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Unread 29-10-2014, 13:20
AustinSchuh AustinSchuh is offline
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Re: Best gyro for frc.

Quote:
Originally Posted by compwiztobe View Post
Austin,

Do you expect any differences between integrating on your co-processor and integrating with the accumulator in the FPGA, in particular with integral error and drift? What was the SPI bus clock speed/integral dt on your co-processor? Do you happen to know the SPI frequency on the roboRIO? (I think I saw 4MHz in a myRIO document...)

Thanks,
Aren
Aren,

We integrated in software on our co-processor. Since the gyro is SPI, I'd recommend just doing the integration yourself in software on the roboRIO in a RT thread running at high priority. That's what we'll be doing. I like being able to audit the code, especially for something like a gyro where I've seen horrible bugs in the past. We got 2 ish degrees of error over 2 minutes with the ADXRS453.

I checked our uC code, and it looks like we read the gyro at 200 hz, and ran the bus at 7.5 MHz. 200 hz is above the gyro's bandwidth, which is good.

The roboRIO's maximum SPI clock rate is 500 KHz (as reported by WPILib's documentation.) The datasheet for the gyro lists the maximum clock rate to be 8 MHz, but doesn't list a minimum. This should be fine.

seg9585: This is a SPI gyro (digital). The ADC is inside the gyro chip, and seems to be very accurate from what I've seen.

Austin