SONAR Sensor Software Driver

[Tom Bottiglieri]

Originally Posted by gnormhurst

Just a further update on the sonar system. We were successful in using the sonar to control our distance to the corner goal (our doors won't open if we're too close, and the balls won't go in if we're too far away). We used sonar both in autonomous and as a driver control (driver initiates "autonomous" using a button. Control is returned when the balls have been dumped or the driver hits the "abort" button.) We even got a Xerox Creativity Award for the system.


But here's why I'm writing this note...

We had a strange problem. The sonar system would give steady values until we enabled autonomous, and then the values would start to drop: 150, 150, 150, [start auto] 150, 150, 130, 115, 90, 75, ... All this while the robot was on blocks and unable to move!

I figured it was some bizzare resource interrupt limitation timing thing. Until I discovered that it would do this just by me running the motors. It took a mechanical engineer to put his hand on the frame and say, "I bet it's picking up vibration from the motors!" We removed the sonar unit and held it -- the problem went away. We ended up mounting the unit on a block of foam (a block we made by cutting up one of those balls from the game).

Oddly, the autonomous code seemed to work anyway. It only did this for long distances -- at short distances ( < 30" ) we didn't see this problem.

So, everyone --- be careful how you mount the sonar unit -- it can pick up vibrations and give bad readings!


Thanks again for the driver code -- we never would have been able to complete this in time without it!

-Norm

What were you trying to read a distance off when this happened? Sometimes the sensor gets screwy readings when it is pointed at a curved object. Silly sound waves.