Hey Mark,
I usually see this kind of issue going the other way (external nodes unable to send data to MATLAB/Simulink), but it's possible to happen the other direction as well. Try setting the ROS_IP environment variable on both sides of things (set to the IP address of the machine it is on). It needs to be set in MATLAB as well as in each terminal that runs any ROS nodes on the external machine. Then restart all the ROS nodes.
Also make sure that ROS_HOSTNAME is not set if trying ROS_IP. This helps to ensure that the IP address of the node is advertised correctly so that point-to-point communication between nodes is possible.
If that doesn't resolve the issue, here are some further steps:
- Can you check if you can do "rosnode ping <simulink node>" from the remote machine. If not, it may be a DNS resolution issue.
- See if you can publish messages from MATLAB to the remote machine, to see if it's just a simulink issue.
- Try a different message type (one of the std_msgs). It may be possible (though not likely) that there is some kind of message type difference that is causing ROS to drop the messages due to mismatched md5 checksums. This usually gives an error, but maybe Gazebo is silently catching it? If you need to update your built-in message types, here are the instructions.
-Cam
