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Re: [PSUBS-MAILIST] Once again
Specs of the Microstrain unit are here:
http://www.microstrain.com/3dm-gx1_specs.aspx
It has 3 angular rate gyros, 3 accelerometers and 3 magnetometers. I
have used its predecessor, the 3DM-G, which was a good little unit but
couldn't keep up with the high frequency dynamic accelerations I needed
to measure, so I ended up using a servo accelerometer instead. This
isn't really an issue for sub navigation, so perhaps the 3DM-GX1 would
work? I've seen the math, and you're right - it's messy, but not
insurmountable. The major stumbling block is dealing with the integrated
error, which leads to the question: how good is good enough, given that
we can externally measure rate of change of depth and so have a
correction input in the gravity vector direction?
-Sean
Jay K. Jeffries wrote:
Sorry that I haven't responded sooner as we have had a power outage
for most of the day on the facility where I reside.
Not familiar with the Microstrain 3DM-GX1. It appears that it is a
3-degree of freedom unit and for proper navigation 6-degrees of
freedom are required…3 gyros (with low drift) and 3 accelerometers.
You can review the /IMU 6-DOF v2/ unit at www.sparkfun.com
<http://www.sparkfun.com/> that I briefly glanced over. They do not
provide drift information and this is critical for determining the
accuracy of your dead-reckoning. If the drift of this unit isn’t bad,
it still has to be integrated into a nav package and the mathematics
aren’t inconsequential…major matrix manipulation.
I believe that there are sonar units that will provide SOG information
but haven’t looked into the matter for some time.
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
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