I am building a Goldberg Ultimate and want to install two elevator servos in the tail. I want to have the servo horns on the outside of the aircraft. Is there any way to set this up so that both servos pull in the same direction using a Y-harness?

Yes mount one servo high and the other low so you are using different sides of the servo arms. In other words one servo arm would be pointing up and the other one down. Be sure to align the servo arms with the "stock" elevator pushrod exits.

Two choices...with a simple Y
Contact the maker of you're servo and see if they can wire a reversed servo and use it on that side...

The other and one I've used before. but looks real bad,
Put one servo low in the fuse tail and use the top of the arm to one elevator...set the other high in the fuse tail and come off the bottom of the servo arm..but is much easier with a reverser..and a whole lot less measuring, and fiddiling around.

Easier is to buy a Y harness with a servo reverser built into it..
(If you can't slave two channels together in you're radio..)


I hope I splaned this right for ya..

Just get the reversing Y harness. Make it easy on yourself.

tonyc

One high and one low will result in differential throw to the elevators, with one elevator moving more than the other on certain commands, etc. Think about the geometry (for lack of a better word)....the servos driving off the bottom of the wheel is in the same arc as the control horn, giving a fairly "pure" push or pull as it rotates. The other servo, driving off the top, is rotating downward as the control horn is rotating upward, and will throw less.

Go with the other advice....a reverse servo, or reverse Y yoke if one is available. Or.....do as I have done on my GB Ultimate, which is 9 years old.....one good servo (JR 4031) and a "Y" bass-wood pushrod. Is plenty for that airplane.

Clair Sieverling
AMA 15654

reversing y is the best & easiest way to go

Gil

You're still going to get differential throws with a reversing Y.

Here's why:

No servo will travel the same amount in both directions. Period. Let me give you an example. Let's say a servo will travel 65 degrees clockwise. It will only travel about 58 degrees counter-clockwise. Thats a fact- and it's just the nature of the beast here. No getting around it. This is true of ALL servos. Even the expensive JR and Futaba digital servos. They just don't travel the same exact amount in both directions. No servo does.

So; if you have two servos and they both travel 65 degrees clockwise and 58 degrees counter-clockwise-- then the reversed servo is only going to travel 58 degrees while the non-reversed servo is going to travel 65 degrees when you pull back on the stick.

What will happen is this:
When you pull back on the stick-- your left half will go up 1" and your right half will only go up 3/4". Now: when you push down elevator-- your left half will go down 3/4" and your right half will go down 1". They will be TOTALLY OPPOSITE. One goes up a bunch and down a little and the other servo/elevator will go up a little and down a bunch. I've tried this-- believe me. I cussed a reversing Y harness for a month once. They just don't work for this application.

Most reversing Y harness' will have a "centering" pot. It allows you to re-center the reversed servo. Big deal. It doesn't make them both TRAVEL the same amount in BOTH directions. It only allows you to recenter the reversed servo. It doesn't allow to to adjust the travel of each servo. You still got differential throw.

What you need is a JR Matchbox. They cost about $65. Or you can go here>>>>>http://www.smart-fly.com/ and look at the Equalizer. It's basically the same thing as a JR Matchbox-- but a few $$$ cheaper.

Your only other option is to tear one servo apart and reverse it internally. I did this with a Hitec 625MG on my H9 Cap 232 and it worked perfectly.

To reverse a servo internally-- you gotta be REALLY CAREFULL. You can't just reverse the wires on the motor. You MUST also reverse the TWO OUTSIDE wires on the POT.

If you only reverse the wires on the motor -- it will go up in smoke the instant you put power to it. The motor will be trying to go clockwise and the pot is feeding power too it trying to make it go counterclockwise. It fights itself to death and soon melts internally.

On a Hitec servo-- there is one brown wire and one orange wire on the motor. Reverse these two. There are three wires on the pot. I can't remember the colors-- it's not important anyway. Just reverse the TWO OUTSIDE wires. Leave the center wire on the pot alone.

After an internal reversing operation/abortion-- your servos will work together and you will be happy as a pig in .....well, you know. All you will need is a standard Y harness. No reversing nessecary at that point. Now that you have both servos traveling together-- you can adjust your elevator throws with your computer radio. You're still going to have 65 degrees travel clockwise-- and 58 degrees counterclockwise-- but they will be working together-- not opposite of each other. You can use your travel adjustments (end point adjustment) on your radio to get equal movement both--up and down--on the elevators.

I know that some will say that it's possible to manually adjust your linkages and your servo travel to make a reversing Y harness work fine. Not true. No matter how much you twist the linkages and alter the servo travel-- you'll always have differential throws. Everytime you pull back on your elevator stick; you plane will corkscrew because of the differential throws.

Either reverse it internally or get an Equalizer or a Matchbox. That's the only way to do it right.

I hope this helps you out.

Either reverse it internally or get an Equalizer or a Matchbox. That's the only way to do it right.

You hit the nail on the head, but, how many people would go through the extra expense of doing that...

Now that I have got into bigger and better planes, I'm really beginning to see how even the slightest oops in a linkage throw will turn a genteel giant into a hand full...