27 Mar 2006 cschur   » (Master)

Sonars in the Outdoors

We made more big progress on our quadrate sonar array on the Geobot this weekend. Last I posted, we had just mounted the array on the front of the robot, and started testing a new sonar PIC to do all the dirty work to take the load off the main processor. Well now we have finished the sonar processor, and it puts out both serial and paralell data to indicate both the distances for each sonar, and which zone the closest danger is in. And now, last night late we wired that processor into the main 16F877a controller.

I next set up the priority arbitration architecture in the program for the sonar, which takes second place only to the bumper. And a quick run indoors at some targets on the floor, and its veering and banking away proportionally from the obstruction!

So whats next? We found that in an outdoor enviornment, the sonar is picking up the rough ground about 2 feet in front of the bot, even with no rocks around. In the house with the flat plywood work table we have it on, it did not do this. So heres the catch - If you aim the sonar straight ahead, it will still see the ground intermittently and think there is a giant rock out there its heading for. IF I tilt the sonar up, I miss the ground, but also miss close by rocks that are too tall.

Sonar is very broad beam, and very sloppy of course and is quite a challenge to use out of doors! Also, there is the problem of a slope. When the robot sees a bottom of an easy to climb hill in front of it, it still sees it as an obstacle to avoid.

So for small rocks and the ground, a low lying sonar will not always see the comming impact. But It will see many feet straight ahead so it doesnt encounter a huge boulder or more commonly a tree trunk. So there is a small zone Ill have to cover between the bumper and bottom of the sonar beams with another set of some sort of sensors.

Our next step is to take the bot outdoors and run it through an array of obstacles such as rocks, branches, logs and ditches to get the sonar tilt set to optimal.

Its the wierdest thing to see a tank tread vehicle with differential PWM drives running figure 8's all over the yard!

Write me: comets133@yahoo.com

Chris

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