How to model simple URDF objects?
I'm trying to model a simple hammer for use in Gazebo; I'm using ROS Fuerte in Ubuntu 12.04. It doesn't have to be terribly complicated, it's just to do some grasping stuff with the NASA Robonaut r2 model (which runs just fine). I've tried modeling a simple rectangle with a static joint to a cylinder in URDF, but I can't get anything to spawn. It either says it can't communicate or crashes Gazebo outright. I feel like I'm stumbling in the dark; there's precious little I can find for how to do object modeling for Gazebo, and any help would be greatly appreciated.
First step, please post your URDF and the command you're using to try spawing it.