Comment by sobot for Here's a Poor man lidar, that could be used for mapping. It uses a sharp IR sensor and a servo.http://www.pirobot.org/blog/0014/The xv-11 laser is a fairly cheap setup for under $100 on eBay. http://wiki.ros.org/xv_11_laser_driver

just for eliminating moving parts (risk of mechanic failure) and also i wanna put a cover over the robot, panning IR will need a wide opening in the robot's cover. but I'm thinking a ring may have some overlapping and blind spot problems.