Field setup

• Using ArduIMU: Place level on the ground, power on, and don't touch until the IMU LEDs stop flashing, showing that calibration is finished. Now wait for the blue GPS lock LED.

• Using XY and Z thermopiles: Just wait for the blue GPS lock LED. IR calibration happens automatically.

• Using just XY thermopiles: In addition to waiting for GPS lock, if you don't have a Z sensor you need to perform a field sensor calibration. This is required with every flight because weather conditions can change quickly and the IR sensors looks for the temperature differential between the sky and ground--this calibration routine sets the IR Min/Max values for each axis. Once the calibration is performed, it is saved to memory in case the aircraft reboots in mid-air. Calibration can be performed anytime the plane is on the ground. Just rotate the plane so each lens of the IR sensor points directly at the sky and ground for a few seconds.

(Note: if you're using Xbees for telemetry, make sure the signal line is not connected until everything else is powered up. If you power up ArduPilot with the Xbee signal line connected, you'll probably corrupt the firmware and you'll have to reloaded using the process described in the bottom of this section.)

Troubleshooting

If you find the plane flies untrimmed due to a mis-mounted IR sensor, you can compensate using these definitions in the header file:

#define PITCH_TRIM 0 //(Degrees +- 5) allows you to offset bad IR placement #define ROLL_TRIM 0 // (Degrees +- 5) allows you to offset bad IR placement

Technical details

Sensor calibration: This tells Ardupilot the temperature difference between the sky and the ground. This value is used to scale the input and generate two angles - pitch and roll. WIthout the scale, what seems like a 30° roll on a hot day could appear to be a 10° roll on a cold day.

GPS lock: Here's what ArduPilot does during startup:

1. Power on
2. Begin looking for a GPS fix - Flash the blue LED until a fix
3. Set the Blue LED to solid to indicate a GPS fix
4. Save home location and flight settings to memory