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is digital "tune up" needed?

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Old 12-09-2004, 04:59 PM
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lownslo
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Default is digital "tune up" needed?

I am new to the digital servos. I am putting an ARF together for a club member and he bought a Hitec MG digital servo for the rudder. He has a supplied me with a PPM Hitec RX. Is there some kind of "tuning" that has to be done to the digial servo" ? No matter where I rotate the splines of the duel servo arm, (I tried 4), the arm will not line up perpendicular to the length of the case. I have to slide the trim tab on the TX about 2/3 of it's travel to get the arm 90 degrees to the case. This servo is for a pull-pull rudder system so I really need this thing to be at 90 degrees to the case. Any thoughts?? ....... thanks......lownslo
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Old 12-09-2004, 05:50 PM
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Default RE: is digital "tune up" needed?

It is not necessary to do anything for digital servo to work; they work straight out of the box. However, Hitec digitals can be programmed for centre position so far as I know. Certainly the Multiplex ones can be and they use the same technology. Since the splines are always an odd number, have you tried just turning the arm through 180 degrees to sse if it lines up that way?
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Old 12-09-2004, 07:29 PM
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Default RE: is digital "tune up" needed?

Thanks John, I have tried turning it 180 degrees and it lines up the same. Like I mentioned...... I also had some extras and I tried a total of 4 and they all come out the same. (all tried at180 degrees too). I am a pack rat and I save all my servo arms in the packages. In building other planes I have run into the same thing with HS425BB regular servos too. I just dig into my drawer of extra arms and start putting them on. I would say that 1 in 4 or 5 will line up perfect. Here again....... I am going to assume that the servo is not centered, and the one arm out of 4 or 5 that lined up was probably itself not manufactured correcly. This is not a "one time thing". I have done this procedure at least 4 or 5 times. I wrote a post explaining this once and no one understood what I was saying...(or didn't believe me)You mentioned "programmed" and I assume this takes some special equipment. A friend of mine told me something that digitals needed... and maybe that was it. He was not sure either. Thanks....lownslo
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Old 12-09-2004, 09:45 PM
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Default RE: is digital "tune up" needed?

Hitec Digitals can be programmed by the end user for center with the Hitec HFP-10 programmer. Its not required unless you desire to not use trim or sub-trim to center the servo. That said the centering problem generally lies within the TX, but not always.

1500 micro-seconds pulse-width is considered the neutral zone for most servos. In order for the servo to center at the 1500us, its has to receive a signal as such. Herein lies the problem, virtually every TX you get your hands does not transmit exactly at 1500us, so we generally use sub-trim or trim to solve the problem.

The beauty of the Hitec digital is you can program the servo to center on the pulse-width of the specific TX in use. Lets say your TX transmits 1508us for neutral, you simply program the servo to position the arm at center for this pulse-width and arm configuration...
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Old 12-10-2004, 05:24 AM
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Default RE: is digital "tune up" needed?

Thanks to all for the info. It is what I needed.............. lownslo.
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