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.

[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:

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]

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]

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.

[scott m lyons]

No it doesn't have that fuction.You actually burn up two mixxes just for setting up two elivator servos using two separete chanles.

[scott m lyons]

Seth with your setup wouldn't that mean if the servo was in the stab you would have to tilt the arm back?You could just flip the servo to the top meaning in the stab and the end of the servo arm were the linkage connects would be the same distance from the stab.I'm trying to make sence of it because I always setup my stuff like extra260 does and my stuff is always the same length and square.My end points are the same also meaning up is the same as down.I don't program the servos i do it in the radio and match-em.

[borealnw]

Thanks agian for all your help. After reading all your advise I am going to first yard my servo's out and send em in for service. I am going to buy a new TX 9303 then start over on the geometry. Figured if I am going to get it done might as well do it right.

Anyway I will post what I find out along with some pics and let you guys know how it turns out.

[Flatlandman]

You dont have to have a diff Tx. I have set 3 planes up with the same Tx and was very able to have equal travel. Although i like my 9303 better :197:

[smokin]

you really can't go wrong with a 9303. you'll love it!

[castlebravo]

Subscribed........Good luck Jeff.....I have a similar issue with the same servos but different radio. I still dont understand the part about the servo arm geometry needing to be positioned forward instead of 90 degrees to the linkage. I think your going to have to dumb it down for me Seth.

CB

[Flatlandman]

Subscribed........Good luck Jeff.....I have a similar issue with the same servos but different radio. I still dont understand the part about the servo arm geometry needing to be positioned forward instead of 90 degrees to the linkage. I think your going to have to dumb it down for me Seth.

CB

Im not seth but ill add a little bit. You dont really need to understand why just pay attention to your travel adjustment if you get more end points on the push than in the pull for equal throw then you just shorten your push rod then readjust the sub trim vise versa if more in the pull lengthen your push rod until you have your equal throw. The arm offset will be what ever it needs to be. Then just start the opposite side near the same place the original side ended up at.

[JoeAirPort]

Right on Flatlandman...right on....

[jon595]

Right on Flatlandman...right on....

Ditto...

BTW, this is how it was done before computer radios and programmers. Once you see someone do it this way you will not use anything else. Get yourself a throw gage to make it easier to see.

[The_Wreck]

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

Your drawing actually shows why the servo horn should be close to 90 degrees from the hinge line. If you draw a line from the hinge to the servo horn connection it is 90 degrees with the servo horn. Your illustration is the best I've seen yet that shows this. The servo horn relationship to the case never matters only its relationship to the hinge, whether it is in plane or out of plane like on a surface mounted aileron. There is a lot of different geometry issues that can cause the best position to be something other than 90 but it is a good place to start.

There is an excellent thread on setting up linear geometry.
http://www.flyinggiants.com/forums/fg92/38381-setting-up-perfect-liner-geometry.html

I have attachaed a couple of different servo protractors I have created. Depending on the installation they either go over the top of the case or over the whole servo.

[blackbeer]

After reading this thread through a couple of times I think I will go over my set up in my Yak. One thing I found buried deep in the manual for my 8U super is that there is a difference in the resalution between channels 1-4 and 5-8. I have one elevator servo plugged into channel 2 and one plugged into channel 8, or is it 7, I'll have to check, same with ailerons, one in channel 1 and one in channel 8, or 7 can't remember. I can center them and I can match max throws but in between is a different story. Any ideas on that situation. I'll be moving into the 2.4 relm this winter but for now it is my trusted 8U that gets the nod..............

Tom

[sweetpea]

matchboxes and Smart-fly equalizers can be had for very little money. (I have at least 5 matchboxes I'd sell as I have moved to the EQ PE's ).

This keeps them on the same channel and you can adjust endpoints and neutral as well as reverse them. In the realm of IMAC precision is the key. Or you can spend the money on a new radio.

[Flatlandman]

I prefer the matchbox set up rather than programing a servo.

