Help with water speed please

[Tobias]

Russian joke aside, make your own algorithm.

Write up code to set up your sub to go X speed for Y amount of seconds. X speed meaning a set number for the duty cycle controlling the prop. Make sure Y is long enough for speed to stabilize then save the PSI measurement. Increase X a couple of times, each time saving psi data. You will make your own plot based on your data. It might not be exact according to their 'top secret' calculation method but you shouldn't care. Its all relative. You measure then associate a number with the PSI settings.

If you want to be trick, make your own speed trap using another Microchip and a couple of sensors to make your own algorithm. That might be a bit overkill.

[Demon]

Simple speed trap:

Tie a magnet at the end of a length of string.
Place a residential alarm switch inside the tail of the sub.
Apply a metal plate using tape over the switch.
Extend the plate beyond the prop to protect the string.
Monitor the switch from your PIC.

Then you have a simple repeatable way of calculating distance travelled over time while you tweak your formulas.

Edit: watertight, with no holes to plug up later either.

Robert

[Ramius]

Thanks guys!
I will not receive my pressure sensor until after the first of the year. I have set up a way to test pressure vs speed with a tub of water and a motor attached to a shaft that spins in the water and travels a known distance with a stop watch that starts and stops at rev.

All my best, Ed

[Jerson]

This seems an interesting possibility though it is currently used as an air flow sensor

http://www.edn.com/design/sensors/44...-a-flow-sensor

[Acetronics2]

Hi, Jerson

Halas, this measuring principle has to be used only with gases, as the heather power must be somewhat reasonnable:

Water would need 700+ times more power than air ... @ same temp rise.

Ultrasonic measurements also could be made ... but it needs meters between sensors !

I believe the best @ this scale, is to use an axial floweter ( with a small propeller inside ).
I got one years ago for gasoline, from a JAEGER brand car onboard computer ( Years 75-76 , when oil began to cost a lot ... )

it sure must still exist somewhere ( probably Water flowmeters for camping cars ... )

http://dx.com/p/hs05-high-precision-...r-white-227090

The real advantage here is there are no flow change ( and no false measure ) when the sub makes a sharp turn ...
as pitot tube needs to be close to flow direction ...

Alain

[Ramius]

Thanks Guys!
Some very interesting ideas! There is not a lot of room in the bow of the sub as there are torpedo tubes, missile tubes and bow plane mechanics so the intent is to keep everything as small as possible.

Happy Holidays to all! Ed

[Demon]

You want something like these:

http://koolance.com/ins-fm16-coolant-flow-meter

They have a link for the fittings, depends on what size tubing you will use (they also have tubing).


About plumbing, to avoid corrosion:

Do not use aluminum with bare (unplated) copper or bare (unplated) brass in the same system.
Do not use silver with nickel in the same system.

Robert

[Vett58]

Simple speed trap:

Tie a magnet at the end of a length of string.
Place a residential alarm switch inside the tail of the sub.
Apply a metal plate using tape over the switch.
Extend the plate beyond the prop to protect the string.
Monitor the switch from your PIC.

Then you have a simple repeatable way of calculating distance travelled over time while you tweak your formulas.

Edit: watertight, with no holes to plug up later either.

Robert

You are a practical genius .