but will have a look later with my soldering iron to hand

Happy to post more pics of it when it's finished
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Old 11-12-2012, 12:58 PM   #7
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Originally Posted by solentlife View Post
I had a similar dilema on a F15 scratch I built recently ... how to link to a central elevator pivot rod.

I decided not to in the end and fitted external control horns and did it conventionally. With a couple of tiny servos instead of the single larger - I ended up with similar weight and CoG and easily maintained control system.

With yours you could leave the rod passing through as your axle ... fit control horns on each elevator at the axle pivot line ... small servo each side ...


TBH - would never trust the collet in there with repairs ... and epoxy would be near useless I reckon. Only way would be to get hold of a bottom thread tap to re-thread the collet...

I still think external modification ! The other point also is that the F16 ... F15's etc. are far better controlled with combined aileron / elevator system ... the roll rates are amazing !! and pitch authority is awesome.

Nigel
Thanks, I hadn't thought of adding a control horn... Did you have separate axels for each elevator side? I have one axel, so just one servo should do it... Hopfully the one in there already

Ok, thanks guys, will have a look and another think and report back...

S.
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Old 11-12-2012, 01:16 PM   #8
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Originally Posted by bugjam1999 View Post
Thanks, I hadn't thought of adding a control horn... Did you have separate axels for each elevator side? I have one axel, so just one servo should do it... Hopfully the one in there already

Ok, thanks guys, will have a look and another think and report back...

S.
I actually split the elevators of from the stabs in the end and fixed the stabs .. hinged the elevators.

But as you say - you have a central axle already pivoting ... so a single horn on one would do the job - but I would still consider horn on each as then you have no loss of action on the other side ...

Nigel

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Old 11-24-2012, 12:16 AM   #9
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solved! decided to try soldering it,figuring that if the soldering attempt damaged anything in the vicinity i was going to have to tear the elevators off anyway. So... put as much flux as i could down the hole, covered the screw in it, placed paper towels on the surrounding foam and made them wet and poked the screw with the soldering iron....

thought I'd got it, but turned out on the first attempt i'd only managed to solder the screw to the collet, but not the collet to the rod. Had another go and kept putting in solder until it was dripping off - whilst working quickly of course - and this time it seems to have done the trick! so, i suppose i should finish that project now then...

many thanks for your help

And another thing - the clevis in the picture is a parkzone one, which i tend to like using. They don't have the biggest diameter pins though, so using horns etc that aren't parkzone tends to lead to a bit of control slop... not good. Sudden inspiration whilst connecting the clevis up to the newly fixed elevators... the pin is sleeved with a tiny off-cut of servo lead insulation. Bit fiddly to put on, granted, but the linkage is slop free


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