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Question on 9C's actual trim range

Old 11-05-2007, 07:09 PM
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NormS
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Default Question on 9C's actual trim range

This question is specific to the 9C Super, but the answer may be generally applicable to all Futaba transmitters. The question concerns the actual size of the trim range. The reason I would like to know is so that I can trim something out while flying, and then look up (in the trim menu) the amount of trim I used and figure out exactly what number to use as a percentage or an offset in a pmix to get the same amount of control throw. Yes, I know I can measure it, but this would be easier and more accurate.

In the 9C, I think the entries in the sub-trim and trim menus can be anywhere from -120 to +120, but these are just numbers with no reference I’ve been able to find to the actual trim range. It makes a lot of sense to me that the actual trim range would be a small percentage of the maximum servo throw as defined in the endpoint menu, but that may not be the way it works.

I’m not sure if I’m being clear, so to make it easier I’ll ask some specific questions. These numbers are just made up, but let’s say my elevator endpoints are adjusted to +120 up and -80 down and I’ve got -20 set for the elevator in the subtrim menu. If I set the elevator trim to +100 up, can you tell me what percentage of the maximum up elevator I’ve actually trimmed in? How about if I set the trim to -50 down?

Thanks a lot.
Norm S
Old 11-06-2007, 02:21 AM
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electricpete
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Default RE: Question on 9C's actual trim range

Does the same happen with the trim

Peter
Old 11-06-2007, 05:18 PM
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Bax
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Default RE: Question on 9C's actual trim range

If you look up a channel's position in the servo position screen, increments of trim are not a percentage of total travel, but just small increments of movement. Trim moves the entire throw in one direction or the other...i.e.: it adjusts the center, and the endpoints move with it. Sub-trim is in smaller increments than trim, but they are not a fixed percentage either. They will vary a bit from system-to-system, depending upon the calibration of the stick pots.

You can't look at the amount of trim deflection and then use it to determine the exact amount of sub-trim. On one of our transmitters, about 40 points of sub-trim equals about 7 points of trim. You don't want to use sub-trim to take out trim. You measure the amount of control deflection, center the trim and sub-trim, and then adjust the control surface as closely as possible mechanically, by adjusting the control linkage. Only then do you adjust sub-trim for the few fine points to get the control surface exactly right.

If you need a bunch of trim, then you'll need TONS of sub-trim to center the trim. If you add a lot of sub-trim, this can have adverse effects upon the throws, and you'll find that your endpoints have moved. It's best to adjust things so that trim and sub-trim are as close to zero as possible. Adjust control linkages first, and set sub-trim once the mechanics are as close as can be done.
Old 11-11-2007, 05:52 PM
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NormS
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Default RE: Question on 9C's actual trim range

Great.
I guess I knew this wouldn't be easy.
Thanks a lot.
-norm s

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