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Control Throw Problem

#1
Hello guys, this is my first post, so I hope it is in the right place. I'm kinda a noob, and today I just finished building the nutball speed build kit. The problem I am having is that whenever I move the elevator or rudder, one way they move like 19 degrees, and the other way they only move like 10 degrees or so. I don't know if it is a problem with the servos or the push rods or something. If anyone knows how to fix this it would be greatly appreciated.
 

earthsciteach

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#2
The first step to fixing this is to remove the servo arm from the servo, power up the servo and let it center. Then reinstall the servo arm so that it is as perpendicular to the control rod as you can get it. You can then fine tune it by adjusting the clevis or quick connect attached to the control horn.

Welcome to the forum!
 

Craftydan

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#3
Hey Magicman!

Welcome to the forums! (and yes this is the right place)

Couple of things can "gotcha" here, so we'll start with the most typical and work our way down.

With your surface at neutral (flat with the rest of the wing) is your control horn hole lined up with the hinge? If you made a line from it to the hinge it should be at 90 degrees to the paper when neutral. A little forward/back and you loose throw to one side.

If that's not it, the next thing to check for: Is your horn or control rod bending more in one direction? The shouldn't bend much either way, but the hinge may be stiffer when you bend it inward if the bevel isn't tight (you're crushing the foam in the hinge), or tape/glue is getting in the way.

Finally, check your servo horn. When it's centered, is it pointing 90 degrees from the fuselage line? The servo will normally throw 90 degrees (45 CW, 45 CCW). If you have the horn pointing too much off 90, the forward back motion you want is cut off as it starts to swing around the circle. You'll get the most back-and-forth throw if it's centered at the middle of that circle front-to-back, or 90 degrees off the fuselage.
 
#4
Thank you guys for the help, I think all of the above checks out, as in I don't think that any of those are the problem, but then again, this is my first build, so I could be wrong. I think I'm going to take a video and upload it to you guys tomorrow so you can see what is happening and what I am doing wrong.
 

Craftydan

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#6
Wow. That's a lot of bend.

Notice how going one way it strikes the body? you'll get more throw that way because the body is helping keep the rod straight. This will be worse in the air when you've got wind pushing against the control surfaces.

couple of things you can do:

1. stiffen the rod

you can stiffen by getting a thicker wire or tying a skewer (or something else light and stiff, like a CF rod) onto it.


2. Control the bend

we don't really care if the rod is straight or bent, so long as when one end moves a 1/4", the other end moves 1/4" (think bicycle brake cables). we also want to keep weight down. Chad's idea of using zip-ties for control rod guides would be perfect here. The episode escapes me at the moment . . .
 
#7
Thank you very much, so to control the bend, I could maybe insert a zip-tie in the middle of the rod going through the foam and that would hopefully control the bend? Or I can use a bamboo skewer and zip-tie that onto the rods?
 

Craftydan

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#8
um. strike that (sorta)

re-watched the video -- you're speed clevis on your servo horn isn't rotating, it's bending the rod. it should turn freely on the servo horn.

the thing that got em to take a second look is the rod *SOULDN'T* bend when it's being pulled on, but it's bending both ways.

loosen the connection between the speed clevis and the control horn so it can spin freely. I've had to drill the hole out in past to get this.
 

Craftydan

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#9
arg. it's not called a speed clevis. I know this, but I'm having one of those brain fart kinda days. the screw on thingy to hold the control rod . . . arg. durbro calls 'em "EZ connectors", but there's another name for them . . .
 

Craftydan

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#11
Thanks, Scilia.

Got a mild head cold and it's playing havoc w/ my thinking. Good thing people viruses aren't spread over the 'net'!

Hey Magicman, you up and flying yet? (or has my cloudy thinking spread to your plane too? ;) )
 
#12
Craftydan,

I wasn't able to loosen the linkage stopper, and I didn't really have access to a drill to drill a bigger hole in the servo arm today, so tomorrow I'm going to go down to my local hardware store and see if they can drill a slightly larger hole. Also, it was pretty windy today so I wouldn't have been able to fly anyway I don't think, especially because I'm a beginner and can't fly well in the wind. Thanks again for the advice. O, one more thing, do you think I would be able to put a drop of something inside the hole of the servo arm to make it more slippery so the linkage stopper would be able to move? Or do you think the best way would just be to drill a slightly larger hole?
 

Craftydan

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#13
Magicman,

probably a good call on the wind. Nutballs are said to like it, but it's better to start calm and work your way up.

As long as the screw can still bite well enough it doesn't slip on the control rod, a little oil/lube/WD40 could help. might also try just manually twisting it to loosen it up. I couldn't even get mine in the servo horn w/o drilling, but you might not have the same ones I got. just make sure they turn freely -- a little stiffness is ok, so long as it doesn't cause the rod to bend.

Good luck and fair weather!
 
#15
So instead of drilling a bigger hole, I just went widened the hole with an exacto knife, and it worked like a charm. Thanks again for all the feedback and help.
 

Craftydan

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#16
Great!

If you dare to film the maiden, feel free to post it! We could all use the encouragement of a good launch (or join you in commiserating another foamy death).

Either way, if you only get 30s of pure joy of flight, trust me, it'll be worth it all! (and you'll be back for more foam . . .)
 
#17
I just flew the maiden, and boy was it a blast! I was actually able to keep it up for 11 minuets or so until the battery was out, my landing was a bit hard, as it was my first flight, but all in all, it was a great flight and an awesome time.