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*!$^ $*&! Push Pull Rudder Help

Old 10-19-2015, 04:01 AM
  #1  
dereckbc
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Default *!$^ $*&! Push Pull Rudder Help

DOH! This is driving me crazy. I got my PA Addiction S. Beautiful airplane but do not believe a word that this dang thing can be put together in two evenings. BS It to me more like 45 to 50 hours. Granted it has been a long time since I built one, thus why I went ARF.

So anyway took it out for the Maiden flight today. During 2nd flight I lost Yaw control, not fully, but very sloppy and loose. Brought it in low and slow to see what was wrong and seen the rudder flapping around.

Here is the beauty of this plane. I am a rank beginner 3D pilot. Have a Visionaire and could never hover or do harriers worth a darn. Made another pass to land. It was almost effortless to bring the damn thing in real slow, go into a Harrier, then Hung it on the prop, and snatched it out of the air.

OK enough background and bragging. It took me forever to get the rudder even close with -18 trim. None the less still had specified travel. Well during the second flight, the control linkage bar slipped. Not sure how as I had the set screw tight as I could without twisting ther head off.

I need some experienced help or tips sitting up a Pull-Pull Rudder It uses Kevlar string, and hooks. What makes it really challenging is the Rudder Servo is in the Motor Box.

So how the HECK does a guy Dead Center the Servo and Rudder with tight ropes?


I have not seen other setups but PA IMO is Piss Poor. One would think they would use some type of Augar or Helical Screw to adjust linkages without takingg anything apart. But NO, not PA. No they use Pins that slides through collar with a set screw. You have to take the Servo arm off, adjust the Pin length, set ths screw. and string it back on the Servo Arm under tension, like an ole cross bow string.

Then by some Magic you end up centered with the proper tension on the string WTF
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Old 10-19-2015, 04:20 AM
  #2  
fhhuber
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The strings should cross. that helps make the pull-pull need less slack in the line not being pulled as deflection increases.
Ground handling is the main reason you care about minimizing the slack due to deflection.

The lines need to both be tight ONLY when the rudder is centered. Start deflecting and one will go loose. The airflow holds tension on the pulled line.

I use a 4-40 clevice and 4-40 eye bolt for tension adjustment. (usually my pull-pull is on a 50cc size model) A heavy duty nylon clevice will not tend to unscrew itself like a metal clevice on the metal eye bolt.

You CAN find 2-56 and metric clevices and eye bolts or short threaded hardware intended for doing scale "flying wire" rigging. Whatever size you feel is appropriate for your model

Note that the drilled holes in some of the flying wire rigging pieces will cut the kevlar thread if you don't debur the holes. Eye bolts never have the sharp edge to worry about.

The first 3 or 4 flights plan on needing to retension.

PUT A LITTLE WHITE GLUE ON THE KNOTS or they will slip. Some use CA.. but I find the thread breaks in the CA'd area at a lower pull than the main thread. White "school glue" doesn't harden enough to cause the fibers of the Kevlar to break when bent.

You can also use "Spider Wire" or similar composite multi-strand fishing line instead of the kevlar.
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Old 10-19-2015, 04:43 AM
  #3  
dereckbc
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THX. I had to go look up what 4-40 and 2-56 clevis. My PA uses those or something very much like them. But I am missing something, Mine are made for Carbon Fiber rods clued in place. Cannot visualize what you are doing.

As for getting it centered I know it needs to be done, but the question is how to center both Servo and Rudder Control. Mine is required to be under tension. PA words are "String tension is similar to plucking a bass guitar string, and nice low note?

As for Kevlar IMO is a perfect choice. I have a PA Addiction X. 50 inch wingspan and weighs just under 3 pounds with battery and soaking wet. So I do need a Micro System. PA gave me this for Pull Pull Rudder. I hate it.

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Old 10-19-2015, 05:02 AM
  #4  
fhhuber
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http://shop.dubro.com/p/2-56-pull-pull-system-qty-pkg-1

Note the kits tend to come with metal clevices... these tend to unwind in flight even with the lock nut. good way to end up with no control.

