page_title: Rigid-framed electric locomotive
section_title: 2′Do1′
hierarchical_section_title: Rigid-framed electric locomotive / 2′Do2′ / 2′Do1′
caption_attribution_description: Deutsch: Locomotive Ae 4/7 11026 im Bahnhof Bauma.
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: The Swiss also used a large four-axle similar to the 2D2 5500, the 2′Do1′ Ae 4/7 (1927–1934). If length of service is considered, these were one of the most successful electric locomotive classes, lasting seventy years in service. They were a development of an earlier three-axle 2′Co1′ class, the Ae 3/6 ᴵ. Both of these had an asymmetrical layout, with the pony truck at one end replaced by a four-wheel bogie. The Swiss low frequency AC system had the drawback of requiring heavy main transformers, compared to a 50 Hz system, and these were mounted at one end of the loco, needing the extra axle to carry their weight.
  All of these, both French and Swiss, used Buchli drives to couple the traction motors to the driving axles. The original Swiss drive used a single Buchli gear on one side to drive each axle, the French locomotives used a double-sided drive with the Buchli gear duplicated for each end of the axle, which was considered to reduce wear.
   Media related to 2′Do1′ locomotives at Wikimedia Commons
caption: 2′Do1′ Swiss SBB Ae 4/7, showing the large external housings over the Buchli drives
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