Hello all! I am going to use a pull pull set up on a CA model Epsilon 90 that I am building. It was between this setup and an mk Bellcrank setup but I think I can get more throw using this setup. Does anyone have any pointers? I think the best way to do it would be to put the servo on its side and then run 4 equal lenghts of pull pull cable, but judging by the room in the fuz, that might be hard to do. Does anyone know if it will work with the servo upright and some of the wires crossing?
I appreciate any input anyone has.
Thanks for looking!

To see the pull-pull setup used by Quique at the world championships go here on RCU and look at the picture in post 13: http://www.rcuniverse.com/forum/m_6674422/tm.htm

Quique used pull-pull on both the elevators and the rudder and both servos are mounted in the upright position.

I did this on a Hydeout (as yet unflown). I layed the servo on it's side. If you don't do this you will get slight variaton in throw between the elevator halves. Look at the figure in [http://www.rcuniverse.com/forum/m_5622168/anchors_5636267/mpage_1/key_/anchor/tm.htm#5636267"] to see why. This will give you a little roll coupling with elevator input.

I used two servo mounting platforms, one for elevator, the other for rudder. The elevator plate is mouted with screws so I can access the rudder servo.

What I would suggest, if you have not built the fuse yet, is to take the plans, draw the servo on them and use a straight edge to draw the path of the cable from the servo to the control horn. Use this information to trim any bulkheads and formers that get in the way. Do this on the side view also so that you can cut the cable exits in the fuse sides before to start gluing stugg up. This is a lot easier than trying to do it once the fuse is built.

This will work if you use two servos, but with one, it has to go on it's side.

Running your elevator servo pull-pull on its side , mounted at the lower area of the fuse will give you the necessary room to clear a pull-pull rudder servo and cables that are mounted closer to the top of the fuse . In fact , my Pursuit 120 ( a great Sam Turner design ) , has a narrow fuse and there are no problems. Recommend you invert the rudder servo. Run 6-32 bolts through hard points to extend 1" above elevator surface, top and bottom. Ditto rudder bolts.Drill the hole through the hardpoint with the elevator top facing your drill press base and in the top foam shuck ,if you have one. This technique places the bolt at an angle for the best position over the hinge line. Run your pull- pull cables through the fuse attached to a length of thin solder wire simplifies the connections. It's a great , lightweight and slop free setup .Good luck !

Running your elevator servo pull-pull on its side , mounted at the lower area of the fuse will give you the necessary room to clear a pull-pull rudder servo and cables that are mounted closer to the top of the fuse . In fact , my Pursuit 120 ( a great Sam Turner design ) , has a narrow fuse and there are no problems. Recommend you invert the rudder servo. Run 6-32 bolts through hard points to extend 1" above elevator surface, top and bottom. Ditto rudder bolt.Drill the hole through the hardpoint with the elevator top facing your drill press base and in the top foam shuck ,if you have one. This technique places the bolt at an angle for the best position over the hinge line. Run your pull- pull cables through the fuse attached to a length of thin solder wire simplifies the connections. It's a great , lightweight and slop free setup .Good luck !

but the pull pull sistem , used by quique, worked fine to win the world championship

DESPITE THE OBVIOUS FLYING ABILITIES.....this sistem, won the WC, so it isnt too much " rolling elevators " coupling...

i dont know...the plane was equiped with that sistem

the world champion wouldnt use it if its not good...

IMHO...

You got it..... Pull-pull on elevators works just fine. Have done it for more than 20 years that way

Frank I. gave very good info. I would add that as long as you place the servo output arm in the center of the fuse, both latterally and vertically, it will matter very little whether the servo is upright or sideways. Upright is a simpler set-up but sideways is a very slightly more accurate set-up....but hardly enough difference to notice.

MattK

One more thing on the 6-32 bolts as horns that Frankie mentioned. These can be bent forward to get the clevis exactly on the hinge line. A simple tool I use for the task is a 1" length of aluminum threaded stand off stock from the local ACE hardware store. It's generally 1/4" diameter by various thread size. You simply thread it down, bend forward slighlty, then unthread a bit and bend forward some more. Work the horn deliberately like that until you get the desired curve to the horn. Pliers will also work, crudely. The aluminum stand off stock produces an easier, cleaner result

MattK

Thanks guys this is all excellent info. How tight do you normally tighten the wires?

Tight enough to eliminate slop, but not so tight as to damage the servo. Equaly as important is that both halves be tightened to the same tension. A good way to check this is to pluck them like a guitar string. They should sound the same ''note''. A higher note is a tighter cable.

