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1st pull pull setup?
I just bought a morris 3d profile plane with pull pull rudder and elevator ( so - do - somthin or other??? ). ( I'll put my OS .55 on it which is at the top end of its power rating)
I already installed the control horns on the elevator and rudder, the holes are about 1/32" behind the hinge line. ( is that ok? ) Any tips or things to watch out for on the pull pull set up? Looks like one end just loops through the servo and has a single crimp. Just squish with plyers? Should I but a drop of CA on the crimp? Its very thin cable with a plastic coating... Does pull pull put any more strain on the servo? should they be ball bearing? nylon gears alright? I plan on pulling 2 servos out of old equipment, is there a way to tell the condition of a servo? Which servos would be the most critical? throttle - used rudder - used elevator - buy new aileron - buy 2 new thanks steve |
RE: 1st pull pull setup?
You don't want any play in the surface, but also the cables don't have to be drum tight either - that will strain the servo. And just follow whatever instructions came with your pull-pull kit and you will be fine.
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RE: 1st pull pull setup?
Not much for instructions with this Arf....
They would be tough to follow if I hadnt done most of this stuff before... Pictures are useless...... steve |
RE: 1st pull pull setup?
ORIGINAL: Popriv I just bought a morris 3d profile plane with pull pull rudder and elevator ( so - do - somthin or other??? ). ( I'll put my OS .55 on it which is at the top end of its power rating) I already installed the control horns on the elevator and rudder, the holes are about 1/32'' behind the hinge line. ( is that ok? ) Any tips or things to watch out for on the pull pull set up? Looks like one end just loops through the servo and has a single crimp. Just squish with plyers? Should I but a drop of CA on the crimp? Its very thin cable with a plastic coating... Does pull pull put any more strain on the servo? should they be ball bearing? nylon gears alright? I plan on pulling 2 servos out of old equipment, is there a way to tell the condition of a servo? Which servos would be the most critical? throttle - used rudder - used elevator - buy new aileron - buy 2 new thanks steve |
RE: 1st pull pull setup?
Having the holes in the horn behind the hinge line is okay as long as it is not very far. This gives what is commonly called positive Ackerman. You want the lines just barely snug at neutral. When you move off neutral, you will see the line not being pulled get a bit of slack as long as you have positive Ackerman. This is perfectly okay as it will not cause any control problems and is much easier on your servo. Should you error and get the horn holes forward of the hinge line, you will have problems as the non pulled line will tighten up as you move the surface off neutral which can be so severe it damages the servo and/or stalls the controls. Now this assumes that the attach points of the lines at the servo end are exactly at 90 degrees to the pivot of the servo arm. If they should be aft of the center of the pivot, you will wind up with negative Ackerman which again tightens the non pulled line if you move off neutral (a bad thing). Properly installed, you will find pull pull to be far superior to a push rod as well as less weight and more reliable.
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RE: 1st pull pull setup?
Done a number of pull-pulls, its a bit intimidating the first time, and it may take a couple tries to get it right. I prefer to start on the rudder end, getting the cables on the horn or coupler and crimped there first. One, make sure you have a plenty long piece of wire, too short and you'll be cussing.. Run the wire thru the crimp tube, then thru the horn or coupler.. bring it back around and back into the tube from the 'top', so you have both wires coming out the bottom. Then take the short end and loop it back thru the tube again. Holding the tube in one hand and long part of wire in other, pull the wire taunt and slide the tube down toward the horn until its about an inch or so from where the wire is looped thru the horn. (Or you may be using a turnbuckle type item attached to the horn, either way do same thing). When its where you want it, the wire in the crimp tube is nice and tight, crimp it nice and hard. Trim any excess. Do the next side. Run the cables to the servo.
At this point you want something on the servo arm such as Dubro threaded couplers so you can tighten the wire. Then I normally turn my radio on so the servo stays in neutral. Tape the rudder so it stays straight or have a friend hold it, and do the same procedure as with the rudder connections. Try to get it nice & tight before crimping, not heave-ho'ing on it, just good firm pressure. Once done.. start adjusting the couplers to tighten the wire. A little on side and then the other. When its complete, you should be able to pluck the wire and get a dull bass sound, akin to a guitar out of tune. Don't overtighten! Should be just enough to firmly hold the rudder in position without slop. First time it took me maybe 3 tries to get it right. Nowadays its no big deal, well... can still be a bit of pain sometimes.. but its my preferred setup if I can make it fit the plane. Google pull-pull, lots o' good pics and such.. |
RE: 1st pull pull setup?
i think one thing you should try to achieve is to have the control horns and the servo control arm the same distance . For ex., 3" servo control arm=3" on the control arms. That way every thing moves as one unit. If MinnFlyer is around he will post a picture of what I am talking about.
