CH. XI DESIGN OF KAILWAY MOTORS 249 



46,000 pounds. Trains of two, three, and four cars are 

 made up according to the demands of the traffic at 

 different hours. We shall consider a train of one 

 motor and three passenger cars, weighing in all 90 

 tons. 



The maximum grade on one out of the four lines 

 radiating from the power house is 0'75 per cent., ascending 

 for 2,350 feet and descending for 1,950 feet; other grades 

 do not exceed 0'03 per cent. The average distance 

 between stations is 2,000 feet. E = 500 volts. 



We will take the case of two stations separated by 

 2,500 feet of level track. The time table requires that this 

 distance shall be covered in 100 seconds from start to stop. 

 Experience shows that the brakes may be counted upon 

 to stop a train of four cars weighing 90 tons, running 

 at 25 miles an hour, in 500 feet in 20 seconds, leaving 

 2,000 feet to be covered in 80 seconds. Using Equation 

 104, remembering that the weight per motor is 45 tons 

 and taking the drop at full speed to be 5 volts, we 



Mv 



obtain the relation ~- =3'46. Inserting this value in 



Equation 103 we find that c,, = 226 amperes. 



The wheels now in use have a diameter of 33 inches ; 

 we will adopt this size. The velocity ratio is 3'18 ; for 

 the present we will take this value. Using the relation 

 already found, we get l/ = 35'9. 



Since 1,000 feet must be covered in two-thirds of 80 

 seconds, the maximum speed is 37'5 f.p.s., or 25'6 miles 

 per hour, or 13'8 r.p.s. of the motor. To find the resist- 

 ance of the motor we must know the amount of frictional 

 and other torque opposing the motion. For this purpose 



