1300 THE BELL SYSTEM TECHXICAL JOURNAL, NOVEMBER 1954 



for the stud-to-case coefficient of friction, ju, and governor input torciue, 

 G. Experimental evidence indicates a m of 0.25 exists during normal 

 operating conditions for hard rubber on brass. The values for governor 

 input tor(iue given in Tables I and III and used in the theoretical analy- 

 sis for the governors were determined as follows. 



The initial torcjue applied to the governor for the period up to the 

 critical velocity was calculated from oscillograph string traces. These 

 traces were obtained by mounting on the end of the governor shaft a 

 thin disc having 36 radial slots spaced uniformly about the circumference. 

 Light, detected through the slots of the rotating disc on the element of a 

 photo tube, appeared as a distorted sine wave on the photographic paper. 

 The distance between two successive wave peaks represented 10° of 

 rotation of the governor. By noting on the trace the time between peaks, 

 it was possible to determine the average velocity of the governor at 10° 

 intervals after release of the fingerwheel, or start of rotation of the gover- 

 nor mechanism. The complete plot of these velocities appear as the 

 experimental speed curve on Fig. 6. Inspection of the experimental curve 

 for the drive-bar governor shows constant acceleration immediately 

 after release. This appears as a straight line in the velocity time cun^e. 

 Using the slope of this line and the moment of inertia, Jo = 7.4 gm cm , 

 the initial governor torque was calculated as follows: 



^ J, h 100(7.4) .oA^f^A 

 Gi = Ico = -J = — — — = 13,480 dyne-cm. 

 t 55 



The governor torque value during normal rundown was found by first 

 determining the governor stud-to-case force, F„ , and using this value 

 in the equation 



G = 2nFnr 



The fly-bar governor mechanism was used to determine the F„ force 

 since the moment equation for this type governor contains measurable 

 values. Referring to Fig. 7, the schematic of the fly-bar governor, the 

 moment equation about B is as follows: 



F„,b - F,h - Fnd + nFnC - 



To solve this equation for F„ one must determine the centrifugal force, 

 Fm , and the spring force, Fg . Using electronic flash equipment with an 

 exposure time of Ho,ooo of a second, it was possible to take distortion 

 free photographs of the governor mechanism at the middle of the run- 

 down. These photographs were taken with the governor in the horizontal 



