Possibly Saturn 3 (1980)???
Ahh, that's it! I checked it out on YT and it's definitely that movie. I swapped Peter Fonda in for Kirk Douglas, which is understandable, but I was right about Farrah. Not sure how I missed it in her filmography. Now that I've seen it again I totally remember Harvey Keitel, but I have absolutely no memory of the giant robot. Wondering what kind of state I was in when I saw it, or maybe I just nodded off midway though.
Anywho, thanks a million!!