|
What is a pull-pull system?
Iv heard about a pull-pull system where one servo has two control rods coming from it. What is that system for?
|
RE: What is a pull-pull system?
Most often for the rudder and most often found on larger planes. You use two strings ( or Kevlar or steel cables) to connect each end of a double servo arm to similar horns on the rudder. Picture a parallogram. when the servo turns, the rudder turns. It is lighter than a push/pull rod that you typically see to control movable surfaces.
|
RE: What is a pull-pull system?
oh thats it thanks! And one more question when you have a plane body any plane, and you have twin elevators where the flaps arent connected how do you make both of the elevators move exactly the same?
|
RE: What is a pull-pull system?
Best thing for dual elevator servos is to have each servo on a separate channel and control them independently. With a computer radio you can adjust center and end points. Second best thing is to have programmable servos or a matchbox which coordinates the servos. Worse option is to use a Y harness and try to get equal throws with the mechanical setup. Last thing is to use one servo with two pushrods that connect inside the plane with a wheel collar or something.
|
RE: What is a pull-pull system?
oh okay thanks:D
|
RE: What is a pull-pull system?
One important thing to remember about a pull pull is that the setup has to be a parallogram. If the servo arms and the rudder horns don't have the same length between the holes, and the holes are exactly on the hinge line, one cable will go slack as soon as the servo starts turning. My first attempt was really bad, and at half movement, I had close to 1/2" slop in the rudder, even though it was nice and tight in the center.
Just remember that the two ends of the parallogram have to be bisected at the hinge line and at the axis of the servo output. A tip on setting them up, After setting up the horns and the servo arm as above, the lock the rudder in the center, Center the serov, and with the clevis adjustment set for the longest length, tighten and crimp the cables. It is all but impossible to get them to tight at this step, and all to easy to get way to much slop. Now equally tighten the cables until they are tight and the servo and rudder are still in netural. Maybe one or two more of these setups and I'll get it right the first time.[&o] I do like them when they are right though. Don |
RE: What is a pull-pull system?
ORIGINAL: Campgems One important thing to remember about a pull pull is that the setup has to be a parallogram. If the servo arms and the rudder horns don't have the same length between the holes, and the holes are exactly on the hinge line, one cable will go slack as soon as the servo starts turning. My first attempt was really bad, and at half movement, I had close to 1/2" slop in the rudder, even though it was nice and tight in the center. Not true, the arms on the servo can be a different length than the arms on the servo as long as, at extreme positions, the throw on one does not exceed 90 degrees. Just use your protractor and a piece of paper to draw the extremes and you will see this is so. Just remember that the two ends of the parallogram have to be bisected at the hinge line and at the axis of the servo output. A tip on setting them up, After setting up the horns and the servo arm as above, the lock the rudder in the center, Center the serov, and with the clevis adjustment set for the longest length, tighten and crimp the cables. It is all but impossible to get them to tight at this step, and all to easy to get way to much slop. Now equally tighten the cables until they are tight and the servo and rudder are still in netural. Maybe one or two more of these setups and I'll get it right the first time.[&o] I do like them when they are right though. Don |
RE: What is a pull-pull system?
Rodney, I had SO mcuh ackerman in my first attempt that I ended up with the huge sag in the cable. The horn width was different than the servo arom width. No, I am NOT a good pilot, but I didn't have any issues with it, However other than center, it was a loose goose. I just rebuilt the plane, going to Robart hinges and closing up the huge hinge gap I had. This last cable job seems to be great, very little slop at netural and along the full travel.
I haven't tried the elevator on pull pull yet. I've got a 1/4 scale Laser 200 and a 1/3 scale Cap 232 waiting for the bench. I'm going to give it some serious thought. HUmmm. My Ruperts Dad has two elevator servos. Would it be possible to Y the cables and use just one elevator servo up front? Don |
RE: What is a pull-pull system?
Here are two sources for some pretty good info on your pull-pull
http://members.cox.net/bdfelice/Ackerman/ackerman.htm http://www.rcuniverse.com/forum/m_72...tm.htm#7237017 Note also how you can make the cable length adjustable with the proper hardware at the end of each cable. |
RE: What is a pull-pull system?
I have just finished installing a pull pull system on both my rudder and elevator, very happy with it and I will never go back to pushrods on a big plane ever again! here is a little info for you which also works well
|
RE: What is a pull-pull system?
Here's what I know about that. Good info with lots of good pictures.
[link]http://www.rcgroups.com/forums/showthread.php?t=615748[/link] Frank |
| All times are GMT -8. The time now is 06:32 PM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.