Hmm. Given that OTL it was coined in 1921 (and would thus be well after the POD), would the term 'robot' still exist? If so, maybe you could take a page from Asimov and simply have unmanned vehicles prefixed with 'R' - a UAV becomes an R. plane, an underwater ROV becomes an R. sub, and so on.
On the other hand, given the strong butterfly principle in the writing of this TL, 'robot' probably won't exist as an English word to begin with, and so per the above you could prefix your unmanned craft with any number of things. IOTL, 'robot' comes from Czech and is derived from the term for (roughly) 'forced labor' or 'drudgery', so perhaps something like 'servitor' or 'helot' would become the accepted English term instead. Depending on who first described the concept, 'golem' might work quite well as a generic replacement for OTL 'robot', but might already be too recognizable and widely understood in its other meaning to stick.
'Drone' might just be the best overall option anyway, as it's short, intuitive, easy to remember, and distinctive, but ultimately that's up to you, Mac.