[PSUBS-MAILIST] Nav systems

[irox <irox@ix.netcom.com>]

Hi,

I've been working a navigation system for a submarine for some
time.  This stems from a conversation I had a with Jay at the
Maine psubs convention.  The main aim of the nav system is to
(accurately - for certain values of "accurate"...) determine the
position of the submarine when it is submerged.

My system currently consists of 6 degrees of freedom (6DOF)
inertia measurement unit (IMU), which gathers data from: 3
magnometers (providing a 3d compass); 2 gyros for pitch and
roll; and 3 accelerometers providing movement in 3d space.
Plus a fiber optic gyro (FOG) which augments the compass
bearing with a super accurate (greater than 0.01 degree
resolution) heading which isn't effected by magnetic field.
This is hooked up to a laptop which processes the data from
the IMU and FOG, and provides a 3D display.  Not including
the laptop I have around $1200 invested in this project so
far.

I was hoping to have a first version working system by the
convention, but I've not had much time to work on it recently.
The outline components/software are there, but it's prone to
drift off in some direction or other and rapidly loose
accuracy.  Each iteration of the project is more accurate
than the last, but it is far from providing useful position data.
It should how ever be able to provide accurate heading data
as well as pitch and roll.

I am currently trying to decide if it's worth bring this to
the convention.  I can demonstrate the principles behind it
on land - it might be useful to put it in a sub and gather
some data to used later for developing and testing of the
software behind it.  But we would need to accurately know
the movements of the sub so we could correlate the results
of the processed data with the physical position changes
of the sub.  The main reason for not bring it is to avoid
the hassle of taking it on a plane and dealing with airport
security.

This project has a large potential scope.  Once I get the existing
set up working to some degree, it can be farther augmented
with a second IMU, then with more environment data, for
example: a pressure sensor supplying depth information; a
water speed sensor providing relative water speed of the
subl; motor power input sensor and rudder angle sensor
allowing the system to estimate the future position based
on what the operator is doing to the controls.  Add a
GPS or DGSP to provide accurate surface state and position,
so that nav system is initialized with good data.

There are many other projects which can spawn from this, one
am interested in doing next is combining an active sonar
system with the positioning system to provide on the fly
mapping capability.

I plan to release the software as open source so anybody
can use it.  Although I imagine each submarine to use it
would require a fair amount of changes/customization to
the software.

Let me know what you think.  Also I am interested to hear
about what other people are planning/doing for nav/positioning 
systems.

Cheers!
 Ian.





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