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Topic: detecting obstructions on the sea (Read 3 times) previous topic - next topic

arbarnhart

Nov 17, 2010, 02:04 pm Last Edit: Nov 17, 2010, 02:04 pm by arbarnhart Reason: 1
I have been looking at ultrasonic transducers like the ones here:
http://www.futurlec.com/Ultrasonic_Sensors.shtml
but even the waterproof ones typically have something like this in the datasheet:
Quote
... do not use this sensor in the following, or similar conditions.
a) In strong shock or vibration.
b) In high temperature and humidity for a long time.
c) In corrosive gases or sea breeze.


I am not looking for anything too sophisticated; navigation is by command and/or GPS. Obstruction detection is mostly a safety feature (try not to hit anything at full speed). I think a couple of wide cone with overlap in front (so if I detect something roughly the same decreasing distance away in both, it is likely in front of me) would work.



jackrae

#1
Nov 17, 2010, 02:13 pm Last Edit: Nov 17, 2010, 02:13 pm by John_Rae Reason: 1
Ultrasonic detectors such as you suggest will be totally useless in this application.  Firstly their range is very short - in the order of say 10 metres maximim.  On a pitching boat their ability to detect an obstruction in anything other than a dead flat calm will be questionable. And lastly, placing ones life (at full speed - your quote -) on a device that will not work is suicidal.
Radar is what you need !

jack

arbarnhart

#2
Nov 17, 2010, 02:24 pm Last Edit: Nov 17, 2010, 02:25 pm by arbarnhart Reason: 1
I have been programming the bot too much lately. By "me", I meant the unmanned USV. I am concerned mostly with close range. I figured I would have to correlate with pitch and yaw, which I have sensors for. The primary use for my device is almost guaranteed not to have an obstruction that isn't known to the GPS routing code. My main motivation to add this is so that I don't destroy a unit during testing if the route is wrong.

jackrae

Does USV = Submarine

If so, and if it's underwater obstructions you are concerned with,  then ultrasonic detectors are exactly what you need.
Howevre you need to get hold of the type used in echo sounders, which for obvious reasons are waterproof.  I believe they work at somewhat lower frequency than the "air" ones.  Somewhere in the order of 22kHz, I think.

jack

arbarnhart

#4
Nov 17, 2010, 02:41 pm Last Edit: Nov 17, 2010, 02:43 pm by arbarnhart Reason: 1
USV = Unamanned Surface Vehicle
UUV = Unamanned Underwater Vehicle

So "unmanned USV" was redundant and needlessly reiterative...

I didn't make these up, they seem to be pretty standard in robotics. It's a boat what drives itself...  :D

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