That sounds like a pretty good idea to this dumb country boy.. If you needed to you could setup a guide for the 3/16" tube to slide back and forth through to make sure it doesnt torque undesirably if the span of the 3/16" tube was too long..

Keith,

You really want that "V" as shallow as possible or you will still end up with binding. I would suggest looking a some sort of block to join the front 3/16" rod to the .070 rods.

Just how far apart are your control horns? (as a comparison, mine are 70mm)

Scott

Scott,

My control horns are 89 mm apart (over the posts). This is due to where the hard points were located coming from Piedmont. I could have moved them slightly closer, but at the expense of being further from the hinge line.

If you look closely at the photo below you'll notice that the hard points are not even. One is closer to the inside than the other. My main concerns when mounting the horns were 1) equal distance from the hinge, 2) as close to the hinge as possible, and 3) equal distance from the center.

Keith

Wow, that'a an issue...the hard points look fine for tail mounted servos, but not DEPS!

I think I would either install new hard points or build new elevators (but I'm looking at four months of snow!)

Do you think you could drill a 1/2" hole closer to the inboard corner? Forstner bits work well for this.
(When selecting dowels for the hard points, take a piece of drilled material to the hardware store to check the size...there's quite a variance)

I wanted to share a technique I came up with to help determine where the exit holes should be on the fuse.

In pattern planes I’ve installed three pull-pull rudders and one pull-pull elevator. I’ve been able to reliably determine where the exit holes should be top to bottom, using a similar method to Troy’s above, however, I can never reliably determine where the exit holes should be in the front to back dimension. Above Troy demonstrates a method he uses with a ruler and eyeballs. Well, for some reason I can do this five times in a row and get three to four different results. This has to do with the angle at which I look at the ruler in reference to the fuse.

So I got to thinking, how can I make sure I’m looking at the correct angle? There’s got to be some way to measure this.

That’s when I realized that a string between the two end points, elevated above the fuse, and a square was the solution.

Hopefully the pictures below will be sufficient to explain the technique.

Keith B

The exit point can be calculated by considering the fuselage side and the pushrod as the intersection of two straight lines, fuselages being for the most part flat-sided. See this link or a geometry text for the equations... http://astronomy.swin.edu.au/~pbourk...ry/lineline2d/

Regards,

Andre

Another way is to use a set of outside calipers. Just set them to the width you want and slide them along the fuse until the points of the caliper arms touch the sides of the fuse. --Derek

Andre, Nice to hear from you, how's it going in Anchorage? I've considered using geometry before but at the time I had a plane with wing fillets and the sides are never perfectly straight. In addition the distances between the servo, fuse wall, control horn and fuse side are fairly small and difficult to measure exactly for use with the formula. However, I'll try applying the formula and see how close I can come to the true exit holes, it should be fun. Thanks for passing this on.

Derek, I think the caliper idea is good if the servo arm and control horns are equal distance apart such as the typical pull-pull elevator (and you happpen to have a big outside caliper ). However, in this case we're coming from a single center point, also in the case of pull-pull elevator you're also coming from a center point. I don't see how the caliper method would work in this case.

Keith B

Keith,
If the cables are crossed, I make a full size sketch (top view) of the servo horn, rudder horn, and fuselage sides in the vicinity of the cable exits. All these are just straight lines and can be measured accurately. Sear's sells 6" calipers or you can just make some up out of 1/8" ply.

Does anyone have a pic of the hookup after the servo.
This is my problem. Obviuosly, the two carbon rods coming from the elevator come at an angle. If they are to stay truly straight, how can they possibly mount on the hollow carbon rod without bending to be wrapped with the kevlar thread? Hope this makes sense.
Thanks, Chris

They do bend slightly, right at the hollow rod, but only very slightly. All you need to overlap the 2 pushrods with the hollow rod that connects to the servo is about 1", thats it... The trick for me to keeping it smooth was to set it up so that the point at which the pushrods exit the clear tube is several (maybe 4-6") inches back from the servo arm. That way there is 3-5" of clearance for the pushrods to slide without hitting the curved portion right at the joint.

Thanks Mike!!!!!!!

That is just what I was looking for..
That is the pic that should be on Centrals website!!
Chris

Ooooooooh no not that one!!!! My support was crooked if you look close!. I went back in and fixed it since then....

Let me qualify my statement and stress that ...
the point closest to the joint of the three rods that actaully travels into the plastic guide tubes must be STRAIGHT!


If there is any bend at all in the portion that slides in the guide tubes it will bind up some. Just take your time and think it though and it will be fine... If a dummy like me can do it,,, anyone can do it![8D] If you get it just right the pushrods will slide as freely through the tubes as they do when you pull them out of the bag and test fit them..

I go through it in my Genesis build thread and explain my personal experience installing the DEPS. I got a lot of help from Troy and some other folks that really helped me to get it right...

I noticed the crookedness but your rods are really straight compared to the ones on the central site.
Did you use kevlar thread or something else.
Thanks again Mike. You helped me proceed on one of the last parts of my build!!
Chris

Nope, I just used a heavy sewing thread. I think kevlar would be ok but it would be overkill. Once I had it all laced up and ready I just lightly went over the wrapping with thin CA to secure everything in place.
Actually the pushrods were arrow straight except for right at the head end near the servo arm where it all came together..... but that support that is holding the two pushrods up,,, yuk! It was about 1/2" lower on one side than the other,, but I fixed it.

Anyway, Im glad I could help out and pay it forward for a change...

Hey guys,

one question about pull-pull: I keep hearing about crossed wires... but why? No problem with the touching wires? Ok, they are not metallic in the outer face...

Thanks!

Yes, you cross wires on the rudder setup. It allows you to get the exit holes further back in the fuse. Think about you rudder servo sitting in the tray. Draw two mental pictures. One from the left side of the rudder to the left side of the servo arm. And then draw it from the right side of the servo arm. You will see the difference and it should make sense.
I have had no problems with the wires touching and I was using control line cable. Now I use a fishing line called sevenstrand. 90# coated stainless steel. They have easy to us connectors and also a special crimper for them.
If you don't want the wires to touch mount the servo on its side and have a little different exit hole heights.
Chris

Thank you Chris for your clear explaination!

Here's a pic or two of the crossed cables.

Patternflyer,

many thanks to you too for taking the pics!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Another option for connecting 2 CF rods.. .070 rods - titanium rod 4/40 fittings - MK BB rod ends --- 2mm screw through 1 rod end into threaded alum servo arm 2nd rod end lock nut and locktite all around. Been using this for over a year now with solid result. Also if one rod is damaged it is easier to repair this setup

mike

Now that idea I really like Mike..
I think I may have to borrow that from you!!!!
Chris

So here's what I have so far. I have to move the servo further over yet. (BUILDER ERROR)
He has been fired though!!
Just figured I'd post a pic as pic's help people researching..
Chris

Did you make the lightened plate that the elevator servo is sitting on?

I recessed in a plate into the plate that came from ca models. This is an Eclipse. I recessed it in and will carbon fiber it at some point for the cool factor. It not something I would normally do but I didn't realize when I put the elevator tray in that I would be using DEPS. Otherwise I would have just made a side mount in the first place. I still have some dremel work to do on the plate that I put in. I just wanted to post some progress pics. If this were a glow plane I would probably have mounted in on the pipe tunnel. It's got Axi/F3A power so no tunnel.
Chris