Re: Gyros and Compass Modules

[Greg Teiber <wolfe19@megsinet.net>]

flux gate compass's really operate very well in the presence of STRONG electric fields.  the one on my dad's boat is 2 feet in front of 2 VERY large engines, in fact 2 454's :)  In steel boats they use conventional compasses, but they use compensation weights...  Well not really weights, they are large balls of iorn positioned around the compass to even out the magnetic fields.  As for the motor screwing up the compass's reading, either put the motor in a properly insulated cage/ gauss shield.  OR you can put the motor inside the boat and the compass outside :)  (I think the boat would make a GREAT cage to stop the motor's magnetic field)

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On 8/26/99, at 8:20 AM, Dale's wrote: 

>-----Original Message-----
>From: protek@shreve.net <protek@shreve.net>
>To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
>Date: Wednesday, August 25, 1999 8:37 PM
>Subject: Gyros and Compass Modules
>
>
>>Bill,
>>    There are a series of small solid state gyros now available.  All to my
>>knowledge are "Rate" gyros.  These output a voltage related to the rate of
>>turning for a given axis.  The cheapest that I have come across is from
>>Gyration.  They are listed on the Internet as www.gyration.com and have
>>specs available.  The problem with rate gyros is that unless you use
>>electronic integration, either analog or digital, of the rate to yield
>>angle, you can not use them as a compass.  And even if you do integrate
>>their outputs they drift to some degree.
>>    Your best bet is to purchase a used flux gate compass or get a Vector
>>brand compass module made by Precision Navigation form Jameco, Inc.  They
>>are also listed on the web and have specs on these modules available.
>>Check out Jameco.com The compass must be placed outside the sub where the
>>effects of magnetic fields are not going to cause too much error.  House it
>>in PVC, aluminum, brass or something that is not magnetic like iron.  These
>>modules are about $50, or $100 for the one with gimbles.  You will have to
>>use some electronic expertise to connect it to a readout of your own
>>design.  Or I think maybe they have a readout module you can purchase.
>
>
>I'll check out the web site.. I was thinking of a directional gyro,
>independant of the magnetic field of the earth.. Airplanes have them, and
>when set (ie before you take off) they only drift a couple of degrees an
>hour, and that is primarily because of the rotation of the earth.. I figured
>that the longest I would be down at one time is about an hour, the
>directional gyro would only be out a couple of degrees, and therefore would
>be a very good primary navigation source..  I am not sure how far from the
>sub you would have to mount a magnetic flux module, to get as accurate a
>reading.   I am looking at some airplane wreckers to see if I can find a
>price on an electric directional gyro..
>The only place I have found so far (and they didnt have any in stock) said
>they would run aprox $600.00.. I figure I should be able to locate one for
>half that price,  perhaps get a vaccuum driven one, and incorperate it into
>the air scrubber system somehow..   Just some ideas....
>Bill