[Dprglist] BNO085 and vibration

[David P. Anderson]

Chris,

Are you sure that the yaw error is being caused by the vibration of the 
lidar?  Rather than the magnetic effects of the spinning motor and 
electronics?   I've seen normal servos alter the yaw when driven back 
and forth if they are too close to the IMU.

David


On 7/22/21 9:20 PM, Chris N via DPRGlist wro
> 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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