martinjaymckee
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- Mar 14, 2015
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So, I have a question to anyone who has taken a close look at the data from the gyroscopes on the QMI8658 on these boards. With my current setup, I'm getting spikes in the readings from time to time. They are not correlated with spikes in the accelerometer, so I don't think they are real. Also, they are only showing up on the X and Z axes - the Y axis is beautifully clean. Currently, I have the chip configured to read with a full-scale of 2048 degrees per second (~35.7 radians per second) and and output data rate of 470 Hz.
To take these readings, the board is fixed in an orientation (one is vertical, the other on one side) and 10000 readings are taken at the maximum rate that I can while storing all the data directly to a file (roughly 100Hz). As such, the data covers about a minute and a half. In both orientations the X and Z axes show the spikes while the Y axis does not. The temperature reading, and accelerometer readings are exactly what I would expect while the gyroscope readings would be were it not for the spikes.
I'm not actually sure that they will cause me any issue, it's mostly just interesting. If they are an issue, I can also test out increasing the data rate and enabling the low-pass filter on the chip.
On the plots, the y-axis scale is radians per second and the x-axis is in seconds. As can be seen in this dataset with the board vertical, the gyro X and Z channels show small spikes (certainly not saturating) with some frequency, but not often enough that it significantly impacts the reading if it's being filtered.

By turning the board on its side, the Gyro X Axis does seem to change. The spikes are no longer bidirectional, and seem to be less frequent. Both the Y and Z axes are very similar however.
This isn't great for using the gyros to track the rocket's orientation, but it's rare enough that I don't expect it to be a huge problem.
Anyone else seeing this?
To take these readings, the board is fixed in an orientation (one is vertical, the other on one side) and 10000 readings are taken at the maximum rate that I can while storing all the data directly to a file (roughly 100Hz). As such, the data covers about a minute and a half. In both orientations the X and Z axes show the spikes while the Y axis does not. The temperature reading, and accelerometer readings are exactly what I would expect while the gyroscope readings would be were it not for the spikes.
I'm not actually sure that they will cause me any issue, it's mostly just interesting. If they are an issue, I can also test out increasing the data rate and enabling the low-pass filter on the chip.

On the plots, the y-axis scale is radians per second and the x-axis is in seconds. As can be seen in this dataset with the board vertical, the gyro X and Z channels show small spikes (certainly not saturating) with some frequency, but not often enough that it significantly impacts the reading if it's being filtered.

By turning the board on its side, the Gyro X Axis does seem to change. The spikes are no longer bidirectional, and seem to be less frequent. Both the Y and Z axes are very similar however.
This isn't great for using the gyros to track the rocket's orientation, but it's rare enough that I don't expect it to be a huge problem.
Anyone else seeing this?