I am working on a submarine project where I need to communicate with servo motors and send speed and direction and so.
I am looking for a solution that helps me communicate with arduino for at least 100 meters.
I tried xbee and it works. but connection cuts after 15-20 meters.
any ideas or suggestions ?
A 2.4GHz XBee (or similar frequency anything) is not a good choice. You want to use as low a frequency as possible. From the projects I've seen the older, 27MHz RC frequencies are typically used.
If you're aiming for 100 meters of depth then you need to use a tether (wire). You won't find any non-professional (reasonably inexpensive) product capable of that depth.
I think you may need something like this
http://www.dspcomm.com/products_aquacomm.html
Or perhaps fiber optic link from device to device.
Googling
underwater wireless communication projects
brings up some interesting stuff.
CrossRoads:
Try this one
Redirect Notice
That is a very cool hack.
The paper describes using an underwater speaker to transmit to the Arduino.