The Nimbus PC-186 used a non standard keyboard protocol.
It used the XT scancode, using inverted TTL at a set baud rate
This combination of factors means that the original RM Nimbus PC can only use the original keyboard.
The later slimline version used a standard PS/2 keyboard.
There tend to be more Nimbus base units than there are keyboards and finding
a keyboard seperate to the Nimbus is, in my experience, almost impossible.
Here I have created an interface to the Nimbus that allows a standard PS/2 keyboard to control it.
It uses an Arduino Nano and is powered from the Nimbus keyboard port.