A neat and simple technique you could use to simulate flight load is to wrap a couple rubber bands around the horns and secure them behind the model. Then pull and lock the plane placing the bands in tension. Measure the elevator halves travel as you move the sticks, observing if there's any difference. If you go to Ron Ellis' site, Grotto2, you should find the technique referenced there.

Ron's technique also involves a servo driver which drives to specific millivolt output, and that would complete the loop of a fairly sophisticated arrangement, but it may not be necessary for your application

MattK

In post #2 there is a link to a picture of QQ's set up. I notice that he uses a wheel/pulley on the rudder servo, but not on the elevator servo. (I assume that it is not the other way around.)
However, the reason that you get a slight rolling coupling with a vertically mounted elevator servo is that you have a sideways movement of the servo arm as this moves away from neutral, thus pulling more on one cable than the other.
Would not this be removed if you used a wheel (pulley) on the elevator servo, keeping both cables equally tight?

Magne

In theory no, it does not change much. If I recall right Ã*t is pythacoras function (and up to cotangent trigonometric functions) which to use if you want to calculate how little it makes diffetence with 2m ship. I bet you can not notice anything when flown. But closer the servo is to the hingeline and control horns wider to each other it has more effect and it causes tightening and slack on lines too.

(edit)

Hello Funtana 140. Here's my Epsilon 90 with pull-pull elevatos system.

When you mount the sideways elevator servo, be sure not to just glue your mounting structure down to the pipe floor. Floors are notoriously flimsy and will "oil can" as your servo rocks back and forth.

Thanks Delta Fly they are very good pictures. Would you have a picture of your radio installation in the fuselage?

Thanks Funtana, here are some pictures of my radio installation in the fuselage.

FWIW, the rubber bands will fail quickly stretched as they are. around the RX. Suggestion....buy yourself some really small silicone rubber cord or tubing (1/32 to 1/16) and tie a length into the rubber band size you need. Silicone rubber has at least a 100x life span over typical rubber in stretched shape

MattK

one more thing guys, how do you thread the two pull-pull wires through the single hole in the threaded eye bolt on the elevator servo end? do you bore the hole out a little to accommodate the two wires? i'm using the dubro 4-40 pull pull system and the hold is only wide enough to take one wire trace through it

Actually, I only use one wire to the top elevator horns and one wire for the bottom.

Each wire loops through one side of the elevator servo wheel and has a single crimp an inch or two away from the wheel.

Both left and right sides of the up-elevator line go through a single crimp near the wheel.

I hope this is clear.

Thanks for that. The system i'm running is exactly the same as what you are saying but where the two wires come in for each side of the elevator servo horn (two up elevators one side, two down on the other) there is a little bolt with a hole in it that the wire goes through, the bold then goes into a clevis that snaps on to the servo horn allowing for adjustment. I bored the hole out last night with a 1mm drill bit vertically so I didn't weaken the bolt.

Man, I know all you guys understand all of the above but I have read about servo wheels, ackerman setups, small pullys,parallelograms and more than likley a lot more.

All I really need to know is the single servo tiller bar elevator setup in a used sig spacewalker II is ok to use ? I do not know if I has a ackerman set up or not .

Thanks from someone who really needs to learn about stuff like this.

Glenn.

Sense my last post I have read a lot info on the pull pull systems, the only thing I did not see was anything about mechanical advantage for the servo, on normal systems they tell you to use hole nearest the servo shaft and one out aways on the control horn for better leverage for the servo. I guess this is not needed when using high torque servos? Guess i will stop before I look like a total idiot, to late,right?

Thanks, Glenn.

The only dumb question is the one not asked, eh Glenn?

However you set things up, you'd like to maximize the travel distance for your cable or pushrod. That way you minimize slop. (Imagine 1mm of linkage slop in a quarter inch of throw versus the same slop in two inches of throw.)

So you'd like to maximize the throw out of your servo wheel. I use the biggest wheel that comes with my servos, cut it into a 'D' shape, and cable to the outermost holes.

On the elevator control surface you will want at least as much distance between the horn holes as you have between the servo wheel holes....if not more. Keep in mind that you have plus and minus forty-five degrees of throw out of your servo and if the holes are the same at the elevator, that's the throw you'll have there.

So here's where you can get some mechanical advantage. You really only need maybe 25 degrees max elevator throw for most pattern flying. So you might lengthen your elevator horns to get that with your servo output throw.

If you stay with the 45 degrees of throw you will probably need to reduce it electronically which will give up some resolution. That's where servo quality, e.g. torque and resolution become factors.