Your set with the brass cotter key will tend to slip unless you bend the ends away from each other. the set screw is virtually useless.
Since your kit calls for the light duty set using the cotter pin, 2mm would be appropriate and plain white nylon clevices will be fine.

http://www3.towerhobbies.com/cgi-bin...?&I=LXEMF8&P=7
Special clevices specific for the control horns in the kit...but they are heavy duty glass-filled nylon and won't slip on the threads for years.
the threaded bits to connect the pull-pull cables to the clevices are the kind that can cut the line if not deburred.

Eyebolts (come in many sizes)
http://www3.towerhobbies.com/cgi-bin...?&I=LXFV31&P=7

Note: DO NOT use the picture hanging eyebolts that have wood screw style thread in a clevice. They will cut the clevice and it will fail.

Do not use 2mm threaded rod or eyebolt in a 2-56 size clevice. It will feel fine as you install it but the clevice will slide off in flight.
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Old 10-19-2015, 06:54 AM
  #5  
solentlife
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Originally Posted by dereckbc View Post
PA gave me this for Pull Pull Rudder. I hate it.

I LOVE THOSE screw links ... I use them almost universally now.

OK reading through your first post ... WHY are you taking servo arm of to adjust ? The screw should be available to you when arm, is on servo. If not then you have them 180 degree upside down ...

Second. Pull Pull only goes slack on one line when deflected IF one or both connections at RUDDER end are not in line with hinge line. Get the offset horns that put holes dead in line with hinge line and no slack.

Third it is not necessary to cross lines ... some are better for it if fuselage tapers severely ... but if not - then no need to cross them. Not crossing them also improves the angle to servo keeping them more at 90 degrees - another reason to avoid slack when deflected.

OK - how to modify to have adjustment ..... You can use the solder ends for wire cables. They have a hole across the solder part that the pull pull wire passes through and then you use a CRIMP to fix. Forget all this knots and CA / Glue malarkey. Get into a Fishing Tackle shop and buy fishing trace wire and packet of crimps. Same stuff actually as Model Sellers provide relabelled and price hiked !
So you have your wire trace crimped to the threaded cable end. Now fit a clevis + small nut to tighten to clevis to lock it and clip to servo arm / rudder horn ... whichever end you wish to have adjustable.

Now you can slack the locking nut ... and actually if only a turn or so .. you can turn the cable end while STILL connected up .. till just tight and then lock it with the nut again.

Tip : Do not over-tighten the cables. They need to be reasonably tight but not so they strain servo gears or rudder horn.

Really Derek ... the screw connectors you have are very good ... just needs a little thought to fit to advantage. Unfortunately I'm not at home to photo any links and set-ups for you ...

Here's my 58" Extra with Pull Pull .... look to left of photo and you see the rudder servo and connections ...



With tight threaded nylon clevis ... often the lock-nut is not necessary.

On some models you don't even need clevis or connectors ... you can loop the trace wire through the horn / arm and crimp as is ...

Here's using servo dual arm through a rudder to give horn either side .. with cable crimped :



Here you see other end .. similar ... its a small 30" model lightweight so no big deal to just use Tx trim to adjust.



Yes with this I get slight slack of cable when deflected BUT flight performance is not affected. You also see the screw connectors set so I can adjust while still fitted to servo .. here on aileron.

Cheers
Nigel
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Old 10-19-2015, 09:02 AM
  #6  
JetPlaneFlyer
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I did warn you that PA builds tend to make you ask "why the hack are they making me do this"

But in this case the adjusters should work ok, you do need to do as already suggested and put a little glue on the knots so that the cables dont pull loose and fine adjustment can be a bit fiddly but with a little patience it should work ok.
Personally I use metal 'lay-straight' type cables as they dont stretch.
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Old 10-19-2015, 07:25 PM
  #7  
dereckbc
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Originally Posted by JetPlaneFlyer View Post
I did warn you that PA builds tend to make you ask "why the hack are they making me do this"
True that, but it i snot as easy as all of you think. The way the Servo is oriented in th eMotor Box you cannot access the Set Screws. You have to remove the Servo Arm and GUESS how much lengthen or shorten. Its hit and miss, mostly miss up to this point

Would be a peice of cake if it were a Turnbuckle arrangement. .
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Old 10-19-2015, 07:35 PM
  #8  
dereckbc
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Originally Posted by solentlife View Post
OK reading through your first post ... WHY are you taking servo arm of to adjust ? The screw should be available to you when arm, is on servo. If not then you have them 180 degree upside down ...

