Elevator Mis-match

[3D-Seth]

With the servos mounted in the fuse, you don't want the servos at 90º to the surface/servo case. First off, because you will get a ton of down elevator travel, and little up. So actually, you need to angle the arms on the servos one to two gears forward (towards the nose of the airplane). This allows you to get equal travel up/down.

Just as Joe said:

	Quote:
	I 2nd the using all the end point you have. But before you get into the tx programming, I'd match the linkages mechanically: Slap some little paper protractors on the 2 servos and 2 surfaces. With no power move the elevator halves from center to +45 then -45 degrees (or whatever your 3D max throws are). Observe how far the servo arm moves. The servo should move exactly the same + and - from the elevator half neutral position (+55/-55 degrees for example). Adjust the push rod length to get the +/- to be equal. After all this you may see that one servo is 52/52 and the other 55/55. To get both halves equal adjust the horn height on one of them. Once you get a setup that is for example: surfaces 45/45, 45/45, servos 55/55, 55/55 then you can move onto programming the servo using the hitec programmer, a matchbox or equalizer. Or you can do what I do and just use the tx subtrim and end points. Yes it actually works. You use the sub trim and massage the end points to act as the servo programmer, matchbox/equalizer. As long as you have them mechanically synch'd this works. I'm only talking about one servo per elevator half here. Ganged servos are another story. If I could show you a video of two 50cc 3D planes that I have setup this way, you would not be able to see any difference in the speed or positions of the two elevator halves. I should actually make one since I see this problem come up all the time.

This should get your mechanical geometry all correct.

Seth

[KnowCrashes]

Ya beat me to it. That was what I was gonna suggest is check the geometry of the arms to linkages.

[extra 260]

Not 90degs to the suface.The hindge line.If you're links are the same length like there supposto be and you angle the arms forward woun't you get less up and more down?That's with equal amounts of atv of cource.I've setup at least two of these radios with dual elivators and it's a pain but will work,and work with any servo too.I never had a issue with what servo i was using jr,Futaba<hitec done them all .Mechanical geometry is were you start everything equall.The only time I've ever used diffrent length links is when useing dual servos on a serface.The inside are usually shorter but both right and left inside servo links were matched.

[3D-Seth]

	Quote: Originally Posted by extra 260
	Not 90degs to the suface.The hindge line.If you're links are the same length like there supposto be and you angle the arms forward woun't you get less up and more down?That's with equal amounts of atv of cource.I've setup at least two of these radios with dual elivators and it's a pain but will work,and work with any servo too.I never had a issue with what servo i was using jr,Futaba<hitec done them all .Mechanical geometry is were you start everything equall.The only time I've ever used diffrent length links is when useing dual servos on a serface.The inside are usually shorter but both right and left inside servo links were matched.

Servos are mounted in the fuse, not the stabs, so there is no "parallel" to the hingline. They must be mounted like my post above, or equal travel is impossible.

Seth

[3DHobbyShop]

It's not an easy procedure to get dual elevator servos agreeing on a DX7, even when the linkages are perfect. Any sub-trim necessary to align the arms throws the mix off. Then, you have to juggle the end point and mix percentage numbers (by trial and error) to end up with equal throw and (approximately) equal travel rate. So, yes, any or all of the suggestions above could be the cause, and certainly linkage perfection will make the process easier, and certainly a bum servo will make it impossible. However, it also requires the fiddling with the mix percentage vs. endpoint to get the rise curve as close to the same as possible.

Also, an X9303 2.4Ghz can be had for about $550 for a smart shopper, and is a really, really excellent step up from the DX7.

[Flatlandman]

Also on top of what every one else here has said. If the control horn is off the hinge line then the parralel rule wil noit hold up.

If the pivot point of the control horn is off by x° the servo arm must also be offset the same x° say the pivot point was -15 degrese off the hing line AKA 15 towards the rear then the servo arm must be offfset 15° towards the rear of the ele also. Those are extreme amounts, just number i pull out to show what im trying to say.

an easy way to check is if the servo is factory set; the end points will be about the same for the same throw up and down. example 120/120 end point/travel adjustment for the surface to travel 35° up and down. If your set up with the same end point is 120/120 and the push is 35° and the pull is 50° your push rod is to short. Fix: shorten your push rod adjust your sub trim for center and recheck the throw if its closer but not equal redo the fix until your throw is equal. After its equal adjust the control horn hight to get the amount of total throw you want so if its 35up and down with equal end point ( high as you can get them imo) and you want 45° then make your control horn shorter until you just have the 45°.

Thsi will allow you to optimize your pushrod length and control horn hight for proper mechanical set up

Your hitec programmer programmed servo will not let this test work properly you wil need to reset to factory settings for it to work.

only after this should you then program your servos after seting your tx to 0 subtrim and max end points 140/140

I hope this wasnt to confusing.

[JoeAirPort]

Makes sense to me. I forgot to mention the control horn pivot being off the hinge line as one of the reasons for the offset from 90 degrees. The mechanical part is the most time consuming. Programming it after that is the fun part.

[extra 260]

sorry seth.I'm miss wording what I'm trying to say.You need to be 90degs of a zeroed stab.that meens level the fuse then zero out the stab and drop 90 degs from that.parrallel all that out so you make a box with two 90degs t each end one at the stab and one at the servo.then your linkages will match.

[bodywerks]

Well, regardless of the whole 'proper geometry' stuff, even if you were doing the geometry wrong it would not affect your mis-match issues if they were both equally 'wrong'. By your description, the geometry of both elevator halves are the same(servo arms at same angles, pushrods same length, control arms same length and both are equally positioned over the hinge line). If that is absolutely the case, then it's down to your tx or your servos. The DX7 is definitely not helping since you don't have a multipoint mix, but I would bet the two servos are just not responding identically. The quick fix is a 9303.

[borealnw]

Oh WOW I got home from work and checked the forum before going out into the hanger and WOW. Thanks so much for the help, I realy apreciate it. I will get to work on it and let you all know how it comes out. I just found a 9303 for $200.00 and trade for my DX7 so I am thinking I will get it and also do the mechanical. This is going to be my back up next season. This has opened and whole new world of the art in building thank you all for the help.

[3D-Seth]

	Quote: Originally Posted by extra 260
	sorry seth.I'm miss wording what I'm trying to say.You need to be 90degs of a zeroed stab.that meens level the fuse then zero out the stab and drop 90 degs from that.parrallel all that out so you make a box with two 90degs t each end one at the stab and one at the servo.then your linkages will match.

No.

You will end up with un-equal elevator travel this way. See attached picture that I drew.

Because the servo is below the stab, when the servo turns towards the elevator, the linkage goes straight much quicker. When the servo turns away from the elevator, it has the reverse effect; pulls the linkage away much quicker. This is why it needs to be mounted with the servo arm towards the front of the airplane.

**Note: this is only for fuse mounted elevator servos, not stab mounted elevator servos.

Seth

[PSF]

I have a 9303 and set the left elev to the elev channel and the right elev to aux 1 (flap channel). Instead of mixing I mate the aux1 to elev. This is found under device select. everything works fine elev trim sets both. I am not sure if the dx7 has the device select mate channel program.