Creating a dive computer with Location and Communications

[dmaziuk]

They have room, power, and the budget for things that us recreational divers do not.

Also actual rooms full of maps and charts and things, and people trained to use them.

 

[Hatul]

They have room, power, and the budget for things that us recreational divers do not.

Hi Stuart, yes they have maps, money etc, but I'm referring to the physics which is the same whether for a sub or a diver. How do they know where they are on the map?

 

[stuartv]

Hi Stuart, yes they have maps, money etc, but I'm referring to the physics which is the same whether for a sub or a diver. How do they know where they are on the map?

Me, too. Well, not so much the physics of it as the current state of the technology. They have technology that allows them to do it. But, the current state of that technology is that it is too big, takes too much power, and is too expensive for recreational divers.

 

[Lorenzoid]

Okay, I'm intrigued. Does anyone know what IS the technology that allows them to do it? Does a sub rely entirely on inertial navigation for the entire time it's below radio (e.g., GPS) penetration depth?

 

[NAM001]

I wonder how submarines that stay deep for long periods of time navigate. They use sonar to avoid objects but how to navigate?

Again being one that has seen a clark gable movie or so. I can tell you with some credibility.

Submarines primarily use passive (no noise emiting methods) means.. we use maps/charts in and gyros that are accurate with in perhaps a few feet over months in most applications . North pole excluded. we have a fathometer as a very low level verifying check to see if the water depth is what we expect from teh chart position. of course if there is 400 miles of 2200 fathoms of water a depth does not help much. when we put up a communication antenna we pick up satalite signals like gps and other transmissions to validate our position on a chart (may be electronic and not necessarily paper charts) different systems omega Drai loran gps navsat a variety of ships gyros perhaps 4 or more. All that is in the water is on a chart. under water mointains oil platforms bouys etc that are known are used. All data is plotted to determine where we are and those that do not agree are now perhaps get designated as in need for maintenance. Pure underwater navigation is done by gyros. for ships that have a 1000 foot antenna cable dragging behind at the surface there are still radio signals that can be picked up. We can and have based on secureity level at the time have used active sonar to determine a mountain peak location and match that on a chart. but that is a noise emitting process.

 

[NAM001]

I would worry about the battery.

$60-ish for raspberry pi, $40 for the IMU, you need to have someone with CNC mill to cut the body plus some CAD-fu to design it. And a pressure pot for testing. Maybe not a high school project, but 1st year college for sure.

you are correct about the battery. life expectancy varies depending if the compass is used or not,,,,, on computers that have compasses.

 

[NAM001]

Okay, I'm intrigued. Does anyone know what IS the technology that allows them to do it? Does a sub rely entirely on inertial navigation for the entire time it's below radio (e.g., GPS) penetration depth?

You may or may not be very surprised in the accuracy of todays gyro systems It is not unusual for a system to be up 6 months and not be off more than a few yards. I suspect that your question is based on movies like hunt for red october where a sub is shown cruising along the bottom floor at 20 knots through canyons and never hitting anything,, using a stop watch and counting down the turn. To that I will say something has to add suspense to a movie.

 

[dmaziuk]

If your modern gyro is inside a moving frame of reference, you still get all that Einstein stuff, right? So what, they start them at perfectly calibrated standstill and keep them spinning until they're back in the pen?

 

[NAM001]

If your modern gyro is inside a moving frame of reference, you still get all that Einstein stuff, right? So what, they start them at perfectly calibrated standstill and keep them spinning until they're back in the pen?

NO THERE IS A START UP PROCESS AND STABILAZATION that may take a few days because after all,,,, if tied to a pier that is still ships movement from tides and currents to average out and reconcile to a perhaps virtual fixed platform. once done you use it in real world. And gyro sets that used to be perhaps 3 feet square cabinets are n 10" or so cabinets. Im sure what I was used to is mostly antique and may only be used on surface ships. In general ships no longer have paper charts it is all displayed on a computer monitor now and the computer has ships parameters being entered. that means no faulty charts only diffeences since the last dvd of charts were distributed. For all I know with this technology all the nav inputs will now auto input to the display so you dont ave to get them and plot them. Just a logical conclusion. To your question a bit more. a couple of days to stablize the gyro internals then you tell the attached computer system your current location in lat and long and it becomes a new starting point in the life of the gyro. till it is shut down and reborn again on the next start up.


Back to the main topic. It should not take long perhaps a month to take a shearwater ,,,, redo the guts install a couple of accerometers and write a basic program to record the movements sensed and present it as a number of vectors on a screen The start being the entry point and the end being current position relative to the start. After that it will probably take a few years to refine the system but the cost really should be low 200 perhaps. all off he shelf items. only the program will be unique. None of this is communications so the battery issues and low power cpu usage should be ok.

 

[Manjula Ellepola]

Back to the main topic. It should not take long perhaps a month to take a shearwater ,,,, redo the guts install a couple of accerometers and write a basic program to record the movements sensed and present it as a number of vectors on a screen The start being the entry point and the end being current position relative to the start. After that it will probably take a few years to refine the system but the cost really should be low 200 perhaps. all off he shelf items. only the program will be unique. None of this is communications so the battery issues and low power cpu usage should be ok.

Lol KWS you sound like a fellow engineer trying to sell an interesting idea to management...good to see people coming up with ideas...