How to add collision properties to an actor

Hello, I'm trying to add collision properties to this simple actor in Gazebo 5. It works nice, but keeps going through objects. Maybe I'm missing something. Any ideas? This is my world file: moonwalk.dae1.00 0 0 0 0 0-0 0 0 0 0 00 0 0 0 0 0mesh://moonwalk.daewalk.dae1.000000true Thanks!