Skyhawk940

I’m having big problems setting up twin servos for my elevator half’s on my Seagull Extra 260 (90). This is the first time I’ve tried to use two servos to control a control surface. I’m using one channel through a splitter/reverser to Hitec 645’s. First of all the servo arms will not line up. One is off about a half a servo arm tooth. It’s either too far one way or the other if I rotate it a tooth. Now if I line up the elevators at neutral, one half travels further than the other at the limits. I’ve tried using two channels on my JR 6201, but the trim only works on the elevator channel and not on chan. 5 or 6. I’ve tried to compensate by moving the control horns to different distances. The plane flies OK, but the elevator causes rolling as is. A tight loop goes into a tight roll.
Am I going to have to go with digital servos?

DavidAgar

My Feedback: (108)

Digital servo's will not fix the problem. You need to get a match box or a radio that will allow you to mix 2 channels together to operate as one. I am not familar with JR radio's, however with a Futaba 9C, you program the elevator as the master channel and then program one of the other channels as a slave. Doing this will allow both servos to operate as one and the trim will adjust both servo's. Good Luck, Dave

masonman

Smart-fly Equalizer 3D...........Fix you right up...They work great.

scooty

Don't bother with splitters and reversers, you'll never get things perfect, even with digital servos. The proper way to do this, is with a radio that has an extra channel and dual elevator programming. I'm not sure about JR but with Futaba the 7C is the cheapest with these features. If you really don't want to buy a new radio, then mount a single elevator servo in the fuselage and use wheel collars to Y a second pushrod onto the the first one, so you'll have two pushrods, one for each elevator half. Use a servo with twice the required torque rating.
Or else live with a plane that rolls while looping...

flying pastor

Skyhawk. I think that you mix the 2 channels that you need but then treat them separately as far as sub-trims, expo and travel adjust are concerned. The more up market jr sets have a twin elevator function but this won't help you. Have you got the manual? and is there a help desk that you can contact? In the UK the importers are very helpful.
Chris.

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.

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 advertisingto sell carsthey 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 fusethat 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 upwhat 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 downwhat 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. (rememberdown 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 deflectionit 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 timetrying 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 directionsa 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.

Gray Beard

My Feedback: (-1)

If you don't have the radio then a matchbox is A very good way to go. In my 9-C I just plug into ch. 2 & 8 then actavate ch. 8. If I'm using A 7 ch. RX then I plug into ch. 2 then go into A mix using ch. 2 {elevator} as the master and another ch. like 5 as the slave. not very hard to do.

Skyhawk940

Thanks for all the help, but what is a Smart-fly Equalizer 3D?

Skyhawk940

Thanks again for the help. I found the book for my JR 6102 transmitter. If I use mix # 4 for two channels it includes the trim on both. I can set the offset and travel for each channel. I'm sure this is going to make things MUCH better now. I'm glad I didn't have to re-invent the wheel.

Happy landings for all of you guys.
Michael Lavender
Sandusky, OH