31 Mar 2006 cschur   » (Master)

More on Outdoor Sonar....

We have spent many more hours this week on getting our quad sonar array to work outdoors. I have discovered a very useful fact about doing this, Id like to share. With a sonar mounted just above ground level, say six inches or so, you will be detecting the ground at some point a few feet away, and it will change rapidly in some cases from a foot to over four feet in a heartbeat.

We tried aiming the sonar upward about 25 degrees which pushed the ground detect point outward only slightly, but now it was picking up beams on the overhanging roof! So dont point your sonar upward.

This "ground effect" requires you to do one of two things to make the sonar useful for obstacle detection. First, you can always jack it up a foot or so off the ground. Then youll miss some pretty major obstacles, but your ground detect point will move out to past the detection limit of about 8 feet for the SR04 sonar.

Alternately, we can try to reshape the beam. Research into this on the web has shown mainly failed attempts, the general consensus is you CANT change it. Well, we found thats not entirely true!

You cant add like tubes or cones in front of the beam or over the emitter/detector because it just sees the tube and its signal overwhelms the detector. BUT you can modify the pattern by reflection. Here we put a smooth surface for the beam to deflect off of, exactly like a mirror. By intelligently putting a flat piece of lexan under the sonar xmitter, we can deflect the sound waves that would hit the ground up into the air. so now we are determinng the shape of that flat plate, and how big it should be. Im guess ing it will be D shaped, and about four to six inches radius.

More to come, working with a sensor system that literally sprays signal all over the place outdoors is quite the challenge!

Write me if you have any suggestions.

Chris

comets133@yahoo.com

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