[yakpilot]

Using a matchbox is usually quicker and easier, but if you want the servos to be in sync through their entire travel you have to program them. I've used matchboxs many times and they work well to set end points and centering, but often times you can't get the servos to match in the in-between points where they spend most of their time while in flight. Of course there are variables. If you've optimized the linkages and start off with servos that happen to match well then you are golden. But I've had servos the that were not matched very well from the factory, and once you start changing subtrims and endpoints by very much, you will get one servo that moves farther than the other for a given stick deflection. Anyways thats been my experience.

[blackbeer]

Well I used an EQ2 once on a 7C to get both elevator servos in sync but it put out so much noise I could barely get a ground check with that radio so I'm not ready to go that route again. Maybe I will need to break down and get a programmer but I wonder if that will overcome the difference in resalution between the channels in my radio.....................

Tom

[yakpilot]

Tom yes it would since you can then just use a Y harness and run them off of one channel.

[3D-Seth]

Seth with your setup wouldn't that mean if the servo was in the stab you would have to tilt the arm back?You could just flip the servo to the top meaning in the stab and the end of the servo arm were the linkage connects would be the same distance from the stab.I'm trying to make sence of it because I always setup my stuff like extra260 does and my stuff is always the same length and square.My end points are the same also meaning up is the same as down.I don't program the servos i do it in the radio and match-em.

No, Unless you mean parallel to the hinge line. Because the servo is rotated 90º

With the fuse mounted elevator servos, in the bottom portion of the drawing (incorrect way, mounting the servo arm 90º to the case), the arm and linkage straightens out very quickly, ending your travel, which differs from when it is pulled away from the horn, which pulls more throw much faster. Basically, you have 30º of up elevator, with 70º of down elevator (just random numbers), but yet in the same amount of time.

Basically, the same reasoning as to why your linkage isn't 90º to your servo arm on your wing mounted aileron servos, or stab mounted elevator servos. More travel.

Basically, its just offset to equal your travel in the same amount of time between your up/down throw.

Hope this makes sense.

Seth

[scott m lyons]

No y harness in giant planes.Or any plane for that matter if you can help it.

[blackbeer]

Ya, I'm not into Y harnesses at all. Been there, done that. I just went over to Servo City's site and there seem to be 3 different programmers with a huge difference in price. Could some one clue me in on which one to get. The one that is over 150 bucks is out for now but if one of the others would program my 5945s and 7955s I might be able to swing it.

Tom

[scott m lyons]

I Think we're miss understanding each other maybe? I mean like this.

[yakpilot]

No y harness in giant planes.Or any plane for that matter if you can help it.


If they are heavy gauge, why not? BTW we are not talking about 43% Carden here. For a 50cc it's just fine.

[scott m lyons]

I do think they make y's that will handle the amps.But if you bind or lose one servo the likely hood of the other one going is very high.Just alittle bit of safety.Exspacially when the radio WILL do split elivators he just has to work on it some more.Dude don't give up till you figure it out.I wouldn't use match boxxess either.Remember weight plus money??You don't need them.Spend the time to figure it out .Go over the setup again.It will make future setups go easier and you'll learn how to do it right.Which is most important.

[3D-Seth]

I Think we're miss understanding each other maybe? I mean like this.

Right...

The linkage will straighten out faster when up elevator is given. Giving you less throw.

Which is why you offset it forward like I showed...

[1bwana1]

OK, I have been following this thread and we are not getting to far answering the question. My perspective is this. I have set up planes successfully using all of the methods discussed on this thread. However, you bought very good Hitec PROGRAMABLE SERVOS. You should be able to use them to set up your plane properly. I have used them in two ways.

