The plural suffix -pu' is used for "beings capable of language". Klingons generally do not consider robots to be "beings". Some of them even are not capable of language. It's a philosophical question for the ages when a robot or computer crosses that line into being a "being capable to language". You'll have to take a course in Klingon philosophy if you want to get into those details. This course follows the standard Klingon concept that robots are "things", not "people". Thus we will use -mey for the plural on all robots.