Underwater speed?

[tasmod]

Hmm, your driving it with a propeller. Why not a small free rotating prop on conning tower and measure rotations.

There's example code on here somewhere for wind speed anenometer, which is basically same.

Rob

[Demon]

Won't work when surfaced.

Robert

[tasmod]

Conning tower location was just a suggestion, it could just as easily be on hull etc.

KISS. Small prop with photo reflector for pulse count. Mounted in small tube.

Easier to get going, then maybe try sophisticated solutions.

Rob

[NickMu]

Hi Ramius,

Can you provide some more information on your radio controller?
I’m interested on range, maximum depth and more importantly where do you purchase it from?
Regards,


Nick

[Ramius]

Hi Nick!
Here is a link to the radio controller: http://www.conrad-uk.com/ce/en/produ...ains&insert=8X It has two throttles, one for the port motor and one for the starboard motor and a ton of expansion modules! I originally bought it from Ships n' Things. Range and depth are a funtion of the both transmit and receiver antenna's and how they are configured. You basically are trying to simulate a "dipole" for receive and you can use a yagi for transmit. Part of the other factors are where you place all your electrical cables and how you have prevented EMI (Electrical-Mechanical) and RFI (radio frequency) interference. For example motors produce small sparks which are basically a radio signal. So you have to use bypass capacitors. How you ground the motor cases and how you run power all make a difference. The technique I use is called "single point" power and ground where all the power wires connect to one single point and well as the ground wires. In addition power and ground wires have been put in an electric drill and twisted together. There are a lot of technical reasons for doing this. If I strike out with a pressure sensor then the propeller idea will be next!

Best to All, Ed

[NickMu]

Hi Ed,

Thank you for your detailed reply.
I had an application that needed to read the thrust of a jet of water and before our order of force sensors came in we used a paddle wheel to determine the speed of the jet.
The results were within 5% of the real sensors readings.
Depending on your precision and accuracy requirements any of the suggested methods should work but with some penalties.
IMHO your biggest problem will be the changes in water density due to various reasons (salt, temperature…..)

Thank you again and good luck.

Regards,

Nick

[Ramius]

Hi Nick!
Thank you and I would not mind a paddle wheel type except they all seem to be really big! I do not believe water density will be much of a problem since I will only be operating in fresh water and for a sensor I am using an MS5541C's which are temperature compensated. What I really do not know is the actual formula for velocity. Water density values seem to be all over the map. Do you know of or have a simple formula I can program into a PIC (PIC Basic)?

Antenna work is almost a "Black Art". For a transmitter your main concern is what is called SWR (standing Wave Radio). Basically you are sending power up a coax and when the power hits the antenna if you have the correct antenna and correct impedence (AC resistance) then none or a very minor amount of power will be reflected back to the transmitter or used to "heat" the coax. On a receiver you have the same problem in reverse where you want all the received signal you can get! A dipole (two wires 180 degrees from each other) has an impedence of 300 ohm. When the two wire are at 90 degrees you are looking at about 50 ohms. It even becomes more complicated with the lenght of the antenna wires! That is full wave lenght, half wave lenght, 5/8 wave lenght, 1/4 wave lenght. It can boggle the mind!

Best, Ed