Second. Pull Pull only goes slack on one line when deflected IF one or both connections at RUDDER end are not in line with hinge line. Get the offset horns that put holes dead in line with hinge line and no slack.

Third it is not necessary to cross lines ... some are better for it if fuselage tapers severely ... but if not - then no need to cross them. Not crossing them also improves the angle to servo keeping them more at 90 degrees - another reason to avoid slack when deflected.

OK - how to modify to have adjustment ..... You can use the solder ends for wire cables. They have a hole across the solder part that the pull pull wire passes through and then you use a CRIMP to fix. Forget all this knots and CA / Glue malarkey. Get into a Fishing Tackle shop and buy fishing trace wire and packet of crimps. Same stuff actually as Model Sellers provide relabelled and price hiked !
So you have your wire trace crimped to the threaded cable end. Now fit a clevis + small nut to tighten to clevis to lock it and clip to servo arm / rudder horn ... whichever end you wish to have adjustable.

Now you can slack the locking nut ... and actually if only a turn or so .. you can turn the cable end while STILL connected up .. till just tight and then lock it with the nut again.

Tip : Do not over-tighten the cables. They need to be reasonably tight but not so they strain servo gears or rudder horn.

Really Derek ... the screw connectors you have are very good ... just needs a little thought to fit to advantage. Unfortunately I'm not at home to photo any links and set-ups for you ...

Here's my 58" Extra with Pull Pull .... look to left of photo and you see the rudder servo and connections ...
Thanks Nigel for taking the time. I guess I have not explained my problem adequately.

1. The lines do cross as the fuselage does taper to almost a Profile.

2. The Adjustment arms cannot be Reversed. Already thought about that. If I did the string would rub and cut through a Balsa fuselage strut. It has to be upside down.

3. As for Tightness or slack, the instruction manual clearly states to enough to be Plucked and Vibrate like a Bass Guitar String.
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Old 10-19-2015, 07:38 PM
  #9  
dereckbc
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Originally Posted by fhhuber View Post
http://shop.dubro.com/p/2-56-pull-pull-system-qty-pkg-1

Note the kits tend to come with metal clevices... these tend to unwind in flight even with the lock nut. good way to end up with no control.
I think this is what I am looking for. Is it Light Weight?
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Old 10-19-2015, 09:03 PM
  #10  
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I found that the rudder control horn holes must be dead in line with the hinge line and this prevents the line going slack on one side. I see in the pic that your line attachment points are back behind the hinge line.
Your horns need to curve forward to the hinge line.
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Old 10-19-2015, 09:08 PM
  #11  
solentlife
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Originally Posted by Panther View Post
I found that the rudder control horn holes must be dead in line with the hinge line and this prevents the line going slack on one side. I see in the pic that your line attachment points are back behind the hinge line.
If by pic ... you mean my Mintana ... I know and well aware of that when built. But the flight is not affected as I said ... the aerodynamic forces on the rudder keep it taut on the line pulled ... so not a problem.

As to Derek's quote on PA manual ... better be a deep bass guitar !! Any higher and I would expect wear and tear to set in ... It's a common misunderstanding to overtighten PP systems.

Nigel
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Old 10-19-2015, 09:29 PM
  #12  
fhhuber
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2mm eyebolt + 2mm plastic clevice would be reasonably light but not as light as the cotter key + screw link. without hunting up parts and a scale I'd expect the clevice + eyebolt to be about double the weight of the cotter pin + screw lock connector.
A couple of grams vs maybe 4 grams.

DuBro makes smaller size nylon clevices but finding the smaller eyebolts could be difficult.

