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pull pull system help!

Old 12-10-2007, 02:34 PM
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Default pull pull system help!

hi all ,
i am trying to setup a pull pull system on a rudder of a 85in span sbd plane .it is my first time using this setup and i am not sure.
how do i crimp the wire?(what do they mean by crimmping?}
the servo is a futaba s5303 with 223 oz torque. i think.
do i attach the wire directly to the servo arm or attach it to a belcrank and then attach the arm to the belcrank with a rod?
do i have to use swivel ball links?
2-56 or 4-40 ?
please help.
any information will be apreciated!
Old 12-10-2007, 03:01 PM
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Default RE: pull pull system help!

ORIGINAL: rxAxilleas

hi all ,
i am trying to setup a pull pull system on a rudder of a 85in span sbd plane .it is my first time using this setup and i am not sure.
how do i crimp the wire?(what do they mean by crimmping?}
the servo is a futaba s5303 with 223 oz torque. i think.
do i attach the wire directly to the servo arm or attach it to a belcrank and then attach the arm to the belcrank with a rod?
do i have to use swivel ball links?
2-56 or 4-40 ?
please help.
any information will be apreciated!

It's easier on the servo to connect it to a bellcrank. And connect your pull-pull cables to the bellcrank. That way you are putting the side load on the bellcrank bearings instead of your servo. The bellcrank bearings are usually a lot bigger and more robust.

4-40 on everything. 2-56 is for throttle pushrods on 40 size trainers.

Here is a pic of how to crimp the cables.

Run the cable through the little brass tube. Now pass it through the eye of the bolt or keeper on the bellcrank. Run it back through the brass tube. Now wrap it up and around the top of the brass tube and back through the tube one more time.

Cinch the wires up and get them all as tight as possible before you crimp. See second and third pics.

To crimp, simply squeeze the hell out of it with a pair of pliers. It should smash down a bit. That will crimp the tube nicely on the wire cables. Never had one come out.

In the last pic is one of my planes. I've circled the brass tubes. Those tubes were crimped exactly as I described above. Servos have sonce been switched to JR8411 digitals.

Thats a mock-up from last year. So, pardon the wiring mess inside. I've finished the plane, but haven't taken any pics yet.
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Old 12-10-2007, 03:15 PM
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Default RE: pull pull system help!

Here is a good example of a properly setup pull-pull. It uses a SWB 4" offset arm with 4-40 ball links and pull-pull adjustable connectors.

The best way that I have found to crimp the wire is to use a set of side cutters and crimp the sleeve that will hold the pull-pull wires. Either that or you can use a set up electrical crimping pliers if you get the right set.

Hope this helps
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Old 12-10-2007, 03:20 PM
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Default RE: pull pull system help!

I wouldn't do it like that. That places a tremendous side load on your servo bearings and output shaft.

That's where you'd be better off to use a bellcrank. The bellcrank takes all the side load. The bellcrank has bearings that are twice as big as your servo bearings, so it can handle the loads. And bellcranks are cheaper than servos if you wear it out.

But, thats just my opinion. And I'm kinda anal. So, take it for what it's worth. $.02
Old 12-10-2007, 03:39 PM
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Default RE: pull pull system help!

hi guys,
first of all THANKS for the help.the pics is very interesting!
the plans shows a bellcrank made of plywood and a bolt or something. no bearings! thats why i started wondering. the futaba s5303 is a very large servo abd has two balbearings. do you think it is still needed a belcrank?any idea where to find ones with the bearings you mension?
one reason i am asking this is that i am thinking that a 223oz torque is very much for this plane. am i wrong???
85in j.bates SBD plane

also i am wonderind about ackerman . in many threads everyone says it is necesary. i canot understand why it is important to have slack in the non pulling cable.
thanks again
Old 12-10-2007, 05:40 PM
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Default RE: pull pull system help!

SWB makes nice bellcrank systems.

http://www.swbmfg.com/

Chief Aircraft sells aluminum servo trays for ganged servos:
http://www.chiefaircraft.com/rcmsec/...ories/SWB.html

Chief sells servo trays for single servos with a bellcrank. They also sell trays for 2, 3 and 4 servos.
Old 12-10-2007, 05:51 PM
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Default RE: pull pull system help!

To diminish tremendous side load in the servo bearings. "A lo BVM style"

BR

Jesus

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Old 12-11-2007, 10:01 AM
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Default RE: pull pull system help!

ORIGINAL: rxAxilleas

also i am wonderind about ackerman . in many threads everyone says it is necesary. i canot understand why it is important to have slack in the non pulling cable.
thanks again
You don't need any ackerman angle unless the cables are crossed and the bellcrank attachement points are in front of the pivot, I will dig out the instruction manual from the QQ Yak which shows this in deatil and post as soon as I find it.

Mike

EDIT: found it, I think its all self explanatory, the 7deg angle has to be equall at both ends. And by the way its not inportant to have slack in the non pulling cable, its just that most can't do it any other way so they satisfy there own ego by saying its neccesary, now watch the fur fly. If your cables are not crossed and the servo arm is the same width as the rudder horn then it should all stay alligned and the cable tension should not increase or deacrease during operation.
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Old 12-11-2007, 11:04 AM
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Default RE: pull pull system help!

Where's the popcorn?
Old 12-11-2007, 11:43 AM
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Default RE: pull pull system help!

Or you could use Air Wild's attachment systems, they have 2 that work great.
http://www.airwildpilotshop.com/More...product&id=377
http://www.airwildpilotshop.com/More...product&id=470
I use the lower one and a ball link which is the most secure set up for any plane, I have never had a problem.
Old 12-11-2007, 01:45 PM
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Default RE: pull pull system help!

thanks for the help!! i you have helped me a lot!!
Old 12-11-2007, 03:03 PM
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Default RE: pull pull system help!

in many fotos i see a nut after the clevis. why this ? is it nesesary?
thanks

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