Elevator Mis-match

[borealnw]

I am going to decribe the situation as clear as possible. For months I have been fighting an elevator dual servo mis-match.

Plane TOC 30% Yak
TX DX7
RX Spectrum 9000
Servo's 7985 X2 coreless Digitals
Controle horns Dubro large scale.
Arms Airwild 1.5 inboard
Linkage Carbon fiber with Desert Aircraft Titanium rods.


Here is what I have done.

Drilled controle surfaces on a jig and drill press with elev level both ways.
Set up the horns at same angle and same distance from leading edge.
Distance from elev to horns end is the same. 1 1/8" making the arm on controle horn 1 3/8"
I've used a Hitech Digital programmer to center and set ends points of servo's.
I have the servo's plugged into the RX Elev and Aux 2.
I have mixed the TX using mix number 5 elev to Flaps (Aux 2)
Mix is set to 100% up and 100% down. NO offset.

In the TX.

I have 0 subtrim in both elevators surfaces. Set that up mechanically in linkage distance.
End points Elev set at 110 or 45% full up and down. Hi rates.
I have the Flaps end points set to match the 45% but the numbers are different (why I do not know)

All that done I have both half's set equal for center. Full up they are equal. Full down they are equal.

Problem #1 Low rates or IMAC they are not centered and way off both ways.
Problem #2 Moving the stick the Aux 2 side moves Faster then the elveator side both up and down.

Some at the airfield thinks it is the RX. Being a DX7. They say I am limited in adjustments and the DX7 does not allow me to seperate the trim from the endpoints. The signal from Aux2 is faster then elev therefor is throwing off the speed and Low rate endpoints.

today I talked with another fellow IMAC pilot and he says it is not the RX because his 12X and one of his planes has the smae problem.

Anyway I am wondering if some in FG have run into this porblem and possible fixes to try.

At the moment I am going to run the endpoints equal for IMAC rates and let the high rates fall where the may. But is this porper thinking is it that crucial to have the elev equal for 3D.

Would spending money on a 10X or a 9303 remedy the problem.

Would a Smart fly power expander fix the problem.

I have tried a Smart Fly EQ3D and compounded the problem in that the equalizer would cause the DX7 to loose its "bind" on the plane. Something to do with the self check in the Smart Fly when the TX is linking up with the Spectrum RX. Causing the code to not be seen loosing the bind???????

[Rick Sowell]

The easiest thing to do is get a matchbox and run one channel to it Elev. and do all the matching with it, set centers, end points, that takes the transmitter and it's programming quirks out of the picture. JR matchbox about $70.

[sweetpea]

What you see here is a both a TX and servo issue. It has happened once on my 10X. I swapped out one of the servos and it went away. Before I got that servo I used a matchbox and fixed it as well. With digital servos and digital TX's there will be some tolerances that are not quite equal and by being digital they are more precise in how they adjust/move which gives you a larger time they may not match up.

[3D-Seth]

Are the servos mounted in the stabs, or in the fuse?

Are your linkages the same length?

How are the end points in the transmitter? Equal? Close? Not close at all?

I ran into a similar problem with a QQ Python that I built for this year, and it was not a digital issue at all, but mechanical. After playing with the linkages, and various distances off of the control surface, I finally got them to where they matched.

Seth

[borealnw]

The servo's are mounted in the fuse.

The distance from bolt to bolt on the linkage is Right 4 15/16" . Left just a smigen under 5". So I have a 1/16' difference.

[Flatlandman]

Why would you program your servos witht he endpoint low at 110? When you program them go as high as you can get 140/140.

First try unplugging the eles and plugging them in again in the opposite so ele into aux and aux into ele.

Second send pics of your ele set up with the power on and the ele's centered.

[JoeAirPort]

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.

The reason you can't simply make the push rods the same length is that there are imperfections in the geometry of all planes that need to be tweaked out using the above method. When you get them perfectly synch'd mechanically you could actually end up with push rods that are slightly different in length.

[extra 260]

you may have to use some sub trim just make sure the serco arm is 90degs to the hindge line.All my linkages are equal.

[JoeAirPort]

Actually I use sub trim to make the servo center in the middle of that 55/55 I mentioned above. That's not always 90 degrees to the hinge line. It can be, but not the rule on my airplanes so far. On the Extreme Flight elevators it's pretty close since the servos and elevator hinges rotate in the same plane (servos inside the stabs). When the servos are on the fuse usually they have a few degrees of offset from 90 degrees.

[extra 260]

as long as you make the servo arms 90degs from the hindge line and the links the same legth you can make them match up and down with minamal diffrancess in the end points.

[bodywerks]

It's the servos. Had the same problem with Hitec5945's and 5955's. Removed them and installed 8611's and the problem went away. The DX7 isn't helping, either - you really need a tx with multi-point mixing.

[JoeAirPort]

I've done it with 5245, 5945, 5985, 5955, 7955. All worked great.