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Unread 22-01-2011, 23:54
Michael Simmond Michael Simmond is offline
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Join Date: Jan 2011
Location: Bozeman, Montana
Posts: 13
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Re: COTS gyros for 2011

I agree that designing around an obsolete chip on an obsolete PCB is not very good engineering.

We purchased two models of gyro from SparkFun: ADXRS613 and LISY530AL.

The ADXR output is ratiometric to the supply voltage, so you could carefully read the supply voltage on a second analog input to improve accuracy. It also has a temperature output that can be useful as a linear correction for thermal drift of the signal zero. These two features add more complication, but they reduce drift sources. It makes for an elegant solution.

The LISY uses 3.3V power, so you will need a regulator. It gives an absolute voltage output (not ratiometric to the supply).

As far as I can tell, the cRIO analog inputs are fixed at 0-10V, so for best voltage resolution you should consider using a rail-to-rail output OpAmp running from 12V to add some additional gain to either gyro.

There was some concern voiced about having at least 300 deg/sec range. But in testing the ADXR (with 150 deg/sec range) we found that nothing bad happend when we saturated the output with rapid rotation. We just straighened the robot out with the joystick and kept on truckin.

We need the gyro feedback signal to reduce unwanted rotation when trying to drive straight. Otherwise the holonomic wheel tends to make the frame orientation wander substantially.

We have not even tried the LISY yet: The ADXR is doing everything we need.
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