Finally finished and fully functioning hand controller.
Arduino USB -> ModBus -> Mach3

https://www.youtube.com/watch?v=Nd6aTHJTkZI

That looks great man!

Can you share any info about how you setup the modbus stuff? I am also futzing with arduino modbus for mach4.

Thanks!
-Kaleb

Thank you!

On the Arduino side, you could check my code, there are some comments, it might be helpful:
https://www.dropbox.com/s/x76rtm1rwg0mv7w/AND.CUSTOM_PENDANT-FINAL.zip?dl=0

I'm not sure how does mach4 works with modbus, but in mach3 you have to play with Brains, out there you can read incoming registers from Arduino and address it to any action, and other way around, read information of what machine is doing and change registers, that Arduino can read.

Registers are like a storage, you can think of online cloud. You can send information to the cloud, and you can access that information from many different computers/devices.