Thunder Tiger Neptune Upgrade


#1

I have a Thunder Tiger Neptune that I build nearly 10 years ago and equipped with a composite video camera and a surface float to transmit 90 MHz back to shore.

http://www.diannebest.com/Projects/Sub/Submarine.html

Technology has advanced considerably so I am in the process of replacing the composite video camera with a 5MP digital camera with USB interface and a 2.4/5GHz link back to shore.

A couple of shortcomings in the original system were lack of directional and depth information. When the sub has been submerged for awhile, I would loose awareness of which direction it is moving and what depth I am at.

Since I already have the composite video camera and 900MHz link, I thought I would relocate the camera and have it focused on a miniature compass and differential pressure gauge to send the situational information to shore and display it on a separate video screen (since I don’t want that information imposed on the high-resolution video). There isn’t much space in the hull of the Neptune but enough for a compass. The problem is the differential pressure gauge - I can’t find one smaller than 2" diameter.

I ran across the IMU/Compass/Depth module on Open ROV but the literature says it uses absolute pressure measurement. To get an accurate depth indication, the actual depth would be absolute pressure minus surface pressure. Am I missing something here???

The module also provides a data output that is not directly displayable or transmittable on the 900MHz composite video link and I don’t have enough space within the hull to add much more in electronics.

Does anybody have any ideas on an alternative?

Thanks for listening and for any suggestions.


#2

For the depth gauge, you can use an absolute pressure sensor, and then subtract off a bias (zero the output) before the dive. IIRC, in the OpenROV software we automatically subtract out a bias based upon the mean atmospheric pressure. That way, if you forget to zero things, your depth reading is pretty close to the true depth. When you are diving in the mountiains (such as in Lake Tahoe), you have the ability to zero things pre-dive and still get an accurate depth reading.

If you are upgrading your system to a digital camera with a USB interface, why are you trying to put the digital depth on the old composite video? It can be done, but not without some hassle. Why do this for a system you’re about to replace?

-W


#3

Good point. I had arrived at the same conclusion in a round-about way when I couldn’t find a suitable analogue differential pressure gauge.

Since I have broadband USB, I might as well move the telemetry to the USB link. I can get compass chips and pressure transducers, digitize the signal, and pick them up at the other end of the serial stream.