—— 
BRAKES AND DYNAMOMETERS 357 
of CD, These four forces acting on the wheels E and F will produce a 
torque on the lever AB equal to 4Pr. Hence if the weight W on the 
lever is at a radius R from the axis of CD, WR=4P7y, and the torque 
transmitted from L to M is WR. 
If the wheels H and K run at a speed of N revolutions per minute, 
WRx2rN_xWRN 
2x 33000 33000" 
When unloaded, the lever is balanced by the weight w. 
Stops SS limit the motion of the lever. 
304. Belt Dynamometers.— When a belt is transmitting power from 
one pulley to another the tangential effort on the driven pulley is equal 
to the difference between the tensions on the tight and slack sides of the 
belt. If T, and T, are these tensions in pounds, and V is the speed of 
the belt in feet per minute, then the horse-power transmitted is 
(T, = TV 
33000 * 
Several forms of dynamometer have been introduced for measuring 
T, —T,, directly while the belt is running ; one form is shown in Fig. 551, 
p- 362, another is shown in Fig. 547. The latter illustration and the 
then the horse-power transmitted is 
ey bo? 
H —IH 
Li += | E Ss 
ne --f == 
re : 
TTF 
= i: Te 7 Elevation 
B H 
D 
4] Ce jb 
e 
WD © 
c Plan . 
— A H 
H f 
Fig. 547. 
following description are taken from a paper by Mr. 8. P. Watt in the 
Transactions of the American Society of Mechanical Engineers, 1891. 
The dynamometer (Fig. 547) consists of a set of pulleys mounted on 
a suitable frame and disposed as follows. The pulleys A and C are fixed 
to the shaft a, and B and D are fixed to the shaft 6. The pulleys E and 
F revolve freely as independent loose pulleys on the shaft g. The shaft 
q has a second shaft /, fixed to it midway between the pulleys E and F. 
Shaft f constitutes a pivoting axis, parallel to the shafts a and }, for the shaft 
9, together with the frame K and the weight lever L, all rigidly connected. 
Only enough motion of L is allowed to determine the direction of action, 
Instead of the weight of the lever L, the end of the lever could be con- 
nected to a small platform scale, and its tendency to rotate weighed. It 