As I said earlier... I don't like a metal clevice in a pull-pull. The only way I have found to make them not come unthreaded is to use locktite, which has to be reapplied (then wait for it to set up) if you adjust. You can apply CA as thread locker but then its 50-50 on being able to adjust ever again.

CA also makes many plastics brittle and weak, so keep it away from plastic or nylon clevices. Yo don't want to find out that CE weakened your clevice.
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Old 10-19-2015, 10:20 PM
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I have been using pull-pull on most of my models, 1/4 scale on down to the smallest electrical powered and find it to be far superior to other methods. There are two things that you must do to have it successful. One; never have any negative Akerman, a bit of positive Akerman is desirable; and Two; do not over tighten the lines, just enough tension to have no slack at neutral. That bit of slack (with positive Akerman) as the surface moves off neutral is not at all detrimental, in fact desirable as it prevents any overloading of the servo.
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Old 10-19-2015, 10:31 PM
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solentlife
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You can use these :



http://www.hobbyking.com/hobbyking/s...mm_Length.html

or lighter and better in my mind :



http://www.ebay.co.uk/itm/2MM-SOLDER...cAAOSwqu9VT4qg

Nigel
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Old 10-20-2015, 12:01 AM
  #15  
fhhuber
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On the brass ones... look at the machining burs at the hole edge. You have to debur or that will cut the line.
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Old 10-20-2015, 01:09 AM
  #16  
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I prefer the ones at the front of the pic. They are very light and I use the Dubro small nylon clevis with them. I only use metal clevis on the large (1/4 scale) stuff.
The back ones are fairly old but still OK.


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Old 10-20-2015, 01:43 AM
  #17  
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Never have liked setting these up. Good info here though! Thanks all.
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Old 10-20-2015, 02:32 AM
  #18  
kyleservicetech
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Originally Posted by dereckbc View Post
THX. I had to go look up what 4-40 and 2-56 clevis. My PA uses those or something very much like them. But I am missing something, Mine are made for Carbon Fiber rods clued in place. Cannot visualize what you are doing.

As for getting it centered I know it needs to be done, but the question is how to center both Servo and Rudder Control. Mine is required to be under tension. PA words are "String tension is similar to plucking a bass guitar string, and nice low note?

As for Kevlar IMO is a perfect choice. I have a PA Addiction X. 50 inch wingspan and weighs just under 3 pounds with battery and soaking wet. So I do need a Micro System. PA gave me this for Pull Pull Rudder. I hate it.

IMHO, this type of a device is not good for the larger models. I've seen a couple of models go in when this type of unit slipped.
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Old 10-20-2015, 05:41 AM
  #19  
solentlife
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Originally Posted by kyleservicetech View Post
IMHO, this type of a device is not good for the larger models. I've seen a couple of models go in when this type of unit slipped.
Never had one slip yet on small and large ...

Of course when you use the larger - first thing to do is change for Black 12.9 machine bolts to tighten down onto rod. The phillips screws or grubscrews haven#t enough bite.

Nigel
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Old 10-20-2015, 07:25 AM
  #20  
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Just set up a pull-pull today on my Reaktor but I used fine piano wire instead of trace wire or thread. Working a treat.
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Old 10-20-2015, 08:03 AM
  #21  
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Originally Posted by Panther View Post
Just set up a pull-pull today on my Reaktor but I used fine piano wire instead of trace wire or thread. Working a treat.
This works and can hide minor "Ackerman"
I've seen it in a couple of kits.

There's even an added safety factor due to the wires being able to push (at far lower authority than a normal pushrod) if the other one fails for some odd reason (one clevice coming loose for example)
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Old 10-20-2015, 09:10 AM
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Originally Posted by fhhuber View Post
This works and can hide minor "Ackerman"
I've seen it in a couple of kits.

There's even an added safety factor due to the wires being able to push (at far lower authority than a normal pushrod) if the other one fails for some odd reason (one clevice coming loose for example)
Yes that is one thing I did think of as I had one come loose on me a while back on another plane. Lucky a pre-flight uncovered it before I flew.
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