・urdfファイル
<?xml version="1.0"?>
<robot name="toybox">
<link name="base">
<visual>
<geometry>
<mesh filename="package://ptcam_description/meshes/toybox/model.dae"/>
</geometry>
</visual>
<collision>
<geometry>
<mesh filename="package://ptcam_description/meshes/toybox/model.dae"/>
</geometry>
</collision>
<inertial>
<mass value="1000"/>
<inertia ixx="1" ixy="0" ixz="0" iyy="1" iyz="0" izz="1"/>
</inertial>
</link>
</robot>

・コマンドラインでspawn
rosrun gazebo_ros spawn_model -file toybox.urdf -urdf -model toybox

・pythonでspawn
#!/usr/bin/env python
import os, rospy, tf
from gazebo_msgs.srv import *
from geometry_msgs.msg import *

rospy.init_node("toybox")

rospy.wait_for_service("gazebo/spawn_urdf_model")
s = rospy.ServiceProxy("gazebo/spawn_urdf_model", SpawnModel)

dirname = os.path.dirname(os.path.abspath(__file__))
with open(dirname + "/../urdf/toybox.urdf", "r") as f:
toybox_xml = f.read()

orient = Quaternion(*tf.transformations.quaternion_from_euler(0, 0, 0))
pose = Pose(Point(0, 0, 0), orient)
s("toybox", toybox_xml, "", pose, "world")