I'm completing an arf and it has an aileron servo mounted on each wing with a "Y" harness going to the receiver. I don't remember what the plans call for in terms of up and down travel but lets say its 1 1/4 up and about 3/8 down. I'm just not sure how to adjust the down travel. The instructions that came with my Futaba 6XEA radio just say to move the stick to the right and adjust and then move it to the left and adjust. I did that, got the up travel just fine, but the down is way off. And on the same subject, according to the plans, the down travel is the same for both high and low rates.....if I punch in a low rate percentage, this will also change my down travel......I think.....I'm thinking the answer is pretty easy, but for the moment, its eluding me.....any help?

First you need to get it as close as possible mechanically by adjusting linkage positions on the various arms and horns. THEN, if your radio has this feature, you can use EPA or End Point Adjustment. If the model design calls for differential (more up than down or vice versa) this can also be done at the servo output wheel/horns. I am going to have to leave it to MinnFlyer or one of the graphic guys to draw that up for you. I hope this gets you started. It's easy to do but hard to put in words.
On reflection, what you described really is a differential situation and not endpoint so disregard that part. You need like a 6 arm output wheel and to connect the rods on the arms forward of the drive axle. Could really use a picture right now couldn't you, I could. I'm gonna try to hunt down a picture for you if nobody else posts one.

There's two ways to do this, electronically, and mechanically. I'll briefly describe each.

One way to do this electronically would be to set the ailerons to travel the same up and down and then use the end point adjustment function to limit the down. You would make these adjustments on high rates and then set low rates to be a percentage of the max. The disadvantage to doing this is that you are not allowing the servo to travel its full range so you lose some sensitivity.

The mechanical method relies on just offsetting each servo arm so it's not square to the control rod. Rather than trying to describe it with words, here's a link to a thread that contains one of MinnFlyer's famous pictures
http://www.rcuniverse.com/forum/fb.asp?m=1706117

I recommend the mechanical choice, it's simple, and allows you to use the entire servo range.

Yup, Chuck posted exactly what I was trying to get at.

I thought it might have to do with moving the servo arms. That raises a lot of questions but I think I'll go mess with it and see if I can figure it out....Thanks for the input guys!

Just an added note. Once you get the mechanical part set, your EXA does have end point adjustment, though I don't remember just how to set it and the manual seems to be stored in that "special place" between dimensions

Perhaps this will help: http://www.futaba-rc.com/manuals/manual-6exa.html

With the radio turned on, center the ailerons/trim. Then connect the aileron linkages and play with the position/angle of the wheel on the servo output shaft until you get the correct RATIO between up & down. This is where you will want the servo arm. Then you can move the rods in/out on the servo arm or up/dn on the horn until you get the amount of throw you want or close to it. This is not an exact science ya know and for many things close IS good enough. Do spend some time playing with it, you will learn a lot.

Thanks for all the replies......sorry I'm being such a bonehead but some things just don't make sense. Again, this is 2 servos with a Y going into the receiver. The ARF plans call for 1" up and 3/8" down

I have the radio manuel and it says to adjust the EPA by moving the aileron stick to the right, adjust it, and then move it to the left and adjust it. Well, when I move the stick and adjust it, both ailerons move in opposing directions...so how can I adjust them independently?

Also, the crummy manuel suggests....just suggests.... that you can adjust both up and down independently....this doesn't seem to be the case..am I right?

Looks like I need to get some longer control rods.....when I move the servo arm and then try to reset the surface to 0, I'm running out of thread. If I put longer rods on, move the servo arms to get my 3/8" down, won't that greatly reduce my up throw? And if I then move the up EPA, won't that just change my down throw?

I think the answer may lie in what Bruce said.....maybe its not the measurement thats important but the ratio between the 2

If anybody sees where I'm thinking wrong, chime in..I appreciate it all....

For now, forget EPA. Refer to my post #8. Can you post a picture of one of your aileron servo setups so we can tell you where to go from there? You sound like you are just not understanding because this is actually quite easy. Also, do you have any friend who fly that can help and have you checked out any clubs/instructors yet? They would be able to set this straight in seconds. NOT an insult, you are learning a new skill. It WILL take time. How quick did you learn to drive a car or cook or anything else worthwhile? I assume you have to cook for yourself on occasion. BBQ?
And yes, the ratio is the most important right now. We'll work on total throw after that

Because you are using a y-harness on the ailerons, you can't adjust the up seperately from the down. Because the "up" direction for one is the same as the "down" for the other.

If it was elevator, you could set more servo travel in one direction than the other.

Now, if you get rid of the Y-harness, select a flaperon mix, and plug one aileron in to the flap channel (channel 6), then you can adjust the "left" and "right" directions for each servo independantly. "Left" will mean "up" for the left aileron AND "down" for the right aileron and vice versa.

The best plan is to set the EPA values to the same for left and right. Then just move the servo arm one "spline" or notch on both servos, so that the arms are "swept" fowards, towards the LE of the wing. (assumign the servos are on the bottom of the wing. If the servos come out the top, then sweep the arms to the rear). (this is what Chuck and others are suggesting, just trying another wording).

Thanks all......Yes, I've been taking lessons....joined a club.....flew the heck out of my Avistar. I know I could ask the instructor, and I might....I was just hoping to get the plane all together, take it to the field and have him check it out. It looks to me that I only need to get some longer control rods, move the arms around until I get a reasonable ratio and couple that with some EPA and I'll have it....I do believe I'm understanding whats going on......I think I'll mess with this before I get involved with flaperons... Thank you all very much for your comments,.......and patience!!

Fwiw, having the ailerons set up using two channels in "flaperon mix" doesn't mean you acutally have to drop them as flaps, or have the ailerons move together as flaps at all, ever. Some radios (don't know about yours) allow you to set the travel adjust on the flap channel to 0 to keep you from accidentally moving "flaps". I've set up a couple of my planes this way, it makes installation and trimming easier at times.

Montague is on the money. You cannot set aileron differential electronically with a Y harness. You can however set up the linkage as per Minnflyer's picture.

I first of all question why you need aileron differential in the first place. Its only function is to make rolls more axial (reduces adverse yaw). It is NOT a concern for the average Sunday flyer and at your stage of expertise, you probably couldn't tell the difference. No RC airplane needs aileron differential to fly with the possible exception of a J3 Cub.

Shoot, I have no idea if I need differential or not. The plans call for it so I figured I'd try to do as they say. I'm actually glad to find out I can't do it electronically. I was getting the idea I could but was becoming frustrated that I couldn't figure out how. I was playing with moving the servo arms last night and was pretty pleased with the ratio I was achieving. Unfortunately, to move the servo arms means getting a bit longer control rods so its off to the hobby shop later today. Thanks for everybody's input. Its these kind of issues that helps us newbies learn a lot. Next plane I'll be much smarter than now!!!

How about just turning the servos around in the wing 180 degrees, would that put the arms closer to the ailerons and also make the linkages a little stiffer(less flex)? Can't do this in all installations. You would then have to rotate the servo arms 180 also, of course.

Thanks, I hadn't considered that.....I'll have a look.....sitting here at my desk, I'm thinking that reversing the servos might actually make my control rods too long, but I'll have a look see...thanks, again