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Re: [PSUBS-MAILIST] Nav systems
Hi Alan,
the nav system should handle this case.
The accelerometers will detect that submarine has not accelerated
and maintain that the model state is unchanged (i.e. the sub is
stationary). The system model will understand that the water
speed sensor is not an indication of absolute (or geospatial)
speed. However, if you increase thrust, the IMU will detect
acceleration and the speed sensor will indicate an increase in
relative water speed, these inputs in to the system should
result in accurately updating the model state with the appropriate
movement.
Cheers,
Ian.
-----Original Message-----
>From: Alan James <alanjames@xtra.co.nz>
>Sent: Jun 25, 2010 6:02 PM
>To: personal_submersibles@psubs.org
>Subject: Re: [PSUBS-MAILIST] Nav systems
>
>Sounds great Ian,
>How does it deal with water current?
>i.e.. If you are doing 3 knots into a 3 knot current you are
>going nowhere, but data would tell you you are doing 3 knots.
>Alan
>
>----- Original Message -----
>From: "irox" <irox@ix.netcom.com>
>To: <personal_submersibles@psubs.org>
>Sent: Saturday, June 26, 2010 7:56 AM
>Subject: [PSUBS-MAILIST] Nav systems
>
>
>>
>> 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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