joseph185

Do most on 29% and larger planes use an servo reverser or program a slave channel when using dual elevator servos

mandtra

My Feedback: (29)

I have done it both ways. and have not had any problems either way 30% is as large as I have tried it on though. I'm sure some people will tell you to use a matchbox or a smart fly set up, but a reversar works just fine for me and I fly pretty hard 3D

Tired Old Man

My Feedback: (1)

Usually it's done one of three ways. Transmitter programming, program matching of the servos ala' Hitec, or by using an after market product like a Matchbox. Very, very rarely is a servo reverser used due to electrical resistance (changes with heat) and independant servo trim issues.

DKjens

My Feedback: (50)

When people get into 30% gas planes and larger, they usually have a radio that has an option for dual elevator servos.

joseph185

So a slave channel is the way to go?

martinarcher

My Feedback: (10)

That's what I do.

nonstoprc

My Feedback: (90)

It depends on the radio. With Futaba 9c 72mhz, I use Y-split. The two halves are not synced up 100% with the slave channel approach.

David Jackson

My Feedback: (15)

I fly a 40% Yak with a total of four servos (2 for each side of the elevator). I use the JR 10X which has a programming function for split elevators. I also use a the Smartfly EQ10 which has functionality that allows you to sync dual servos.

Rcpilot

My Feedback: (78)

I have the following response copied to a document. Whenever the question comes up, I just paste it. It comes up 2 or 3 times a year and I just got tired of all the typing, so here ya go.

A servo reverser doesn't work for a precision setup. Aerobatic planes are the ULTIMATE in precision aircraft. We're not dealing with your 40 size sport plane here and these aren't warturds where if it will just go UP when the guy pulls back on the stick--he's happy. We're dealing with precision thoroughbreds here. Set it up like you want it to perform as good as it can be.

No servo will travel the same amount of rotation in both directions. This is true from the cheapest Blue Bird special used on very small foamies, all the way up to the most expensive digital Hitec, JR or Futaba.

(Let the symbol * stand for degrees. So that I don't have to type out degrees 100 times during this post)

For instance:
Plug any servo into a RX and push the stick all the way in one direction. Note servo travel. For arguments sake, let's say it moves 55*. Now move the stick all the way in the opposite direction. Servo will travel 60*

I don't know why servos are built like this, but they are. It's just like a car. When they (auto manufacturers) give you the turning radius, it's always to the left, because 99% of cars are designed with the steering linkages so that they just happen to turn left in a tighter circle than to the right. So, for advertising--to sell cars--they only give you the turning radius as calculated to the left.

Now-- if you agree --keep reading:

Servo A is on the left side and must operate clockwise to push the elevator up when the stick is pulled back.

Servo B is on the right side. It must be reversed so that it will travel counter-clockwise to push the elevator up when you pull back on the stick.

Remember, servos always travel more in one direction. Be it clockwise or counter-clockwise.

So, let's say the clockwise rotation of these two servos is 55* and the counter-clockwise rotation is 60*.

Are you catching on yet?

When you put the servo reverser on Servo B to make it rotate counter-clockwise on the right side of the fuse----that servo is traveling 60* of rotation.

Servo A on the left side is traveling clockwise, but it's only going 55* of rotation.

Now, you pull back on the stick to go up--what happens?

Looking from the back of the plane:
Left (clockwise servo) elevator goes up 1" The left servo is traveling 55* before it stops.

Right (counter-clockwise servo) elevator goes up 1.5" The right servo is traveling 60* before it stops.

Now, you push forward on the stick to go down--what happens? Exact opposite thing.

Looking from the back of the plane:
Left elevator goes down 1.5" The left servo is now traveling 60* because it's going counter-clockwise. (remember--down elevator)

Right elevator only goes down 1" The right servo is now traveling clockwise and it's only traveling 55*.


Using reversing Y-harness' just doesn't work right. You can adjust your endpoints, but that won't do any good. It gets them close, but it also screws up your resolution. All that does is make each servo travel less. Doesn't fix the differential * of rotation in each servo when they go opposite directions. The servos are moving in opposite directions from each other. The problem isn't as pronounced at lesser control deflections, but when you go to max deflection--it shows up and bites you.

Some guys claim that you can adjust the linkages to compensate. You can, but you NEVER get it perfect. Want to fly IMAC or Pattern? Have a good time trying to pull a perfect loop without corkscrewing out at the top. Want to do some low down 3D on the deck? Try doing a slow speed Wall with full elevator deflection. Your going to snap out every time because one elevator is moving farther than the other. Harrier? Lots of wing rock because you've got an elevator fighting you the whole time--trying to roll the plane over. Rolling harrier anyone? Try that one with elevator servos that are out of synch with each other.

Using a reversing Y just NOT the right way to do it on any type of aerobatic or pattern ship. It's just not. These are precision planes. A tiny bit of control surface deflection results in a BIG response from the plane. Having your elevators 2* or 10* off at max deflection is just not going to cut it. They need to be perfect, and you can't get that out of a reversing Y. I don't care if it's a $15 reverser, or a $100 reverser. Until the manufacturers start making servos that travel the exact same rotational * in both directions--a reverser will never work.

Use a JR Matchbox. Buy a Hitec servo programmer. Buy a Smart-Fly Equalizer. Buy a radio that will do the mixing for you. ANYTHING but a reverser. That's ghetto.

Hope this helps.