The first way is the method taught by Joe Hunt in the following videos. It takes some fiddling, but works great.

link to video #1 http://www.flyinggiants.com/gallery/...hp?photo=56318 (http://www.flyinggiants.com/gallery/showphoto.php?photo=56318)

link to video #2 http://www.flyinggiants.com/gallery/...hp?photo=56320 (http://www.flyinggiants.com/gallery/showphoto.php?photo=56320)

link to video#3 http://www.flyinggiants.com/gallery/...hp?photo=56321 (http://www.flyinggiants.com/gallery/showphoto.php?photo=56321)

The second is to use the programming to get the servos matched perfectly. To do this, I program them using Joe Hunts method off the plane using a protractor as described in this article:

http://www.rcuniverse.com/magazine/article_display.cfm?article_id=486

To make it super easy, you can buy one of these:
http://www.servocity.com/html/servo_protractor.html


I then tweak the physical setup to get them matching perfectly on the plane.

If you really think your radio is causing you the problem, don't use a mix, run both elevators out of the ELE channel through a "Y" harness. If you are using a good quality twisted servo extension, the wire is not the problem with a "Y", it is the connector. Just make a "Y" using a Deans 3 pin connector:

http://www.hobbypeople.net/gallery/625083.asp

It will easily handle the power to feed two servos, cheap, and you only need one.

Honestly, you won't program that much, so buying the Hitech programmer may not be cost effective. I have one, and share it locally with my fellow flyers. I'm betting someone in your area has one he would share as well.

I have been able to easily achieve perfect setups without using Sub Trims or other radio programming on my and fellow fliers planes.

Hope you find these links useful.

[borealnw]

off the subject a little what in your opinion is the best Throttle servo for IMAC and 3D?

1bwana1 thanks so much for the links and the advise. I do have a buddy who has a programmer and we both are following this thread. He is one of the best builder and pilots I know and together with everyones helpfull advise we hope to fix the problem. Thanks again.

[bgold]

If it's good enough for your flight surfaces it's good enough for the throttle. Use the servo you are using on the rest of the plane, your throttle is kind of important also.

[infinitemass]

I know this has probably been covered but have you taken a look at this?
http://www.rcaerobats.net/Spektrum/dual_elevator_and_dual_ailerons.htm
Especially step 5 on elevator set up.

[JoeAirPort]

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

This is a really good example of what Joe Hunt called the "to be determined center" (from his old DOD site's instructional video). It's "to be determined" by your air frame's servo pocket postions, control horn type..etc. In this case it ended up a few degrees away from the hinge line. If you had the servo pocket higher and the push rod going under the servo, then your "to be determined center" would be in a different place. Possibly towards the hinge line this time. I had an Edge that was like that. People thinking they can do all this in a servo programmer, match box, equalizer, radio etc. had better study up. Because the brothers in this hobby that have figured it out know better (Joe Hunt and others that taught us this...credit to them).

[JoeAirPort]

Here's some interesting pic's that show linkages that have perfectly symmetrical throws on the servos and surfaces. This is the Edge I mentioned in my previous post. The elevators end up opposite of what Seth posted on page 2 because the servo is up higher, the push rods are under the servo, and also these are Nelson horns...they are not pivoting on the hinge line. That's adds to the offset from 90 degrees. The ailerons have some offset too but not as much. I probably could have drilled that elevator horn bolt more straight but that can all be dialed out with the push rod length adjustment. I think I would have prefered that servo pocket a little higher.

The 2nd elevator is the Ultra RC 87" Yak (Extreme Flight with different covering). That really shouldn't have any offset but I probably glued the horn in not on the pivot...or the horn slots were not cut quite close enough. Again all dialed out in the push rod length.

The last is my Extreme Flight Extra aileron servo. This was the first I ever had that the servo arm tilted away from the hing line at center. It's all in where the servo pocket is located with respect to the horn.

[borealnw]

Thanks for the info Infinite. I see from the list (from the link) that I have them reversed. I have elev in Aux 1 (flap). Will reverse them to see if there is any difference.

Thanks Joe I think I see your point on the geometry issue. On my plane the servo is on the fuss and the elev horns are 1 1/8" down off the surface. The servo arm goes in a down position at 1 1/2" This offsets the linkage just off of level. So if I am reading your info right then my servo arm should tilt slightly to the rear of the servo (plane) toward the elev horn. Question? Both linkage arms need to be the same size to aquire the same speed of travel (correct???).

