Yaw Rate Sensor Drift?

[EricS-Team180]

Hi,
Last year we used an Analog devices adxrs150abgnd yaw rate sensor. It had 2 purposes:
1) use it to detect undesirable yaw rate and trim it out
2) integrate the yaw rate to give us a "poor man's electric compass"

Hooking it up as a 10 bit analog input gives you a 0-1024 range. So the theoretical neutral point is 512, 0 and 1024 represented +/- 150deg/sec...which is really not that fast of a turn rate. Anyway, in practice we found out that the neutral point was typically biased somewhere away from 512 and that the input "dithered" about neutral. What we did to compensate was:
1) during comp mode ( the time between power up and autonomous), we simply averaged the input with the previous, which allowed us to determine whatever the neutral point would be for that particular time of day, temperature, phase of moon ...etc
2) we set up a deadband (we settled on +/-11) about the neutral point. Anytime we read a value inside the deadband, we stored it as 0.

This worked great as a yaw trimmer, and OK as a "compass" - really a yaw position calculator - not a North/South direction finder.

Since we could not mount the sensor on the c/g, we had an inherrent error. I also speculate that mounting it in the chassis pan close to wiring, speed controllers, and motors may have been adding electrical interference - but I have no proof. In the end we moved the sensor away from the electronics - as much as possible and tucked it in as close to the c/g as we could. With trig of 2 decimal place accuracy, we averaged about 1.7deg of error over 360deg of rotation....something we'll definitely improve on. To compensate for that error, we added an additional operator reset switch. The driver could always re-align our 'bot with the up-field direction as re-zero the compass.

Hope that helps
Eric

PS we are also experimenting with an x/y accelerometer, which shows similar behaviors