the SNCF 'Waterman'

The 5546-5550 (5 units) of the SNCF 2D2 class, for 1.5 kV DC, delivered from April 1942 to October 1943, had the nickname of 'Waterman' after the resemblance of the nose to a well-known ink-bottle, but from a technical viewpoint, an interesting feature was the use of Buchli drive.

In a Buchli drive a driven gear wheel is securely fixed to the locomotive frame. Inside this gear wheel are two levers, coupled to gear segments that mesh with one another. The other end of the levers is coupled via universal joints to tension bars, which are then coupled via more universal joints to the driving rail wheel. Vertical movement of the driving wheel results in the gear segments moving due to the internal mechanism, and the driving wheel can move in a horizontal or vertical direction with respect to the gear wheel, while still transferring the momentum of the gear wheel. See diagram.

A disadvantage of the drive was the large number of moving parts, which demanded frequent lubrication and careful maintenance. The Buchli drive system was mainly used on express train locomotives, as there were no other drive systems that gave the same performance at high speeds. However, at higher speeds the drive components became unbalanced, causing issues at speeds over 140 km/h.  See also the post about the femme enceinte.