Underwater speed?

[NickMu]

The paddle wheel I used is completely sealed and, after finding the right spot for it, all you have to do is run the three wire cable inside. There will be only one time calibration required (determine the “active diameter” of the wheel) and after that just use your favorite method (frequency or period of the pulses) to calculate the speed.

Regards,

Nick

[languer]

I agree the paddle wheel is a good, simple idea. But I don't think the paddle wheel by itself can tell you the speed of the boat. If I remember my dynamics class, the paddle wheel will tell you the flow in the wheel. Which will be a function of two forces; (1) thrust of the sub, and (2) thrust of the water. In other words if the sub is travelling against a strong stream, the paddle wheel (I think) will incorrectly state the sub travelling at higher speed. If the sub is travelling in the same direction of the stream, the paddle wheel (again I think) will incorrectly state the sub travelling at slower slower speed. If the sub is travelling in still water, the paddle wheel will correctly indicate the speed. I believe you also would need to know the thrust of the sub (i.e. propeller movement) to properly calculate the actual speed of the sub (or maybe I am all screwey - which happens quite often).

[NickMu]

Hi Languer,

40 – 45 years ago these things were much clearer in my mind.
I can safely say that you are correct. And to add to the injury when checking the speed with paddle wheel in a stream not only that your readings are shifted with ± stream’s speed but they will be different depending on your position within the stream’s body: the closer to the walls and bottom the slower the water speed.

So the only accurate way to check the speed will be counting the time spent between two telegraph posts (LOL) or GPS based. Any other of the suggested methods will require some sort of calibration before each use if the environment changed.

Let’s look at the bright side: I recall some posts ago that Ed’s answers to various questions suggest that he will be using his sub only in fresh steady water.

Regards,

Nick

[AvionicsMaster1]

Ok, here's what you do. Instead of all this rigamoro (sp?), get yourself a Defense Department contract to come up with a sonar useable on an inlet waterway. Sequester, schmester the DOD always has money somewhere floating (no pun intended) around.

Then you develop this totally awesome system but forgetting to tell them it can be sensed by a North Korean satellite orbiting near earth. Then, when they ask you to protect it from emissions, you tell them you can't and they will suddenly lose interest. Presto, you get to keep the hardware cause the government can't figure out where to store it. You don't care if the North Koreans can track your submarine. They get to spend lots of money 'cause that's they do and we're all happy. Well, we'll be happy if you send pix and code. That'll solve your problem and you might make enough money so you won't have to work again. Only in America could this scheme work.

[Ramius]

Hi All!
Again you guys are very correct. I cannot imagine running the sub in a stream, only a lake, pond, or swimming pool with still waters. In aircraft there are two measurements of speed, IAS (indicated air speed) and TAS (true air speed). IAS is the speed weather into the wind or with the wind while TAS is the speed over the ground as if you were a car. In this case we can realistically only work with IAS as far as I know.

Best, Ed

[AvionicsMaster1]

How much money do you have? I found this http://www.airmartechnology.com/uplo...res/CS4500.pdf by accident and wonder if it might work. I'm also wondering if you couldn't find one used at a dock or salvager.

The brochure is light on how to hook it up but it would fit your needs almost perfectly. After a quick search I couldn't find anything on the "Airmar paddlewheel format" this is supposed to put out.

[Demon]

How much money do you have? I found this http://www.airmartechnology.com/uplo...res/CS4500.pdf by accident and wonder if it might work. I'm also wondering if you couldn't find one used at a dock or salvager.

The brochure is light on how to hook it up but it would fit your needs almost perfectly. After a quick search I couldn't find anything on the "Airmar paddlewheel format" this is supposed to put out.

That's very interesting.

I wonder what would be involved in rolling your own version. Ultrasonic implies the use of sound, are there new devices out for robotics that could be used for this?

I'm looking at the speeds involved in the specs at it's not NASA-type stuff. Except for the sensitivity of the sensor device, the rest seems within our grasp.

Robert