DIRECT-CURRENT DYNAMOS AND MOTORS. 45 
in which k is a constant varying between the following 
values, according to the diameter of the armature and to 
the height of the winding space, the average length of a 
convolution hes 17) being the greater, the larger the 
i] = 
of 
= i] Be 
oo i} 
et \t--—-—- 
=== rk iy 
— vier eo 
» i 
Fie. 17 “CoifvOLUTION ON Fic. 18 —- LENGTH OF 
Drum ARMATURE. MEAN | URN IN KING 
APO Oa gels. ARMATURE. 
o 7 hd ae 
area of the shaft, and that of. the winding space as com- 
pared with the end- surface of the armature core: 
For smooth-core True = ood 25+ to 1.75; average, k = 1.5; 
** toothed drums = 1.5.40 8.0; average, k = 2.25. 
The smaller values. apply to large armatures having a com- 
paratively smallk winding depth (below the average given 
in Table 14), whereas the larger values are for small 
armatures in which the winding depth is comparatively 
large (above the corresponding average given in Table 
14). 
For a spirally wound ring armature—that is, one in which 
the turns are completed spirally by winding the inner 
surface of the ring—the total length of the armature wire 
is directly given by the dimensions of the armature core, 
thus: . 
20, + 2B, + haz 
= nae ts (26) 
bie Ox 
where /, = total length of armature wire, in feet; 
= number of armature inductors; 
and (2L, + 2B, + h.z) = length of mean turns, in inches 
(see Fig. 18), L, being the length and B, the radial 
thickness of the armature core, and h, the winding depth. 
