Back shot of a Y-frame robot
The Maternal Obedience Maintenance Medicating Y-frames (M.O.M.M.Y.s) are robots in 4U City, talkative and designed to maintain the city.
For Y-frames, the primary maintenance operation is to keep citizens happy, and to drug anyone that are gloomy or upset.
Matty, Riff's personal Y-frame
Riff named his Y-frame "Matty", refusing to call it "Mommy". [1]
The hovering Y-frames have a female look, with chests serving the function of drug canisters. When seen from behind or while changing canisters, it is obvious that the Y-frames are indeed robotic parts held together by a Y-shaped frame.[2]