page_title: Rigid-framed electric locomotive
section_title: 1′Do1′
hierarchical_section_title: Rigid-framed electric locomotive / 1′Do1′
caption_attribution_description: For documentary purposes the German Federal Archive often retained the original image captions, which may be erroneous, biased, obsolete or politically extreme. Die Eröffnung der großen Schau "Deutsches Volk-Deutsche Arbeit" am Kaiserdamm in Berlin! Ein Meisterwerk deutschen Eisenbahnbaues. Die Triebachse der stärksten und schnellsten deutschen elektrischen Lokomotive E18 auf der Schau. Sie entwickelt eine Kraft von 2400 kW. Information added by Wikimedia users.English: Bogie of 2400 kW german electric locomotive E18 shown at "Deutsches Volk-Deutsche Arbeit" show in Berlin, 1934.
context_page_description: Rigid-framed electric locomotives were some of the first generations of electric locomotive design. When these began the traction motors of these early locomotives, particularly with AC motors, were too large and heavy to be mounted directly to the axles and so were carried on the frame. One of the initial simplest wheel arrangements for a mainline electric locomotive, from around 1900, was the 1′C1′ arrangement, in UIC classification.
  Some of these locomotives had their driving wheels coupled with coupling rods, as for steam locomotives. Others had individual motors for each axle, as would later become universal.
  By the middle of the century, the bogie arrangement for locomotives became more popular and rigid-framed locomotives are now rare, except for small shunters.
context_section_description: Electric railways in the US had begun with low-voltage DC systems: 675 V (Baltimore) and 660 V (New York). These early systems were based on direct connection to DC traction motors, without needing rectification, transformers or large diameter motors. Adequate power for main line haulage, even for the slower services through tunnels to the major urban terminii, required multiple motors. The Baltimore and Ohio used articulated Bo+Bo steeplecabs from the outset in 1895, the first main-line electric locomotives and over nine times heavier and more powerful than anything electric before. The New York Central S-Motor though was a single rigid frame with four separately driven axles and two leading and trailing trucks.  The traction motors at this time were simple ungeared motors, with the rotor mounted around the axle shaft. Two-pole bipolar motors were used, where the rotors were sprung with the axles and wheels and the field coils fixed. As there were only two poles, horizontally to the sides of the rotor, the rotor was free to move up and down between them with the suspension.
  The multiple motor Do arrangement, compared to the rod-drive locomotives and despite their powerful AC motors, had advantages for running at high speed, with no reciprocating mass to balance or give hammer blow. Once geared and isolated traction motor drives were available, their unsprung weight could also be reduced, encouraging smooth running. Although many locomotives adopted the Bo′Bo′ bogie arrangement and abandoned rigid frames, some fast passenger locomotives retained them into the 1940s and remained in service into the 1990s. Their large diameter driving wheels encouraged smooth running at speed and reduced the speed required from the motors and their gearing. Retaining frame-mounted motors also allowed large motors and adequate space for cooling airflow. A further advantage for four-motored Do locomotives, rather than the three-motored Co arrangement, is the ease with which the four motors can be switched between series, parallel and series-parallel circuits. When this was used for three-motored locomotives, a double-wound armature on the motor was required.
  Germany constructed a series of these pre-war, the DRG class E 16, E 17, E 18 (Austrian  ÖBB 1018) and E 19. They were of increasing technical sophistication, the first having the Buchli drive, later cup drives.
  The power required for the last of these, the E 19, was such that double traction motors were required with two motors for each axle.
   Media related to 1′Do1′ locomotives at Wikimedia Commons
caption: E 18 traction motor, driving wheel and cooling fan blower
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