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Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor
From: |
Gareth Roberts |
Subject: |
Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor |
Date: |
Mon, 02 Jul 2012 15:56:30 +0100 |
User-agent: |
Opera Mail/12.00 (Linux) |
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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