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# Setting Spoilers/Speedbrakes via Offset 0BD0

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Hi all,

I'm working with Jason Fayre on the Talking Flight Monitor project, the accessibility add-on for FSX and Prepar3d. One of our users asked for the ability to set spoilers/speedbrakes to an arbitrary percentage; in the sim, the keyboard command (slash key by default) either sets them to full or off, with no way to fine-tune their extension. The notes for the offset (0BD0) say that a value of 4800 is armed, but that 5620 is the minimum you can set that actually causes extension. 5620 is 7% extended, and 16383 is 100%. I'm fairly good at math, but I'm confused by the snippet that says: "The percentage extension is the proportion of the distance in the range 4800 to 16383..." I can't figure out, for the life of me, a good formula that can be used to convert an arbitrary percentage value into the value to write to the offset. I consider myself a decent coder, but the way FSUIPC and SimConnect represent things can sure make for some difficult calculations. :) Any help would be greatly appreciated.

Thanks,

Tyler

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3 hours ago, TRodick said:

I can't figure out, for the life of me, a good formula that can be used to convert an arbitrary percentage value into the value to write to the offset.

As it says, 5620 is 7% and 16383 is 100% (well, on the ground -- bear in mind that in flight the maximum the spoiler really goes to is about 70 or 80% (don't remember which). In the latter case it is known as "speedbrake" rather than "spoiler").

So, if you want x% then if x < 7, don't bother.

Otherwise, consider 93% is spread over (16383 - 5620) points in this scale.  So 1% = 10763 / 93 = 115.73, near enough.

So for x% where x >7, you'd use 5620 + ((x - 7) * 115.73), rounded down to an integer.

3 hours ago, TRodick said:

I consider myself a decent coder, but the way FSUIPC and SimConnect represent things can sure make for some difficult calculations. 🙂

It's really neither FSUIPC nor SimConnect, just the way that axis works internally.

Note that this is not the same in MSFS.

Pete

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You said round down to an integer. Are you saying follow the standard math rounding rules, or a simple truncation?

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9 hours ago, TRodick said:

You said round down to an integer. Are you saying follow the standard math rounding rules, or a simple truncation?

Sorry it wasn't clear. "Rounding down" is the same as truncation if you mean just discarding the fractional part.

Pete

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