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RE: 1st pull pull setup?
ORIGINAL: goirish i think one thing you should try to achieve is to have the control horns and the servo control arm the same distance . For ex., 3'' servo control arm=3'' on the control arms. That way every thing moves as one unit. If MinnFlyer is around he will post a picture of what I am talking about. |
RE: 1st pull pull setup?
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Hey Billd76, thats great. let me know how you make out withthe maiden..
Yes its the same plane and engine. I've been flying a couple flat out 3d foamies and look forward to playing with this nitro plane.... Did your servo covers have the holes pre drilled? on the side with three servos mine is pre drilled with three hole all in a row but in the manual they show the holes stagered with the middle servo rotated 180 degrees. I have 3 older servos, FP-S148, would these be ok to use or should I just spring for all new servos? any pics? good luck steve |
RE: 1st pull pull setup?
ORIGINAL: goirish i think one thing you should try to achieve is to have the control horns and the servo control arm the same distance . For ex., 3'' servo control arm=3'' on the control arms. That way every thing moves as one unit. If MinnFlyer is around he will post a picture of what I am talking about. If you follow Rodney's comments regarding where the control horn holes are in relationship to the hinge line - you are good to go. The servo arms don't have to be the same length as the control horns unless you want a one to one ratio of movement - just like you would do with a standard pushrod setup. We have been hammering this out over in the "Questions and Answers" section under the "Pull/pull wire crossing" thread. More than you would probably ever want to know! Kurt |
RE: 1st pull pull setup?
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yep same as mine. I did see the pre drilled holes, but drilled my own and staggered them. Be sure to use more than just CA on the servo trays when mounting them. I'm using Hitec HS-485 HB's servo's for all but the throttle. They are ball bearing Karbonite gear with 66 oz of torque. I also added two washers under the forward two holes of the engine to give a tad of right thrust, not sure it really matters, but just thought a little right thrust would be a good thing. I placed a 1100 LiFe battery in between the the servos on the left wing. I didn't realize the the pull pull wires would be so close to the switch where I mounted it. It will be fine where it is, but had I realized it I would've mounted the switch more towards the outside of the wing instead of where I did. The instructions called for mounting the fuel tank in the wing as well, I decided to mount mine extrenal. I like the ease of being able to access everything with the profiles. Makes the engines easy to tune, and fix fuel lines, etc... I set my CG at 4.5 inches. The manual says 4.0 - 5.25! Will have to see how it flies and adjust as needed. The 55 AX should get this thing airborne in less than 10 feet!! :D:D:D
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RE: 1st pull pull setup?
As Bosarth says in post 10, the control horn and servo horns DO NOT have to be the same length. The same force arrangements hold as for push rod set ups, you can change the amount of throw by moving the attach points at either end to get other than a 1 to 1 throw, just do make sure that the set up does not bind up at full throw.
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RE: 1st pull pull setup?
ORIGINAL: Popriv I have 3 older servos, FP-S148, would these be ok to use or should I just spring for all new servos? any pics? good luck steve |
RE: 1st pull pull setup?
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Actually, having the horns and the servo arms the same length is not necessary. It's good to keep them close - that is, not RADICALLY different, but being the same length is not really important.
Having "Positive Ackerman" - That is, having the linkage points behind the hinge line, means that the linkage on the outside of the curve will travel a shorter distance than the one on the inside. This insures that the wire which is NOT the one that is being pulled will go slightly slack when the surface is moved. You can see in the illustrations below that two rods of equal length do not stay centered on the holes when the surface is deflected. |
RE: 1st pull pull setup?
ORIGINAL: Radical Departure Done a number of pull-pulls, its a bit intimidating the first time, and it may take a couple tries to get it right. I prefer to start on the rudder end, getting the cables on the horn or coupler and crimped there first. One, make sure you have a plenty long piece of wire, too short and you'll be cussing.. Run the wire thru the crimp tube, then thru the horn or coupler.. bring it back around and back into the tube from the 'top', so you have both wires coming out the bottom. Then take the short end and loop it back thru the tube again. Holding the tube in one hand and long part of wire in other, pull the wire taunt and slide the tube down toward the horn until its about an inch or so from where the wire is looped thru the horn. (Or you may be using a turnbuckle type item attached to the horn, either way do same thing). When its where you want it, the wire in the crimp tube is nice and tight, crimp it nice and hard. Trim any excess. Do the next side. Run the cables to the servo. At this point you want something on the servo arm such as Dubro threaded couplers so you can tighten the wire. Then I normally turn my radio on so the servo stays in neutral. Tape the rudder so it stays straight or have a friend hold it, and do the same procedure as with the rudder connections. Try to get it nice & tight before crimping, not heave-ho'ing on it, just good firm pressure. Once done.. start adjusting the couplers to tighten the wire. A little on side and then the other. When its complete, you should be able to pluck the wire and get a dull bass sound, akin to a guitar out of tune. Don't overtighten! Should be just enough to firmly hold the rudder in position without slop. First time it took me maybe 3 tries to get it right. Nowadays its no big deal, well... can still be a bit of pain sometimes.. but its my preferred setup if I can make it fit the plane. Google pull-pull, lots o' good pics and such.. |
RE: 1st pull pull setup?