Looked at the links for programming the servo's and the write up on mismatched servo's. When my servo's come back from hitech I will go over them again in setting them up.

What are the cons of using a y harness. My first thought is power overloading or underpowering the servo's. Is this also the case with using a matchbox or a smart fly EQ.

Thanks so much all for your help.

[1bwana1]

[quote=borealnw;924900

What are the cons of using a y harness. My first thought is power overloading or underpowering the servo's. Is this also the case with using a matchbox or a smart fly EQ.

Thanks so much all for your help.[/quote]

The big problem with a "Y" harness is that the standard servo connectors are not designed to carry the current that two high powered servos can generate. This can cause a loss of performance in the servos, and rarely a failure in the connector. The matchbox can solve it, as can the Smart-Fly EQ. The mini-Deans Connectors I provided a link to can solve these power issues, but will not help with matching the servos like the PowerBox or EQ. Since you have programmable servos you should be able to just use the better connector and save some money.

[jonathanmanopla]

does anyone have a protractor for hitec 7955

[JoeAirPort]

On my plane the servo is on the fuss and the elev horns are 1 1/8" down off the surface. The servo arm goes in a down position at 1 1/2" This offsets the linkage just off of level. Q1) So if I am reading your info right then my servo arm should tilt slightly to the rear of the servo (plane) toward the elev horn? Q2) Both linkage arms need to be the same size to aquire the same speed of travel (correct???).



Q1) That's my guess but go through the procedure I outlined earlier and it will end up where it ends up...likely you're right though.

Q2) Both horns and servo arms should be the same size. After you go through the process you may end up with push rods that are very close but still a fraction of an inch different. No two sides of a plane are identical. I match my linkage on each side separately instead of just doing one then making the other side equal. But I like tinkering with this stuff and don't mind doing both. You could probably get away with it.

[PSF]

hitec makes their own protractor that the servos fit in.

[TManiaci]

I know I'm a little late in the game here, but I thought I would throw in and try to help. To illustrate the importance of mechanical geometry balance, this first image shows how an offset from the linkage connection point on the Surface Horn is offset from the hinge centerline can cause a differential throw. In this example, a 1/2" offset from the centerline is shown. For an equal stroke/displacement of a 90º servo push-pull stroke, you can see that the offset throws are significant.

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In this example, a 5/8" rod travel fore and aft shows an 8º throw differential. Geometry MUST be as perfectly balanced as you can possibly attain. A 1/16" erros is no small matter, it can result in a substantial travel error. Bad geometry can not be "programmed away" 100%.

I don't like using protractors or angle toys, they still leave you with errors. The resolution of those tools do not provide enough accuracy unless you magnify the size considerably. An alternate method is to magnify the throws by extending the surfaces with long straight bars, like these 1/2 hardwood sticks. Attaching them to both elevator halves in the same place on either side, and extending way out beyond the Rudder, you can eyeball the parallel lines of the sticks very easily.

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You would be amazed at how much more balance precision you can attain with this method. With this approach, you can actually see a huge change with just one click of the subtrim when you stand so your line of sight is 90º from the side. Using your radio with rates, you can check solid stable points at any mid-throw point to verify the travel is balanced throughout the throw.

You can also see the speed of the throws much easier too. Magnifying the motion really enhances your visual capacity to make all aspects of the system perfectly matched. Using slow stick action, you can watch the parallel effect really well.

My contribution.... :209:

[blackbeer]

That is pretty much the way I do it Tman except I use cf rod and angle the two ends at each other just behind the rudder. It is the method I used to see that even though my neutral was dead on and my full up and down was dead on the movement of both sides was not the same speed or degree of movement. It also showed me that when I switched from high to low rates it changed again, as well as when I changed expo and changed the travel settings. It's why I dove into the manuel for my 8U and found that there was a difference in resalution between channels 1-4 and 5-8. By messing with the expo settings, the travel settings, and the rates I have been able to get them close but then if I hit my mix switch for knife edge it gets cranky again. I think it's time to make the jump to 2.4. Anyway, great thread, lots of good info.

Tom