coupling servo arms

[sportflyer1]

The SU31 from GP uses 4 heavy duty screw lock push rod connectors to couple the servo arms. Do you think this is good enough for 80 inch span plane? I was thinking of replacing them with 4-40 ball links and turnbuckles to couple the servo arms together. What do you guys use? Tks

[Mr. Nobody]

Hi sportflyer1.

I see nobody has answered your quesh, so I thought I would add my two cents;

Have you considered using just one servo? I'm flying the 27% GP Extra and Edge, both with rudders powered by a single Hobbico CS-170 servo. Puts out like 333 oz/in torque @6.0V. More than enough--probably overkill. Other servos would probably work as well.

As far as answering your question directly, this is the same setup (large screw-locks) I used during development of the Extra. It worked fine.

I know you were looking for more objective answers from someone other than a person from the Company to answer your question, but that's the best I can do for you.

[sportflyer1]

Next time I will use a large servo for simplicity. Anyway this time I went for the dubro 4-40 turnbuckles and HD ball link config. It took quite a while to set up the servo throws on both servos to reduce servos fighting each other . The 4 screw locks would have saved some time. I was just worried about the screw locks working lose due to vibrations. Tks

[Tired Old Man]

They do, and they will. That's the big benefit of doing it the way you did. There are other methods, such as using H-9 Pro Links, self adjusting servo trays, and direct coupling similar to what you have done. Matching the servo travels is critical to success. Using an amp meter to measure the current draw at various positions to see precisely how well they are matched is also necessary. One can be pulling qiute an additional load from the other and you won't know about it until a servo fails. With any direct ganging of servos, failure of one pretty much assures failure of the others in the series.

[sportflyer1]

I used an ammeter to check the current draw of one servo while I moved the ganged servos. Otherwise it would be impossible to get reasonable balance. The servos tracked quite well after I got the center and end points dialled in. I could have done a 5 point servo adjustment but I thought that the 3 point is good enough. Servo current draw is definitely quite high when they are fighting each other . Tks