Help with water speed please

[Ramius]

Hi all!
I wish to measure the speed of my sub in the water. I am told that a MS4514 sensor with a part number of MS4515-DS-5-A-002-G-P should be a good choice (?) with a range of 0-2 psi. My guess is that with a 10-bit external A/D there should be a decent number representing speed. I know to use "long" as part of the program what I do not know is what formual to use to do the calculation since this is in water and not air! Thanks in advance for any and all assistence!

Best, Ed

[Acetronics2]

Hi, Ed

is that what you were looking for ???
http://www.engineeringtoolbox.com/pitot-tubes-d_612.html
and
http://docs.engineeringtoolbox.com/documents/916/water_velocity_head.pdf

so you can check if your sensor range matches your speed range ...

Wish you a Merry Xmas and a Happy new Year.

Alain

[Ramius]

Thank you so much Alain for the links! To be perfectly honest my math skills are not good enough to write the formula so a PIC can process it.

Hope you and your family and friends also have a great Christmas and a Happy New Year!

Best, Ed

[Acetronics2]

Hi, Ed

as the speed range will be limited ( even for Red October !!! ), I think you'd better use a retrieve table plus linear interpolation.

the 32 bits square root calculations needing too much CPU time ... for the expected result ;)
( and I hope your sub' not used in sea water or "not so clean " water ... you might use a different density coeff : http://www.csgnetwork.com/h2odenscalc.html )

may be you also could have a look for a possible temp coeff use ...

Wish you all the best
Alain

[Ramius]

Thanks Alain!
I do have and can add a seperate temperature sensor for the same PIC and the sub only run in swimming pools, ponds, and lakes with clear water. According to the fine fun folks at Eagletree systems I could never reach the top speed in water as the 0-2 psi range is for airplanes and speedboats. They use a "strange" calculation method they do not wish to disclose. Good catch by the way! My sub is very close to the sub used in the movie "The Hunt for Red October" which is a Russian Typhoon! So what would the caculation code look like?

Best, Ed

[Tobias]

ъжлйбес3=8игфефгш

[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. :frown: 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/4426243/Use-a-heated-diode-as-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 ... :rolleyes:)

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

http://dx.com/p/hs05-high-precision-water-flow-sensor-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

[Acetronics2]

Hi, Ed

Hope your speedo just is here " for the show " as its lack of precision never will allow any usable positionning info ( through math. integration ).

BTW you already DO have your formula @ #4 ...

Alain

[Ramius]

Hi Alain!
Thank you and Happy holiday's! The only way to work with positioning would be limited to the surface with the use of GPS. The catch is that once you are underwater, GPS is useless. http://www.eagletreesystems.com/index.php?route=product/product&product_id=131 shows their boat speed sensor. As for a formula I think maybe you meant the formula referenced in #2? Again my math skills and understand of how the math works is seriously lacking especially when trying to even begin to write the code for a PIC.

Best, Ed

[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

:cool: You are a practical genius .

[Acetronics2]

Hi Alain!
Thank you and Happy holiday's! The only way to work with positioning would be limited to the surface with the use of GPS. The catch is that once you are underwater, GPS is useless. http://www.eagletreesystems.com/index.php?route=product/product&product_id=131 shows their boat speed sensor. As for a formula I think maybe you meant the formula referenced in #2? Again my math skills and understand of how the math works is seriously lacking especially when trying to even begin to write the code for a PIC.

Best, Ed

Hi, Ed

you're right was @Post #2 ...
If I'm right ... you're begging for the full PBP calculation :rolleyes: ...

Sorry, but I won't be able to take care of it before next year ... as I'm the WHOLE family cook for the moment.

Please, Understand it needs ... a little amount of time, as a retrieve table has to be calculated , and you need the full working subroutine ...

BTW ... knowing which processor you use could be necessary ...

Alain

[Ramius]

Hi Alain!
Thank you please take care of the family first. I will not even have a sensor to test until after the first of the new year. Probably a MCP3202 A to D and an
18f1320 although I am open to any and all suggestions. I can test the sensor in a tub of water much like part of a wooden barrel with an arm that spins the sensor in the water and there is a stop watch with a switch to start and stop the stop watch for the time part. I have 6 different speed for the motor that drives the arm that spins just above the water with just the sensor pick up tube in the water. I hope you and your family had a great holiday and that everyone will have a happy and prosperous new year!

Best, Ed