Mating Arduino Uno WiFi to a motor controller

[skyeyedoc]

Try searching for "replace serial link with esp8266"
This is one:
https://github.com/jeelabs/esp-linkf

or "replace serial link with radio link"
commercial products

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Clarification and thoughts:
Are you just wishing to replace just the serial cable between the motor control and the RPI openplotter?
Maybe consider installing the tinypilot RPI zero w next to the controller an give the openplotter the IP address of the zero W.
They need to be connected to the same network of course.

My fall back plan is to get a pi-zero-w, and just go with tiny pilot. Still, I would like to try this other first. Thank you for the link and search string. ESP-link is an especially good tip, as it appears to be a native Uno WiFi library.
Elliott