ORIGINAL: goirish i think one thing you should try to achieve is to have the control horns and the servo control arm the same distance . For ex., 3" servo control arm=3" on the control arms. That way every thing moves as one unit. If MinnFlyer is around he will post a picture of what I am talking about. The spread of the servo arm can be 1 foot, and the spread at the rudder horn can be an inch. The only critical aspect in setting up a pull pull setup is that the attachment points at the horn be colinear with the hingeline and the attachment points at the servo be colinear with the pivot point of the servo.. If the relationships are maintained properly, only the slightest amount of tension on each cable is required. |
RE: 1st pull pull setup?
ORIGINAL: j.duncker ORIGINAL: Popriv I have 3 older servos, FP-S148, would these be ok to use or should I just spring for all new servos? any pics? good luck steve The S-148 is a bushing output shaft servo that doesn't rotate around the intended axis well after much stress. Implementing the S-148 in a pull-pull configuration compromises the entire intent of using a pull pull system. Servos using bushings on the output shaft wallow out the bushing quickly. The output centering pot might think it is "home", but the servo output shaft can be anywhere in relationship to the output pot. Misrigging a pull pull system with a lot of tension on a bushing output shaft is asking for a snootload of slop at the shaft in a hurry. There are gobs of good aftermarket metal gear servos with dual ball bearing supports on the output shaft. Take a look at these; the price is 12 bucks, the power is strong, the speed is rapid, and the centering is precise for a pull pull setup. http://www.servohut.com/HTML/low_profile_series.htm (the s9102 HPX) |
RE: 1st pull pull setup?
Everything you wanted to know and some stuff you don't:D:D:D
[link]http://www.rcuniverse.com/forum/m_10847192/tm.htm[/link] Ken |
RE: 1st pull pull setup?
I have use the 148 servos in many big planes, one a Phaeton90 with a Quadra 72CC engine for literally hundreds of flight with pull-pull on both rudder and elevator with absolutely no problems. Just do not put excessive tension on the lines, just enough to eliminate any droop or slack at neutral. A high tension will ruin any servo after a time. I have found that the Futaba 148's to be one of the most reliable and relative inexpensive servos ever made.
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RE: 1st pull pull setup?
[qu ORIGINAL: goirish i think one ote]ORIGINAL: DustBen thing you should try to achieve is to have the control horns and the servo control arm the same distance . For ex., 3'' servo control arm=3'' on the control arms. That way every thing moves as one unit. If MinnFlyer is around he will post a picture of what I am talking about. The spread of the servo arm can be 1 foot, and the spread at the rudder horn can be an inch. The only critical aspect in setting up a pull pull setup is that the attachment points at the horn be colinear with the hingeline and the attachment points at the servo be colinear with the pivot point of the servo.. If the relationships are maintained properly, only the slightest amount of tension on each cable is required. [/quote] SEE BOLD ABOVE Sorry but this is not the case. It is basic geometry. Aim to keep the servo arm lengths and control horn lengths the same + - 10% |
RE: 1st pull pull setup?
ORIGINAL: j.duncker Aim to keep the servo arm lengths and control horn lengths the same + - 10% Kurt |
RE: 1st pull pull setup?
ORIGINAL: Bozarth ORIGINAL: j.duncker Aim to keep the servo arm lengths and control horn lengths the same + - 10% Kurt http://farm8.staticflickr.com/7146/6...7d133b46_z.jpg |
RE: 1st pull pull setup?
Thanks Grosbeak
That is what I mean. They have to be about the same length. Ideally with horns on the hinge axis. Re using bushed servos on pull pull. Yes ball raced ones are better but I have had a few really high airtime set ups using bushed servos and pull pull without noticing rapid wear. |
RE: 1st pull pull setup?
The only limit to the ratio of servo arm length and horn length is that, at maximum servo throw, you do not jam the moving surface by having the servo arm excessively greater length than the control horn. There is no limit in how much longer the control horn can be than the servo horn other than you may reach the point where the surface does not move enough to give you adequate control.
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RE: 1st pull pull setup?
Once again I agree with Rodney. The +/- 10% idea doesn't stand.
Kurt |
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