Bax:

I may have solved my problem (with the help of a friend), but want to confirm something about the Futaba servo arms.

I have always had Airtronics radios, never had a problem with zero centering the arm on the servo, just set tx trim to center, and arm went right on first try, centered. Simple.

Then I got my first Futaba radio, a 6yg. When I installed the servos/pushrods, I centered the tx trim, but couldn't get the arms to center (90 degrees). The manual says the arm should be centered, but doesn't tell how to achieve that. I fought this thing for a week. So I called Futaba to discuss the problem. The story I got was that the tx was made on one assembly line, the rx from another, and the two get dumped in a box for a set, and the band width could be different. In other words, the tx and rx are not precisely matched or calibrated. I was told I would have to send the whole set in for repairs. The technician made no mention of the following.....(next paragraph)

A week later, I talked to a friend who has had several Futabas. He informed me that there were 6 positions on the star arm, and only one of them would center properly. I tried it and it worked ok. (after much fumbling around). I still have a problem with the large cross arm, tried both ways and won't center. So if I use those arms, I will always have unwanted "differential".

Apparently the older manuals explained this, but went into a bunch of detail about the angular differences, blah blah, all I wanted was for the arm to center. I can make the 6 arm work, but that takes a lot of cutting. Why doesn't Futaba make a standard (small) cross arm that will center without all this extra work. Frankly, I am about ready to go back to Airtronics, but I like the 6yg, it's the only standard 6 channel left that has both a meter and dual rates. I don't want a computer radio, have no need for one.

Next item....I have a need for smaller servos (mini) for a plane, but need at least 50 or so torgue. Futaba doesn't seem to make one like that (reasonable). The servo I need turns out to be a Hobbico CS-35, right size, right price and right torgue. Is the Hobbico servo a good one, is it made by Futaba with a Hobbico name...or what.? Tower has the same thing, called a TS-35, same price, but you get less arms with it. Why doesn't Futaba make a reasonable mini with the higher torgue.? I don't like the "universal" connectors, as they can be plugged in backward, doesn't hurt, but have to watch the color coding, etc.

If I am having these arm problems, surely others must be also. I didn't want to post this in an open forum, but the phone call to tech didn't solve my problem, and my emails have been unanswered.

BO

The splined output shafts on modern servos have an odd number of splines. By fitting the output wheel in various positions when the servo's centered by the transmitter, you can get the alignment of the arms just where you want it. Usually, you'll find the arm just off by a small amount. Rotating it 180 degrees usually helps. On a six-pointed arm, just try each of the arms until you get the one that lines up.

Generally, even on the 2-pointed arm, one postion will be centered when the servo's centered with the transmitter control and trim centered.

You can check all the available specs of Futaba servos at:

http://www.futaba-rc.com/servos/index.html

You should be able to find one that suits your need.

Hobbico servos are made by major players, that's all that can be said.

(edit to fix typos)

As I understand it Futaba servo's have an odd number of splines, 13 I think. Hi-tec's and other have an even number of splines 12?? The multi legged arm you can get to centre but not the 2 pointed arm, it will always be out by 1 spline. This is how it was explained to me by one of our field wrinklies.

With the odd number of splines, you can always get a servo arm centered, no matter how many points it has. If it's off, turn it 180 degrees. People with older transmitters may have the centering off a bit, as the circuits and pots in the transmitter and servos age. Those transmitters may need to have the pot centering recalibrated.

Seems I'm not the only one with this "problem". A couple of my friends just got new Futabas and couldn't get the arms centered. I showed them how to do it. I would think this should be explained in the manual. If there wasn't a problem with the 12 spline, then why did Futaba go to a 13 spline?

I went to the Futaba servos page as you suggested. The only one that fits my needs is the S3002, you show it as 53 oz torgue, in Tower catalog they show only 36 oz. In their Tower Talk, they show 53oz, but the check list says it is not suitable for airplanes ???..Anyway, no way can I afford $50 for a servo, as I need 5 of them. It's getting to be a rich man's hobby.

Well, I don't want to beat a dead horse. But it seems that instead of solving problems for us fliers, Futaba is just creating new ones. As I said, I like my 6yg, and the rx is ok, fortunately the Airtronics servos are now compatible.

Thank you for your prompt reply, no further assistance is needed.

BO

The servo specs on the Web site are correct. Tower's info may be off a bit in the catalog. In the past two years, a lot of the servo specs got revised as better testing methods came available. All of the servos got retested with better equipment to determine output torque.