A drive assembly for a mechanical reducer for a turbomachine, in particular for an aircraft, includes planet gears, a planet carrier having at least one transverse wall, plain bearings for guiding the planet gears in rotation, and an oil supply circuit for the plain bearings. The planet carrier has collars for attaching the planet gears to the at least one transverse wall, and each of the planet gears includes at least one external cylindrical surface for forming an oil film with an internal cylindrical surface portion of each of the collars for forming said oil film.