Does anyone have a working speed sensor?

[ramius-ii]

Re: Does anyone have a working speed sensor?

Thanks Scott!
Both are very good ideas. The catch to the pedometer is it depends upon the "bounce" in your step. At the frequences cell phones work at it would be highly doubtful they would operate underwater. However it great to see how many thinker are here!

Best, Ed

[Guest]

Re: Does anyone have a working speed sensor?

Agreed cell phones won't work underwater, like the 2.4ghz radio equipment.

If you had a little towed barge that remained on the surface, with GPS sensor, that could measure speed fairly accurately. It could at least be used to calibrate an underwater sensor.

[ramius-ii]

Re: Does anyone have a working speed sensor?

Yes and it is a great idea and much simplier than what I have been doing! I took a long board, mounted a geared motor and slip ring assembly on it with a stop watch and switch, then placed this whole thing across the top of the Jacuzzi with a test sensor in the water and let it spin in a 3' circle. By changing the voltage to the motor you get different speeds. The power supply has a switch so you can choose from 3v to 4.5v to 6v to 7.5v to 9v to 12 v giving you 6 different test points. Here is one sensor I tried and I think maybe it was too small to get and real readings from.

[raalst]

Re: Does anyone have a working speed sensor?

maybe this can help :

http://www.robotshop.com/seeedstudio-water-flow-sensor.html?utm_source=google&utm_medium=base&utm_campaign=jos

it is basically a free running propellor, you count the revolutions.

[ramius-ii]

Re: Does anyone have a working speed sensor?

Thanks Raalst!
That's about as small as I have run across so far. I carefully looked at John Robertson's 12 foot sub and at that size the whole world of "off the shelf" sensors are available. I am not so certain about the "electronics" he may or uses, one post on the site he is on said someone was helping him with a compass! I think you all know I made a highly accurate compass years ago! I did register at the modelboatmayhem.co.uk/forum so I could ask him some questions as there does not seem to be an e-mail address for him. Just to share with everyone, here is a picture of the depth sensor I just finished. Good to increments of 1/2"!


The silver part is the actual sensor. The plastic is just for protection and making it easier to handle.

Best, Ed

[Guest]

Re: Does anyone have a working speed sensor?

Not sure what posts you were reading in that thread, but the boat has a working compass module. Also has full depth control, static and dynamic and can hold very accurate depth.

Most of the electronics in this boat date back about 20 years, and pretty much everything is scratchbuilt, even the R/C equipment. Some of the stuff has been rebuilt and/or upgraded.

I'm sure John will answer your questions in due course. The Mayhem forum had a major brown out a few weeks ago, and things are still in recovery mode.

[raalst]

Re: Does anyone have a working speed sensor?

about compasses,
that is easy these days (be it that they still suffer from stray magnetic fields from e.g. your motor).
they do need calibration and maybe a bit of averaging the measurements, but you do get your roll and pitch as well, since it is 3-axis !

have a look at this thing, I have it, it works nicely(as a compass). I have it for other reasons and it has not been used in a boat. it is reasonably small. It sounds you are having a microcontroller in the boat. it needs one.

The controller I show below is somewhat arduino compatible, so it is easily programmable. check out that JeeLabs site and modern devices for more sensors, like pressure sensors (check out the BMP05, which detects a feet of altitude difference in air! and the MPXV with tube attachment on Modern Devices; these could be used as "pitot tube" as well)

compass module : http://shop.moderndevice.com/products/3-axis-compass
main controller with 868 Mhz transmitter]http://jeelabs.com/products/jeenode[/url]

as for a speed sensor, maybe it is as simple as a heated resistor. that is a trick that works in air. it should work in water as well. maybe better even. following this principle ]http://shop.moderndevice.com/products/wind-sensor[/url]

[ramius-ii]

Re: Does anyone have a working speed sensor?

Thanks Ron!
You have some great ideas! Yes I am very familar with the problems with a simple compass and the compass design and software I did compensates for calibration errors. The compass sensors put out two sin waves that are 90 degrees from each other thus they become equal at two points. Initially these "crossover" points are the references used. I put a small subroutine in the PIC code to check when the crossover points occur and use these readings as the new reference points. So as the compass turns it "self- calibrates" compensating for variations in voltage and temperature. According to some Chinese engineers who "tested" my compass it was consistantly accurate to 1/10 of 1 degree! Everything is posted and free to everyone. Just as an update, I am about 95% finished with a "pitch and roll" sensor (X and Y). The PIC code basically works and just needs some cleanup. Then I will probably get back to seeing what I can do with speed. I am set up to work with PIC's using PICBasic Pro and many other projects are written for Stamps or other microprocessors. The "fun" part will be taking all these individual small programs and combining them into one big 40 pin PIC!

Best, Ed

[raalst]

Re: Does anyone have a working speed sensor?

I would love to have a look at your project, do you have a link for me ?

I work with AVR chips mainly but I just repaired the digital side of an
aerial analyser for my dad (he's a HAM like you). it uses a picaxe chip. nice stuff.
I made a programmer for it: three wires. It took me longer to find the matching
pc with a db9 serial plug on it

[ramius-ii]

Re: Does anyone have a working speed sensor?

Yes, 9-Pin can be a "challenge" and I found it easier to use a 9-Pin to USB adaptors such as the TU-S9. The compass and all details are at http://www.picbasic.co.uk/forum/forum.php under my screen name of Ramius. Depth sensor, servo angle indicator, tilt sensor, etc.