[PSUBS-MAILIST] gyroscope compass

Wed Dec 3 14:46:00 EST 2014

Gyros in aricraft are not north stable - they need a magnetic compass or
other device to set course. But they are okay  if you set course
according to your GPS course before you dive. They can hold the course
for some hours with a movment of 2-4 deegre per hour. Okay for a slow
and small Psub. They are vaccum driven or electric. Vaccum driven you
can not use in a small submarine. (Or you need a silencer and eardrums
as in Spurdog). Electric you can use if it is a 12 or 24 V DC driven
one. For other voltage you need a special power converter. The Ebay
units are sometimes cheap - between 100-800 USD - but most of them work
not proper. They are build out of the planes for exact that reason and
sold as they are and without any waranty.. Size is around 100x100x400mm.
Volume 4 Liters.. Good solution if you buy a unit in aircraft condition
with papers from a aircarft surplus dealer with a working garanty. Make
sure that they get not wet or 100% humidity. 

Gyros in ships are north stabilzed. The need around 40 Minutes to warm
up. They are much bigger - the smallest one are around 300 x 400 x 300
mm. Volume at minimum 36 liter. They need no calibration or reference
and they are stable over month/years. Problem is that they normal switch
on in a ship and never switch off.. If you switch of them - make sure
that you not move the sub in the next hours - otherwise they can be
damaged. They are expensive - about 30000 USD new and 3000-9000 USD
second hand.  There life time is limited 30000 -  40000 hours between
first failtures. 

I have both types in the Euronaut. And a magnetic one also. 
The gyros are both cheap Ebay ones. One from a aircraft one from a ship.

And both not working anymore. And the third magnetic one has a big error
because of the 60 ts steel below. 

I will by next a second hand one north stabilzed ship gyro for around
3000 USD from a ship scrap yard electronic dealer with a confirm that
they test it and its run stable but without any further waranty. 

A fluxgate its a kind of electronic coils magnetic field compass and
will in most cases not work proper on a strong magnetic metal shell like
a submarine with strong electric motor fields etc. To test on your
submarine if these cheap devices runs on you submarine install a simple
magnetic compass temporary on the sensor spot in mind and than turn the
submarine 360 degree. Switch on and off all electric devices. 
Cross check with another compass (or the same  one) far away from the
sub. 

In most cases an electric 12 or 24 V Dc driven Airplane direction gryro
in combination with a gps course before diving will do the job. But in
99% a ebay 100 USD item will not work proper. 

vbr Carsten

"hank pronk via Personal_Submersibles" <personal_submersibles at psubs.org>
schrieb:
> 
> There are all kinds of them on ebay for under 100 dollars, problem is how to make it work. I assume they just have a small motor that spins. There is a nice ship gyro sitting at 50 dollars right now but it is about 1 foot dia. That would be awesome in a big sub.
> Hank --------------------------------------------
> On Wed, 12/3/14, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Subject: Re: [PSUBS-MAILIST] gyroscope compass
> To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
> Received: Wednesday, December 3, 2014, 1:48 PM
> 
> Absolutely. You can get small ones for civil
> aviation and they are used in subs. One challenge is that
> most airplane ones are powered by a vacuum, but there are
> 12V models. Unfortunately they're expensive, but a great
> solution if you can afford it. 
> Alec 
> On Wed, Dec 3, 2014 at 1:28
> PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
> wrote:
> Hi
> all,
> 
> Ever hear of a gyroscopic compass, seems that ships used to
> use them.  It seems they would not be effected by a
> submarine hull.  What am I missing besides they are very
> big.
> 
> Hank
> 
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