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Old Dec 28, 2011, 11:26 PM
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How to repair an RDS wing

So what happens when you damage a servo in a closed RDS in the molds wing? I found out this past summer. Not because I spanked it, or even landed way out in distance. I had a cold solder joint at the fuselage to wing connector, it was diabolical to diagnose! Unfortunately I had to pull the entire connector from the fuse, covered in 5 min epoxy. In the process I had to cut the wires free and start from scratch. Well like a dummy, I didn't triple check the wiring sequence before I assembled the plane. I have built 10 planes from Martin Weberschock, and each has had the same wiring sequence. Totally interchangeable from left to right and I know it like the back of my hand right? Wrong.

The result is that I fried the aileron servo and my LiFe battery pack by reversing the polarity of the positive and negative.

So here is a photo documentary of how to remove the faulty servo and repair the wing with a minimum of protrusion.

Tools - A dremel with a roto-zip tile bit, a hook shaped pick, soldering iron, epoxy.

Step 1 - Dremel the skin away from the servo to expose it.

Step 2 - Use the pick to slide under the servo output shaft to pry the servo out. I also opened up some holes in the servo case to apply force at a couple spots. This is a scary step, but it works and I have yet to damage a wing with this process.

Step 3 - The servo will eventually come out. It also takes some effort to remove it from the RDS coupler.

Step 4 - Clean up the previous epoxy and wire up your new servo. MAKE SURE IT WORKS before you go any further.

Step 5 - Clean the surfaces and bond it in place.
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Old Dec 28, 2011, 11:45 PM
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Step 6 - I made up a servo hatch from a donor wing. Use a template and carefully sand it to match.

Step 7 - Make some "shear ties" just composite pads for the new cover to sit on. This ensures that the torsional loads are transferred properly thru the new servo cover to the rest of the wing.

Step 8 - Bond the servo cover in place, I also eposied it to the servo, tying the top and bottom skins together.

Step 9 - Complete! I actually hit it with a little light sandpaper and will touch up the paint when I get a chance. But the result is much cleaner than most servo installations with covers.
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Old Dec 28, 2011, 11:57 PM
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Nice work!

I had also good look with using a fishing leader around the output shaft. Before pulling the servo out I used a cold pack (used for sport injuries) on the top side of the wing to freeze the epoxy and make the servo pop easier. I was lucky enough to not have to drill in the servo
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Old Dec 30, 2011, 01:04 AM
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Hi Aaron,

how did you know where the servo was?

Would I be hijacking your thread if I asked how to repair slop in a RDS system?

Cheers,

John.
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Old Dec 30, 2011, 03:15 AM
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Hi John, I emailed Martin to find out where it was within a couple centimeters. Then I started slowly dremeling to find the edge of the servo.

-Aaron
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Old Dec 30, 2011, 10:23 AM
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Aaron, thanks for posting all this information! Hopefuly it will be a long time until I have to use it. Seeing it done takes a lot of the pucker factor out of it! The Radical wings are so stiff do you think glueing the covers back on really helps that much?
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Old Dec 31, 2011, 12:40 PM
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Hi Shawn,

It doesn't hurt to glue them on. The servos are bonded to both skins on the inside of the wings it you have a closed RDS wing. It is just good practice to do that. Aileron/Flap blowback on an F3B launch is not very desirable.

-Aaron

PS- I have no experience tightening up an RDS pocket. But if I did, I would cut the surface loose and just paint some MGS epoxy on the inside of the pocket. Then once cured, use a good quality flat file to get it back to the right tolerances. Check with the wiper frequently to ensure it is the correct tightness.
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Old Dec 31, 2011, 03:09 PM
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Quote:
Originally Posted by luvF3b View Post
Hi Aaron,

how did you know where the servo was?

Would I be hijacking your thread if I asked how to repair slop in a RDS system?

Cheers,

John.
John,

It might be worth dropping a note to Jiri to see if he has any suggestions.

My initial thought is similar to Aarons, but instead of sanding by trial and error, it may work better to create an insert of the proper dimensions (accounting for mold release thickness). The insert may need to be three pieces to make it easier to get out (I'm thinking a wedge shaped center piece). By filling the loose pocket with epoxy (maybe filled with finely chopped carbon) and pushing in the insert, you should be able to restore the pocket back to its original dimensions.

This may be overly complex, but it should be repeatable and ensure that you have a nice uniform pocket of the correct dimensions. Hopefully what I described makes sense.

Tom
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Old Dec 31, 2011, 03:25 PM
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A little back to the topic, any way to figure out the wiring on a sealed wing with the connector glued, meaning not been able to see the wire colors.

Would moving a surface generate enough measurable current to figure out the positive and negative wire for flap and aileron?

I'm afraid to do what Aaron did and burn a servo. I have several fuse wiring harness along 2 sets of sealed wings, don't want to guess if they are all the same or not. I think option b would be ungluing the connector and check the wire colors.

Thanks

G
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Old Dec 31, 2011, 05:38 PM
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Glauco,

If you know which fuse harness goes to which wings, it should be pretty easy. Even if you don't you can check to see if the fuse harnesses are the same. If the fuse harnesses are glued into the fuse, you can just do a continuity check at the servo connector to figure out which pin is which at the wing connection.

Tom
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Old Dec 31, 2011, 06:21 PM
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Glauco, email me and I can send you a picture of what the wiring harnesses look like. I have a few He has been wiring his planes the same way for years. That way your wings will plug into my fuse.

Tom's idea works too. Just use a multimeter to ring out the Multiplex connector to the servo leads.
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Old Jan 02, 2012, 12:35 AM
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Glauco, check your gmail...
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Old Jan 02, 2012, 02:17 AM
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Thanks Tom and Aaron,

I have no problems with Jiri's RDS system, Fosas are still as tight as...

Have repaired another model with a beer can slipped into the pocket (ie a shim) which seemed to work OK in the short term.

John
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Old Jan 02, 2012, 10:37 PM
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Quote:
Originally Posted by luvF3b View Post
Have repaired another model with a beer can slipped into the pocket (ie a shim) which seemed to work OK in the short term.
How many beers did it take to come up with the idea John ?
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Old Jan 02, 2012, 11:33 PM
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Perhaps getting a selection of feeler gage could be the best route? I don't so much care for the idea of metal on metal, but it might be real easy to slip it in there.
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