This electric locomotive uses a drive system that eliminates the gearing normally used between the motor and axle. It does this by making the axle part of the motor itself. The armature of the motor is mounted on the axle, and the motor's poles and magnetic fields are mounted on the frames next to them. As there were two of these field magnets per motor the term "bi-polar" came to be used. The geared electric drives of the period were limited by the large size of the motors needed for mainline locomotives. They were difficult to fit into the space available between the frames and next to the wheels. The "bi-polar" avoided this problem although it had a considerable amount of weight not cushioned by its springs. They operated for long and successful careers, but the development of lighter and more compact motors made geared designs universal after WW II. The Milwaukee Road's "bi-polar" was a passenger locomotive. It could haul a 1000-ton train of a dozen steel cars up a 2.2% grade ( arise of 2. feet for every 100 feet of distance) at 25 mph wihtout a helper locomotive, or speed it along at 60 mph on level track. Its maximum safe speed was 65 mph. It ran on 3,000 volts of direct current power. It has 12 motors to drive its 44" wheels, and only the end axles with 36" wheels are not powered. It produced 3,517 HP for short periods. It is 76'
long and weighs 521,000 lbs. New York Central #113, on exhibit nearby, also uses the same "bi-polar" drive, but uses 660-volt D.C. power.