Subtrim

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plasticbaldy
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Subtrim

Post by plasticbaldy » Thu Feb 12, 2015 5:42 am

Is subtrim the function where I can move the servo center to compensate for a servo horn not positioning at 90 degrees to the servo ? Is it achieved with 'Offset' in the mix ? If so then what about when I have the Elevon/Delta Template set ?
So I have ;
Ch 2
100 ELE
+- 100 AIL
I edited the ELE with Offset -14 but I'm not sure that the travels with Ele and Ail match the other Elevon servo.
Should I use another ER9x function to change the center position of this servo ?

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MikeB
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Re: Subtrim

Post by MikeB » Thu Feb 12, 2015 10:02 am

Subtrim is in the Limits menu, the offset there.
The problem you will have is if you set the subtrim to +14.0, then on one side the travel is from +14 to +100, a range of 96, while on the other side it is from +14 to -100, a range of 114.
Up to 10% of sub-trim may be compensated for automatically by setting the "Auto Limits" value in "Model Setup/General".

If you set auto limits to 5.0, then set the sub-trim to 4.0, a negative limit of -100 will adjust to -96 and a positive limit of +100 will adjust to +104. If the sub-trim is set to -7.5, the limits will adjust to -105 and +95, limited to a change of 5 due to the value set in auto limits.

Note that on er9x (and openTx) a limit of 100% corresponds to a limit of 80% on most commercial radios. So, if you need a subtrim value of 14, you could set the one limit to 94 (14 + 80), and the other limit to -66 (14 - 80).

Using the offset in a mix has a resolution of 1 (-100 to +100), while the subtrim has a resolution of 0.1 -100.0 to +100.0.

Mike.
ersky9x/er9x developer
The difficult we do immediately,
The impossible takes a little longer!

plasticbaldy
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Re: Subtrim

Post by plasticbaldy » Thu Feb 12, 2015 11:40 pm

Thanks so much Mike. But my head is spinning. Re; 'Note that on er9x (and openTx) a limit of 100% corresponds to a limit of 80% on most commercial radios' These words tell me that at 100% stick on my ER9x the servo has only moved to the equivalent 80% position on other radios. Is this correct ?
I wish you'd used my 14% requirenent instead of 5, 4 and 7.5 so I can understand better.
Also I still don't know how the servo travel will compare to the other Elevon servo travel with your suggested settings. Aileron travel differences might not be significant but I don't want my model to roll onto it's back when I use elevator.
I see that I can select more than 100% in the setup of mixing. So if I set;
CH2
116ELE
+-116 AIL
then can I set my OFFSET -14 and adjust LIMITS > CH2 to compensate ? Would the linit settings be -116 and +84 with an OFFSET of -14 to achieve matching servo travel to the other Elevon servo ?

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MikeB
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Re: Subtrim

Post by MikeB » Fri Feb 13, 2015 12:01 am

I'm sorry, I typed this wrong. I should have said 80% on er9x (and openTx) is 100% on commercial radios.
So when you have moved the stick 80% on er9x, this is the equivalent of 100% on other radios.
This is why you may well use limits of +/-80%, then move tham out to match any sub-trim you may need.
I was also being lazy, I copied some text from another post for the examples.
14% is quite a lot of sub-trim needed to centre the servo arm. What you might find, if the servo arm is "two-sided" is if you rotate the arm 180 degrees it may centre better.

I suggest therefore you try the limits at +/-80%, then if you need 14% sub-trim do as I said above:
"So, if you need a subtrim value of 14, you could set the one limit to 94 (14 + 80), and the other limit to -66 (14 - 80)."

Don't try to adjust thing in the mixer lines, it will just confuse everything (more!).

Mike.
ersky9x/er9x developer
The difficult we do immediately,
The impossible takes a little longer!

plasticbaldy
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Re: Subtrim

Post by plasticbaldy » Fri Feb 13, 2015 1:38 am

Thanks Mike. I've got it now.

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