The auto-combatants are drones used by Autobots (and presumably other Cybertronians) to practice fighting while in long voyages.
The Transformers cartoon
Hot Rod sparred with an auto-combatant while the group is on their way to Cybertron. It managed to knock him out, and Hot Rod was about to strike back when it called a time-out when the Decepticons attack.
Dreamwave Generation 1 comics
The auto-combantants were solid holograms that could be generated by computer in a specifically-designed room.