A good design of loco has to include the mechanical arrangements as well as arriving at a good electrical system. Old Maud.[see link in an earlier post, this thread], was Engineer Batchelder's attempt to have a gearless design [= low friction], with the motor windings
on the driving axle, an idea tried by the C&SR a few years earlier with limited success. A stunning adaptation and improvement of the Brit idea, much less complex and with a performance better than all its contemporary steam locos,
but..
[there's always a but!]... the unsprung weight of this heavy drive-axle led to complaints of Old Maud "pounding the rails". Here's the rub; ac motors are even bigger and heavier than a comparible dc motor; unsprung they can damage the track. Sprung and we're back to a complex drive arrangement, [= more friction losses], to accomodate a suspension. Getting the vibration and stress levels wrong was highlighted in 2003. 30 passengers were injured when a London Underground unit's motor fell off and derailed the train.
http://news.bbc.co.uk/1/hi/england/2694361.stm Alan
