Mixer Subtrim Not Available

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Which board (stock / gruvin9x / sky9x / Taranis) are you using?

Taranis

What is your openTx FW version?

2834

What is your openTx EEPROM version?

215

What steps will reproduce the problem?

1. When using Mixer menu’s Edit Mix feature, there is no Subtrim parameter.

2. Mixer’s Weight% and Offset% can be used to adjust the outputs, but the way 
Offset% is applied mathematically, the output is not as straight forward.  
Offset% is always added to the input before Weight% is applied to the result.  

What is the expected output? What do you see instead?

1. As an example of using only Weight% and Offset%, if you wanted to channel 
output range between +50% and +80%, with typical input range of -100% to +100%. 
 The solution requires either “trial and error” method or simultaneously 
solving two equations with two unknown variables.  If Subtrim was available, 
the solution would be much easier, as the Weight% would be applied to the input 
and the Subtrim later added to the result.

2. A Mixer Subtrim parameter would greatly simplify adjusting linear outputs 
without resorting having add more complexity by using of linear curves with a 
mix.

Original issue reported on code.google.com by barry.m....@gmail.com on 18 Dec 2013 at 7:15

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You can simply do it with 2 mixer lines, one with 15% input, the second with 
65% MAX. 

Original comment by bernet.a...@gmail.com on 19 Dec 2013 at 10:11

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Good point.  Your suggested second line would be equivalent to a Subtrim since 
it is added (multipx: Add) to the first line.

However your solution adds complexity and is not intuitive to the user. Using 
the  curve option in the Edit Mix menu is more obvious and only requires one 
line on the mixer.

The best solution would be to add a Subtrim parameter to the Edit Mix menu.

Original comment by barry.m....@gmail.com on 19 Dec 2013 at 8:19

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The problem is that adding a parameter is too wasteful of resources on the 9x, 
and doing it only on Taranis would break intercompatibility, we really want to 
avoid that in core places like the mixer.
We'd rather prefer to change the current Offset's function to being an end 
offset instead of an input offset (something that nobody never understood why 
it was done that way loong ago even before er9x...). But then it needs to be 
done without breaking existing models.
So as a 2nd mixer line is possible and quite intuitive, and actually clearer in 
common cases where the subtrim needs to change depending on flight mode it was 
though we'd leave it as is for now. 

Original comment by bernet.a...@gmail.com on 22 Dec 2013 at 5:33

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For input range -100% to +100%, I've worked out the mathematics of setting up a 
range of outputs based on Wt% and Offset% using only one line mixer.  So, by 
varying these parameters, one can set a output with the desired range%.

Problem is the Offset% parameter is limited to plus or minus 500%.  As an 
example, for a range% of between +35% and +50%, a Weight of 8% and Offset of 
567% is required.  See attached MS Excel spreadsheet.

It might be better if this Offset% parameter could be expanded beyond the 500% 
limit to cover more possible options.

Original comment by barry.m....@gmail.com on 22 Dec 2013 at 6:33

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Using such high numbers is just silly and obscure... imagine reworking that at 
the field. 
The way to do it for now is really to use a second mixer line with MAX.

And I actually forgot, but next on github already has the offset parameter 
reworked to act as an end offset so it will be sorted in the next major 
release. 

Original comment by bernet.a...@gmail.com on 4 Jan 2014 at 6:26

• Changed state: Fixed