[Dprglist] BNO085 and vibration

[Chris N]

It looks like I missed a great meeting this week!  I watched the recording
of course.

On the topic of how vibration (in my case induced by my spinning lidar),
impacts BNO085 measurements:   it's bad!

Without the lidar spinning, the yaw drifted only by 0.3 degrees over the
course of one hour.
With the lidar spinning, the yaw drifted by >1 degree every 30 seconds!

The robot was stationary in this test.

The BNO085 operating / reporting mode I'm using is called "Game Rotation
vectors".  I'm not 100% sure what degree of sensor fusion - if any - is
taking place in that mode, because this mode is optimized for quick
response as I understand it.

I should probably  also try some of the other reporting modes that the
BNO085 has.

I'm also wondering if I can address this via my own filtering.  I'm already
post-processing the yaw output from the BNO085, because it is
consistently off by about 2 degrees for every 360 degrees worth of
rotation.

So what I'm doing to compensate for this strange
2-degrees-per-every-360 error, is the following:   I look at the delta
between the reported yaw from t(now) and the yaw from t(now-1),  multiply
that with a constant to compensate for error issue, and then I integrate
the new delta over time to produce my own yaw output.

What I was thinking of trying is to simply throw out very small delta
measurements, since they are likely to be due to vibration rather than
actual robot rotation.    Of course I would be throwing away information
and hence accuracy.    My guess is what I'll find is that this is too
simplistic of an approach and I end up with an error in yaw over time
because I'm throwing out too many small measurements.

Last week I talked about using foam etc to dampen the vibration.  The other
solution that I read about online was to eliminate the source of the
vibration - which most often is an imbalance with these spinning lidars.
Somebody managed - with a lot of trial and error apparently - to find the
right spot and the right weight to attach to the rotating part of the
lidar, and the vibration was mostly eliminated.

Chris
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