[gnormhurst]

Originally Posted by Tom Bottiglieri

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.

We were pointing it at a wall in the Drexel gym. Big, flat and perpendicular to the robot's axis. The test we did of removing the sonar unit from the robot and just holding it there, an inch from where it was mounted, seemed to be conclusive proof that it was indeed vibration pickup from the robot. Further, mounting it on foam stopped the problem.

SPEAKING OF MOUNTING IT ON FOAM: be careful how you mount it to the foam. Just putting a block of foam behind the unit and screwing it down through the foam doesn't work: the screws transmit the vibration from the frame directly to the sonar unit. You must mount the unit to the foam, then mount the foam to the robot's frame. This gives isolation.