Best way to connect two computers running ROS within same robot.

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My robot comes with a PC and everything works nicely out-of-the-box. I need to expand the functionality of the robot (add more cameras, GPS, etc) but the PC is limited in the number of USB ports and due to power constrains it cannot power devices using a hub (even if the hub has external power). My best option right now is to purchase a Jetson board and use it to connect the other devices. The big question now is how to best connect the two systems? The robot has a wireless router and I can connect both machines to it, then use this tutorial to have a common master, etc but the wireless connection is very unreliable. Is there a wired way to achieve a more stable connection? I cannot use a network cable because the original PC needs to be connected via such cable to the router. Can I use USB? Please advise.