Industrial copiers (large office machines that weighs in at around 100lb or more) is always run on 24V (to keep currents down).
Usually the motors (whether DC or steppers) found in such devices won't be very usable for small robots, unless you find a particular fine specimen that would justify building a boost circuit, but that is rare, given the added complexity.
But put them aside for something else - one of them might be good for eg. a generator for a Savonius wind mill, or perhaps some stationary application.
For a 4 RPM turntable, a small motor with a couple of worm gears should do.