Re: [Paparazzi-devel] motor current calculation ?

[Reto Büttner]

Hi Chris,

as you mention correctely the current is very non-linear in respect to
the throttle. In paparazzi this is simpified and approximated using a
linear function. The energy estimate works pretty well if it is tuned
to a certain working point and you have similar flight patterns.

If you need a more precise current estimate that works on various
working points I recommend to use a superellipse instead of a linear
function. See: http://en.wikipedia.org/wiki/Superellipse

I cannot give you code for this, as I have not implemented it yet myself.

Good luck,
Reto

2010/10/26 Chris <address@hidden>:
> Hi.
> I was watching my plane's current draw at various throttle levels  and it
> looks like the calculation is a bit off.
> When the throttle is at 50% the current draw is ~25% of the:
> <define name="MILLIAMP_AT_FULL_THROTTLE" value="40000"/>
> It is logical since at 50% rpm the propeller only produces 25% of it's full
> rpm power.
> Here is what i used instead in main_fbw.c file (broken down for clarity):
> #if ((! defined ADC_CHANNEL_CURRENT) && defined MILLIAMP_AT_FULL_THROTTLE)
> #ifdef COMMAND_THROTTLE
>    float percent_throttle =
> (float)commands[COMMAND_THROTTLE]/(float)MAX_PPRZ;
>    percent_throttle *= percent_throttle;
>    fbw_current_milliamp = Min((percent_throttle *
> (float)MILLIAMP_AT_FULL_THROTTLE), 65000);
> //    fbw_current_milliamp = Min(((float)commands[COMMAND_THROTTLE]) *
> ((float)MILLIAMP_AT_FULL_THROTTLE) / ((float)MAX_PPRZ), 65000);
> #endif
> #   endif
>
> Is this correct or i am doing something wrong?
>
>
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