Tired Old Man

My Feedback: (1)

You have such a way with words

Rcpilot

My Feedback: (78)

[sm=red_smile.gif]

I have a degree in English literature. Mostly, it comes out in my writing. (you wouldn't know it from some of the drivel that comes out of my keyboard on RCU) I did a LOT of writing to get that degree. It's totally worthless, unless I'd like to spend my days teaching teenagers English in a high school for about $30k per yr. Uhhhhh, no thanks. Id rather get run over by a large bus. Twice.

nonstoprc

My Feedback: (90)

In my case, a Hitec programmer was used to program the two elevator servos. Both are installed on two elevator halves and jigged together to get a almost perfect match.

FBaity

My Feedback: (2)

Rcpilet,

Are you saying one can't obtain exact equal travel using program mix ...lets say in a JR 10X without a matchbox?

Frank Baity
AMA 38026

yarom

My Feedback: (82)

While there is the option to plug and mix from the radio, I have always used a Marchbox or Equlizer on 30% planes and up.

It is just that much easier in all aspects, even after the Hitec programmer has centered and or adjusted travel for the servos.

This, and all other methods, assume you have your linkages absolutely identical, or as close to it as humanly possible.


Trying to make up for linkages that are not symmetrical with electronic means will result in something that is perhaps accurate in the middle and possibly at the end point, but will by different at all point of travel in-between. So for maneuvers like a harrier, were the elevators are deflected a lot but not all the way to the end, you will have a mismatch and will need to compensate somehow...

Hooked-On-RC

My Feedback: (16)

Well one thing I have found is that when you are setting up a new plane or even revamping an old plane, chances are you are using several of the same servo model. The good thing with this is you can usually find two servos that are as closely matched as possible right out of the box to use on your elevators. I made myself a servo measurement tool where I can measure the degree of throw on each servo using a protractor, that way I can select two that are really close and minimize my need for adjustments if at all possible. I like to run my elevator halves on seperate radio channels as well, that gives me the ability to "program" my servos from my radio. Correct Symmetrical setup is crucial on aerobatic planes for all the reasons RCpilet mentioned, english lit degree or not!

bbagle1

The Futaba 9c has a program for using dual elevator servos without using a slave. it is the ailvator function under the advanced menu. To program just the elevators you use the program but keep the ailvator values set to 0. Or you can use the elevators with your ailerons if you prefer.

Rcpilot

My Feedback: (78)

No. Thats not what I'm saying.

I'm saying reversing Y harness' don't work.

I don't have a 10X, but I DO have an 8103. It doesn't have the right kind of software to do it right. You can mix dual elevators on a PMix. Use ch5 or ch6 so that trim works on both servos. Now you can set them up and adjust all the travel. Works great.

Now flip the dual rate switch. No longer works. Travel is off at the extreme throws.

I just discovered this little flaw in programming about 6 months ago. As far as I know, the 10X and 9303 don't have this issue. Both are much better radios than the 8103. All you can do with an 8103 is use a JR Matchbox or some other type of servo programmer. []

IscarRep

My Feedback: (8)

No servo will travel the same amount of rotation in both directions. This is true from the cheapest Blue Bird special used on very small foamies, all the way up to the most expensive digital Hitec, JR or Futaba.

RcPilet,
Does this also hold true for a reversed from the factory servo?

IscarRep

My Feedback: (8)

A little clarification is needed here.... I bought some JR 126's a while back and didn't want to use a reverser.I ordered 1 servo reversed for one of my elevators.Is that a good way around this differential problem?

Tired Old Man

My Feedback: (1)

DKJens said it perfectly a lot earlier for those going to larger aerobats. When you start running multiple servos on a surface you should have already stepped up with your radio equipment. If you did not or could not the plane should wait until better equipment is in your hands. You're not ready to take the step until you have and understand the equipment to do the job.

Rather than explain what servo does what and whether a reverse servo has the same travels each direction as a standard servo, hook up your servos and look for yourself. Obtain a surface deflection gauge or two, preferably two, since you will need them anyway to set the plane up. Many of the aerobat manufacturers state control deflections in degrees so when those without a degree gauge how how much that is in inches they may not get an answer. The best education in the one that's right in front of you.

I can't count the number of times someone has posted how their plane would corkscrew off to one side or snap in a maneuver. Then eveyone tries to help with numerous posts about how to correct something that was assumed to be wrong in the aircraft quality. Then it comes out that an inadaquate or cheap component was substitued over what's normally used in order to save a couple of bucks, becoming the root cause of the problem.

IscarRep

My Feedback: (8)

I am not going to try to set up a plane with a clothespin and a protractor with a level.I set my plane level and use a digital height gage.Going up and then down from zero deflection (neutral) and a little trigonometry gives me what I need to know.I have a JR XF 622 and a Futaba 7C. Are these radios not capable? I believe them to be.

Rcpilot

My Feedback: (78)

Yep. I got 2 JR 7005 coreless servos here to prove it. They DO NOT travel the same amount. They both move the same direction when placed on opposite side of the fuse (elevator servos) but one elevator moves more than the other. Had to use a JR Matchbox to fix it.

It must be the servo pots. You can reverse the current flow, but for some reason they just don't move the same in both directions. Reversing the current flow just makes it go backwards. Doesn't do a thing to correct the travel problems.

100% agreement with Pat. If you haven't got the components to do the job right, then leave the airframe in a box until you have upgraded your TX or saved the money to buy the right equipment and do it right.

IscarRep

My Feedback: (8)

RcPilet,
I must have gotten lucky because my reversed servo and the other one I used came out VERY close.I don't have any corkscrewing or any of that.This plane came out very nice.Thanks for the info.

Rcpilot

My Feedback: (78)

If you already knew the answer, then why did you ask the question?

What servos are you using?

yarom

My Feedback: (82)

This is way you are not supposed to set them up to travel the entire way to their maximum travel.

If you set them up to 140% and use just 100%, you will be fairly close.