Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor

[Gareth Roberts]

Hi Tilman,

It's the same sensor as the ardupilot classic - it's not great.
http://cache.freescale.com/files/sensors/doc/data_sheet/MPXV7002.pdf?pspll=1

The ardupilot classic code is less nasty to read usually.

From  
http://code.google.com/p/ardupilot/source/browse/ArduPilot_2_8/sensors.pde

// in M/S * 100
void read_airspeed(void)
{
        #if GCS_PROTOCOL != 3
        airpressure_raw = ((float)analogRead(AIRSPEED_PIN) * .10) +  
(airpressure_raw * .90);
        airpressure     = (int)airpressure_raw - airpressure_offset;
        airpressure     = max(airpressure, 0);
        airspeed                = sqrt((float)airpressure /  
AIRSPEED_RATIO) * 100;
        #endif


        airspeed_error = airspeed_cruise - airspeed;
}

#define AIRSPEED_RATIO 0.1254   // If your airspeed is under-reporting,  
increase this value to something like .2

Cheers,
Gareth


On Mon, 02 Jul 2012 12:39:38 +0100, Tilman Baumann <address@hidden>  
wrote:

> I just got a Ardupilot Airspeed sensor from DIYDrones.
> (Eagletree was b it too expensive)
> http://code.google.com/p/ardupilot-mega/wiki/Airspeed
>
> The way Ardupilot calculates the airspeed seems similar, but not quite  
> the same.
> https://code.google.com/searchframe#iTqA9ErfVSM/ArduPilotMega/trunk/sensors.pde
>
> I have not fully grokked it yet how to derive AIRSPEED_QUADRATIC_SCALE  
> and AIRSPEED_BIAS from that.
> They seem to be using AIRSPEED_RATIO 0.1254 for this sensor.
>
> But since this is such a default sensor, I was thinking chances might be  
> good that someone has already done that?
>
> Thanks
>   Tilman
>
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