OpenCR Board Can't Publish, Can Subscribe (WSL)

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I've converted this comment into an answer as I believe it is the answer.

@ros_noob_corgi: if you don't have a working DNS for all involved hosts, then try to use IP addresses, and use ROS_IP instead of ROS_HOSTNAME.

Hello, I will use ROS_IP instead and see if it fixes my issue. Please see edits :)

Could you describe your network setup a bit better perhaps? How many hosts are involved? How are they connected? How are they communicating? Etc.

I have a WiFi router (no WAN though). RPi has static IP; PC has static IP. Only two hosts. They can ping each other. When I run roscore on the Pi, everyone can now see the odom data, but when I was running roscore on my PC, I couldn't see it.

Could you please add this to your original question? Also add the values (ie: hostnames and/or IPs) that you've used for ROS_MASTER_URI, ROS_HOSTNAME and ROS_IP.

O, wait. I just noticed this:

PC OS: WSL Ubuntu 18.04 Bionic

there is a good chance this is the cause of your problem. WSL is still not quite there yet with everything, especially networking can be finicky.

Okay, What about ROS on Windows then? Or should I go with Linux?

ROS on Windows is worth a try. It's not going to be as invasive as installing another OS.

Linux (Ubuntu) is definitely going to give you the best user experience (at least with ROS), but may not be necessary.

And I'm not saying that you should install a different OS to solve your problem. Just noticing that you're using WSL, and that it has had problems in the past with this.

If you have an option to use something other than WSL it might help figure out where the problem is.