I'm sure the headline made you curious? :-) But I'm serious, and I am not referring to toys but actual household machines. We have a Roomba floor vacuum cleaner and a lawn mower.
My 20-month son is afraid of these machines, even when they're parked and turned off. He will back away from them and start to whine. I've told him, and shown him, that the machines are harmless and not evil, but that didn't convince him.
He is not afraid of kitchen machines that are much more noisy. He's also (mostly) not afraid of the regular vacuum cleaner and the regular electric lawn mower that we also use, nor of other machines or cars, mopeds, bikes, etc. even if they are noisy. But he is afraid of the power drill. And terrified of mascots operated by a person inside (as in Disneyland).
Do you have experience with similar situations? What can be the cause? What helped?
Note: Just to be clear, I'm well aware that any lawnmower can be very dangerous, and we make absolutely sure that there is no way for the lawnmower to get near our son. But he can still see it.
I'm including some marketing photos so you can see what size the robots are: