50 TIIK iHiMKT-rruKKNT .MOIOI; cfl. in 



In many cases it is convenient to be able to express M 

 in terms of the torque on the shaft to which the motor is 

 geared. If t is the torque in inch-pounds on the main 

 shaft, which rotates at n revolutions per second, the 

 induction factor of the motor is given by 



-tf=4| 1 +-v / (i- 8I P' < l 



Example 16. A motor having a resistance of O04 

 ohm is geared to a main shaft with a velocity ratio of 4. 

 The main shaft has to rotate at 5 revolutions per second. 

 The tension of the line is 150 volts. Find the induction 

 factor of the motor, when the whole resistance to be 

 overcome is 8,000 inch-pounds of torque on the main shaft. 

 The term under the root is 0*798. so that the value of 

 Mis7'l. The motor rotates at 1,200 r.p.m. The cur- 

 rent is 200 amperes. We may check the results thus. 

 Since the motor rotates at 20 revolutions per second the 

 induced tension is 142 volts ; the heat drop is 8 volts, and 

 the sum of these two makes up the tension of the line. 

 Suppose now that we require, over and above the 8,000 

 inch-pounds of torque on the main shaft, 400 inch-pounds 

 of torque to turn the motor shaft in its bearings when the 

 magnets are excited, and 600 inch-pounds to move the 

 gearing, the torque in both cases being measured at the 

 motor shaft. 



The term t in Equation 1 8 represents the torque on 



