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Servo centering

Old 03-08-2020, 06:27 PM
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Tequesta
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Default Servo centering

Is there a tool or way to change the center point of a servo. I have some servos that will not center at a true 90 deg. Any help will be must appreciated.

thanks

John
Old 03-08-2020, 08:24 PM
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Depends....
Hitec used to sell (and maybe still does) a servo programmer for use on many of their servos that allowed you to "tune" them for that. Most other brands do not have such a tool.
I'd guess that 99.9% use the "subtrim" function on their radios to do the same thing. But, if it requires a lot of correction, using that depends on the brand. Some have their programming such that large amounts of subtrim will result in "dead" spots at the extremes of stick travel. But other makes don't have that flaw.
Some radios allow you to adjust the center and the high/low maximum points of servo movement, which is ideal. Some make it a combination of subtrim and end point adjustments.
Inexpensive systems may not have any of the above.

In the olden days, we used to take them apart, and adjust the "pots" inside to do the same. Not possible with modern day servos.

Part of the issue is that there is no hard standard for what is "center". One manufacturer may make their TX/receivers/servos center at 1500uS, and another at 1520uS. Or even 1480uS. Fine within their own brand, but plays havoc when mixing brands. And the aftermarket companies will pick whatever compatibility they decide is best. That noted, generally most have settled into using the 1500uS number....but not all.

Tell us what servos (brand and model) and what Radio transmitter you are using, and you will likely get much better "how to" answers.
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Old 03-09-2020, 04:03 AM
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Sometimes (maybe often) the "failure" to center at 90 is just the servo wheel on the wrong arm. Most servo arms are an odd number of teeth (25) and only one arm will be centered. If you already knew this I apologize.
Old 03-09-2020, 04:28 AM
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It's called Sub-Trim

Get it mechanically as close as you can then dial up some sub-trim
Old 03-09-2020, 04:18 PM
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Tequesta
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Thanks for all your replies. I do know about sub trim, but I was going to use my DX5 radio and it is not a computer radio. I do have a Hitec Optic 6 but I can't find feather light receivers like the Lemon RX DSMX.
Old 03-16-2020, 06:11 AM
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Originally Posted by Tequesta View Post
Thanks for all your replies. I do know about sub trim, but I was going to use my DX5 radio and it is not a computer radio. I do have a Hitec Optic 6 but I can't find feather light receivers like the Lemon RX DSMX.
The receiver doesn't matter. It's what the transmitter is sending, and what the servo translates that to be.
I just had a new bargain basement $6 servo I had to replace for other reasons. To get it to center, I had to change the output of the radio to center at 1598uS (!) Which is really, really far off. Changed to a Hitec, and it was spot on at 1500uS, which is the most common timing for centering. Get a Hitec or Spektrum servo, and you should be good.
Old 03-17-2020, 10:41 AM
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DGrant
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If you can't use sub-trim, or the radio isn't equipped with it, then either reprogramming the servo is in order(not likely if you're not equipped for it), or try different control horns. Not all control horns are clocked the same. The spline teeth can and are slightly different from brand to brand, and many times the splines are different in identical arms, which will put the arms a degree or a few degrees different from each other.

Another thing to try is flip the arms 180degrees on the output shaft. On a 25t spline arm, putting the arm on 180degrees either way makes a difference too(because of uneven tooth count).

Many servos can all be different. Much of it depends on assembly, and where/how the gears are placed, and it could even boil down to idler/intermediate gears being off one tooth. Much of it is usually adjusted or compensated in ways I described above. We're not flying space shuttles, so it's not a big deal, but we do want everything as good as we can get it. Good luck with it.
Old 03-17-2020, 05:25 PM
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Tequesta
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Thanks for the insight never tried different horns. I got all kinds.
Old 03-18-2020, 02:20 PM
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Many of the multi arm servo horns have numbers on the root. This number is how many degrees off center that particular arm is. Find the one that works, cut off the rest and go.

David
Old 03-18-2020, 04:57 PM
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Tequesta
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I did know that Dave thanks

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