One of the helpers drive the Spool Starter. This is a rubber tire used to accelerate an empty paper spool to running speed prior to indexing to the new spool (turnup). The spool starter is a helper to thepope reel winder.
The spool starter cannot be started unless the pope reel is running. It is started using a 4 stage resistor starter. The motor is started across the full voltage though a resistor to limit current. As the spool accelerates, the armature current reduces. When the current is sufficiently low, part of the starting resistor is shorted with a contactor. This increases the armature current and acceleration continues. The process is repeated over 4 stages to get the spool to speed. The shunt field is set to match the speed of the spool slightly faster than the pope reel.
Clever, but not at all a modern design.