Gazebo and PR2 simulation setup publishing nan values on base_odometry/odom

edit

Some background: Essentially I have set up pr2 in simulation in an empty world on gazebo.

I would like to set the initial pose of the robot, so I have done the following:

model_state = gazebo.msg.ModelState()
model_state.model_name = 'pr2'
model_state.pose.position.x = map2lab[0]
model_state.pose.position.y = map2lab[1]

rospy.wait_for_service('/gazebo/set_model_state')
try:
    sms = rospy.ServiceProxy('/gazebo/set_model_state', SetModelState)
    print 'Model State: ' + str(model_state)
    sms(model_state)
except rospy.ServiceException, e:
    print "Service call failed: %s"%e

At this point, I'm not sure if it has broken yet, but I then would also like to move the robot around, so I set up the following:

self.pub = rospy.Publisher('/base_controller/command', Twist)
rospy.init_node('locomotionCommand')

Which later I use to publish something like the following (in which v and w are always real numbers):

twist = Twist()
twist.linear.x = v
twist.linear.y = 0
twist.linear.z = 0
twist.angular.x = 0
twist.angular.y = 0
twist.angular.z = w
self.pub.publish(twist)

So sometime in here, the pr2 jumps and disappears and I get the following error repeated at some high frequency:

[ERROR] [1343312019.823059305, 40.582000000]: TF_NAN_INPUT: Ignoring transform 
for child_frame_id "/wheelodom" from authority "default_authority" because of a 
nan value in the transform (nan nan nan) (-nan -nan -nan -nan)

I'm fairly certain it is only on /base_odometry/odom, here's a sample:

header:
  seq: 5320
  stamp:
    secs: 58
    nsecs: 971000000
  frame_id: odom
child_frame_id: ''
pose:
  pose:
    position:
      x: nan
      y: nan
      z: 0.0
    orientation:
      x: nan
      y: nan
      z: nan
      w: nan
  covariance: [4e-06, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4e-06, 0.0, 0.0, 0.0, 0.0,     0.0, 0.0, 1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,         1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.00028900000000000003]
twist:
  twist:
    linear:
      x: 2.2798345089
      y: 2.02649641037
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: -0.20633020997
  covariance: [4e-06, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4e-06, 0.0, 0.0, 0.0, 0.0,     0.0, 0.0, 1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.7976931348623157e+308, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.00028900000000000003]

I'm at a loss to figure out what is going on here.