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CHAPTER XI 



DESIGN OF RAILWAY MOTORS 



WE shall now proceed to determine the best 

 arrangement for starting up from rest and 

 covering a given distance in a given time. 



If we are at liberty to adjust K so that the drop at full 

 speed is independent of M, v, and d, the best arrangement, 

 if M is constant, will be that in which the motor accelerates 

 for two-thirds of the given time, ' and covers one-half of 

 the given distance during the period of acceleration. 



We have then two conditions given by the two processes 

 of accelerating and running at full speed ; the first is 

 deduced from the formula s = ^ft^ from which by substi- 

 tuting the value of the acceleration in terms of M, r, and 

 d, remembering that s = ^D and , = , we obtain the 

 equation Mv DW 



This gives us the best value of - - in terms of the 



QJ 



accelerating current c,,. We have, however, to satisfy 

 the condition that one-half the distance is covered, at full 

 speed, in one-third the given time ; substituting the value 

 of the final speed in terms of H/, v, and d } we get 



U ;'=(H7I7 ^(E-cM ........ (104). 



ft 2 



