Quote:
Originally Posted by juchong
Figured I'd clear up a couple of responses in this thread.
Incorrect. MEMS devices are manufactured using non-ferrous materials, thus making them immune to strong magnetic fields. A single axis gyro simplifies the mounting on the robot. You only have one axis to worry about! The ADXRS450/453 are "rate gyros" which mean that they are designed to only report back...rate... in one axis!
You probably want the ASXRS453BRGZ version since the sensor will be easier to solder onto a PCB and the measured axis is located through the center of the part. You would solder the sensor down to the PCB just like any other IC. I would recommend purchasing the breakout board, though!
The 450/453 differ from the gyros used on the AndyMark breakout board in that the Analog to Digital conversion is performed within the sensor. This makes them much less susceptible to EMI. In an ideal setting, you would want the accelerometer attached to a rigid portion of your robot, and the gyro would be located as close to the center as possible.
Although the 6-axis and 9-axis sensors are cool, they are not designed for precision navigation applications. Noise levels on those sensors are orders of magnitude greater than what's available on application-specific sensors. I would strongly suggest that teams invest some time looking into the 450/453 if they want to have a solid drive system.
Another caveat of systems such as the nav6 is that they are not calibrated. Each sensor is unique and will provide a slightly different response when used in different applications. In that case, an integrated IMU such as ADI's iSensor product line would be ideal.
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I absolutely agree that there are much higher noise levels on 6/9-axis sensors, and the dedicated yaw-rate gyro like the ADXRS453 is a very good sensor for the field-oriented drive application. The 6/9-axis sensors in the nav6 are consumer-grade (e.g., iPhone, Oculus Rift), rather than the industrial grade of the ADXRS453.
However - please be aware that the nav6 is definitely calibrated, as it features factory-calibration of accel/gyro biases, and also continually re-calibrates the gyro biases during periods of non-motion (accounting for gyro temperature changes). This behavior, implemented in the Invensense digital motion processor (DMP) silicon and the on-board microcontroller, is what enables the yaw error rate of approximately 1 degree/minute. The navX MXP features the 2nd-gen MPU-9250 w/even lower gyro noise levels - so we're seeing this technology continue to improve and mature as the MEMS noise levels decrease, and the implementation of the data fusion and calibration algorithms continue to improve. More info on the gyro/accel calibration is available at:
https://code.google.com/p/navx-mxp/w...celCalibration
The nav6 technology does require about 16 seconds of calibration time before a match, during which the robot must be held still. The navX MXP lessens this period, but this may be a difference between the two approaches worth noting.
The nav6/navX MXP technology is cost-effective and viable for use in a field-oriented drive system. Several teams have been doing this successfully, and enjoying the ease of integration it provides. Sounds like a bake-off between a ADXRS453 and a navX MXP would be helpful to the CD community....