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Mar 25, 2007, 08:39 PM
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10 good sensors


So the magnetometers, gyros, and GPS are all finally sending data to the Gumstix. The LIS3LV02DQ was a real winner.

I2C for the LIS3LV02DQ was a fiasco. It constantly locked up. With no reset mechanism and no way to underclock it, it was just too
unreliable. I2C is good for consumer electronics, but for aerospace, this Dutch disaster is going in the closet.

Using SPI required running it at 5V because the PIC only runs at 5V and buffering would be heavy. So far the LIS3LV02DQ has been running many hours on 5V without problems. It couldn't do 16 bit reads at all. It has significant Y offset in both 3V and 5V and can't run in 2g mode without reconfiguration, but 2g is unlikely to be enough range on a copter.

GPS consumes a sick amount of power and is heavy. Though older than the inertial sensors, we consider GPS the most advanced because it uses spaceships. It's our first direct interaction with a satellite.

TX and RX were reversed on the Gumstix BT-1 serial port. GPS generates 1 reading every second. For relative positioning, GPS is 200ft off when using 3-5 satellites. Altitude is 50m off. Can't measure absolute positioning because google satellite may be off.

SPI implementation for the Micromag3 was surprisingly easy and the Micromag3 is working despite running on 5V and being bent.

Yaw gyro continues to fail high occasionally. May just swap it with the one spare.

Had 1 erased firmware on the PIC. Took it out of the socket for a while and it was erased when it went back in. Possibly PGM got raised when out of the socket.

So the PIC ended up doing all the I/O except GPS. Further development requires compiling all the flight software for an x86_64 test harness,
recording all the sensor data during flights, and simulating it on x86_64, but there is only enough room on the Gumstix for 30 minutes of sensor data and the data rate is too fast to use minidisc recording.

Writing files on the Gumstix locks up periodically. Flight software will be heavily threaded.

Our next test flight is another huge one probably around a month after the last one, to collect 10 sensor data and introduce 12 satellite GPS. We're led to believe the test pilots of the 60's got up and flew every day. In reality it was probably many weeks of preparation between test flights but still much busier than today. They had to win wars back in the old days.
Last edited by Jack Crossfire; Mar 25, 2007 at 11:36 PM.
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Mar 26, 2007, 12:18 AM
Chris Anderson
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